Low caloric intake can lead to serious consequences for your performance and your overall health.

You follow your training plan to the letter and rest religiously on your days off. But for some reason, you’re getting slower and feeling worse and worse.

The problem might be low caloric intake. The condition is called “low energy availability,” or LEA, and it affects professionals and novices alike. “We’ve found that about 55 percent of individuals who are training every day are in low energy availability,” says Stacy Sims, exercise physiologist and nutrition scientist at the University of Waikato Adams Centre for High Performance in New Zealand.

The consequences are serious. After four days of LEA, the thyroid becomes dysfunctional, fatigue sets in, and athletes find they can’t exercise at the intensity levels they’re used to. They recover slower, and often develop belly fat as their metabolism slows to a crawl; over time, men’s testosterone levels drop, and women’s menstrual cycles become irregular, Sims says.

She recommends carefully timing nutrition throughout training and warns that athletes should not work out in a fasted state. Instead of heading to early-morning swim practice on an empty stomach, athletes should at least drink a glass of almond milk or eat half a banana to boost their blood sugar and limit cortisol—a hormone that’s naturally high in the mornings. This is critical, Sims says, because too much cortisol leads to increased blood glucose, muscle breakdown, and poor recovery.

Post-exercise nutrition is arguably even more important. Sims and her fellow researchers found that Ironman triathletes who ate immediately after workouts didn’t experience LEA, even if they didn’t consume enough post-race calories to meet their needs. Aim for a mix of carbs, fat, and 20-30 grams of protein in the half-hour after exercise; a yogurt smoothie (see recipe below) is a convenient option.

It also helps to be aware of how your body handles different foods. Fibrous whole grains and foods high in fat and protein provide a more gradual energy supply without spiking blood sugar, but take longer to digest, making them best to eat well before a training session. Simple sugars, on the other hand, provide a quick, easy-to-process source of energy, ideal for pre-workout or mid-exercise fuel, according to Bob Seebohar, a sports dietitian, USAT Level III triathlon coach, and founder of eNRG Performance. He cautions that your regular diet determines what your system can tolerate. Athletes who habitually eat a high-fat diet will be able to utilize fat as fuel at higher intensities of exercise, according to Seebohar. They’re also more sensitive to carbohydrates, so consuming a moderate amount pre-race will give them a higher benefit than athletes on carb-heavy diets.

Snack On

Dr. Sims suggests these high-protein, healthy-carb between-meal solutions to ward off LEA.

1 banana, 1 cup low-fat milk, 1⁄4 cup almonds
~380 Calories

2/3 cup low-fat granola with 1 cup low-fat milk
~380 Calories

1 cup low-fat Greek yogurt, 1/2 cup berries
~ 180 Calories

2 T almond butter with two slices sprouted-grain toast
~ 360 Calories

1 5-ounces tuna (in water) with whole-grain crackers (30g); 1 banana
~ 415 Calories

Favorite smoothie recipe:
1 frozen banana, 1 scoop of your favorite plain protein powder, 1 shot espresso, dash of cinnamon, 1 tsp. vanilla
~ 220 Calories