Question: Is whole wheat considered a whole grain? As I understand it, foods with a low glycemic index are supposed to leave you feeling fuller, take longer to digest, and have health benefits. I thought whole grains were supposed to do those things too, but I’ve also read on the Internet that there’s no difference between wheat flour and white flour. What’s the truth?
Answer: Whole grains — whole wheat among them — are a healthy source of carbohydrates. There are three important classes of carbohydrates where human nutrition is concerned: sugar (sometimes called “simple carbohydrate“), starch (sometimes called “complex carbohydrate”), and fiber. All three classes are made up of small chemical building blocks called monosaccharides, which means “single sugar unit.” Sugars consist of one or two monosaccharides. Starch is made up of long chains of many monosaccharides, chemically bonded together. Fiber is, like starch, made up of long chains of chemically bonded monosaccharides. The difference between fiber and starch is that the human digestive tract can break starch down into its monosaccharide building blocks, and can’t similarly break down fiber. The gut can only absorb monosaccharides, and consequently, humans can’t absorb fiber. As such, fiber has no caloric content. Sugar and starch, on the other hand, get broken into their monosaccharide constituents, absorbed into the bloodstream, and burned for energy by the body cells.
That fiber has no caloric content doesn’t mean it’s of no utility from a nutritional perspective, however. Fiber serves a number of important roles in the body. It helps to provide mechanical bulk, which improves intestinal function and increases regularity. It binds certain toxins and dietary cholesterol, helping to reduce the risk of heart disease and colon cancer.
Fiber also slows the digestive process, which is a particularly important function of fiber-containing foods. When a person consumes sugar or starch with no fiber present, the digestive tract breaks the sugar (if necessary; not all sugars consist of more than one monosaccharide) or starch into its monosaccharide components and absorbs them into the bloodstream. The digestion and absorption processes occur very quickly. In a very real sense, then, there’s no chemical difference (as the body sees things) between a spoonful of pure sugar and a spoonful of white rice, which is made up of nearly pure starch. Even though sugar tastes sweet and starch does not — this is because the sweetness receptors in the mouth can bind smaller carbohydrates, but not larger ones — both are broken down into monosaccharide sugars and absorbed at a nearly equivalent rate.
Rapid breakdown of starch leads to rapid absorption of monosaccharides into the bloodstream, which causes blood sugar — a measure of how much sugar is in the blood — to increase rapidly. The glycemic index (GI) is a tool that quantifies the rate at which the sugar from a food enters the bloodstream, relative to glucose (pure sugar, with a GI of 100). White rice has an average GI of 80 , while brown rice, which is much higher in fiber, has an average GI of 55. The major difference between brown and white rice is the presence of the bran, or grain coating, on brown rice. Bran is made up of fiber, and significantly slows the rate at which the starch in the rice is digested into monosaccharides and absorbed. Similarly, white bread (made of white/wheat flour) has an average GI of 95. Whole wheat bread (made of entirely whole wheat flour) has an average GI of 31. Again, the difference between the breads is the presence of the bran in whole wheat; whole wheat and white flour are otherwise nearly identical.
In addition to the health benefits of the fiber in a wholegrain food, the lower GI of these foods is directly related to their healthfulness. Slow-to-digest foods are more satiating and promote a feeling of fullness, which is a useful thing for those individuals who are trying to control weight and caloric intake. Further, the rapid increases in blood sugar associated with high GI foods increase risk of type 2 diabetes and lead to greater storage of body fat.
Unfortunately, when it comes to making purchasing decisions, it can be difficult to accurately assess the healthfulness of a particular product. This is because marketers use a variety of techniques to sway consumers. For instance, many wheat-based products that contain a small amount of whole wheat flour will contain the term “whole wheat” in product name (e.g. “whole wheat bread”). A product’s name can therefore not be used as an accurate means of determining the proportions of whole and refined grain present. Further, many wheat-based products list “wheat flour” as an ingredient, in the hopes that the consumer will confuse this with “whole wheat flour.” White flour is made from wheat, and is therefore “wheat flour.” The term “wheat flour” must always be taken to mean “white flour.” Products that list “wheat flour” or simply “flour” near the beginning of the ingredients are made up of a large proportion of refined grain, regardless of the product’s name.
The healthiest wheat-based products are those whose only source of wheat is “whole wheat” or “whole wheat flour.” The next best wheat-based products are those that list “whole wheat” or “whole wheat flour” first in the ingredients, followed by “wheat flour” or simply “flour.” Products that list “whole wheat flour” later in the ingredients than “wheat flour” or “flour” are made up of a small proportion of whole grain, and aren’t as healthy.
- Fosterpowell, K., Miller, J. B. (1995). International tables of glycemic index. Am J Clin Nutr. 1995 Oct;62(4):871S-890S.
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