Carbohydrate: The Great Nutrition Debate

May 2005

Carbohydrate: The Great Nutrition Debate

By Angela M. Miraglio, R.D.Contributing Editor

Scientists and consumers both honor and vilify carbohydrates. Many health authorities recommend low-fat, high-carbohydrate diets as part of a healthy lifestyle, while other researchers cite a high-carbohydrate intake as the culprit in many disease processes. Athletes seek out carbohydrates for peak performance and recovery, while people with diabetes and/or weight concerns avoid carbohydrates to manage blood sugars and weight. In reality, excessive carbohydrates can create problems under certain circumstances, but carbohydrates are nonetheless essential to many body functions. Now, as interest in no- and low-carb foods wanes, the recently introduced Dietary Guidelines for Americans 2005 from the Department of Health and Human Services (HHS) and USDA remind consumers that eating the right amounts of the right carbohydrates is a nutritionally sound strategy.

Edible carbohydrates include numerous compounds that may, or may not, be digestible. The fully digestible and absorbable sugars and starches contribute substrate for energy metabolism and key cellular structures. The less-digestible or nondigestible dietary fibers serve as moderators of gastrointestinal functions, with known benefits for regularity and cardiovascular disease risk. Additionally, many act as prebiotics that help establish the beneficial bacteria in the gut and are associated with improved blood-sugar and cholesterol levels, as well as with a decreased risk of colon cancer.

The basic necessities Glucose is at the core of energy metabolism and, more importantly, functions as direct fuel for the brain. To ensure adequate glucose for the brain, the body has a number of backup mechanisms to synthesize it in times of need. For example, a number of amino acids and glycerol are converted to glucose and can meet the basal requirements of the neurological system.

In 2002, the Food and Nutrition Board (FNB) of the Institute of Medicine, at the National Academies of Science, established the first-ever Recommended Daily Allowance (RDA) and an Estimated Average Requirement (EAR) for carbohydrates (sugars and starches) and total fiber. In the case of carbohydrate, brain glucose utilization was the criterion used to establish the EAR of 100 grams/day and the RDA of 130 grams/day for children and adults -- the typical American consumes much more than this level. Although data were lacking to establish an Upper Limit (UL), the recommended range of intake for a healthy diet was set at 45% to 65% of total energy, with a maximum of 25% of energy from sugars added during production and processing.

For dietary fiber, FNB established an Adequate Intake (AI) level, using the intake level that provides the greatest protection against coronary heart disease -- 14 grams/1,000 kcal -- as the criterion. Because it is based on energy requirements, the absolute value varies by age and gender. For adults under 50, the report recommended 38 grams total fiber per day for men and 25 grams for women, and only 30 and 21 grams, respectively, for men and women over 50. Most Americans fall far short of these goals.

Keeping good company The varied food sources of carbohydrates provide numerous opportunities to supply the body with not only the glucose it needs, but also with other components that contribute to health. Whole foods with high levels of digestible and nondigestible carbohydrates, such as fruits, vegetables and grains, contain myriad vitamins, minerals and phytochemicals. High-biological-value protein, calcium and other minerals are companions to lactose in dairy products. Even honey, a simple carbohydrate source, contains significant levels of antioxidants. Today, product designers are reformulating many traditional, sugar-laden, empty-calorie beverages to provide nutritional bonuses, such as vitamins and minerals.

The true value of the nutrient package found in whole grains was first recognized when refined versions of wheat and rice led to nutritional deficiency diseases. Fortification regulations corrected this problem for the known vitamins and minerals that processing removed. However, the negative impact on dietary-fiber intake was mostly ignored until research in the 1980s demonstrated its health benefits. Current research associates folic acid, insoluble and soluble fiber, and antioxidants in grain foods with potential risk reduction for some cancers, cardiovascular disease, obesity, birth defects, diabetes and Alzheimer's disease.

A recent Australian study, as published in the Nov. 2004 issue of Diabetes Care, found that high-glycemic-index (GI) breads and starches -- products such as white bread -- increased the risk of developing type 2 diabetes. It's no wonder that major food manufacturers are now increasing the whole-grain content in products, from cereals to frozen meals.

Naturally high in dietary fiber, thiamin, folate, iron, magnesium and phosphorus, legumes also contain high levels of protein that, when combined with other complementary proteins, can meet nutritional needs for amino acids. In many cultures, main dishes contain legumes in combination with rice, wheat or small quantities of dairy products to achieve this important balance. Legumes are low in fat and generally have a low GI, making them a good choice in diets for weight management and diabetes.

The other main high-carbohydrate food group, fruits and vegetables, is quite heterogeneous in its nutritional values. Some are good sources of fiber and vitamins C and A; others contain high levels of minerals like potassium and magnesium. And as researchers discover more about the physiological roles of antioxidants and phytochemicals, a new appreciation emerges for plant foods, like broccoli, tomatoes, blueberries, cranberries, dried plums, onions, garlic and pomegranates.

A recent prospective cohort study, published in the Nov. 3, 2004 issue of the Journal of the National Cancer Institute, confirmed that increased fruit and vegetable consumption lowered risk for cardiovascular disease, but not for cancer. In this study, consumption of green leafy vegetables was associated with a decrease in major chronic disease and cardiovascular disease. Another small study demonstrated that eating two bowls (500 ml total) of gazpacho soup every day for two weeks significantly increased blood levels of vitamin C and decreased key stress molecules associated with inflammation and oxidative stress, believed to be the cause of many chronic diseases.

Nutrition boosters A variety of carbohydrate ingredients can boost the nutrition in processed foods and beverages. Several, such as cellulose, polydextrose, inulin and resistant starch, qualify as dietary fiber and are associated with improved gastrointestinal health and blood levels of glucose and cholesterol. These ingredients, along with sugar alcohols, can help create good-tasting, low-calorie, low-glycemic products for dieters. Other ingredients from fruits and vegetables offer increased antioxidants and phytochemicals in products for health-conscious consumers.

The federal Dietary Guidelines for Americans 2005 encourages consumption of fruits, vegetables and whole grains as part of a healthful diet. The largest public-private partnership for nutrition, the 5 A Day for Better Health Program, is well-poised to promote the recommended five to nine daily servings of fruits and vegetables and has a number of initiatives underway.

A recently introduced program by the Whole Grain Council, Boston, aims to help consumers recognize whole-grain foods so that they can choose at least three servings each day. Manufacturers can now include one of three Whole Grain Stamps on packaging. A product with at least 8 grams of whole grains per labeled serving gets a "Good Source" stamp while one with at least 16 grams whole grains per labeled serving rates an "Excellent Source" stamp. Foods with at least 16 grams of whole grains and no refined grains qualify for the "100% Whole Grains, Excellent Source" stamp.

Clearly, carbohydrate and carbohydrate-containing foods are nutritional friends that are essential to a well-balanced diet. Additionally, many carbohydrate foods and beverages, such as folate-enriched grains and calcium-fortified orange juice, are great vehicles for delivering necessary nutrients. Manufacturers need to offer even more products that capitalize on the nutritional advantages of carbohydrates by formulating with whole grains, legumes, fruits and vegetables.

Angela M. Miraglio, M.S., R.D., ([email protected]) is a Fellow of the American Dietetic Association from Des Plaines, IL. Her firm, AMM Food & Nutrition Consulting, provides communications and technical support to the food and beverage industry.

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