The Truth About Carbohydrates

All of us living the Low Carb lifestyle use the words carbohydrate, sugar, and starch on a daily basis.But although we use the words freely, not everyone is clear on just what those words mean, how the substances relate to one another, or how they relate to other things we eat. So, let's start at the very beginning, and build an understanding. Just take one sentence at a time, and I promise that you will be an expert when we reach the end.

First, it is important to understand two basic facts that lie beneath all discussions having to do with food.

Fact 1: Every single thing we eat, without exception, can be classified as one or a combination of only these five substances: carbohydrate, protein, fat, vitamin, or mineral.

Fact 2: All the things we eat (which are one or another of those five substances) are composed of one or combinations of some of the 100+ 'basic elements' that make up everything known to exist in the world, or in the universe, for that matter.

I'm certain that you are already familiar with many of these basic elements, although you might not have known that basic elements are what they are. For example, you already know the names carbon, oxygen, hydrogen, sodium, and calcium. If you want to know the names of the rest of the basic elements, look in any chemistry book for what is called "The Periodic Table of Elements."

How Carbohydrates Are Digested

Now that we know the two basic facts, we can go on. The word carbohydrate means 'a combination of carbon, hydrogen, and oxygen.' We generally use the abbreviation 'carb' for carbohydrate, but you may also have seen it abbreviated as "CHO." Those letters stand for carbon, hydrogen, and oxygen.

Let's divide the word carbohydrate into its components. The "carbo-" part means carbon. Note that the "-hydrate" part of the word is like 'dehydration' or 'hydrant,' as in fire hydrant. These words relate to water; water is composed of hydrogen and oxygen. So, now we can understand that carbohydrate more specifically means "one of many different combinations of carbon, hydrogen, and oxygen, whose various sections join and break apart by taking on, or releasing water." This explanation may seem a bit technical, but knowing it will help you understand what happens to sugar, as we go along.

Now we know what a carbohydrate is. The next question is: "What things are carbohydrates?" The answer is that carbohydrates are sugars, starches, dextrins, and gums. I'll discuss dextrins and gums at another time. For now, we are going to focus on sugars and starches.

One of the important words that refers to sugars and starches is saccharide. (Think about the artificial sweetener, saccharin. They made up, deriving it from the word saccharide.) There are two types of saccharides that concern us here, the mono-saccharides ("mono-" means "one"), which are also called the simple sugars, and poly-saccharides ("poly-" means "many"), which are also called the complex sugars. Complex sugars are broken down in the human body by digestive process into simple sugars. They do this by coming apart at the water connections in a process called hydrolysis ("hydro-" means water; "-lysis" means breakdown).

The Sugars

The simple sugars in foods that are most important to human nutrition are called sucrose, fructose, lactose, and maltose. But the body wants the simple sugar called glucose, so these other simple sugars break apart in the body to become glucose. They do this by coming apart easily at the water connections.

Sucrose is table sugar. Sucrose is the form of sugar we are most familiar with. It is obtained from sugar cane, sugar beets, and the syrup from sugar maple trees. It is also naturally present in some amounts in most fruits and vegetables, along with higher amounts of other sugars. Whenever the word "sugar" is used in common conversation, it is usually sucrose that is being referred to. Two other names for sucrose are dextrose and saccharose.(Do not confuse saccharose with sucralose. Sucralose is the artificial sweetener, Splenda.)

Fructose is the form of sugar found in fruits, honey, and corn. It is sometimes called levulose. In recent decades, fructose has been super-refined to make the sweeteners known as corn syrup and high fructose corn syrup. Since fructose in those forms can be made to be very concentrated, and since it is much sweeter to our taste buds than sucrose, fructose is the poster child for economic success in the food industry. Pushers of fructose tell us that it is better to use it because "It is natural," or "Since it is sweeter, you'll use less of it than table sugar," or even that foods containing it are "sugar-free."

Yes, fructose is natural. So is sucrose, and so is arsenic, for that matter. Yes, it is sweeter to the taste, and you can use less of it, but even the lesser amount is too much. Yes, it is "sugar-free," but that's because there is a legal definition of "sugar" in the food industry. Under the legal definition, if a food product doesn't contain sucrose, it may be called "sugar-free." Governmental officials who make these stupid rules should read this article, and become informed as to what "sugar" actually means!

Lactose is the sugar found in milk and cottage cheese. Maltose is the sugar in grains. And, all four of the sugars we have been talking about break down easily into glucose in two simple, water-related steps.

You will notice that many sugar-related words end in the letters "-ose." When you read ingredients on labels, consider every word that ends in "-ose" (or "-oses") to be sugar. There are two notable exceptions: cellulose and sucralose. Cellulose, while it is a complex sugar, is not digested by our bodies, and therefore doesn't enter into sugar considerations. Sucralose/Splenda does not provide usable carbohydrates in its pure form.

The Starches

Now, let's talk about starches. Starches include such foods as potatoes, cereals, wheat and other grains, and rice. A few paragraphs above, we talked about mono-saccharides and poly-saccharides. Mono-saccharides are the simple sugars. Poly-saccharides are the complex sugars. Starches are complex sugars, and complex sugars break down into one of the simple sugars (maltose), and then to glucose by (you guessed it!) easily breaking apart at the water connections.

Since starches do not taste very sweet, they do not jump to mind when sugar is mentioned, but they quickly become the simple sugar maltose, and then the simple sugar glucose because the breakdown of starch from the complex sugar form to the simple sugar form is quick and easy. Essentially, starches are sugars that merely require a few more steps to make them into glucose, but they are no better for the low carb diet than sugar.

Starches are often given names than end in the letters "-an," such as glycan or mannan. When you read labels and see ingredients you don't recognize, it is best to assume that any word that ends in "-an" (or "-ans") is a starch.

In Conclusion

A Review Of Carbohydrates

We have previously discussed what is actually meant by the words 'carbohydrate,' 'sugar,' and 'starch,' and how these dietary elements relate to one another. As a quick review, you will recall that carbohydrates are either simple sugars, complex sugars, or starches.

Remember that both starches and complex sugars very easily and quickly break apart into simple sugars by coming apart at their water bond connections. The simple sugars are broken down (digested) by the body, into the simple sugar called glucose, because the body runs on glucose. Since all carbohydrates that can be digested become simple sugars, there is no such thing as a 'bad' or 'good' carbohydrate. There are only carbohydrates that can be digested and carbohydrates that can't be digested. This is where we encounter the concept of dietary fiber.

What Is Dietary Fiber?

Although words ending is the letters '-ose' are sugars, some of them, like cellulose, are not available to our bodies as sugar.

You will recall that the actual definition of the word 'carbohydrate' is 'one of many combinations of carbon, hydrogen, and oxygen that come apart at water bonds.' But there is nothing in this definition that implies that all carbohydrate combinations come apart during the digestive processes of our bodies.

Consider this. The bonds holding carbohydrate substances together can't merely come apart by themselves. If that were so, they would just fall apart all over the place, and there couldn't be such a thing as a 'complex' carbohydrate. The bonds must have structural strength, and that means something is required to cause or permit the breakdown of the carbohydrates to occur. This something is called a 'catalyst.' For digestion to occur, the necessary catalysts for digestive breakdown are substances in our bodies called 'enzymes.'

The human body secretes carbohydrate-digesting enzymes of several kinds both in saliva and in the gastrointestinal tract, but we don't secrete an enzyme for the breakdown of every conceivable kind of carbohydrate. Since we don't secrete an enzyme which digests cellulose, we can't eat trees. Wood is made of several types of carbohydrates, but we don't have the right enzymes to break the connecting bonds of those kinds of carbohydrates. So when we say that a certain carbohydrate (like cellulose) is not digestible, we mean that we do not produce the necessary enzymes to break the water bonds, and therefore the simple sugars that would be in those non-digestable complex carbohydrates are not available to us as food.

Non-digestible carbohydrates are variously called dietary fiber, crude fiber, indigestible residue, gums, and roughage. Although the fiber doesn't contribute to our nutritional needs directly, it is essential to our bodies because it causes the action necessary to clear the intestinal tract. In particular, fiber helps with diets designed for weight loss because it takes up room in the digestive tract without adding useful sugars. This is the reason some low carb diets tell us we don't have to count fiber. A person could mix a pound of saw dust into a cup of ice cream, and it wouldn't make the slightest difference in how much simple sugar reached his or her digestive system. The only food available to his or her body would be in the ice cream.

Some dietary fiber dissolves in water or absorbs water. We call this type of fiber 'soluble fiber.' Fiber that does not interact much with water, we call 'insoluble fiber.' Soluble fiber is very useful as prevention for constipation, since the water causes the fiber to swell up, thereby producing more bulk in the intestinal tract. But do not confuse solubility with digestibility. They aren't the same thing.

We now understand that how (or if) carbohydrates are (or can be) digested in the body depends upon how they are put together by nature, and whether or not we have the enzymes to break the bonds to get at the simple sugars. This leads to the next subject: the glycemic index.

What Is The Glycemic Index?

The word 'glycemic' means 'having to do with glucose in the blood.' The glycemic index is a number that represents the speed of carbohydrate breakdown in an 'average' person's body, and the 'average' effect on the blood sugar levels of that 'average' person of any particular carbohydrate food. It is not a very scientific measurement, and we should all take it with many grains of salt!

Different carbohydrate foods have different glycemic index numbers for four basic reasons: the differences in the way the carbohydrates are put together by nature (as we discussed above), the ease in which the complex carbohydrates come apart under the action of our bodies' enzymes, the degree to which the carbohydrate foods are already broken down by other processes outside our bodies (such as the difference between cooked carrots and raw carrots), and how much fiber, protein, and/or fat is in the food, in additional to the digestible carbohydrates.

How Is The Glycemic Index Of A Particular Food Determined?

A group of people is assembled, and the fasting blood sugar levels for each individual are measured. The test subjects then all eat a specified amount of a particular food. Their blood sugar levels are measured frequently for next several hours, and an average of those various blood sugar levels is determined. From this information, a glycemic index value is given on a scale of from one to one hundred, comparing it to a so-called reference food, which is given the arbitrary value of 100.

Now it gets even more confusing. There is no standard for what constitutes the reference food. Some glycemic index systems use glucose as the standard, but others use white bread. On the scale where glucose is 100, white bread is 70. But on the scale where white bread is 100, glucose is over 125.

While it is true that the lower the number, the less the impact that food will have on the 'average' person's blood sugar, the actual numerical values depend on which scale has been used, and there is no particular reason why someone else might not come up with another scale in the future, based on a completely different reference food. Furthermore, there is really no such person as 'the average person.' We are all unique.

Why Is Knowing The Glycemic Index Of Foods Valuable To Low Carbers?

Even with all its faults the glycemic index has value to low carbers. It shows that complex carbohydrates and starches are not necessarily better for our blood sugar levels than simple carbohydrates and sugars are. The glycemic index of some complex carbohydrates is actually much higher than the index number of some simple sugars. For example, pure sugar has a glucose scale index of about 65, while rice cakes have a glucose scale index of more than 75!

A low fat/high carb diet increases the problems brought on by high glycemic index foods because high index foods are recommended, and because foods that would reduce the effect of the rising blood sugar, such as meat and fat, are shunned. This results swings in blood sugar levels, increased insulin release into the blood, hypoglycemia episodes, higher blood sugar levels for diabetics, and all the problems we recognize as being associated with insulin production.

In Conclusion

As we go along in this series of articles, we will be discussing diabetes and the effects of insulin in greater detail. But in the next article we'll continue our discussion of carbohydrate breakdown under the influence of enzymes, and what happens to the carbohydrates once they are in the body.

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By Dr. Beth Gruber

A Quick Review

Let's have a quick review of where we are in our study of carbohydrates. From our previous discussions, you now understand that everything we eat is one, or a combination of, five substances: carbohydrate, protein, fat, vitamin, or mineral. You now know that ‘carbohydrate’ means 'one of many different combinations of carbon, hydrogen, and oxygen, whose various sections join and break apart by taking on, or releasing water,' and that this is done in a process called 'hydrolysis'.

We have discussed that sugars and starches are the major categories of carbohydrates that we are concerned with, and that starches are really just complex forms of sugar. You now know not to be led down the primrose path with talk of high or low glycemic index, since complex sugars break down into simple sugars. And, we discussed that foods that are full of sugar can be called 'sugar-free' if they don't contain table sugar (sucrose).

In the last article, we discussed fiber, those carbohydrates that cannot be digested, and we started our discussion about how the body digests carbohydrates with the help of enzymes. Now we are ready for a further look into enzymes and what happens to carbohydrates once they enter the digestion.

What Is Digestion?

Those of us who are concerned with limiting nutrients in order to drop pounds often forget that the body is in the business of taking in food and using it to its own best advantage. We must remember that the body wants to take in the nutrients in food. Very few foods, however, are ready for use by the body in the state in which we eat them. Water, a few of the simple sugars, vitamins, and some minerals make up almost the entire list of such substances. Everything else must be digested, that is, converted by the body into products suitable for absorption and utilization. We have taste buds so we will enjoy the food, and luckily, the mechanisms for getting the foods to a usable condition has been made easy for us. Digestion is the way.

What Are Enzymes?

The prime movers in the breakdown of foods are called enzymes. In fact, it has been said that enzymes are the mediators of most, if not all, life processes. Enzymes are protein substances that are normally produced by the body to cause or allow specific actions.

The enzymes for food digestion are often named for the food they act upon with the use of the letters ‘-ase’ added to the end of the word. Thus, we produce 'sucrase' to act on sucrose, 'lipase' to act on fat (‘lipo’ = fat), and 'amylase' to act on starch (‘amylose’ = starch). Often the source of the enzyme is part of the name too, such as 'pancreatic lipase,' the fat-digesting enzyme that is produced in the pancreas. Sometimes the letters '-lytic' or '-lysis' are used with the name of the enzyme to signify a breaking apart. (Remember 'hydrolysis', breaking down in the presence of water?) Thus, we have the 'gastric proteolytic enzyme,' pepsin, which is produced in the stomach (‘gastric’ = stomach), and breaks down protein (‘proteo’ = protein).

Enzymes are partially destroyed while performing their digestive function, so the body must continually make more. Any decrease or increase in enzyme production or enzyme activity results in malfunctions and disease. If the enzyme to break down a particular food type is not produced by a person's body, that person is said to be 'intolerant' of that particular food.

People who do not manufacture 'lactase,' for example, are said to be 'lactose intolerant,' and they cannot break down foods containing the milk sugar, lactose. (As unpleasant as lactose intolerance is for the sufferer, it is a relatively mild result of enzymatic problems. Some enzyme deficiencies can cause very serious diseases and mental retardation.)

How Do Enzymes Aid In Digestion?

As a rule, digestion is aided by cooking because the heat causes some foods to begin breaking down. This is especially true of starch, the connective tissue in meat, and other protein foods such as eggs. But most digestion takes place once the food has been eaten.

Enzymes are produced in various parts of the digestive system, and the digestion of carbohydrates begins right in the mouth with the saliva. Saliva contains, and mixes into the food, the amylase enzyme (specifically, ptyalin), which is used for the digestion of starches. The chewing process is also important because it breaks the food into smaller pieces, thereby producing more surfaces for the enzyme actions to take place upon.

In the stomach, digestion continues under the action of hydrochloric acid and enzymes for the break down of protein, sugars, and fats. Hydrochloric acid is necessary, and digestion is harmed by taking antacids. The further digestion of carbohydrates, and some digestion of fats, takes place both in the stomach and beyond the stomach, in the small intestine (the upper part of the bowel). We will talk more about the digestion of protein and fats as we go along, but for now, we are still focusing on carbohydrates.

By the time the food has reached the end of the small intestine, all the usable carbohydrates have been broken down into simple sugars, and the body can begin to absorb and use them. This brings us to the next chapter in our fascinating story: What happens when sugars are absorbed into the body? That is where we will begin when we get together again.
 

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By Dr. Beth Gruber, CarbSmart Contributor

In my last column, we followed sugars and starches through the trail of digestion. We followed the carbohydrate foods through the mouth and down to the upper part of the bowel as they were broken into simple sugars by the action of enzymes produced in the mouth, the stomach, and the small intestine.

A Short Detour: Should We Take Supplemental Digestive Enzymes?

It was my intent, with this column, to continue right along in this discussion with the next part of the fascinating facts of carbohydrate absorption and utilization. But I received a question sent via email from a reader of these pages, and I think her question may also be in the minds of other readers. So we are taking a short detour to talk about the advisability of supplemental digestive enzymes.

As I pointed out last time, those of us who are trying to lose weight, sometimes lose track of the fact that the body wants to take in food and use it to our best advantage. It does this by digesting the food, thereby making it ready for transfer into the body's tissue cells. The necessary factors are enzymes, which are produced in our bodies for this purpose. Only simple sugars can be absorbed into the cells of the body, and enzymes are necessary to break down the complex carbohydrates to the simple sugar stage.

As we learned last time, by the time the food has reached the end of the small intestine, the sugars have been made ready and the non-digestible fiber is in attendance, but there is nothing much else present, in so far as carbohydrates are concerned. However, if there are remaining undigested digestible carbohydrates (either because huge, pig-out amounts of carbohydrates were eaten, or because not enough enzymes were produced), the person will be an unhappy camper because there are not supposed to be large quantities of undigested digestible carbohydrates beyond a certain point in the intestine.

Since there are bacteria in the gut, the bacteria will act on these undigested carbohydrates in a process known as fermentation. This will result in symptoms such as nausea, intestinal gas, flatulence, abdominal swelling, possible diarrhea, possible constipation, and pain. Or, if the carbohydrates are mixed with undigested protein, the bacterial action may result in putrefaction in the gut, which can also result in the same, but often more severe, unpleasant symptoms.

Yes, No, and It Depends

The essence of the question posed by my reader was this: Should a person take supplemental enzymes in order to help the body digest carbohydrates more easily, as was recommended by some (unspecified) diet plan? And, if a person is deficient in digestive enzymes because his/her body does not make enough, is this deficiency a good thing for weight loss?

The answer, dear readers, is "Yes, no, and it depends."

Yes: a person would benefit from taking supplemental carbohydrate-digesting enzymes if his/her body does not produce enough, as evidenced by the presence of the symptoms mentioned above.

No: a person seeking weight loss should not take supplemental enzymes in the absence of such symptoms because, if some of the carbohydrate passes unused from the body, so much the better.

Yes: a deficiency of carbohydrate-digesting enzymes is a good thing for weight loss, in theory, but the weight-loser will be sorry for it. Constant diarrhea is no price to pay for weight loss. Ask any sufferer of Irritable Bowel Syndrome.

No: a person should not try to interfere with their carbohydrate-digesting enzymes by taking such things as Carb Blockers because the resulting symptoms may be severe.

It Depends: taking a general mixture of enzymes as a supplement is only going to help if the proper enzymes are present in the mix. Remember that enzymes are very specific for what they act upon. If a person is deficient in lactase, and is therefore lactose intolerant, taking papain (an enzyme derived from papaya fruit) is not going to help. Papain is used as a meat tenderizer because it acts on protein; it is not a carbohydrate-digesting enzyme.

Back On Track: How Carbohydrates Are Digested

So, all that said, we are now ready to get back on the trail of sugars entering the system. We are in the small intestine and the sugars to be absorbed are all simple sugars. First, some new terms.

New Terms

The term diffusion, as it pertains to carbohydrate absorption, means the transferring of the simple sugars, which are in solution (in water), through the walls of the intestine, and then through the walls of the individual cells of the body tissues.

When we talk about the walls of the cells, we use the term membrane because the wall is extremely thin. The simple sugars and the water diffuse through the membrane walls. But the membrane does not allow everything to flow in or out, otherwise there would be no reason for the membrane to be there at all.

The membrane has what is called selective permeability. That term means that certain things are allowed in and certain things are allowed out, but other substances are blocked passage. The mechanisms by which substance Y is allowed in while substance Z is refused admittance are very complicated.

Only Simple Sugars Are Permitted To Pass Through

For our purposes, suffice it to say that in the case of carbohydrates, the membranes only allow simple sugars to diffuse in, but they does not allow complex sugars or fiber to pass through. Any complex carbohydrates that are still present, all the fiber, and a lot of the water continue down the intestinal tract, where we will catch up to them in another article, some time in the future.

The sugars, meanwhile, pass through the membranes of the intestinal wall and enter the blood, where they are, for the most part, carried directly to the liver. And that is where we will leave it for today.

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By Dr. Beth Gruber, CarbSmart Contributor

 

In Review

As we have discussed in previous articles, digestible carbohydrates must be brought to the simple sugar stage before they can be absorbed. And, as we have learned, this is done in the mouth, stomach, and small intestines by digestion via the action of enzymes in a process called hydrolysis, which involves break down by the removal of water. When the sugars have reached the small intestines, no matter what carbohydrates are the source, they have all become simple sugars. The sugars diffuse through the selective membranes of the small intestines, and then enter the blood.

The Small Intestines

Let's take a look at the anatomy of the small intestines. The small intestines are variously called small intestines, small intestine (with no final S), upper bowel, and small bowel. It is the part of the digestive tract that is located just below the stomach. It is, of course, a tube, but the walls of the tube are folded many, many times.

To get a picture of what these folds are like, carefully slide the paper wrapper off a straw. The paper cylinder is what a straight tube would look like. Now, take the wrapper off a second straw by pushing it down the straw so that it bunches up on itself. Pull the wrapper off the straw so you can see all the folds. Notice how many more surfaces there are on the bunched-up wrapper, up and down the folds. In addition to all the folds of the small intestines, each of the folds has multiple tiny finger-like projections called villi (one is a villus; more than one are villi). Since the tiny blood vessels, the capillaries, are located just on the inside the membrane walls of the multi-folded, villi-loaded small intestines, there are a great number of places for the sugars to transfer across into the capillaries, and into the blood.

How Sugars Effect The Blood

What Does The Liver Do?

Think back to the first article in this series on "Just What Are Carbohydrates?" Recall that I said that the word carbohydrate means 'one of many different combinations of carbon, hydrogen, and oxygen, whose various sections join and break apart by taking on, or releasing water.' To make the complex carbohydrate glycogen, the liver (with help from some specific enzymes) puts the simple sugars back together by rejoining them, using water. The liver does this trick with the substance known as insulin, which is secreted by the pancreas. The process is called glycogenesis (GLY-co-genesis; glyco- means sugar; -genesis means creation).

The glycogen is stored in the cells of the liver, in the muscles, and to a lesser extent, in various other tissues in the body. And, if glycogen is not needed in those places because they are "full," the glycogen converts to body fat.

How Blood Sugar Levels Are Regulated

Carbohydrates furnish the main source of energy for the brain and nervous system, the main source of energy for muscular activity, and provide the energy to maintain body temperature. Sugar must be available at every moment, since it is constantly being used. In order for sugar to be immediately available, a supply of it is always present in the blood. This is what is known as blood sugar, or blood glucose.

As the quantity of sugar in the body is reduced by the expenditure of energy, it is replenished by the intake of food. Since we do not normally eat constantly, but rather eat at intervals, the level of sugar in the blood is kept in line by several hormones that tie up and release the sugar as needed to maintain the level. In an ongoing process, the liver makes glycogen from the sugar, and makes sugar from the glycogen. The reconverting of glycogen to glucose is called glycogenolysis (GLY-co-gen-OL-ysis), which means the breaking apart of glycogen. This is done with the help of another friendly enzyme, glycogen-ase.

The liver stores and then doles out the sugar as needed, maintaining the level much like a thermostat regulates house temperature. The control of the thermostat is done by a balance of hormones: insulin (which directs the liver to store sugar), glucagon (which directs the liver to release sugar), and hormones from the thyroid, the pituitary, and the adrenal glands. Low blood sugar levels trigger the release of glucagon from the pancreas. High blood sugar levels trigger the release of insulin.

Our muscles use the glycogen stored there to perform muscle work, but the work doesn't use up all of the intermediary stages of the break down of the glycogen. Some of the substance that is created by the use of sugar in the muscles still has some usable energy in it. This substance, called lactic acid, is carried by the blood back to the liver, where it is used to make more glycogen, some of which is stored again in the muscles until needed there.

All the various tissues of the body use the sugars, and at the very end, there is nothing left, except carbon dioxide and water. The carbon dioxide is expelled in the breath, and the water is reused, or excreted in the urine. Such a great system!

In Conclusion

So, there we have the essentials of what is supposed to happen in carbohydrate metabolism. But, it doesn't always work that way. Enter diabetes, and other diseases and mistakes of carbohydrate utilization. We will be talking about those things in the weeks and months to come, but first, we are going to continue with what is 'normal' in human nutrition. Next time, we will begin the series "Just What Are Proteins?"
 

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