If you cut calories too drastically, your nutrient intake may not support proper training and recovery.

This can increase your risk of injury, illness, and overtraining syndrome (2).

The latest sports nutrition guidelines also warn against eating too few calories and reaching a dangerously low body fat percentage, both of which can disrupt reproductive function and diminish bone health (2).

The lowest safe recommended body fat percentage is 5% in men and 12% in women. However, these levels are not necessarily best for all athletes, so discuss what’s best for you with your coach and sports dietitian ( 4 ).

Cutting calories too quickly can also negatively affect hormones and metabolism ( 5 ).

To decrease body fat, athletes should eat about 300–500 fewer calories per day but avoid eating fewer than 13.5 calories per pound (30 kilocalories per kg) of fat-free mass per day (2, 3 ).

If you don’t know how much fat-free mass you have, get your body composition estimated with either a skinfold test or bioelectrical impedance analysis (BIA).

You can also get your body composition measured by dual-energy X-ray absorptiometry (DXA) or underwater weighing. These are more accurate but also tend to be expensive and harder to come by.

SUMMARY Crash diets can increase your risk of illness and injury, as well as negatively affect your training and recovery. Therefore, avoid cutting your calorie intake by more than 300–500 calories per day.