For example, when it comes to hormones, ghrelin makes you hungry, leptin and other hormones keep you feeling full, Nadolsky says. Thyroid, cortisol, insulin, testosterone, and estrogen all influence how you metabolize and store energy. Meanwhile, genetics have a large influence on both basal metabolic rate (how many calories you burn just to live) and hormone health. While all of these things are impacted by our diet, they’re not only controlled by the way we eat. And, in fact, while sleep, stress management, and, when needed, medication can help regulate other hormone levels such as estrogen and thyroid, our hormones and other physiological processes are often out of our control. And by the way, being able to impact our hormone levels and metabolism with our diet doesn’t always work out in favor of weight loss. As a 2016 review notes, one of the reasons weight loss by way of caloric restriction isn’t efficacious is because “this strategy is countered by the body’s natural physiological response to negative energy balance.” In other words: The body fights back against caloric restriction.
In a way, moderate-intensity physical activity is that "magic pill" a lot of people are looking for, because the health benefits go beyond keeping your waistline trim: Not only can it reduce your risk of cancer, stroke, diabetes and heart attacks, but studies have shown that physical activity can significantly improve the moods of patients with major depressive disorders.