While a slight caloric deficit should cause sustainable weight loss (think 300-500 calories per day), much larger deficits elicit changes in your metabolism to keep your body in an energy balance and maintain homeostasis. The body—this dynamic, adaptable machine—wants to feel “safe.” With survival as the priority, it is constantly regulating what’s going on in response to our environment.
Undereating can sabotage your recovery. As top athletes know, proper recovery is just as important as the training itself when it comes to seeing progress in performance. When you train, your muscle tissue breaks down, and without adequate calories and protein in your diet, your muscles won’t have the materials they need to rebuild. And if you’re under-fueled while working out, protein from your muscles will actually become fuel for your body to continue running on.
Undereating also causes disrupted sleep, and evidence shows that high-quality sleep is essential for recovery after a tough workout. Poor sleep also causes us to hold onto body fat. So if undereating is causing your sleep to suffer, you can bet you won’t be performing well in the gym or losing body fat.