The latest research findings on carbo-loading, hydration and exercise.
Each year at the American College of Sports Medicine's convention, exercise scientists meet to present their latest research findings. The following information from the June, 1998 meeting in Orlando, Florida, also published in the May, 1998 issue of Supplement to Medicine and Science in Sports and Exercise, offers a taste of what's happening in the area of sports nutrition.
Carbohydrates
Studies suggest pre-exercise consumption of low glycemic foods like oatmeal and pasta provide a sustained release of energy into the bloodstream. This enhances endurance performance. However, the consumption of additional carbs during exercise diminishes these benefits. Don't make a special effort to choose low glycemic foods before you exercise if you plan to consume carbs during exercise.
Carbohydrates should be the foundation of an optimal sports diet. But many athletes choose to consume too much protein, fat and alcohol at the expense of properly fueled muscles. A study of rugby players who consumed a high carbohydrate diet (more than 4 grams carb/lb., as compared to the common 2 grams carb/lb, or less) had almost double the muscle glycogen stores. This could contribute to higher intensity performance.
Carbo-loading can boost muscle glycogen by 1.6 times over baseline. But how long do muscles stay loaded? A study from Northern Arizona University suggests for three to five days post-loading, when the subject does no hard exercise and eats a 60% carbohydrate diet.
For optimal glycogen loading, can athletes just 'load' on carbs or should they first exercise at a high level prior to carbo-loading to deplete muscle glycogen? According to Navy research, depleting exercise followed by six days of a high carbohydrate diet provided a greater stimulus to super-compensate glycogen stores than occurred with no depleting exercises before carbo-loading.
Fluids
What's a good way to optimize fluid intake? Provide a tasty beverage. Studies have shown young boys given a choice of fluid replacers will drink more of a palatable sports drink than of plain water. New research suggests the same holds true for college students--they drank 24% more sports drinks than plain water. This can effectively reduce the risk of dehydration.
Carrying water with you during activity also reduces your risk of dehydration. Skiers, for example, are notorious for dehydration. Water is unavailable on the slopes and 'tanking up' on fluids at lunch fails to do the job. In a study with skiers who used a back mounted fluid carrier, the skiers drank three times more fluid, maintained hydration and reported they felt better.
Water is important during endurance exercises, but so are carbohydrates. Cyclists who consumed a combination of water and carbohydrate (e.g., a sports drink) during two hours of moderate cycling experienced only a 7% drop in cycling power as compared to a 10% drop when they drank the same volume of plain water. Inadequate water--even with carbs (such as energy bars taken with inadequate fluid)--contributed to a 14% drop in power.
Weight Gain Management
Commercial exercise videos claim to 'burn' and 'blast' fat. Subjects who completed 20- to 24-minute workouts burned about seven to eight calories per minute, or about 145 to 170 total calories--not exactly 'fat blasting,' given a pound of fat has 3,500 calories.
Baby boomers who fight middle age spread often ask how much they need to exercise to prevent weight gain. According to NASA researchers, one must exercise the equivalent of running six miles a week or more.
A study from Oregon State University shows post-menopausal women who do more 'hard' and 'very hard' exercise are likely to have less abdominal body fat than women who do moderately intense exercise.
Meal timing may affect body fat. A Georgia State University study involving gymnasts and runners demonstrated those who ate adequately during the day had less body fat than those who under-consumed. Therefore, yes, eat breakfast!
Nancy Clark, M.S., R.D., offers private nutrition consultations at SportsMedicine Brookline in the Boston area. Her Sports Nutrition Guidebook ($18) and NYC Marathon Cookbook and Nutrition Guide ($23) are available at your local bookstore or SportsMedicine Brookline, 830 Boylston St., Brookline, MA 02167; (617) 739-2003.
