Body composition varies by genetics and hormones; excessive fat loss disrupts essential functions

Your body's shape is not simply a matter of willpower or aesthetics. It is the product of a conversation between your genes, your hormones, and the life you live—a conversation that plays out differently in every person. Some people shed abdominal fat with relative ease while others restrict calories and exercise faithfully and see almost nothing change. The reason lies not in discipline but in biology: each of us arrives with a unique metabolic blueprint, a particular hormonal profile, and a genetic predisposition that determines not just how we look but how our bodies respond to food, movement, and time.

Body composition—the balance of muscle, fat, bone, and water that makes up your physical form—shifts across a lifetime in ways that have nothing to do with the mirror. In men, testosterone directs fat storage toward the belly. In women, estrogen deposits it preferentially in the hips and thighs, a distribution that serves a biological purpose: it helps protect metabolic function and reproductive capacity. But this arrangement is not permanent. When estrogen levels fall during menopause, that fat migrates inward, concentrating around the abdomen. Meanwhile, stress levels, sleep quality, the health of your gut bacteria, and the rhythm of your metabolism all exert their own pull on how your body holds or releases fat. According to endocrinologist Érika Fernanda de Farias at Hospital Santa Lúcia Norte in Brasília, the body moves through hormonal cycles that reshape the balance between muscle and fat across decades. Puberty, pregnancy, and menopause are not isolated events—they are moments when the hormonal landscape shifts dramatically, and the body's entire approach to storing energy reorganizes itself.

Yet there is a threshold beyond which fat loss becomes dangerous. Fat tissue is not the enemy; it is essential infrastructure. It manufactures hormones, cushions vital organs, and helps regulate immune function. When body fat drops below what the body needs, the organism interprets this as a crisis. It begins to conserve energy, downshifting processes that seem less urgent than survival. The signs appear across multiple systems: menstruation becomes irregular or stops entirely. Sexual desire diminishes. Fatigue sets in, accompanied by irritability. Sleep becomes difficult and the body feels perpetually cold. Muscle mass erodes. Skin dries out and hair falls. In men, extreme fat loss suppresses testosterone production. In women, it disrupts ovulation and throws the hormones that govern fertility into chaos.

Women's bodies respond more dramatically to fat loss than men's do, and there is a reason. The female body is evolutionarily programmed to preserve the capacity for pregnancy, to maintain enough energy reserves to sustain gestation. Small changes in weight can interrupt the menstrual cycle and alter the production of estrogen and progesterone. Men typically experience a drop in testosterone only after prolonged caloric restriction or intense training without adequate recovery—but when it happens, the consequences mirror those in women: diminished libido, exhaustion, loss of lean mass. Cíntia Cossich, a nutritionist at Rede Casa in Rio de Janeiro, emphasizes that even people who eat well and train consistently can suffer from dangerously low fat levels. This tissue participates in hormonal, immune, and neurological processes. Without it, essential functions fail.

Safe fat loss requires a different approach. The goal should be a modest caloric deficit, not a dramatic one, paired with balanced nutrition that includes adequate protein, carbohydrates, and healthy fats. Eat whole foods dense in vitamins and minerals. Prioritize sleep. Drink water consistently. Manage stress. Avoid extreme diets and punishing training sessions without recovery. The body does not respond well to emergency measures. It responds to patience, consistency, and the understanding that composition is not a destination but a dynamic state—one that changes across a lifetime and deserves respect.