Why do you gain weight more easily after 40, even if you eat the same amount?
After forty, your body burns fewer calories, mainly due to muscle loss and a lower resting metabolism. You therefore do not need to eat more to still gain weight, but eating less or exercising more can partly compensate for this.
Muscles are the engine of your metabolism. After the age of forty you gradually lose muscle mass, and muscles burn more energy at rest than fat tissue does. This means your body needs fewer calories per day, even if you exercise and eat the same as before. This muscle loss (sarcopenia) has been robustly demonstrated and is considered one of the most important causes of weight gain in later life.
On top of that muscle loss, your resting metabolism also falls for a second reason: organs shrink slightly and use less energy per kilogram of body weight than they used to. At the same time, on average you move a little less as you get older. This has both biological causes, such as changes in brain regions that prompt you to be active, and practical environmental factors. The result is that your total daily energy expenditure drops considerably.
Something is also happening inside your cells. A substance that cells need for their energy management, NAD+, declines throughout life. In mouse studies, restoring NAD+ led to less weight gain and improved fat metabolism. In humans the evidence is preliminary: small studies show cautiously positive signals, but a proven causal relationship has not yet been established.
Less well known is the role of fat cells in the bone marrow. These increase progressively with age and, via signalling molecules, influence other tissues, including muscles and fat depots. This is a relatively new area of research and the precise importance for weight gain in humans is still unclear. Finally, mouse studies suggest that epigenetic changes, whereby certain genes are switched on or off differently as you age, also contribute to the tendency to gain weight. Whether this applies equally strongly in humans still needs to be investigated.
Claims based on multiple studies (PMID 19698803, 24576864, 38584513, 37364580, 22682224, 31702948, 32103178). Muscle loss and the decline in total energy expenditure are the best supported. NAD+ and epigenetic mechanisms are, for the time being, based on animal or associative research.
Does excess weight accelerate ageing?
Excess weight demonstrably accelerates biological ageing, but metabolic health counts at least as heavily as the number on the scale. Losing weight and exercising help, and the earlier you start, the greater the benefit.
Does the timing of meals throughout the day affect your weight?
When you eat matters: meals earlier in the day appear more favourable for your metabolism than eating late, although the effect varies from person to person and the strongest evidence is still based on short-term studies.
Does someone with diabetes age faster biologically?
Yes, diabetes noticeably accelerates biological ageing: the risk of cardiovascular disease, dementia, and premature death increases, and keeping blood sugar well under control is the most direct way to slow that process.
Does my metabolism really slow down as I get older?
Your metabolism does not slow down from your thirties onward, but after your sixties energy expenditure does decline noticeably. Muscle loss and reduced physical activity are the biggest culprits, and these are also the areas where you have the most influence yourself.
Why is it harder for me to lose weight than it used to be?
Ageing lowers your energy expenditure through muscle loss and a slower metabolism, making weight loss objectively harder. Strength training two to three times per week is the best-supported way to slow that process and support weight loss, ideally with professional guidance.
Does it matter what time of day I eat?
Eating earlier in the day is more beneficial for your weight, blood sugar and hormonal balance than eating late or at night. The effects have been demonstrated in randomised studies, but the average weight loss is small: around 1 to 2 kg.