Research-driven nutrition

The latest in sports nutrition from researchers around the nation.

by Nancy Clark
The Athlete's Kitchen

What percentage of my diet should come from carbohydrates? … Should I exercise on empty? … How much protein should I eat after I lift weights? … Is whey the best source of protein? 
 
These were just a few of the questions addressed at the 27th annual meeting of SCAN, the Sports And Cardiovascular Nutritionist’s practice group of the American Dietetic Association (www.SCANdpg.org). Over 400 sports dietitians gathered to learn the latest news from prominent sports nutrition researchers. I hope this information will help you choose a winning sports diet.

Carbohydrate Update

Louise Burke, PhD, Director of Sports Nutrition at the Australian Institute of Sport, addressed the following questions:
  
• What’s the best percentages of carbohydrates, protein, and fat for a sports diet: 40-30-30 or 60-25-15?
Neither! A better approach is to define nutrient needs according to body weight. For example, the International Olympic Committee developed these guidelines:

Intensity of exercise	gram carb/kg body wt	gram carb/lb body wt
Low intensity	3-5 g	1.5-2.5
Moderate (~1 hour/day):	5-7 g	2.3-3.2
Endurance (1-3 hours/day):	6-10 g	2.5-4.5
Extreme  (>4-5 hours/day):	8-12 g	3.5-5.5

• How much should I eat during exercise?
--During exercise that lasts 1 to 2.5 hours, you want to target 30 to 60 grams of carbohydrate (120 to 240 calories) per hour. That’s about 1 to 2 gels or 16 to 32 ounces of a sports drink per hour (after the first hour, if you ate a pre-exercise meal or snack).
  
--During longer endurance exercise, 60 to 90 grams of different sources of carbohydrates (such as sports drink, banana, gummy candy) per hour is appropriate, as tolerated. Consuming the higher end of the range (90 g, as compared to 60 g) is associated with greater stamina and endurance.

• How long does it take to refuel from exhaustive exercise?
If you eat a carb-rich sports diet, you can replenish depleted glycogen stores in 24 to 36 hours post-exercise (with no exercise during that time). While it's important to pay attention to your recovery diet, most athletes do not need to eat immediately after exercise unless they are doing double workouts. (Within an hour after exercise, yes; immediately, no.)

• What can I do if I cannot tolerate any food during exercise?
Try mouth swishing with a sports drink. This sends a message to the brain that energy is forthcoming and you’ll feel more energetic. Swishing can enhance performance by 2 percent to 3 percent if you are exercising on empty and have not eaten pre-exercise—as often happens with morning exercisers. (Swishing seems to be less beneficial after a pre-exercise meal, but more research is needed to verify those findings.)

Train low, compete high?

• Should I train with poorly fueled muscles, as a means to teach my body to burn more fat, so it spares the limited glycogen stores?
Training with low glycogen stores (“train low”) drives up the metabolic adaptations to burn more fat. By burning fat instead of glycogen, you’ll spare the limited glycogen stores. Theoretically, this should enhance stamina and endurance because glycogen depletion is associated with fatigue. To date, “training low” has been most effective in research with untrained individuals. Athletes who exercise with depleted glycogen are unable to exercise at high intensity and that may hinder performance.

Training with low glycogen during lower intensity workouts might be one way to stimulate the muscle adaptations to burn more fat (and thus spare the limited glycogen stores). But athletes should do their high intensity workouts when they are fully glycogen-loaded.

Exercise physiologist and researcher John Hawley, PhD of Melbourne, Australia acknowledged that train low/compete high is receiving a lot of attention among serious endurance and ultra-distance athletes. Hawley suggests “train low” should be defined as “train at 50 percent of resting muscle glycogen, 50 percent of the time”—and only for selected sessions. Training with low carbohydrate availability can be achieved by exercising with 1) low blood glucose, or 2)  low muscle glycogen stores. Both generate adaptations that promote the training response and might be advantageous to competitive endurance athletes. Hawley cautions serious athletes that  “training low” compromises training intensity and may lead to inferior performance during an event, particularly if the athlete needs to do a competitive sprint to the finish. That final sprint often determines who wins.

Protein Update

Stuart Phillips, PhD, professor of kinesiology, McMaster University in Ontario, Canada presented an update on protein, answering these questions:

• Do athletes need more protein than non-athletes?
While the recommended protein intake for the average American is 0.4 gram protein per pound body weight (0.8 gram protein per kg), most exercise scientists agree that athletes need more to optimize muscular development: 0.5 to 0.8 grams protein per pound (1.2 to 1.7 grams of protein per kilogram) body weight per day. However, most young women and men generally consume about 0.55 to  0.65 g protein/lb (1.2 g and 1.4 g protein/kg) body weight per day, respectively. They can appropriately meet their higher need without supplements.

• How much protein do I need after I lift weights?  
Consuming 20 grams of protein-rich food (Greek yogurt, tuna sandwich, 16 oz. chocolate milk) after resistance exercise is plenty to optimize the rate of muscle synthesis. Athletes should then continue to eat protein and carbs at meals and snacks throughout the day.

The highest rate of protein synthesis is 3 to 5 hours post-exercise. This raises the question: Should athletes who work out twice a day plan to avoid exercising during that time frame? The “good stuff” (building muscle) happens during that three to five hour period of rest and recovery and the “bad stuff” (muscle damage) happens during exercise. Remember: rest is an essential part of a strength training program!
 
• Should I buy whey protein supplements?
Probably not, unless you are a frail, elderly person with a limited food intake. Drinking milk (20 percent whey, 80 percent casein) and eating a balanced sports diet with adequate protein from many sources can be as effective as whey supplements. Hard, hard work is the basic trigger for bigger muscles!

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Nancy Clark, MS, RD, CSSD (Board Certified Specialist in Sports Dietetics) helps both casual and competitive athletes with nutrition. Her private practice is at Healthworks, the premier fitness center in Chestnut Hill MA (617-383-6100). Nancy Clark’s Sports Nutrition Guidebook and her food guides for new runners, marathoners offer additional information. They are available at www.nancyclarkrd.com and www.sportsnutritionworkshop.com.