You'd think that eating or drinking during a workout would be a sure bet for packing on unwanted pounds—because, after all, the more calories you consume the more weight you'll gain, right? But you almost never see an overweight person eating the gym, while you often see fit people downing shakes mid-workout. Coincidence, or is there something to this?
"Much is made of pre and post-workout nutrition, but eating during your workout can be beneficial as well," says M&F Senior Science Editor Jim Stoppani, Ph.D. "Even if you're not trying to get bigger like bodybuilders are, you need protein and carbohydrates to at least maintain your muscle mass. You would never want to lose muscle, even if you're trying to lose weight. If your goal is to add muscle, then eating during a workout is especially helpful."
The first thing to keep in mind is that whether or not to consume a bar or drink during your workout depends on what you've eaten beforehand. If you hit the gym on a relatively full stomach, scratch the bar or shake during the workout and wait until afterward. Stoppani's nutritional guidelines in or around training are simple: Consume around 20-40 grams of protein and around 40-80 grams of carbohydrates either within 30 minutes prior to training or during the first part of your workout. Ideally a 2:1 carb to protein ratio is recommended, but many drinks and bars are closer to 1:1, which is acceptable too. If weight loss is your goal, aim for the lower end of these ranges. If you're trying to add size, hit the upper ends.
The reasoning for consuming protein is obvious: You use amino acids (the building blocks of protein) during both weightlifting and cardio, and you need to replenish these stores as quickly as you can. Carbs, Stoppani says, help keep cortisol levels down. High levels of cortisol in the body, which is a natural effect of exercise, breaks down muscle instead of building it up. Pure protein drinks are not enough—you need carbohydrates to maintain and build muscle.
"It's hard to find a bar these days that has the amount of carbs you need during and following exercise," says Stoppani. "Most bar manufacturers are sticking to low carb, high protein bars. But around exercise is the time when you most need to get carbs in you."