Fat, Fasting, and Deficit: The Diet Wars Explained

Fat or Caloric Deficit: The Diet Wars

Losing weight means losing fat, and fat only disappears by burning more energy than consumed. This is basic high school thermodynamics. The problem arises when someone asks how to achieve this deficit without triggering the body's conservation mode or breaking willpower by the third week. At this point, consensus splits into two trenches that have been throwing stones for years: those who argue that eating less and moving more is enough, and those who maintain that the key lies in hormones, not arithmetic.

What is caloric deficit and why naming it is not enough

The most repeated argument is that any weight loss reduces to a caloric deficit: if you burn 1,500 calories and eat 1,300, you lose weight. It is true and it is incomplete. As one of the most cited analyses of the discussion summarizes, saying "lose weight with caloric deficit" is like saying "burning fire" or "wet water": it describes the process, not how to achieve it sustainably.

The problem has two fronts. On the intake side, calorie tables are a rough approximation that do not account for each person's actual absorption or food quality. On the expenditure side, metabolism adapts: when the body detects restriction, it lowers spending and increases hunger. The result is the classic rebound, that which turns the diet into a cycle of loss and recovery that leaves the patient worse off than before.

The hormonal thesis: insulin, ketosis, and satiety

The current gaining weight in the discussion argues that the body is not a mechanical machine, but biochemical. Sugar spikes insulin, insulin blocks fat burning, and the brain enters conservation mode with more hunger. Fats, on the other hand, activate satiety and allow the organism to draw from reserves. This is the basis of ketogenic diets and prolonged fasting, states that their defenders describe as perfectly natural: a baby spends most of its time in ketosis, and hunter-gatherer tribes did not go around with an endocrinologist.

The answer to skeptics is blunt: losing weight by fasting is impossible. Another thing is enduring it. And here comes the factor that no table measures: adherence.

Cases that support each side

The circulating evidence is varied. One participant reports losing between 20 and 25 kilos in two separate stages, both cases in six or eight months, removing sweets, fried foods, and breaded items, prioritizing vegetables, poultry, and grilled fish, and minimizing carbohydrates. Another claims to have gone from 114 to 74 kilos walking three or four hours daily and then maintaining with an hour and a half in the gym. A third person says they lost six or seven kilos during confinement by cutting all exercise and eating anxiously, which invites doubt that exercise is the decisive factor.

On the opposite extreme, the case of a man who fasted for 353 days under medical supervision is mentioned without his metabolism suffering significant detriment, possibly because he had enough reserves for the whole year.

The real role of exercise and physical work

The discussion shifts to daily energy expenditure. Some argue that exercise is a secondary actor compared to diet, while others defend that intense physical work radically changes the body. The case of a young man who went from 95 to 70 kilos in one year working in a warehouse without significantly modifying his diet is cited. The conclusion drawn is that constant movement, even if not sport, alters the balance in a way difficult to replicate in a gym.

The factor no one wants to look at: testosterone

One of the most striking turns in the conversation is the warning about sens hormones. Fats are the raw material for testosterone; without enough fat, the hormonal axis suffers. In a strict hypocaloric regimen, this current argues, the first victim is testosterone, with effects on muscle, mood, and behavior. The recommendation is clear: do not eliminate fat from the diet, even when the goal is to lose weight.

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With these premises, the most reasonable prediction is that the debate will not close: thermodynamics will continue to win in textbooks, and hormones will continue to win in practice. What no one disputes is that the method that works is the one that can be maintained without living dependent on a kitchen scale.