∞ generated and posted on 2016.03.05 ∞

Two important macronutrients and sources of Calories are carbohydrates and protein, but dietary fiber even though effectively lacking in Calories is important as well.

Animals obtain nutrients from their diets with these nutrients differentiated into macronutrients versus micronutrients, the former consisting particularly of carbohydrates, protein, and fats as well as dietary fiber, and the latter consisting particularly of vitamins and minerals.

This page contains the following terms: Calorie, Carbohydrate (dietary), Sugar, Moiety, Sucrose, Fructose, High-fructose corn syrup, Complex carbohydrates, Polysaccharide, Starch, Dietary fiber, Insoluble fiber, Soluble fiber, Protein (dietary), Essential amino acids


Amount of energy required to raise one-thousand grams of water by one degree Celsius.
A Calorie is a basic unit of measurement of the energy content of foods. It is not, however, a unit of measurement usually used in scientific discourse. Instead, one employs "calorie" (with a small "c", a.k.a., "small calorie"), which actually is a unit that is exactly one-thousand-fold smaller than "Calorie" (with a big "C", a.k.a., large calorie). Thus, a Calorie (with a big "C") is equal in magnitude to what instead is known as a kilocalorie.

The amount of Calories present in the food we consume averages (dry weight) approximately 4 per gram for carbohydrates and protein versus about 9 per gram for fats. Alcohol, that is, ethanol as found in alcoholic beverages, comes in somewhere in the middle, at about 7 Calories per gram. Thus, on a weight-by-weight basis, fats possess over twice as many Calories as carbohydrates and proteins, while alcohol contains almost twice as many Calories as carbohydrates and proteins. It is important to keep in mind, however, that we mostly don't eat fats, proteins, carbohydrates, or even ethanol in pure forms, though nonetheless foods that are higher in fats generally, simply due to the high caloric content of fats, will be higher in Calories. Meanwhile, alcoholic beverages are unquestionably not Calorie free, not even counting that Calories typically are present even beyond those found in the ethanol itself.

Nice introduction to the complexity that is a Calorie!

Carbohydrate (dietary)

Especially sugars, starches, and fiber which upon digestion is worth ~4 Calories per gram to us in energy.
The three major forms in which Calories are obtained in our diets are as carbohydrates, proteins, and fats. Carbohydrates and proteins both provide relatively few Calories per gram and often are reasonably well hydrated (that is, associated with water). Consequently, on a whole, carbohydrates possess even fewer Calories per gram of food that is actually consumed relative to fats.

These carbohydrates are consumed in three basic forms: (1) sugars that we can digest, (2) starches (which we are also able to digest), and various other carbohydrates that we are unable to digest. The latter can include sugars, cellulose, and various types of so-called soluble fiber. These indigestible carbohydrates do not provide us with Calories but often can be fermented by our gut microorganisms, leading to either good things (e.g., the production by these microorganisms of vitamins that we can then absorb) or relatively bad things (the production by these microorganisms of excessive gas (leading to flatulence) in the course of fermenting these other carbohydrates).

Carbohydrates often are assimilated into our bodies as the sugar glucose though also fructose and galactose. Glucose absorption results in an elevation of blood glucose levels, an elevation that is countered via the release of the hormone insulin, that is, by the pancreas.

The above video is Dr. Andrew Weil's take on carbohydrates and diet.


Carbohydrate that consists of only one or two subunits.
Sugars found in our diets include, particularly, sucrose (i.e., table sugar), lactose (i.e., milk sugar), and maltose (a product of starch breakdown and an important ingredient when making beer). Each of these is a disaccharide. Glucose (blood sugar), fructose (fruit sugar), and galactose, all monosaccharides, also can be found in our diets and have the distinction of being absorbed directly into the blood without modification.

Sucrose, lactose, and maltose, by contrast, must be enzymatically cleaved (hydrolysis) into monosaccharides prior to subsequent absorption of their component monosaccharides. Indeed, sucrose consists of a combination of glucose and fructose "moieties", lactose consists of glucose and galactose, and maltose just glucose (though maltose, as a disaccharide, consists of two glucose subunits).

The hydrolysis of disaccharides occurs via membrane-associated enzymes that are found on the brush border of our small intestine. A failure to hydrolyze disaccharides, such as one sees with lactose intolerance as well as sucrose intolerance, results in digestive problems (bloating, excessive flatulence, diarrhea) due to their subsequent digestion and fermentation especially by colon-located bacteria.

Links to terms of possible interest: Deoxyribose, Disaccharide, Fructose, Galactose, Glucose, Lactose, Maltose, Monosaccharide, Ribose, Sucrose,

The above video provides a nice introduction to just where dietary sugar is "hiding" in the grocery store.

Why we crave sugar. Yes, it's that pesky dopamine reward system again…


A portion, such as of a molecule.
Starches consist of glucose moieties, that is, not actual units of glucose but instead almost-glucose subunits that have been chemically bonded together. Proteins consist of amino acid moieties. Nucleic acid polymers are chains of moieties of nucleotides. The use of the term, moiety, can be quite convenient since it allows us to speak of chemical subunits that are almost but not quite what, chemically, we are referring to.

Links to terms of possible interest: Chemical bond, Moiety, Monomer, Polymer, Polymerization, Subunit


Disaccharide consisting of glucose and fructose moieties.
Sucrose or table sugar is an important source of sugar especially in diets consisting of refined foods, and particularly other than the glucose and especially fructose content of high-fructose corn syrup. Sucrose is typically derived from either sugar cane (cane sugar) or instead sugar beets (beet sugar). Typically when you add a sweetener to foods, that is, not an artificial sweetener or for that matter honey, then the sweetener you are adding is sucrose, in crystalline form.

Honey, by contrast, consists predominantly of the same sugars as sucroseglucose and fructose – though not in disaccharide form. Indeed, high-fructose corn syrup also consists of a combination of glucose and fructose, again as monosaccharides, though here the starting material is glucose, as derived from corn starch, which is then enzymatically converted in part to fructose. When you think of the addition of sweeting agents to foods using real sugars (versus artificial sweeteners), you almost exclusively therefore are referring to various combinations of glucose and fructose including as in the form of a single molecule, sucrose.

The above video provides a nice introduction to the basics of the biochemistry of sucrose digestion.


Six-carbon highly sweet monosaccharide of fruit.
Fructose is combined with glucose by plants to produce the disaccharide called sucrose, a.k.a., table sugar. Individually, that is, as simply the fructose molecule, fructose is the sweetest of naturally available sugars. Fructose, like glucose and galactose, is taken up in the course of absorption directly into the blood.

Its fate in the blood is different from that of, for example, glucose, however, since fructose does not contribute directly to blood glucose levels and otherwise is not affected by nor affects the release of the hormone, insulin. Fructose also is more readily taken up by the liver than is glucose, where fructose can serve a similar role of replenishing liver glycogen levels. Once sufficient liver glycogen levels have been restored, however, then fructose is converted instead into triglycerides, that is, ultimately, to fat. As fructose, unlike glucose, is not also taken up by muscle cells and other cells in the body, the potential for fructose to be converted to fat actually might be greater than the potential for glucose to be converted to fat.

Arguments for why getting fructose in your diet, other than by eating fruit, is not necessarily a good idea; just prior to 3:45 there are 10-15 seconds where the sound has been muted.

The above video provides an argument for eating fruits, probably particularly fresh fruits, despite their containing fructose.

High-fructose corn syrup

Sweetener in which some fraction of glucose has been enzymatically converted to fructose to improve sweetness.
Corn starch, like all starches, is made up of subunits (moieties) of nothing but glucose. Corn syrup is a liquid solution of glucose molecules that is generated via the enzymatic digestion of starch to its constituent monosaccharides, with this digestion accomplished using amylase enzymes.

Fructose is what is known as an isomer of glucose. That is, both glucose and fructose possess the same number and types of atoms, though in a different chemical arrangements (both, though, have the molecular formula, C6H12O6). The conversion of glucose to fructose thus involves what is known as an isomerization reaction, as catalyzed by an enzyme that is described as an isomerase.

The development of high-fructose corn syrup thus occurred over a number of stages that began with its "discovery" in the late 1950s, that was followed by the discovery of a food-grade isomerase enzyme in the early 1960s, and then the economic incentive to be utilized to a large extent following the imposition, by the United States, of tariffs on imported cane sugar (sucrose) which resulted in a search for less expensive substitutes for sucrose (in the 1970s). Of interest, the ratio of fructose to glucose commonly found in high-fructose corn syrup (55% fructose) is approximately the same as the ratio found in honey.

Quick video explaining how high-fructose corn syrup is commercially produced.

High-fructose corn syrup, it's everywhere, and the above video tells you how you (sort of) can make your own.

This is an excerpt on high-fructose corn syrup from a lecture I gave on diet and nutrition.

Complex carbohydrates

Sugar or starch that is found in less refined foods in association with relatively ample quantities of vitamins, minerals, and dietary fiber.
To a large degree the concept of complex carbohydrates is scientifically meaningless but rather a legal and/or political (and/or marketing) construct. Still, the concept does allow one to rather easily – even if mostly semantically – distinguish what can be described as "empty calories" from food that exists is a less refined state. Thus, to a fair extent complex carbohydrates are preferable in our diets to more refined foods, with perhaps the most egregious of the latter being those which contain relatively large quantities of high-fructose corn syrup.

Complex carbohydrates, ideally, pass more slowly through the stomach (longer gastric emptying time thereby helping to stave off hunger over longer periods), contain a greater density of vitamins and/or minerals, and, due to their fiber content, promote faster and thereby typically preferable transit times through the large intestine than is the case for less complex carbohydrates.

The above video provides a nice overview of "good" versus "bad" carbs particularly in terms of complex carbohydrates versus less "complex" starch-based foods as well as simple carbohydrates.


Carbohydrate consisting of more than a few sugars that have been chemically linked together.
The most common of polysaccharides are starches and cellulose. Starch is a digestible polysaccharide that is first broken down to shorter units such as maltose (via the action of especially amylase enzymes) and then to individual glucose molecules (via the action of maltase enzymes). Glucose is the absorbed into our blood in the small intestine.

The more easily amylase enzymes can reach starches along with the shorter gastric emptying time, then the more rapidly available is glucose derived from starch during digestion. Thus, meals that consist of highly refined starch without associated protein and fats tend to both be converted to glucose rapidly and leave our stomachs rapidly, contrasting the lower or slower availability of glucose from starch given ingestion of starch instead in the form of complex carbohydrates.

Cellulose, by contrast, is a form of insoluble fiber that is not digested except to the extent that microorganisms are present which can break it down for us. Cellulose, like starch, nonetheless is a polymer of exclusively glucose moieties.

Links to terms of possible interest: Amylose, Carbohydrate, Cellulose, Glucose, Glycosidic linkage, Moiety, Polysaccharide, Starch, Subunit

The above video considers the digestion of the polysaccharide, starch, via hydrolysis into maltose, with the concept of dehydration synthesis also discussed; note that glycogen, as found in our muscles and liver, is a kind of starch, a point not really made in the video.


Water-soluble, colloidal carbohydrate polymers that serve as storage molecules for glucose.
Starch derived from plants is a key source of Calories in most of our diets. Anything that is made with grains (such as wheat or rice), or with root vegetables (e.g., potatoes), is supplying starch to your diet. In addition, there can be starch associated with animal-based food, in the form of the animal starch known as glycogen. For most of us starch is derived particularly from plants, however.

While starch is a polysaccharide, often relatively complex in terms of its three-dimensional shape, and certainly not a sugar, starches nonetheless are not necessarily "complex" carbohydrates as that term is more of a description of the other materials that a starch is found in association with (e.g., dietary fiber).

As starches are polymers of glucose, they contribute directly to blood glucose in the course of digestion and absorption. The faster a starch is digested, as well as the more that is consumed, then the faster as well as greater amounts of glucose that enter the blood. For those individuals who both produce and respond normally to insulin, this is not of enormous concern, though for those who are diabetic the consumption especially of refined starch can lead to substantial spikes in blood glucose levels (excessive amounts of blood glucose).

The digestion of starch involves a series of enzymes known as amylases, including salivary amylase, but also maltase, which is responsible for breaking down the disaccharide product of amylase-mediated digestion into individual glucose molecules. It is the glucose which can then be absorbed.

Links to terms of possible interest: Amylopectin, Amylose, Carbohydrate, Glycogen, Polysaccharide, Starch

The above video provides a nice introduction to what plant-derived starch is along with how it can resist digestion—not all starches will serve as equivalent sources of blood glucose and Calories.

The above video provides a nice overview of how starch is digested as well as absorbed.

Dietary fiber

Indigestible soluble or insoluble especially long-chained compounds that are associated with plant material.
Dietary fiber is not a digestive aid and indeed can interfere with digestion, that is, the breakdown of food materials into absorbable products. In addition, dietary fiber generally is of plant origin. Dietary fiber also is not an absorptive aid, and in fact can even interfere with absorption. Rather, dietary fiber is helpful to the extent that it slows digestion, thereby interfering with peaks in blood glucose levels.

Dietary fiber interferes with the absorption especially of Calories, thereby interfering with caloric uptake, often a good thing in societies where Calories can be excessively plentiful but exercise less so, or contributes to the growth of beneficial microorganisms in our large intestines and/or the relatively rapid passage of chyme through the large intestine. In a sense, then, dietary fiber contributes to our doing a number of things during digestion that can be helpful to the general functioning of our bodies. Alternatively, the consumption of dietary fiber can lead to increases in flatulence.

Links to terms of possible interest: Dietary fiber, Insoluble fiber, Soluble fiber

The above video provides a quick primer on the difference between soluble dietary fiber and insoluble dietary fiber.

The above video provides an overview of soluble dietary fiber and insoluble dietary fiber.

Insoluble fiber

Indigestible plant material that does not dissolve in water though may absorb water during digestion and is either fermented or serves as a bulking agent during feces formation.
The absorption of water by insoluble fiber literally increases its bulk as well as counters the overall removal of water from chyme in the course of formation of feces. This keeps feces softer, which in turn aids the ability of feces to move through especially the large intestine towards the anus.

Among insoluble fiber is lignin, which is the substance that otherwise makes woody plants woody, as well as the bran associated with grains such as wheat. Generally, insoluble fiber is more likely to not be fermented during passage through the large intestine, though there are exceptions such as starches that resist digestion but then are broken down and fermented within the large intestine.

More soluble dietary fiber versus insoluble dietary fiber.

Soluble fiber

Indigestible plant material that dissolves in water and typically is fermented in the large intestine.
In addition to dissolving, more specifically soluble fiber is able to form colloids, which are highly "wetted" suspensions of materials, e.g., such as most proteins are colloidal as too are starches (though neither of those are examples soluble fiber). Both soluble fiber and insoluble fiber, however, attract water molecules and therefore contribute to the bulk of chyme. Soluble fiber, however, does not contribute to the bulk or softness of feces so long as it instead is digested within the large intestine prior to the point of feces formation. Important sources of soluble fiber- containing foods include oats (as in oatmeal), among grains, but also numerous other fruits or their associated seeds (e.g., beans).

The above video is the American Heart Association's perspective on soluble fiber.

Protein (dietary)

Sources of amino acids during digestion and which upon digestion are worth ~4 Calories per gram to us in energy. g
Proteins are amino-acid polymers, that is, long chains of chemically bonded amino acid moieties. There are 20 amino acids that are used to make proteins in our bodies. Some of these our bodies can synthesize from other substances, others we can't synthesize so we must obtain them in our diets (these are called essential amino acids), and yet others we can't synthesize though nonetheless can covert other amino acids into, particularly those that we obtain in our diets. In any case, our bodies are not able to start with pure atoms and produce amino acids, but instead do so from nutrients that consist of already nitrogen-containing compounds, that is, a nitrogen source.

As amino acids are the key source of nitrogen-containing molecules, proteins are a key source of nitrogen in our diets. Note, though, that nucleic acids, such as make up our DNA, also consist of nitrogen-containing compounds (known as nucleotides) and these too are synthesized from already nitrogen-containing compounds, that is, as also obtained from our diets in the form of a nitrogen source. Thus, dietary proteins supply both amino acids that we can't synthesize ourselves along with a source of nitrogen from which we can synthesize nitrogen-containing compounds generally, including amino acids and nucleic acids.

As most diets contain sufficient amounts of amino acids, adequate protein intake – particularly for diets that are relatively lacking in animal protein, i.e., those of vegans and vegetarians along with starving individuals – is usually measured in terms of relative amounts of essential amino acids that are ingested.

The above video is Dr. Andrew Weil's take on dietary protein and diet.

The above video provides an overview of the digestion of dietary protein.

The above video considers just what is a protein as well as amino acids; note that the video doesn't really consider the issues of dietary protein.

Essential amino acids

Protein primary structure constituent that cannot be synthesized by an organism and therefore which must be supplied to an organism such as dietarily.
Essential amino acids are those that we are unable to synthesize within our bodies but must obtain in a more-or-less fully synthesized form within our diets. Absent access in our diets to all required essential amino acids then our bodies are unable to synthesize all necessary body proteins, resulting in disease. Good food sources of all of the essential amino acids are described as complete proteins whereas food sources that are deficient in one or more essential amino acids are described instead as incomplete.

Most protein from animal sources is "complete whereas protein from individual plant sources typically is incomplete even if the source is relatively rich in protein overall (plants tend to do this "on purpose" since doing so tends to limit the potential for one or more animal species to specialize on the consumption of a single plant species). Protein sources of plant origin nonetheless can be "completed" by combining sources which are deficient in one set of essential amino acids with a second source that is deficient in a different set of essential amino acids, e.g., rice and beans.

The above video provides a good introduction to what amino acids and their role in our diets is all about, though beware of the reference at 1:05 to neurotransmitters being proteins (which they are not, as the video in fact provides a correction of).