Botany of Sugar

Introductory Essay: There are all sorts of poisons that show up as white powders. Perhaps the toxin of most recent notoriety is Anthrax, which has become popular in terrorizing whole populations.  There are even minerals that could be included, like any number of heavy metals – for example arsenic trioxide…., or even salt. Salts can be both essential and wicked. Table salt comes to mind, simple cubic crystals of sodium chloride, present in every larder and necessary for almost any meal preparation. Yet, as we have learned, too much of this salt can mess with your metabolism.

But there are other, more complex white powders, many derived from plants, that are useful as well as dangerous to our health. Cocaine is a good candidate, extracted from the leaves of a South American shrub (Erythroxylon coca), as is heroin, a modified version of morphine (the major constituent of opium) from sap of Oriental Poppies. 

Sugar, however, speaks of a more celebrated dangerous white powder, one that’s part of almost any celebration.  Our sugar year, marked by birthday presentations and occasional wedding cakes, is punctuated nationally with sweets for Valentines, chocolates at Easter, fruit cobblers for July, treats at Halloween, and a sugar-laden feast at Thanksgiving.  A nice-sized serving of candied sweet potatoes has about 15 tsp of added sugar, a bit more than the inevitable slice of pecan pie.  Thanksgiving, of course is prelude to Christmas, the main course in our sugar train.  

Foods of the season hinge on the remarkable nature of sugar, almost universally desired – certainly universally necessary.  But what makes something a sugar, where does it come from, and why do we read articles that denounce sugar as dangerous, even toxic?  Let’s start by reviewing the dossier of this player.

As commodities, sugars are made by plants, which can be an incredibly rich resource – something that has proven crucial to animals of all sorts.  Insects and birds probe flowers for nectar that might have sugar concentrations in the 20% range.  Bees turn nectar into honey, which hundreds of generations of humans and bears plundered for sweet calories.  Native Americans learned to harvest sap from maple trees, harvested and concentrated yet today as maple syrup.  Manna, famed as a miraculous gift, is thought to be sugar exudates from desert trees.  And fruit, from dates to apples and grapes, has provided important sweet, energy-rich food sources.  Dried dates, for example, are 60 percent sugar by weight, while raisins are even higher, around 70 percent.

But trees and vines are pikers when it comes to sugar production.  No other plant group equals the photosynthetic capacities of the grasses, which make most of the carbohydrates we consume.  Corn, wheat, and rice are remarkably efficient photosynthesisers – truly excellent at making glucose  We don’t think so much about those crops in regard to sugar though, because their sweet wealth is stored mostly in the grain as starch (which botanists call amylose).  Plant starch, a complex carbohydrate (a polysaccharide) that is made entirely of glucose, feeds us and our livestock. 

Some of you may have read or even followed Walter Voegtlin’s diet, based on the assumption that pre-agricultural humans consumed fruit, nuts, seed, and grains, roots, leaves, insects, and flesh.  Those Paleolithic folk led lean and brief lives compared to humans today.  The Paleo diet and its contemporary cousins Atkins and South Beach, abjures carbs, and suggests emphasis on proteins.  These diets propose we step back, nutritionally, to a time before agriculture ushered in the Neolithic period.  That Paleo diet is decidedly non-vegetarian, as any anthropologist would predict by studying human dentition.  But development of agriculture drove major changes to the human diet, and it seems those more settled agrarians, the Neolithic sort, thrived on a grain-based foods supplemented with meat and dairy associated with animal husbandry.  That Neolithic diet, despite what you may think about it, supports the world today.   

Regardless as to dietary components, any ancient human, paleo or neo, had a sweet tooth, a yearn which we inherit.  The appetite for sweet foods and the pleasure they bring to the palate necessarily relates to the importance of basic sugars to our metabolism – and some would even say relates to the fruit-eating preferences of ancient chimpanzees that gamboled through the branches of our family tree.

Though proteins and starches are staples, human societies sought and favored sweet substances, which meant a quick energy boost in an otherwise earthy diet.  Those sweet sugars were based on plants – syrups, honey, and fruit were valued wherever encountered.  But only in one place on the globe was there a plant, a cane, known for its perpetually sweet sap.  

That place is thought to be the island of New Guinea, the largest island at the farthest end of the world’s greatest archipelago, anciently the exotic outsider to what we call Greater India….  But it was along some of the 25,000 islands in that archipelago that sugar cane migrated to India, where it became highly prized and was first described in ancient writings.  

Though the cane yielded prodigious sweetness (the juice has over 10% sugar content), the pure extract cannot be stored.  It ferments too rapidly.  Heat reduction to syrup or sticky masses of molasses-laden crystals proved to be the remarkable advance, yielding a sweet substance with shelf life, and portability.  Because brown syrup and sugar are so highly concentrated, bacteria and fungi do not prosper, thus (like honey) these products store well.   But early sugar was never a “foodstuff”…., rather it was used and traded as a spice, and sometimes as a medicine.  Even where the plant grows natively, production required so much effort that early sugar remained rare and costly.

Inevitably, this cane sugar became one of many products to reach Europe through ancient trade routes.  Brown and sticky, with a heavy flavor of molasses, sugar was an expensive novelty, that, as a tropical grass, was limited to cultivation in tropical and subtropical zones. Still, the remarkable plant itself, the easily transported and propagated sugar cane, would migrate with trade. By 600 AD planting and processing was established in warm regions of China, where sugar became a normal component of the cuisine, and west to Egypt, where it was embedded in Muslim diets. 

Westerners, who had grown accustomed to exotic products from the Orient – cinnamon, cloves, nutmeg, black pepper, were equally delighted by parcels of raw sugar as part of early spice trade. Over the following centuries, production of those other spices remained exotic, while cultivation of sugarcane exploded. More easily industrialized and in greater commercial demand, actual cultivation of sugar arrived in warmer Mediterranean areas under Arabic rule, with plantings established in Sicily by the 9th century.  Sugar emerged as a spice that brought much to the table – records indicate the Mayor of Winchester was tasked to provide 3 pounds of sugar for a banquet honoring England’s King Henry III in 1226, paying today’s equivalent of $450 for the pleasure.  Sweetness was a sensation, and Europeans adopted cane cultivation, by the Portuguese in 1425, on the newly settled Atlantic island of Madeira and other Old World sites – lowering the luxury threshold. 

Demand increased and supply remained limited until the age of “big sugar” – the harbinger of which was Christopher Columbus’s second voyage to the New World in 1493, when he introduced sugarcane cultivation to Santo Domingo.   At the time, this was not so clearly a world-changing event.  Europeans had been introducing sugar cultivation to Old World tropical islands, and Columbus’s wife’s family managed some of those Atlantic plantations.  There was even the precedent of running some of those plantations with slave labor imported from Africa.  And Columbus, after all, thought he had discovered a route to the western edge of the Indies, the home of sugar. 

This is neither place nor time to walk through the history of sugar plantations in the New World, which is truly a major story – and many of people will already know some of that history.  Cutting to the chase, the economic, political, and social issues related to development of the sugar industry were globally significant.  A few points to make:

1. Sugar production and supply was nationalized, and control of sugar sources played into the sequence of European wars from 1600 to 1900.
2. Cultivating warm climate lands for growing and processing sugarcane was a major driver of slave labor.
3. Sugar production would not develop as a cottage industry; for many technical reasons it was to become an early “big ag” product
4. Science and technological development introduced
   1. centrifugal separation, 
   2. new selections of higher-producing cane,
   3. the production of sugar from beets – plants adapted to the temperate, even colder climates like Russia, Germany, and Belgium, and most recently….
   4. the ability to manipulate sugar and level of sweetness in corn syrups.

At this point, the story becomes more complex, even more sinister, because the historical sugar of commerce and kitchen, sucrose, has been updated with new allies.  And together those sugars are a powerhouse.  Today’s average American diet includes over 100 pounds annually of added sugar, most of which is sucrose.  Today (year 2025), the USDA projects world sugar production (sugarcane and sugarbeet) approaching 200 million metric tons (nearly 441 trillion pounds).   Considering the fact that pure sucrose was never part of Paleolithic, or even Neolithic diets, how did sugar become such a significant portion of today’s human diet?  What has changed about sugar in our own lifetimes?  What keeps the supply going?  And of course, why might it be considered dangerous?

What is a Sugar?  It is worth noting there are many sucrose allies, many different compounds called sugars.  Nutritionally, things boil down to six compounds – a suite of three monosaccharides (glucose, galactose, and fructose) and three derivative disaccharides – sucrose, maltose, and lactose: sucrose (which is a glucose and a fructose joined together), maltose (which is a two-unit sugar made of pure glucose), and lactose (which is a glucose and a galactose combined).  

We’ll not worry about galactose, and will forgo concerns about lactose and maltose, concentrating on glucose, fructose, and sucrose – their nutritive and flavor-giving character.

In popular culture, sugar implies sweet, but sweetness varies.  Curiously, scientists are not yet prepared to tell us what characteristic of a compound causes it to taste sweet.  We know the most important sugar, the sugar that forms the basis of our metabolism and the only sugar you actually require, is glucose.  It is sweet enough, but other are sugars sweeter than glucose.  Fructose (which we call fruit sugar) is twice as sweet, and sucrose is in the middle. 

Though less sweet, glucose is critical to the story, being the common energy compound for almost all life forms.  Glucose is the sugar plants create through photosynthesis.  Everything about animal metabolism relates to glucose, and it is highly regulated by remarkable and complex mechanisms.  Most of us have around 5 liters of blood, and at this moment systems are working to get the glucose content back to 1 gram per liter.  That’s 5 grams, just a bit more than a teaspoon.  Core reliance on maintaining the right balance of glucose is manifest through the intricate insulin-based management system in place.  The brain, for example, relies almost purely on blood glucose for nourishment, as do the testes.  Indeed, hypoglycemia (abnormally low blood glucose) can prove immediately fatal, while the body has remarkable capacities to cope with short-term elevated suger levels (hyperglycemia.)  In a more natural world, a sweet tooth would have been truly important to promote a diet as rich in naturally-occurring sugars as possible, and it would have been crucial that metabolism could cope with an occasional sugar feast.  

Outside glucose, we ingest galactose and fructose, but neither is “required” as part of our diets.  Galactose, being very similar to glucose, is readily converted to glucose and follows the same pathways.   We also are able to covert fructose to glucose, but that is not the normal course of events.  Fructose is handled separately, through its own transporting system and apart from reliance on insulin.  Unlike glucose, which is metabolized in all bodily tissues, fructose is dealt with in the liver, where it normally is converted to glycogen (animal starch, which is essentially chains of pure glucose).  Most fructose plants make is tied up with glucose to form sucrose, the sugar plants move (botanically, we say “translocate”) from leaves to areas in need of energy and storage products, such as roots, growing shoots, flowers, and fruit.   The prominence of fructose in maturing fruit seems to relate its lure as a payoff to birds and other animals for their role in seed distribution

Sugars in Diets.  Years ago, most of us thought of sugars in terms of sucrose, and calories, weight gain, tooth decay, etc..  Those of you who consult a dietician or dietary coach will know this has changed.  Nutrition is a different world, a world with its own fads, its own language.  Take the term calorie.  In chemistry, we talk about calories (with a lower case c), but Dietitians talk about big calories (C)…. which the rest of the world knows as kilocalories.  

So what are calories and where do calories come from?  Nutritionally, calories are the available energy stored in carbon-to-carbon bonds of the food we consume.  Adding those potential calories up in our diets, we talk about food in terms of carbohydrates, proteins, and fats – with many people being aware that fats are twice as rich in calories as carbohydrates and proteins.  Regardless as to your diet, however, things quickly boil down to calories present in glucose (and fructose).  Proteins, fats, and complex carbohydrates are dismantled, converted to glucose and other compounds in the sequence of events that harvests energy stored in carbon bonds. That means producing carbon dioxide (CO2) and water (H2O) by utilizing oxygen. Thus, no oxygen means no energy and no life.

Importantly Calories become a way governments describe food energy in larger terms – a measure by which we discuss feeding the world.  The FAO (Food and Agriculture Organization of the United Nations) calculates the millions of kilocalories it takes to feed a population, as compared to how many million kilocalories are produced through various agricultural systems.  For example, FAO estimates that in 2008, around 161,016,452 hectares of the world’s arable lands were planted to corn, yielding a food value of 2.974e+15 kilocalories (that is 2,974,000,000,000,000, or 2.974 quadrillion kilocalories).   Don’t imagine this is about reliance on corn-on-the-cob, or cornmeal.  As early as 1844 cornstarch production had become a major industry.  Merely ten years later companies began selling corn syrup (made from corn starch).  Corn syrup, at that time, was natively pure glucose, not as sweet as sucrose, but useful in so many regards.

Today, corn is a major source of pure sugar – not just glucose, but the equivalent of liquid sucrose.  This came about because in 1965 Yoshiyuki Takasaki and Osamu Tanabe (the Japanese Fermentation Institute) developed a stable process to convert glucose to fructose.  That conversion had been the holy grail of the corn syrup industry.  If industry could make corn syrup as sweet as sucrose, the world would change.  And it did, very quickly.  By 1967, Clinton Corn Processing Company had licensed rights to this enzyme for the US, and their scientists worked out the kinks to industrialize the process.   In a complex and rapid series of moves, large companies (particularly ADM) consolidated this emerging resource, marketing and defending what we call HFCS (High Fructose Corn Syrup).  By 1984 both Coca Cola and Pepsi converted to use of the new sweetener.  Already liquid, more stable in solution, easily incorporated, and subsidized by the US government, HFCS quickly rose to equal status with sucrose for industrial food production.  

Where does that leave us with sugar consumption?  Records suggest that around the beginning of the 18th century, when sugar was becoming available to the general populace, annual average consumption was less than 4 pounds a person.  Today, the American per capita consumption of pure sugars (either as sucrose or as the sweetening additive HFCS) exceeds 100 pounds each year.  Each pound of sucrose has 1,775 calories, thus a person with an average intake of 100 pounds of sugar a year is also averaging 500 calories, daily, from sugar alone.  The World Health Organization recommends that an adult keep daily sugar consumption to 6 teaspoons (about 144 calories).  With 109 teaspoons in each pound of sugar, that suggests the upper limit of sugar consumption should be around 20 pounds per annum – a fifth of today’s national average.  

Humans did not evolve in a world of abundant free sugar but we do require enough to keep us going. Though we would suffer under hyperglycemia, as pointed out earlier, hypoglycemia is the far worse concern for society today.  

In fact, it is evident that the nearly-addictive sweetness of glucose, fructose, and sucrose relates directly to that inherent human need for sugars, which were a precious commodity for pre-industrial societies.  Evolution is not predictive; there is no mechanism for selection to have predicted today’s scenario, a time in which agriculture and industry allow us to mainline sucrose and fructose.  Consuming quantities of pure sugar is simply unnatural – unnatural and potentially dangerous.

A century ago, observed incidents of diabetes were 3 cases per 100,000 people, while the incidence today is 8,000 cases.  Much better and more recent data, available from the US Center for Disease Control (CDC), documents reported cases of Diabetes at under 1% in 1958 and nearly 7% in 2014.  Significantly, use of HFCS came about in this same time period.  

What does this mean for you, for me?  It means most Americans are overdosing on sugar.  Perhaps more significantly, we have altered the composition of sugars we consume.  Recalling the three crucial sugars:  glucose, fructose, and sucrose, we know fructose, though having the same chemical formula, is constructed very differently, and our bodies handle it through different mechanisms.  Sure, fructose can be converted to glucose, but it more readily is turned into glycogen (animal starch) or even fat.  The neolithic diet, one based on carbs, is all glucose, because plant starches are pure glucose.  The modern diet has a huge fructose component, because sucrose breaks down to a 50:50 solution of glucose and fructose.  HFCS is essentially the same as sucrose, a mixture of pure glucose and pure fructose.

For years, this was not considered an issue.  Dietitians actually supported consumption of fructose because it does not impact insulin level and it is sweeter than sucrose (or glucose), thus less may be needed.

People have begun to question that wisdom.  Most likely humans consumed modest levels of fructose.  In many societies, fructose appeared in diets seasonally, or at least sporadically.  Given the modern, steady availability of sucrose and high fructose corn syrup, we see the industrial era shift to sweetness has upped the fructose composition of our sugar intake.  

CONCLUSION:    We are all of an age to recall the sequential dietary woes, each decade gives us a new concern:  cholesterol, triglycerides, trans-fats, burned meat, salt, sugar, and now more specifically high fructose corn syrup.  These are the fallout of affluenza.  In reality, everything you ingest has some limit.  The LD-50 for water is 70 g/kg body weight, for salt 3 g/kg, and for sugar, 30 g/kg. 

You are what you eat: The paleo diet reminds us there was a time when people were constantly challenged to power their own bodies – sugar was at a premium.  People like Mark Phelps will have a basal metabolism of 2,000 Calories, and might require 8,000 or more Calories a day when competing.  But that intake does not work out for most of the population, especially for those of us fortunate enough to live longer than our ancestors, with abundant food, in a time of plenty.  There comes a stage when what we consume needs to be regarded as much like medicine as any other substance.

You need sugars, most particularly glucose.  You deal well with fructose, though it is not the primary energy source for body maintenance.  And you are allowed occasional binges…  What is not in the cards is a regular diet rich in carbs (i.e. sugars), especially fructose.  

Maybe Genesis 3 hit the nail on the head (through a contemporary reading):

And the woman said to the serpent, “We may eat of the fruit of the trees in the garden,” but our diet coach said, “You shall not eat of the fruit that is in the midst of the garden, neither shall you touch it, lest you die.”  The serpent said to the woman, “You will not surely die. For the Dietician knows that when you eat of it your eyes will be opened to the sweetness, and you will be like her, knowing the good and evil of the international sugar conglomerates.”  So when the woman saw that the tree was good for food, and that it was a delight, and that the tree was to be desired, she took of its fruit and ate, and she also gave some to her husband who was with her, and he ate. Then the eyes of both were opened, but their triglyceride levels rose, and they became obese and pre-diabetic. So they bought raiment in new sizes that would provide comfort on their couches.

A Bittersweet TimeLine  

Rather than attempt to relate the entire story of sugar globalization (which has been told in many books and web articles), the following recitation of data and developments summarizes the origin, spread, and tumultuous rise of sugar to its apogee at the end of the 20th Century.

7th Century – By this time, sugar cane cultivation had spread from India to China and North Africa

10th Century – Cane sugar was know throughout Europe as a luxury spice.  Cultivation and processing of sugar cane was introduced to the Mediterranean with the spread of Muslim control.  

15th Century – Europeans had begun to establish their own sugar cane plantations on Madeira and the Canary Islands.  At the end of the century, on his 2nd Voyage, in 1493, Columbus imported sugar cane to the island he called Santo Domingo, which today is Hispaniola

16th Century – Brasil became a major producer of cane sugar.  The increasing availability of sugar would lead to lower prices and growing access to sugar for all economic levels.

17th Century – Sugar became a crucial ingredient for the growing popularities of chocolate, coffee, and tea.  

1624 Francis Bacon published Nova Atlantis.  In one passage, he proposed a gallery of inventors, which would include a statue to the “Inventours of Sugars” (Smith, 2015).

18th Century – Though still costly, European sugar consumption was approximately four pounds a person in 1700.  In addition to evolving use in existing foods, preserves & marmalades, candies, and fermented beverages, sugar had been married to newly-globalized products of growing popularity, such as coffee, chocolate, and tea.  With democratization of those beverages, sugar replaced honey as the sweetener of choice.

1747 Marcgrav reported successful extraction of sugar from beets.

1785 Thomas Clarkson spearheaded a boycott against slavery sugar, termed “the blood-sweetened beverage” by poet Robert Southey.  Others joined the discussion.  In his 1788 poem, Pity for Poor Africans, William Cowper wrote:

I own I am shock’d at the purchase of slaves, 
And fear those who buy them and sell them are knaves;
What I hear of their hardships, their tortures, and groans
Is almost enough to draw pity from stones.

I pity them greatly, but I must be mum,
For how could we do without sugar and rum?
Especially sugar so needful we see?
 What?  give up our desserts, our coffee and tea!

19th Century – In 1800, at the dawn the century, English sugar consumption is estimated at 18 pounds per person per year (Aronoson & Budhos, 2010), but that would rise as sugar-based products (such as jams, preserves, and beverages) continued to grow in popularity and affordability among working class peoples. Though still predominately grown and manufactured through slave labor, the century began with the only successful slave-led revolt (which liberated sugar production would shift, gradually, away from that reliance. Haiti from French control).   Most change would come through abolition movements; by the end of the century slavery was abolished in most countries.  But traditional sugar production was changing in major ways.  In 1851 David Weston introduced centrifugal separation to sugar production in Hawaii (see improvements, US Patent Nos. 236,389. Jan. 4,1881). By 1860, Hawaii supported 29 sugar plantations (Smith, 2015), feeding demand in the US. Centrifuging sugar pulls syrup from the crystals and proved a major breakthrough that streamlined production at the very time the cost of labor increased due to the disappearing institution of slavery. 

Cane sugar also gained serious competition as sugar beet production was industrialized.  

20th Century – Sugar production (from both cane and beets) was completely industrialized.  Price controls and regulation became standard procedure, as sugar was now a dietary necessity throughout the world.  

1972 John Yudkin’s Pure, White, and Deadly: The Problem of Sugar was published.

Big Sugar: Over the 20th Century, the story became more complex, even more sinister, because sucrose, the historical sugar of commerce and kitchen, developed surrogates.  Together those many industrial sugars have become a powerhouse.  Today’s average American diet includes over 100 pounds annually of added sugar.  World consumption of table sugar approaches 450 trillion pounds.   Considering the fact that pure sucrose was never part of Paleolithic, or even Neolithic diets, how did sugar become such a significant portion of today’s human diet? 

As Foodstuff, What is a Sugar?   Nutritionally, for humans, sugars boil down to a suite of three simple sugars (monosaccharides) and three dual sugars (disaccharides).  For the moment we need only to recognize three crucial sugars – glucose, fructose, and sucrose, all of which we harvest from plants. We monitor the concentration of sugars present in a solution, like nectar, syrup, or fruit juice through measuring its relative density (RD), which for these substances is the ratio of sugar in a solution (grams of a dissolved substance, a solute, as compared to the mass of the solution), and measure this concentration in various ways. A hydrometer, which you may have seen if someone tested your car battery, compares density using floatation. A float will ride higher in a dense solution than in pure water, just as you may float better in the Great Salt Lake than in a Michigan pond.

Someone studying the quality of a nectar or tree sap for syrup, will probably use a pocket device, a “refractometer.” This measures concentration optically. Light passing through clear substances, such as water or glass, alters course – we say it is “bent.” Because the extent to which water bends transmitted light (like a lens) is altered by dissolved substances; the more solute, the greater the displacement. Refractometers are devices we use to measure the extent to which a sample alters the path of light, which then correlates to the concentration of sugar in a solution.

The more common term for RD in food and beverageproduction is specific gravity (SG), which is expressed in differing scales based on the method typical of an industry. Vintners might use a Brix scale to compare sugar content of grapes while home brewers may simply refer to specific gravity. Some processors might rely on the older Balling scale, while industrial processors likely use the more precise Plato scale, Oechsle, or others. (For a simple discussion of different scales for sugar density, visit Europe’s commercial Refractometer page.

Brix is named for Adolf Brix, who devised one of many systems used to measure the concentration of sugar in a water solution.  In the scale Brix devised, a gram of sucrose dissolved in 100 grams of solution gives a reading of one degree (ºBx).  The This is how vintners field check the level of sugar in their crops. 

In popular culture, sugar implies sweet, but sweetness varies based on the mixture as well as the individual. The degree Brix scale is one measure, but only when we understand what makes up the solution. Sweetness, like Brix, is based on comparisons to Sucrose (see Wikipedia). With Sucrose as “1”, ratings have been developed for other chemicals and compounds. Among the important nutritional sugars, Glucose measures around 0.8, while Fructose measures as high as 1.8, reminding us that when Sucrose (a disaccharide) is broken into its two constituent compounds, the Fructose half is perceived as twice as sweet as its partner Glucose. That explains why fruit is so desirable, but more importantly this simple realization has driven many developments in the food industry, most specifically the push for high fructose corn syrups (HFCS).

We know the most important sugar, the sugar that forms the basis of our metabolism and the only sugar you actually require, is glucose.  Sugars are both building blocks and energy storage. Energy is required to create the carbon-carbon bonds in sugars (and starches), thus in breaking down sugars (we call this “respiration”), organisms release and recapture that energy to drive life processes.

“””Oxidation of one gram of carbohydrate yields approximately 4 kcal of energy, while the oxidation of one gram of lipids yields about 9 kcal. Energy obtained from metabolism (e.g., oxidation of glucose) is usually stored temporarily within cells in the form of ATP.^[36] Organisms capable of aerobic respiration metabolize glucose and oxygen to release energy with carbon dioxide and water as byproducts.””

“””1 joule (J) is the amount of mechanical energy required to displace a mass of 1 kg through a distance of 1 m with an acceleration of 1 m per second (1 J = 1 kg × 1 m2 × 1 sec-2). Multiples of 1 000 (kilojoules, kJ) or 1 million (megajoules, MJ) are used in human nutrition. The conversion factors between joules and calories are: 1 kcal = 4.184 kJ, or conversely, 1 kJ = 0.239 kcal. (from FAO Food and Nutrition Technical Report)”””From the FAO Food and Nutrition Technical Report Series, Human Energy Requirements, (Report of a Joint FAO/WHO/UNU Expert Consultation, Rome, 17-24 October 2001 )

As mentioned in the introduction Glucose is critical to the story, because it is the common energy compound for almost all life forms; it’s the sugar plants generate through photosynthesis.  But it functions at a modest level; the average adult has around 5 grams of glucose, just a bit more than a teaspoon, in his or her bloodstream. As I mentioned earlier, hypoglycemia (abnormally low blood glucose) can prove immediately fatal, while the body has elaborate systems to cope with short-term hyperglycemia.   Even with those safeguards, the subtle balance is problematic in a modern world awash in dietary sugars.

To learn more about the nature, role, and potential issues with sugars, we need more information.

Here are Some Definitions, Historical Notes, & Discussion Topics:

ENERGY

Calories:  So what are Calories and where do they come from?  Nutritionally, calories are the available energy stored in carbon-to-carbon bonds of the food we consume – most significantly in glucose.  Adding up calories in our diets, we talk about food in terms of carbohydrates, proteins, and fats – with  most people being aware that fats are twice as rich in calories as carbohydrates and proteins.  Regardless as to your diet, however, everything boils down to calories present in glucose, because proteins, fats, and other carbohydrates are generally converted to glucose or compounds in its breakdown sequence when energy is harvested.

Be aware that dietitians talk about capital C Calories, which to a chemist are really kilocalories.  Importantly those kilocalories (big-C calories) are one way governments describe food energy in larger terms – a measure by which we discuss feeding the world.  The FAO (Food and Agriculture Organization of the United Nations) calculates the millions of kilocalories it takes to feed a population, as compared to how many million kilocalories are produced through various agricultural systems.  

For example, FAO estimates that in 2008, around 161 million hectares of the world’s arable lands were planted to corn, yielding a food value of 2.974 quadrillion (that is 2,974,000,000,000,000) kilocalories.  Increasingly, FAO and other organizations are moving to discussing food in terms of mechanical energy, which is measured in joules.  For food resources, the useful term is the megajoule, or MJ.

CARBOHYDRATES

What is a carbohydrate?  Pretty much the same thing as a sugar, but even more inclusive.  As the term suggests, carbohydrates seem to be hydrated carbon – molecules made of carbon and water (though, from closer analysis of photosynthesis we know that is not exactly how they are assembled.) Generally, these water-soluble compounds are  constructed of carbon, hydrogen, and oxygen in predictable proportions, mostly C_nH_2nO_n. 

Many important plant compounds are carbohydrates, including the sugars and sugar-based molecules (monosaccharides, disaccharides, oligosaccharides, and polysaccharides).  The most abundant carbohydrate is cellulose, which is a glucose polysaccharide (i.e. many sugars linked together) that is indigestible by most animals.  Plants, of course manufacture quantities of a digestible polysaccharide called amylose, i.e. plant starch.  Carbs, in dietary terms, are mostly starches and other complex compounds that are not sweet, and many are indigestible.

Sugars and Sweetness:  What makes something a sugar? People say “sugar” when their thoughts are directed to the smaller carbohydrates –  compounds we call monosaccharides and disaccharides.  There is also the implication of a “sweet” taste.  But not all sugars are sweet, and even sweet sugars vary.   You can read up on the  “historical theories of sweetness” in Wikipedia, and examine a succession of ideas as to what makes food sweet to humans.  Over a century ago, Georg Cahn (in Germany) noted that sweetness is associated with the presence of several hydroxyl (-OH) groups on a molecule

Cahn also observed that the presence of Chlorine affects sweetness. That leaves a lot of mysteries in its wake.  The understanding is not resolved; people still wonder what causes something to taste sweet.  Researchers assume we will someday discover oral “receptor” sites that are triggered by certain characteristics of molecules we perceive as sweet.  But we remain at odds as to many issues related to the nature of our sweet tooth.  

Things are more complex yet, because there is no absolute way to gauge sweetness. We can and do determine the concentration of known sugars in a solution.  Vintners check sugar concentration (percent concentration is water is measured in Brix, i.e. ºBx) to calculate the probable level of sweetness in order to determine harvest time.  But that assumes we know the composition of the solution, and do not expect other flavors to modify the sweetness level.  

In general, there are so many variables that sweetness remains basically subjective, so we use a bioassay (a taste test) to compare sweetness against a sucrose standard (given a value of 1).  A researcher might ask people to score how a substance tasted at different concentrations compared to sucrose solutions.  Through comparing perceived sweetness at differing concentrations, researchers can generating a scale.  Though this method, people conclude fructose sweetness rates about 1.73 (as compared to 1 for sucrose), while glucose comes in at 0.7.   

Some calculations seem a bit extraordinary.  For example, the sweetest substance (reported in Wikipedia) is lugduname, which is said to have a value of 225,000, suggesting that dropping 1/225,000 teaspoon of lugduname in your tea will have the same impact as a teaspoon of sugar.

Sugars as Organic Compounds: Organic chemists have devised simple ways to diagram and name the molecules they study, ways that help them explain the complex interactions that are possible.  Hermann Emil Fischer, who dedicated his career to studying sugars (and awarded the 1902 Nobel Prize in Chemistry for his discoveries concerning the nature of glucose) established a standard method to diagram their structures in 1891. The Fischer projection depicts a chain of carbons numbered through standard rules.  Glucose a hexose (6-carbon sugar), one of 12 different molecules with the same formula (C₆H₁₂O₆,). Like other organic chemicals, each hexose can each take alternative shapes, including the tendency to form rings – which are called “cyclic” forms.  Different forms have different stabilities and characteristics.

The hexoses are not alone; their are other simple sugars formed from 3-carbon, 4-carbon, and 5-carbon chains, and even more (7-carbon heptoses, 8-carbon octoses, etc.) We call these simple sugars (monosaccharides), and understand they can be linked in pairs to form compound sugars (disaccharides), such as Sucrose, which is a Glucose bonded to a Fructose, or even long chains called polysaccharides (starches, cellulose).

MONOSACCHARIDES:  The simple sugars are the basic carbohydrates plants and animals generate and utilize for cellular functions, such as storing energy and creating other building blocks.  These carbs are linked and polymerized in countless ways to generate disaccharides (such as sucrose), oligosaccharides, and polysaccharides (starch, cellulose, pectins, etc.)  The most common monosaccharides are based on skeletons of 3, 5, and 6 carbons –  groups of compounds we call trioses, pentoses, and hexoses.  

Trioses: Trioses are carbohydrates built from a 3-carbon chain, such as Glyceraldehyde and Glycerone (Dihydroxyacetone, i.e. DHA). These sugars are significant components in many pathways.  You will encounter them specifically when studying the breakdown of glucose – which we call glycolysis (lysis = to split, or break apart)….. 

Pentoses: Pentoses include Ribose (important as a building block for DNA and RNA) and Xylose, a main building block of xylan (a hemi-cellulose), which can comprise up to 30% of dry weight of some trees….

Arabinose & Ribose were named by Emil Fischer, who isolated them from Gum Arabic.

Hexoses (6-carbon sugars):  Hexoses are a big deal, and everything about them is multi-dimensional.  We learn from literature there are 12 possible hexoses, all with the same chemical formula: C₆H₁₂O₆, based on a carbon skeleton to which six oxygen atoms are attached, adorned by 12 hydrogens.

Remembering that each carbon atom has four points of bonding, the carbon chain reflects just a few alternatives – binding to another carbon, binding to a hydrogen atom, or binding to oxygen, which can occupy two bonds with a carbon (a double bond) or a single bond to what is called a hydroxyl group (-OH, oxygen paired to hydrogen). Given these predictable states, Fisher envisioned standards as to how compounds are constructed and can be graphically represented.  This boils down to an elaborate tinker-toy or building block diagram, reflected in an internationally-accepted naming system.  

It matters where a carbon is relative to others and what else is attached to that carbon.  We differentiate these through describing the circumstances for each carbon in the chain (carbons #1 through #6).  Moreover, each different hexose has alternative configurations, from being a straight chain to forming rings – like a wagon train that camps out in a circle.

Eight of the possible hexoses are called “aldohexoses” because the #1 carbon has the aldehyde configuration (that is the end carbon is double-bonded to an oxygen).  The aldohexoses are Allose, Altrose, Glucose, Mannose, Gulose, Idose, Galactose, Talose.  Only three (Glucose, Galactose, and Mannose) are dietary.

The four other possible 6-carbon sugars are considered “ketohexoses” because the double-bonded oxygen is attached to the second carbon.  This reminds us that in an aldehyde the double-bonded oxygen is attached to a terminal carbon in a chain.  The term “ketone” tells us the carbon is not terminal in a chain.  Aldehydes and Ketones behave differently.   The four ketohexoses are Psicose, Fructose, Sorbose, Tagatose

Given a standard system for diagramming sugar molecules, chemists devised a mnemonic to keep track of the possible arrangements for aldohexoses:  “All Altruists Gladly Make Gum in Gallon Tanks”   For students who were required to recall the different structures, the phrase gives clues using a binary counting system from 0 to 7.  The sequence records which hydroxyl group is drawn on the right side of the diagram, with 0 as the hydroxyl (OH) and 1 representing a simple hydrogen proton (H)

For Ketohexoses, you are on your own.  But this doesn’t pose much of a problem.  Of the 12 known hexoses, only three aldohexoses (Glucose, Galactose, and Mannose) and one ketohexose (Fructose) are common in living organisms, and only Glucose, Galactose, and Fructose are dietary. Let’s give greater attention to Glucose and Fructose.

Glucose (Dextrose) was isolated from raisins in 1847 by German chemist Andreas Marggraf, and is named from the Greek term for young, sweet wine (must).  Glucose seems infinitely infinitely transferrable as a source of wealth. 

But, as wealth, glucose can be created through green alchemy…., easier than mining for gold. Here are some points to consider:

• glucose is created out of pure air – this form of wealth really does grow on trees.
• glucose can be dismantled and returned to the air
• so glucose is stored sunlight
• but glucose is a building block…
  • it’s the core carbohydrate, and can yield other saccharides as well as macromolecules
  • and can be broken down to generate other organic compounds necessary for life
• and glucose is a regulator
  • of blood composition and activity
  • of sap concentration and movement
  • of energy level and cell integrity

The direct relationship between glucose and metabolism should not be surprising in that glucose is the main product of photosynthesis; it is the origin of all food on the planet.  The trick is, of course, this is one of the great cycles.  Plants consume carbon dioxide and turn it into glucose through capturing the energy from sunlight.  In the process, they generate oxygen.  By that measure, sugar dissolved in cell sap is truly liquid sunshine and oxygen is a waste product.  When the stored energy is retrieved to drive reactions, like moving muscles, oxygen is consumed and carbon dioxide is released. 

Because it can be dismantled, glucose provides building blocks for other organic compounds.  As the seamlessly transferable source of pure energy and construction material, glucose is irreplaceable, occupying this same role for all life forms. If you want to reduce life to some essential compound, to a material from which all else emanates, you might decide that Life revolves around glucose. 

But Glucose is hard to pin down, moved constantly across membranes.  It is the gold standard, but it’s liquidity makes glucose the only truly fungible molecule among an entire suite of 12 nearly identical 6-carbon sugars (hexoses, or monosaccharides).  Among those 12, only four (glucose, mannose, galactose, and fructose) are significant for living organisms, and just three – glucose, fructose, and galactose – are absorbed during digestion.  Those three dietary sugars pair up to make some important disaccharides:

• sucrose (which is a glucose bonded to a fructose)
• maltose (which is two glucose molecules bonded together)
• lactose (which is a glucose bonded to a galactose)

Fructose and galactose are important, but glucose remains the incomparable and multi-capable star.  When combined (polymerized) in one form glucose yields plant starch (amylose); linked in a different manner it makes animal starch (glycogen); and bonded in yet another manner glucose makes cellulose.  A massive and insoluble polymer, cellulose consists of over 100,000 glucose molecules and is touted as the most abundant macromolecule in the universe.  

We come to appreciate that glucose is so small and facile it must be tied down to be managed.  The world is awash in glucose. It is not immediately obvious, but  Glucose is everywhere.  The wood around you is mostly cellulose, as are clear wrappings we call cellophane.  Any paper in sight is mostly cellulose, as are raiments of cotton or rayon.  And, of course, glucose is half of the sucrose in the sugar bowl, because plants manufacture sucrose for transport, loading it into conduits to ship from source (leaves) to sink (roots and fruit).  

Though crucial to bodily function, high levels of glucose can be dangerous in your bloodstream.   so the concentration is kept low by a host of dedicated mechanisms.  Blood typically carries only one gram of glucose per liter.  The five grams of glucose in an average healthy male (5 liters of blood) are about the same as the mass of two sugar packets.  Humans use insulin to wrangle extra glucose out of the bloodstream so it can be made into glycogen in the liver, or into fats in adipose tissue.  Mainlining glucose challenges the balance, minimally leading to weight gain through generation of glycogen and fats, more significantly causing havoc in brain function and other nervous tissue, as well as damaging capillaries and blood flow in the body’s extremities.  

Fructose (Levulose) was named in 1857 by William Miller, but first isolated in 1847 by Augustin-Pierre Dubrunfaut.

So what is fructose?  Reviewing earlier discussion, like glucose it is a 6-carbon sugar (a hexose, which is a monosaccharide).   The name fructose comes from its abundance in fruit, which is the reason many people refer to it as “fruit sugar”.   Anciently, most  of the fructose people consumed was in it’s simple form, a sweet component of fruit.  Bakers appreciate fructose because it contributes more readily to browning (through the Maillard process) that yields nice color and intricate flavors to baked products.

Today, the great majority of fructose we eat comes from sucrose, which is a “disaccharide” composed of a glucose bonded to a fructose. 

Significantly, fructose does not seem to be required in human diets at any level.  In fact, there are two different diseases related to presence of fructose.  The more serious disease is HFI (Hereditary Fructose Intolerance).  Characterized by the genetic inability to manufacture an enzyme (aldolase B) needed for fructose metabolism (see food-info.net), people with this complication can suffer from a buildup of fructose (in the form of fructose 1-phosphate) which can block pathways for glucose assimilation – a situation that is life-threatening.  The second disease is fructose intolerance, which is similar to lactose intolerance.  Intake of fructose in the small intestines is facilitated by a transporter molecule.  If that transporter is not sufficient in density or activity, fructose passes to the large intestine, where it provides sugar to nourish a range of gut flora, resulting in flatulence and other forms of discomfort.

But fructose is a “ketohexose” – the double-bonded oxygen is not attached to a terminal carbon.  That makes for significant differences in how fructose is metabolized.  Sweeter than either glucose or sucrose, fructose also has less tendency to crystallize due to a reduced stability of its ring forms.  Once absorbed in the bloodstream, fructose is shunted to the liver, where it contributes to formation of glycogen (animal starch)…. 

Galactose: one of two sugars in lactose, converted simply to ascorbic acid, as a sugar acid is major component of pectins

DISACCHARIDES:

Sucrose:  And sugar is so sweet.  When I was a child, my mother saw that I would sit in the yard and eat sand.  So our family doctor recommended they just give me the sugar bowl.  I was allowed to sit at the table and consume sugar by the fistful…..

It isn’t just humans – rats remain lean when fed all of the dog food they want, but grow obese when given access to limitless fruit loops….Nectar is sugar water.  

We thought of sugar as a spice – and it was a chief driver of globalization and imperialism.  We decided sugar is a food, the core carbohydrate – an energy compound – like oil.  The more the better.  

It’s as though the alchemists succeeded and learned to create gold from ordinary materials.  Now everything can be gilded.  Except glucose is more than gold – it is the sun’s energy, life’s basic building block, and a metabolic driver.   It is the genie, all of the world’s power condensed in one simply astounding 6-carbon compound.

Despite our attempts to control everything, we are essentially mortal creatures, transient biological balancing acts, (we are what we eat),,,  Eating pure sugar is like using white gas, it’s like mainstreaming/mainlining/

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