For nearly three decades athletes, particularly those competing in endurance events, have focused on eating large amounts of carbohydrates to improve their physical performance. Then in 1995 the Zone Diet appeared on the scene. According to Barry Sears, Ph.D., Zone Diet guru and author of three books on the subject, eating a high carbohydrate diet causes our bodies to over-produce insulin, which in turn promotes fat storage, and makes our blood sugar drop to the point we feel sluggish.

Sears' recipe for loosing weight and staying energized: A diet that is composed of 40% carbohydrate, 30% protein and 30% fat. Or to quote a Time magazine review "eat the butter; hold the bread." To limit carbohydrate intake to 40% and still get enough vitamins and minerals, Sears recommends people eliminate most of the grain-based foods like pasta, rice, bread, etc., and concentrate on eating fruits and vegetables. Sears contends high-fiber fruits and vegetables are safe sources of carbohydrates because they have a lower concentration of carbohydrates, and because they are rich in nutrients, fiber, and phytochemicals.

But according to sports nutrition experts, the Zone Diet is chock full of nutritional misinformation, and impractical suggestions for food combinations (e.g., combining cottage cheese and beer). They are quick to point out that the reason the Zone Diet works in terms of weight loss is because it is low in caloriesónot because of some magic ratio of carbohydrates: protein: fat.

If your goal is to lose weight, the Food Guide Pyramid is a good guideline for determining dietary balance and variety. If you are someone who has trouble losing weight following a higher carbohydrate: protein diet, you may need to adjust the number of servings of foods you consume from the various categories. For example, increase the number of servings of low-fat dairy products and lean meats from 2 to 3 servings; limit carbohydrates (bread/pasta/grain group) to 8 servings; and fill out the remainder of your diet with fruits and vegetables. (Taking aim at the ZONE, Penn State Sports Medicine Newsletter, vol. 5, #8, 1997 p 1-2)

Can eating large amounts of carbohydrates improve physical performance? The answer to this question depends on the activity you're performing, and surprisingly, whether you're male or female. Carbohydrate loading has been shown to increase the endurance of male endurance athletes but not female endurance athletes. Why the difference between male and female endurance athletes? Researchers at McGill University in Canada have demonstrated that female endurance athletes do not store extra glycogen in their muscles when they carbohydrate load like men do, and women burn more fat for fuel from the start of exercise. Carbohydrate loading also will not benefit either male or female athletes participating in power events, such as sprinting, weight lifting, and wrestling.

Power athletes often underestimate the importance of carbohydrates in their performance, and concentrate on eating high levels of protein. (For more information on protein loading see the box below.) While carbohydrate loading will not benefit power athletes, they need to be careful not to overlook this important energy source completely - insufficient carbohydrate intake can actually impair the performance of athletes competing in power events by limiting their body's ability to burn fat for fuel. (American College of Sports Medicine Annual Meeting Highlights, in SCAN'S Pulse vol. 15, #4, pg. 14. 1996)

All athletes, regardless of the sport in which they participate, need at least 200 mg of carbohydrates each day. But be careful. Athletes who consume more than 70% of their calories in the form of carbohydrates tire more quickly than those who consume less than that amount. Researchers theorize that very high carbohydrate levels impair the body's ability to oxidize (burn) fat. (Mermel, V. L. A review of contemporary sports nutrition, Athletic Training: Sports Health Care Perspectives vol. 1, # 3, pg. 228-244, 1995)

Protein loading: Does it build muscle or damage kidneys? Protein loading is to weight lifters and body builders what carbo-loading is to endurance athletes. The practice of eating large amounts of protein to build muscle tissue is an ancient one. It has its roots in the "like makes like" theory of folk medicine found in many cultures. In other words, if you want strong muscles you eat muscle tissue, if you want to be intelligent you eat brains etc. Tradition aside, athletes need to determine whether they really need to consume large quantities of protein, and if it's safe to do so. Because the typical American diet is already very rich in protein, sports nutritionists and physicians believe it contains more than enough protein to meet the needs of most active people. The only exception being endurance athletes who need extra protein to rebuild muscle tissue damaged during lengthy competitions. Scientists familiar with the metabolism of endurance athletes have suggested the RDA for protein could be doubled for endurance athletes. Others experts disagree, insisting that high protein diets put a strain on liver and kidney function. These two organs are involved in the metabolism of amino acids (the chemical building blocks of protein), and excretion of the nitrogen component of the protein molecules. A third camp of experts is not convinced that extra protein is needed by endurance athletes, but refute the contention that high portion diets damage liver and kidney function. So if the experts are still debating this issue what should the physically active consumer do? Following the Food Guide Pyramid recommendations is sufficient for most athletes. Serious competitive athletes should consult a sports nutritionist for personalized advice. To locate a bona fide expert call the American Dietetic Association Dietitian referral service (1-800-366-1655). Only people with a Registered Dietetic credential (RD) or a Certified Nutrition Specialist board certification (CNS) are well trained enough in all aspects of health and nutrition to give accurate advice. (Kleiner, S. The role of meat in an athletes diet, Sports Science Exchange. vol 2 #5, 1995) Protein-conscious athletes also ask whether amino acid supplements or purified proteins are the best way to get the protein they need. Despite the hype in health food stores and commercial gyms, you're better off sticking with whole foods. Purified amino acid supplements are very costly, have no proven benefits in terms of physical performance, and if the supplement contains only a few amino acids it has the potential to create a serious amino acid imbalance. Protein powders lack the potential to create an amino acid imbalance, but they aren't a healthy choice either. Sold as a fat-free, calorie-wise alternative to food, they are often so deficient in vitamins and mineral that they can lead to other types of nutritional deficiencies in people who routinely substitute them for whole foods. (National Institutes of Medicine: Food and Nutrition Board. Report on diet and physical performance, Journal of the American Medical Association 1994:271-98)