Unlike simple calorie restriction, intermittent fasting lowers insulin levels. This hormonal signal allows your body to access and burn its fat stores to make up for a caloric deficit, preventing the metabolic slowdown that typically sabotages diets.
The cultural shift from three to six meals a day was a reaction to 1970s dietary advice. Low-fat, high-carb foods cause blood sugar crashes and frequent hunger, which led to the institutionalization of snacking to manage these new hunger pangs.
Contrary to popular belief, fasting for up to four days actually increases your basal metabolic rate. Instead of shutting down to conserve energy, your body activates a hormonal 'fight-or-flight' response that increases energy expenditure to help you find food.
Typical exercise burns a surprisingly small number of calories compared to your daily metabolic needs. More importantly, it often triggers rebound hunger, causing people to eat more and cancel out any caloric deficit they might have created from the workout.
Reducing calorie intake triggers a corresponding drop in your basal metabolic rate. Your body simply starts burning fewer calories to match what you're eating, which stalls weight loss and explains why "just eat less" is flawed advice.
Eating high-carb foods frequently, even in a calorie deficit, keeps insulin high. This prevents your body from accessing stored fat for energy, forcing it to lower its metabolic rate. After the diet, this suppressed metabolism causes rapid weight regain.