Energy balance, the principle that body weight is determined by the difference between energy consumed and energy expended, is fundamentally correct. What changes after 50 is that the factors determining both sides of that equation become more complex, more variable, and more influenced by hormonal context. Applying the same caloric deficit that produced weight loss at 30 to a 55-year-old produces different results because it is a different physiological situation.
The Metabolic Rate Problem
Resting metabolic rate declines with age, primarily as a consequence of reduced muscle mass rather than ageing itself. This reduces the energy expenditure side of the equation. Caloric restriction accelerates muscle loss through increased cortisol and reduced anabolic signalling, further reducing metabolic rate, creating a negative spiral where each round of dieting leaves the metabolism slower than before.
The Hormonal Context
Insulin sensitivity declines with age. Growth hormone output decreases. In women, oestrogen loss at menopause shifts fat distribution to the visceral region and reduces the metabolic rate further. In men, declining testosterone reduces muscle protein synthesis and increases fat storage. These hormonal changes mean that a caloric deficit of a given size produces more muscle loss and less fat loss in adults over 50 than in younger adults unless dietary protein is high and resistance training is included.
The Practical Adjustment
- Maintain high protein intake during any caloric deficit to preserve muscle mass and metabolic rate
- Prioritise resistance training over cardio for body composition in adults over 50
- Use a more moderate caloric deficit of 300 to 500 calories rather than aggressive restriction
- Address sleep and stress to normalise cortisol before expecting dietary interventions to produce their full effect
- Consider body composition as the metric rather than scale weight, as muscle gain alongside fat loss can produce scale stability while improving health dramatically