That “Carbohydrates are the major source of energy for people throughout the
world” (text, pg. 12-2) should not be surprising to you, given that we have previously discussed
Human Biology as being programmed for carbohydrates as the primary energy source, because cellular
respiration has as its initial substrate glucose (or any sugar analog). Cellular respiration in all
animals [and even plants, protists (protozoa & algae), fungi, and some bacteria] is the same. If
this were on one of the Discovery Channels, we might say that Life on Planet Earth has been
carbohydrate based for the last 2 billion years.
In the broadest overview [least detail] the simplest carbohydrates are monosaccharides [C6H12O6, or perhaps a better description would be H7C6O(OH)5] which are synthesized from Carbon dioxide and Water in chloroplasts using solar energy as the source of energy for the reactions called photosynthesis:
6 CO2 + 6 H2O + sunlight → C6H12O6 + 6 O2.
The resulting sugar is broken down to Carbon dioxide and Water in mitachondria, releasing the stored energy during the reactions called respiration:
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 4 kcal/g.
Simple sugars include the monosaccharides [glucose, fructose and galactose] and the disaccharides [sucrose, maltose and lactose]. Introductory Biology texts state that chloroplasts produce monosaccharides, but Botany texts point out that the assembly of monosaccharides into disaccharides takes place in chloroplasts. Very little, if any, monosaccharides are released from chloroplasts into the plant cells. Most of the sugar delivered to the plant cells, and eventually to sap, by the chloroplasts is the disaccharide sucrose, composed of a glucose [“blood sugar,” (listed on food labels as “sugar”) also called “dextrose” (often seen in the ingredients list on food labels as if it were different from sugar)] and a fructose [“fruit sugar”]. Glucose forms a ring by joining the 1'-C via an O to the 5'-C [illustration available (downloaded from www.palaeos.com/Fungi/FPieces/CellWall.html by Dr LaFrance on 7 February 2009)]. Fructose is an isomer [same chemical formula, but different arrangement (the 2'-C is joined via an O to the 5'-C) or structural formula] of glucose, and is converted from glucose in the chloroplasts. Some plants manufacture, and store, maltose [the glucose - glucose disaccharide], “malt sugar,” but this is converted from sucrose in the plant cells outside the chloroplasts. The third, and final, disaccharide found in living organisms is lactose, “milk sugar,” found in mammals milk. Lactose is the glucose - galactose disaccharide, where galactose is another glucose isomer [with the -OH on the 4'-C rotated]. Galactose is converted from glucose, then polymerized with glucose to lactose, in glandular cells in mammals.
Polymers [“poly” = many; “mer” = units] are large to very large molecules made of many similar repeating units. The synthesis of [reduction to] polymers is referred to as “polymerization,” and the generic chemical name is “poly-(name of unit),” such as polyethylene [a polymer of ethylene, CH2=CH2 molecules], although polyester refers to a polymer in which the units are joined by ester bonds [if you don't know what is an ester bond, ask your favorite chemist to explain]. This becomes relevant to the Science of Nutrition when disaccharides are polymerized to complex carbohydrates (in the next exciting episode… I mean, paragraph).
Complex carbohydrates are polymers of disaccharides, and can be called polysaccharides. The polysaccharides are grouped into starch and cellulose, depending on digestability by Humans. Starch can be digested by Humans (and most animals), and has the 6'-C of both monosaccharides on the same of the disaccharide units. Cellulose can be digested only by some Protista (protozoa) and by some Bacteria, and has the 6'-C of the two monosaccharides on opposite sides of the disaccharide units. For the purposes of the remainder of discussion, I will restrict the term “polysaccharide” to partially digested starch molecules.
For large polymers we can determine the number of units by dividing estimated the molecular weight of the polymer by the theoretical molecular weight of the units. We use chromatography to estimate the molecular weight because the speed at which any molecule moves through the chromatography medium is inversely related to its molecular weight [heavier molecules move slower than lighter molecules]. For example, the theoretical molecular weight of sugar is calculated as follows:
|col 2 X col 3
|Molecular wt (of sugar)=||180|
Those starches which have been studied consist of about 15,000 disaccharides in the polymer. A few
are linear (straight line polymer), but most are branched. Digestion by amylase in Humans begins on
the 1'-C end of the polymer and removes 1 disaccharide at a time. Cellulose consists of about 150,000
disaccharides. Since amylase can digest starch [with the 6'-C, as H2C-OH, on the same
“side” of the polymer] and can not digest cellulose [with the 6'-C, as H2C-OH,
alternating “sides” of the polymer], it has been hypothesized [the Lock and Key
hypothesis] that the shape of the enzyme is important by allowing the enzyme to fit only the
correct substrate. Similarly, my office key fits and opens my office lock, but will not open the
front door to your house. By extension, as the enzyme amylase travels from the 1'-C end of a branch
on a starch polymer, happily removing disaccharides, the inactive end of the enzyme [analogous to the
“handle” end of the key] will eventually bump into the branch point, and be unable to
remove the next disaccharide! This means that after complete digestion of a starch [for
example a french fry], the end products will be a lot of disaccharides and a few undigestable
polysaccharides [which are called dietary fiber]. Cellulose [for example, the cell walls in lettuce]
are not digested by amylase to release even 1 disaccharide, and are considered to be insoluable
fiber. But remember those E. coli that you are giving room & board are expected to digest,
at least partially, some of the cellulose, so you can get to the vitamin-dense [remember the concept
of “nutrient density?”] contents of the lettuce cells.
So if carbohydrates, or “carbs,” are so important [as your primary energy source], where do you find them? Actually, we first have to determine which carbs we want, then worry about where to find them. Historically [assuming that history does not go all the way back to my birth year], we would have given a very simple answer: avoid sugars, and concentrate on complex carbohydrates (easily digested ones if you're planning on intense exercise soon; slowly digested ones if you are planning to avoid exercise). While we all agreed with each other that this was great advice, it is over-simplified, and potentially dangerous to the goal of causing patients to live longer and to maintain quality of life while doing so. Instead, we now have the glycemic index, which estimates “how much your blood glucose increases in the two or three hours after eating.” (downloaded from Mr. Mendosa's website, http://www.mendosa.com/gi.htm, by Dr. LaFrance 7 February 2009) While the original intent of the development of the glycemic index was to assist diabetics in managing their blood glucose, its use has been expanded to include weight management. It is possible that the glycemic index could be useful to the general adult population for managing longevity and quality of life, but at present the research to find low glycemic index foods is too great to make the approach practical.
The premise is that adult Humans should avoid unnecessary spikes in serum glucose. For a discussion of the role of excess glucose in the aging process, read Roizen & Oz, You, Staying Young, especially pp. 136 - 142. The ‘simplest’ solution is to reduce simple sugars in the diet. Sugar is listed in the ingredients list on the food label as sugar, but is also ‘hidden’ on the label as dextrose [synonym for sucrose, a.k.a. sugar], fructose, corn syrup, high fructose corn syrup, alcohol sugars (such as mannitol, sorbitol, xylitol, and other similar -itols). Roizen & Oz (in You on a Diet recommends avoiding any item in the food supply (grocery store) that has sugar [and dextrose and/or fructose], corn syrup or high fructose corn syrup, as well as enriched, bleached or refined flour among the first five ingredients (p. 48). Although the highly processed flours and the sugar alcohols have a lower glycemic index than do the simple sugars, I recommend reducing these items in the diet as well. The other step necessary to reduce simple sugar intake is to use less table sugar (or sugar substitutes); and learn to appreciate the actual flavor of the food rather than the combined flavors of added sugar and salt. [This advice is easy for me to say, my estimated body fat is 18%, but hard for most people to accept because most people have become so accustomed to eating over-sweetened and over salted food.]
The best indicator that a food item contains relatively low glycemic complex carbohydrates is ‘whole grain’ in the ingredient list on the food label. Plant seeds consist of an embryo plant and sufficient nutrients to allow the embryo to grow up to be a healthy young plant able to carry out photosynthesis, to take up minerals from soil moisture, and to manufacture its own nutrients such as vitamins. The cereal grains are seeds of agricultural grasses, and as such contain an embryo and some minerals and vitamins (collectively called the “germ”). The remainder of the seed is stored carbohydrates and/or oils as an energy source for the developing embryo. Degermed means the removal of the germ (along with most of the vitamins and minerals); bleached means that nutrients other than starch and/or oils have been removed from the stored enegry substances, and that the some of the complex starches have been oxidized to polysaccharides. Enriched means that vitamin & mineral supplements have been added to replace the natural vitamins and the minerals removed. The ‘enriched’ vitamin compounds may or may not be absorbable by you. Not only does this processing reduce the nutrient value of the grains, but it probably also increases the glycemic index from ‘good’ to ‘not so good.’
Ideally, Calories from total carbohydrates should be 45 - 50% of the total Calories (including Calories from Protein). [remembering that you will eventually have a term paper due, how does your diet analysis patient compare to this guideline?] The amount of Total Carbohydrates, in grams, from the Nutrition Facts portion of the food label times four (4) will give you the Calories from Carbohydrates. The minimum intake of Calories from carbohydrates should be 40%; and the maximum, 65% of total Calories. The minimum DRI for carbohydrates is 130 g (520 Calories). In Humans who make insulin (Type I Diabetics do not make insulin; Type II Diabetics have become insulin-tolerance, meaning that they do not use the insulin they produce) excess sugars are polymerized (mostly by the liver, and to a lesser extent skeletal muscles) to glycogen, or animal starch. Glycogen is stored in the liver where it can be used to make glucose for return to the blood stream when serum glucose drops, and in skeletal muscle where it is used to make glucose during strenuous exercise. Shier [Shier, David. (2007). Hole’s Human Anatomy & Physiology, 11th Edition. New York, New York: McGraw-Hill] states that typical adult Humans can store up to about 4,000 kcal as glycogen (with 3,000 kcal stored in the liver, and 1,000 kcal stored in skeletal muscle) which is enough to fuel moderate exercise for three hours. Smooth muscle and cardiac muscle neither store nor use glycogen. Excess sugar beyond that needed for glycogen stores is converted to fatty acids, then to fat to be stored in adipose tissue. Each pound (453.6 grams) of adipose fat stores 4,082 kcal (9 kcal/gram) for “future” use. [So… a 160 lb, 5 ft 10 inch, adult Human with 18.5% fat is storing 120,837 kcal (in 29.6 lbs of fat) ‘just in case’ Pleistocene winter returns! (but hoping it lasts only 120 days). To be a candidate for a diagnosis of obesity this same imaginary 5 ft 10 Human would have to have at least 78.6 lbs of adipose fat which would store only 320,871 kcal (enough to fuel 10 days of continuous moderate exercise without eating).]
Diabetics reach the threshold for conversion of excess sugars to fatty acids much quicker than non-diabetics. [In case you missed the implication of this for Type II Diabetics: Type II Diabetes is ‘caused’ by obesity, and the quicker conversion of sugars to fatty acids aggravates the obesity, which aggravates the diabetes…]
Artificial sweetners were invented originally to provide a sweetner which Diabetics could use without producing the dramatic increase in serum glucose which characterizes the disorder. The first of these was saccharin. When sugar shortages occurred during the two World Wars, saccharin was marketed to the general population as a “safe” alternative. After World War 2, sugar became readily available again, and the market for saccharin dropped. A little over a decade later, saccharin manufacturers started marketing saccharin as a “healthy” alternative to sugar. As the baby boomers [at that time defined as those children conceived during World War 2] became young adults obsessed with being skinny [TV had brought the entertainment industry into the American living room, and TV tends to make people look fatter than they are, according to the TV equivalent of gossip columnists of the decade], the marketers of artificial sweetners found an eager target for ‘non-fattening’ sweetners, and the number of such products grew rapidly. We now have saccharin, aspartame, sucralose, acesulfame potassium, & cyclamate. Meanwhile, the rise of “environmental awareness” [which has never been bounded by the principles of the science the supporters of environmentalism cite to justify their conclusions] brought challenges to the safety of artificial ingredients in food or anywhere else for that matter. The “data” in support of the artificial sweetners is biased, being from studies conducted by the manufacturers of the artificial sweetners; while the “data” justifying the scare tactics of the opponents of the products is also biased, being from studies conducted by non-scientists to support their opinions. My personal opinion is that I have had 440 million years of evolutionary time to adapt to acquiring all of my nutrients from ‘real’ food, but only zero (0) generations [in my family tree] to develop adaptive mechanisms to deal with synthetic ingredients in food; besides I like the taste of real food!.
Sugar alcohols have a misleading name. Technically, an alcohol is “An organic chemical in which one or more hydroxyl (OH) groups are attached to carbon (C) atoms in place of hydrogen (H) atoms” (definition downloaded by Dr. LaFrance on 9 February 2009 from http://www.medterms.com/script/main/hp.asp). By this definition all sugars are alcohols; the monosaccharides [H7C6O(OH)5] are organic molecules with 5 -OH's attached to C atoms. However, “Sugar alcohols are neither sugars nor alcohols. They are carbohydrates with a chemical structure that partially resembles sugar and partially resembles alcohol… They are incompletely absorbed and metabolized by the body, and consequently contribute fewer calories than most sugars” (from the International Food Information Council Foundation website, downloaded by Dr. LaFrance on 9 February 2009). This website also notes that these substances occur naturally in many fruits and vegetables, but also synthesized in commercial laboratories for use in food products. Basically, the sugar alcohols are poorly digested carbohydrates, which can be digested by bacteria in the colon producing gaseous by-products. [Later, we will see that these gaseous by-products, which are expelled as ‘rude noises,’ are also one of the symptoms of “lactose intolerance.”]
The risks associated with carbohydrates, either in excess or in deficiency are limited:
Lactose intolerance has become popular with the population of persons with self-diagnosed conditions (aided by access to on-line sources without regard to website reliability). Most such individuals who have explained their lactose intolerance to me have reported signs [not symptoms] of mild food allergies, such as hives, redness & itchy patches on the skin. Medically diagnosed lactose intolerance is a result of incomplete galactose metabolism, and has, as symptoms, gas (belching & flatulence), nausea & abdominal pain, and diarrhea; the same symptoms as are associated with excess consumption of sugar alcohols.
The sugar high does not exist. In children diagnosed with autism or with ADHD, red dye (food coloring) has been shown to produce the sugar high in double-blind trials. Hig simple sugar density food are known to cause the “sugar crash” which normally follows the red-dye high.
Simple sugars consumed in excess may cause caries, even with low sugar-density foods.
Long term, chronic excess intake of carbohydrates, either as total grams of carbs, or as a percent of total Calories, causes weight increase, eventually leading to obesity and morbid obesity (diagnosable medical conditions, requiring diagnosis by a licensed diagnostician).
Morbid obesity greatly increases the risk of developing Type II Diabetes.
The most familiar sign of sub-clinical carbohydrate deficiency is ketosis. Some popular weight management diets encourage the patients to develop ketosis as the predictor of successful weight loss, although from a biological point of view, ketosis as a sign of carbohydrate starvation is more likely to produce weight gain such as is seen in hibernating animals just before hibernation begins. The symptoms of clinical carbohydrate starvation are, in order of development: uremic poisoning [seen as jaundice], kidney shut-down, kidney failure [seen as jaundice of the whites of the eyes, a nursing diagnosis requiring dialysis STAT], followed by death.
TABLE OF CONTENTS
© 2004-2010 TwoOldGuys
revised: 02 Jun 2010