Research on "The Biggest Loser" contestants revealed that metabolic slowdown is a response to significant calorie restriction and exercise. Counterintuitively, those with the largest metabolic slowdown were the most successful at losing weight and keeping it off.
Our conscious control over eating is limited. In a study, participants on a drug that caused calorie loss through urination unconsciously began eating more over time to compensate for the resulting weight loss, revealing a powerful system that regulates body weight.
The obesity crisis is a systemic issue, not an individual failing. The modern food environment promotes overconsumption of unhealthy foods. Critically, the U.S. agricultural system does not even produce enough fruits and vegetables for the population to follow recommended dietary guidelines.
The "carbs vs. fat" diet war is a distraction. The body adapts to its fuel source, and on a caloric basis, excess energy from either carbohydrates or fats is stored as body fat to the same degree. Cutting calories from either source leads to similar weight loss.