What to eat before and after exercise?

DW: There are special nutritional supplements, such as protein shakes, available for people who do sports. Do you recommend them?

Hans Braun: Our normal protein requirement is 0.8 gram per kilogram of body weight. In athletes that number can more than double. When people are actively engaged in sports they usually eat more, so as long as they have a balanced diet, that extra protein requirement is usually covered. This means that extra protein shakes are normally not necessary. Exceptions could be phases when people are ingesting few calories (for example in order to lose weight) or when they need a quick protein fix after intense strength training. But such situations need to be evaluated on an individual basis and only really apply to high-performance sports.

What food do you recommend for before training?

We often underestimate the amount of fluids we need in the course of a day. Studies show that up 30 percent of people doing sports, whether it’s recreational or competitive sports, start training with a slight deficit in liquid intake. That affects not only their performance, but their subjective feeling of well-being….

It makes sense to eat carbohydrates (like bread, muesli, pasta, or rice) one to three hours before doing high-intensity sports. Of course the amount you eat should not be so high as to put a strain on the body. If you want to train your "fat metabolism" you can avoid heating carbohydrates in the hours before the activity – or do sports in the morning on an empty stomach. Typically you can do low-intensity activity for an hour in this way. As a rule the food before training should be low in fat so as to avoid bloating, nausea or intestinal problems.

What should we eat after sports - and how long after?

Since that depends on how intense the training is, you have to decide these aspects on an individual basis. But in general, for quick regeneration it’s important to replace lost fluids by drinking around 1.5 liters for each lost kilogram of body weight, bearing in mind that the body can take up around one liter an hour. If you have done especially intense training you need to replenish your carbohydrate reservoirs in the first two to three hours afterwards. During this phase, that corresponds to two to three grams of carbohydrates per kilogram body weight. After exhausting training or strength training a protein intake of 15 to 25 grams can stimulate regenerative processes (like muscle protein synthesis). But you can get that from normal foods such as milk products. In general a varied, full-value diet will support recovery.

Hans Braun is a nutritional scientist and qualified sports scientist. He works at the Institute of Biochemistry at the German Sport University, Cologne.

Interview: Dorothee Grüner