Alex Hutchinson draws on the latest research to answer your fitness and workout questions in this biweekly column on the science of sport.
What should I eat and drink after working out?
It's always nice when science tells you what you want to hear. That's why several studies in the past few years touting low-fat chocolate milk as a perfect postworkout elixir have been greeted so enthusiastically. Chocolate milk is convenient, cheap and tasty, so what's not to like?
But applying studies based on competitive athletes to casual exercisers is not always straightforward. The basic principles are the same, but new research - and common sense - suggests that those whose main goal is to lose weight should chug milk with caution.
Postexercise nutrition has two primary goals: to recharge the body's depleted energy stores and to provide fuel to synthesize the contractile proteins that increase strength and the mitochondrial proteins that boost endurance.
"It's a continuum between short-term recovery and long-term adaptation," says Trent Stellingwerff, a Canadian scientist in the performance nutrition group at the Nestlé Research Center in Switzerland.
The key factors to consider are when and what you eat. For the first half-hour after exercise, the body is processing nutrients to repair itself at a dramatically elevated rate. After about two hours, the "window" is closed and the opportunity for any accelerated recovery is lost.
In the past, conventional wisdom held that weightlifters should ingest protein to build muscle, while endurance athletes should focus on carbohydrates. Now researchers agree that both macronutrients are important no matter what type of exercise, Dr. Stellingwerff says.
Some sports drinks tout very specific carb-to-protein ratios that companies say will optimize recovery and adaptation. Endurox, for example, has a 4-to-1 ratio - which happens to be the naturally occurring ratio in chocolate milk.
In truth, "there's no magic ratio," says John Ivy, an exercise physiologist at the University of Texas at Austin and author of Nutrient Timing: The Future of Sports Nutrition.
"Anywhere in the range from 2.5-to-1 to 4-to-1 works well," he says. For workouts lasting a few hours or more, a higher ratio of up to 6-to-1 may be appropriate, Dr. Stellingwerff adds.
Whatever the ratio, the idea that the body needs fuel immediately after exercise is now widely accepted. That's why some recent results from Barry Braun and his colleagues at the University of Massachusetts at Amherst's Energy Metabolism Laboratory have caused a stir.
One of exercise's prime benefits for those seeking to lose weight is that it heightens insulin sensitivity, which helps to clear sugars from the bloodstream.
Dr. Braun studied 16 sedentary, overweight subjects who were asked to walk on a treadmill for an hour a day at a moderate pace, burning 500 calories.
Half the participants replaced the lost calories by drinking a sports drink and eating immediately after the workout, while the other half were given nothing. Surprisingly, while insulin sensitivity spiked 40 per cent in the abstaining group, no increase at all was seen in the refuelled group.
For exercisers focused on weight and blood sugar levels rather than bicep size and 5K time, Dr. Braun concludes, it may be better not to consume calories immediately after exercise.
Dr. Ivy is cautious in his interpretation of these findings, pointing out that the long-term effects of exercise on insulin sensitivity are more relevant than the short-term effects measured in the study. Also, he says, other studies have shown that people who take in a small amount of protein after exercise are less likely to overeat several hours later.
Still, the Amherst results highlight an important point, Dr. Ivy says: "If you've gone out and burned 300 calories by walking for 30 minutes, don't refuel by taking a 500-calorie dietary supplement."
In other words, let the magnitude of your workout dictate the size of the chocolate milk carton.
Alex Hutchinson is a former member of Canada's long-distance running team and has a PhD in physics.
What to eat
Chocolate milk isn't the only way to refuel after a workout. You should aim to consume about one gram of carbohydrate and 0.3 grams of protein for each kilogram of body weight within an hour or two of finishing a typical cardio workout. Some suggestions from Trent Stellingwerff, who advised the Canadian track team in Beijing last summer:
For a 55-kilogram female
A tuna sandwich and a 500-millilitre sports drink
A cup of oatmeal with milk and a 200-millilitre sports drink
For an 80-kilogram male
A protein sports bar and a 750-millilitre sports drink
Spaghetti with lean meat sauce and a cup of low-fat milk