Minute 1: What happens when your body is running on empty

Physicists tell us that matter and energy cannot be created or destroyed, only rearranged. For runners, that means if you aren’t taking in energy via food and drinks, your energy leaving your body and your running performance is being rearranged – and not in a good way. In spite of this basic science, some athletes and coaches believe that caloric restriction is the right call during training and competition, but most evidence suggests otherwise, according to this thoughtful new piece from Trail Runner: “The Science of Low Energy Availability and Performance.” Individuals will have different thresholds of what counts as underfueling, since we all have our own metabolic rates and exercise habits. However, the impacts are fairly consistent.

In the short term, you can expect an inability to adapt to training, greater fatigue, and increased inflammation. That’s your body’s way of slowing things down to save energy when it thinks there isn’t enough to go around. In the long term, things are a bit more complicated. There’s some evidence to suggest that moderate low energy availability can improve certain bodily functions, given time to adapt. Of course, extreme deficits in energy are considered unstable and disruptive to your health, and most experts recommend listening to your body and reputable dietary guidelines when attempting any sort of restrictive eating practices. Runners who want to tailor their diet to their training and racing should check out these “Nutrition Guidelines for Long Runs and Race Day.” Getting the proper balance of macronutrients is a major component of an effective diet, and most experts recommend getting about 65% of your calories from carbs. That’s especially true if you’re competing for 2 hours or less at a time. If you’re going longer, aim to take in more fats, since they can be stored as energy in greater amounts than carbs.