Traditionally, mainstream nutrition experts have emphasized the importance of consuming copious amount of carbs after exercise to promote glycogen synthesis and recovery. This advice is now being questioned.

If your goal is to lose body fat, new research indicates that consuming carbs after exercise is actually counterproductive. Consider the woman who is trying to lose 10 pounds of body fat and has just finished her 30 minute jog on the treadmill. That workout created a robust stimulus to improve her ability to access and use body fat for fuel. Exercise upregulates many of the metabolic pathways involved in fat breakdown and uptake into muscle. It also increases the energy-burning furnaces called mitochondria in her muscles and it improves her muscle’s ability to take up glucose. These are all wonderful health-promoting effects of exercise. But these beneficial effects have all been shown to be significantly impaired when carbohydrates are consumed post-exercise. In other words, as you consume more carbs you get diminishing returns from your workouts.

This happens in part because carbs increase insulin. Insulin is the key hormone that inhibits fat breakdown and burning, while promoting the conversion of carbs into fat. Thus, if fat loss and metabolic health are your goal, avoid carbs in general but especially for 2 hours following exercise. Instead, during that time focus on consuming 15 to 25 grams of high quality protein like whey. Consuming fat during this post-workout window should not affect the fat burning process.

What if your primary goal is to build muscle?
The advice is not too much different because protein is still the most important nutrient to consume after exercise. Recent work has shown that when adequate protein is provided after exercise, including insulin stimulating carbohydrates does not augment the response further. There is some evidence that carbs may decrease the rate of protein breakdown, which may offer some benefit to gaining muscle. To avoid gaining too much body fat and diminishing the health benefits of exercise, the best post-workout nutrient intake advice is to consume 15 to 25 grams of high quality protein while keeping the total carbohydrate intake below 25 grams (less for people wanting to simultaneously lose body fat) and emphasize a slower digesting form of carbohydrate.

by Jeff S. Volek, Ph.D., R.D