Chapter Introduction

4

CARBOHYDRATES

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Plainpicture/Rupert Warren
Whole Grain Hype CAN SCIENCE HELP US NAVIGATE THE PERILS OF THE CEREAL AISLE?

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LEARNING OBJECTIVES

  • Identify the primary functions of carbohydrates in food and in the body (Infographic 4.1)

  • Describe the classifications of dietary carbohydrates and their chemical composition (Infographic 4.2)

  • Define “whole grain” and explain what occurs when grain is refined (Infographic 4.5)

  • Explain how carbohydrates are synthesized in plants and animals (Infographics 4.2 and 4.4)

  • Outline the steps in carbohydrate digestion (Infographic 4.6)

  • Identify sources of added sugar in the U.S. diet (Infographic 4.7)

  • Describe the differences between nutritive and non-nutritive alternative sweeteners and identify examples of each category (Infographic 4.8)

  • Identify the types and sources of fiber and describe its health benefits (Infographics 4.9 and 4.10)

  • Identify sources of carbohydrates in foods and describe the dietary recommendations for carbohydrate intake (Infographics 4.3 and 4.11)

When Rebecca Mozaffarian and her colleagues at the Harvard School of Public Health were asked to come up with guidelines for healthful snacks to serve in schools, they quickly ran into a problem: it was easy to make certain food recommendations—avoid sugar-sweetened beverages, serve plenty of vegetables and fruits—but much harder to come up with clear recommendations for foods made from grains. Grains include things like wheat, barley, rice, corn, and other cereal grasses that humans use to make everything from granola bars, breads, and breakfast cereals, to pasta, crackers, and cupcakes.

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Whole grain wheat kernels and ears of wheat. The wheat kernels can be ground to make flour.
Elena Elisseeva/Alamy

WHOLE GRAIN cereal grains, or foods made from cereal grains, that contain all the essential parts (starchy endosperm, germ, and bran) of the entire grain seed in its original proportions

REFINED GRAIN cereal grains that have been milled, a process that removes the bran and germ; white flour is an example

ENRICHED GRAIN cereal grains that lost nutrients during processing but have vitamins and minerals added back in; refined grains are often enriched

Scientists generally agree that eating “whole” grains is better than eating “refined” or “enriched” grains. A whole grain is one where all the edible parts of the original plant seed (grains are seeds) are found in the food product, including the energy-rich endosperm, the oil-rich germ, and the fiber-rich bran coating. Refined grains are stripped of their bran and the germ, leaving only the endosperm. Since many of the beneficial nutrients and phytochemicals are found in the bran and germ, refined grains are much less healthful. Enriched grains have some vitamins and minerals added back in, but they still pale nutritionally in comparison with whole grains.

Consuming whole grains has been linked to a host of health benefits, including a reduced risk of heart disease, obesity, diabetes—even cancer. The Dietary Guidelines for Americans advise that Americans should consume at least half their grains as whole grains.

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Foods that boast whole grain content vary in overall nutritional quality and healthfulness.
Kristoffer Tripplaar/Alamy

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Given their importance to health, Mozaffarian and her colleagues knew they wanted to say something about whole grains in their recommendations but soon realized that there was no easy way to identify healthful whole grain foods. Although many food products tout their “whole grain” ingredients, and some even include a “stamp of approval,” some whole grain food choices are much better than others. When it comes to whole grain foods, separating science from marketing—wheat from chaff—can be tricky.

“We were sitting around thinking ‘People are probably struggling with this issue,’” Mozaffarian says. That’s when she got the idea for a scientific study: compare different ways of identifying whole grain foods to see which ones were most useful in identifying healthful food choices. She was particularly interested in distinguishing the types of carbohydrates found in the products.

To appreciate why Mozaffarian and her colleagues were interested in carbohydrates, it helps to understand the different forms that carbohydrates can take and their different properties.