All Complex Carbohydrates Are Not Created Equal

by William Davis, M.D. Health Professional

Conventional wisdom proclaims that "complex" carbohydrates, such as whole grains and beans, are good for you, better than "simple" carbohydrates like white flour and sucrose.

Is that true?

Complex carbohydrates have greater fiber and nutrient content. They are presumably not as likely to increase blood sugar as simple carbohydrates. Following this reasoning, two slices of whole grain bread should not increase blood sugar as much as a similar quantity of carbohydrate eaten as chocolate chip cookies.

That's not what I see in my heart disease prevention and reversal program. In fact, in my view, there is virtually no difference from a blood sugar standpoint between whole grain bread and cookies: It's all the same. It does not mean that chocolate chip cookies are good for you; it means that both bread and cookies have equal blood sugar implications.

This is because "complex" carbohydrates in wheat products are unique, different from the "complex" carbohydrates in, say, black beans or yams.

The carbohydrate in wheat is composed of polymers (repeating chains) of the sugar, glucose. 75% of wheat carbohydrate is the chain of branching glucose units, amylopectin, and 25% is the linear chain of glucose units, amylose.

Salivary glands and stomach both secrete the enzyme, amylase, that digests both amylopectin and amylose into glucose. Amylopectin is more efficiently digested to glucose, while amylose is less efficiently digested, some of it making its way to the colon undigested. Amylopectin is therefore the "complex carbohydrate" in wheat that is most closely linked to its blood sugar-increasing effect.

Not all amylopectin in complex carbohydrates is created equal. The structure of amylopectin varies depending on its source. Amylopectin can differ considerably in branching structure, which affects the efficiency of breakdown by amylase.

Legumes like kidney beans contain amylopectin C, the least digestible form of amylopectin-hence the gas characteristic of beans, since undigested amylopectin fragments make their way to the colon. Colon bacteria feast on the undigested starches and generate gas, while making the sugars unavailable for you to absorb.

Amylopectin B is the form found in bananas and potatoes and, while more digestible than bean amylopectin C, still resists digestion to some degree.

The most digestible is amylopectin A, the form found in wheat. Because it is the most readily digested by amylase, it is the form that increases blood sugar most vigorously. This explains why, gram for gram, wheat increases blood sugar to a much greater degree than, say, chickpeas, kidney beans, or sweet potatoes-even though they are all "complex" carbohydrates.

The amylopectin A of wheat products, "complex" or no, might be regarded as a super-carbohydrate, a form of highly digestible carbohydrate that is more efficiently converted to blood sugar than nearly all other "complex" carbohydrate foods, making it virtually the same in blood sugar effects to "simple" carbohydrates.

William Davis, M.D.
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William Davis, M.D.

William R. Davis is a Milwaukee-based American cardiologist and author. He wrote for HealthCentral as a health professional for Heart Health and High Cholesterol.