Just Because It Isn’t Sweet … Doesn’t Mean It Isn’t Sugar

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From a nutritional perspective, is a spoonful of white rice more like a spoonful of sugar or a spoonful of brown rice? Because they taste and look similar, most people assume that white rice and brown rice share many of the same nutritional qualities. It turns out, however, that this is not the case. The reason has to do with the chemical nature of carbohydrates.

White and brown riceImage credit: Two kinds of rice in spoons via Shutterstock

Carbohydrates can be divided into two major classes: simple carbohydrates and complex carbohydrates.

The simple carbohydrates are colloquially called sugars, and they taste sweet on the tongue. Sugars consist of one or two small carbohydrate units. The individual units are called monosaccharides, a word that means “single sugar,” and of the monosaccharides, glucose is the most ubiquitous. Other common monosaccharides include fructose (“fruit sugar”) and galactose, which is a component of milk sugar. Two monosaccharides chemically bonded together form a disaccharide (“two sugars”), which is also a simple carbohydrate. Common disaccharides include sucrose (“table sugar”), which is made up of glucose and fructose. Lactose (“milk sugar”) is also a disaccharide. The digestive tract can absorb monosaccharides into the bloodstream; disaccharides must be digested into their monosaccharide components before absorption.

Complex carbohydrates, or starches, don’t taste sweet on the tongue. However, starch is made up of long chains of glucose molecules chemically bonded together, and the digestive tract breaks starch into its glucose monosaccharides, which are then absorbed into the bloodstream. As such, while a bite of white rice — which is nearly entirely made of starch — doesn’t taste the same as a spoonful of glucose sugar, the gut quickly breaks the starch from the white rice into glucose, and from that point on, the body can’t tell the difference.

Because it’s such an important fuel to the body cells, glucose is a healthy component of diet. However, the body cells can convert excess glucose into storage fat, so like all calorie-containing components of nutrition, it’s important to consume glucose-containing foods in moderation. Also, the human body responds in a more normal and healthy manner to glucose when it enters the bloodstream slowly; glucose-containing foods that are absorbed very quickly can lead to unhealthy fluctuations in blood sugar. The rate at which the glucose from a food enters the bloodstream is referred to as the food’s glycemic index.

Limited consumption of carbohydrates is the basis for many diet plans. For example, the Atkins diet is based on the theory that overweight people eat too many carbohydrates. The diet plan involves limited consumption of carbohydrates to switch the body’s metabolism from metabolizing glucose as energy over to converting stored body fat to energy (called ketosis). The South Beach Diet is another diet plan that is based on the glycemic index. The diet plan involves replacing “bad carbs” (i.e. carbohydrates with a high glycemic index) with “good carbs” (i.e. carbohydrates with a low glycemic index) and “bad fats” (i.e. trans-fats and saturated fats) with “good fats” (i.e. unsaturated fats and omega-3 fatty acid).

Generally speaking, carbohydrate-containing foods with fiber in them have lower glycemic indices than foods without fiber, meaning that the glucose enters the bloodstream more slowly. This is because fiber slows digestion and absorption of food. While the fiber content of food isn’t the sole determinant of whether that food is healthy, fiber-containing carbohydrate generally leads to a more normal and healthy physiological response than carbohydrate devoid of fiber. For this reason, white rice is nearly identical to a spoonful of sugar, chemically speaking, and is quite different from a spoonful of fiber-rich brown rice.

About the Author

Kirstin Hendrickson, Ph.D., is a science journalist and faculty in the Department of Chemistry and Biochemistry at Arizona State University. She has a PhD in Chemistry, and studied mechanisms of damage to DNA during her graduate career. Kirstin also holds degrees in Zoology and Psychology. Currently, both in her teaching and in her writing, she’s interested in methods of communicating about science, and in the reciprocal relationship between science and society. She has written a textbook called Chemistry In The World, which focuses on the ways in which chemistry affects everyday life, and the ways in which humans affect each other and the environment through chemistry.