Longevity: Why do we get fat with age?

 

 

It's a common observation that most people gain weight as they age. Various reasons are offered to explain this. Perhaps the most common is that as people get older, their level of physical activity declines, but their caloric intake either remains the same, or increases. The resulting imbalance between calories in and calories out inevitably leads to "creeping obesity." or the gradual accumulation of added body fat over the years. Another common explanation for fat gain with age is loss of lean mass. Having a certain amount of muscle mass boosts resting metabolic rate, thus you burn more calories at rest. It isn't a lot of calories, but it does add up. The primary cause of loss of muscle mass with age is lack of exercise. It can progress to a frailty syndrome known as sarcopenia. which literally means "loss of muscle."  The loss of lean mass with age also produces a type of age-related insulin resistance not related to diabetes. This insulin resistance can also contribute to the fat gain common with age.

But the most common reason why people gain fat as they age is simply that they eat too much, and exercise too little. Some scientists who specialize in studying the aging process say that the only reliable way to maximize lifespan is to reduce calories as you age. In animal studies, this involves a reduction of about 30% of daily total caloric intake. But recent studies that used monkeys as subjects found that caloric restriction isn't quite as effective as thought in higher mammals, including monkeys and humans. Others have calculated that if you follow a calorie-restricted diet after age 40 or so, you can expect to live about 7 years longer than if you didn't. While 7 years isn't bad, it's hardly the Holy Grail sought by most CR advocates of living to 100 or more. Those that do live that long can usually attribute most of it to a lucky draw in the gene pool. While reducing calories as you age might not guarantee you live to 100 or more, it does reduce a few risk factors linked to premature death. These include high blood pressure, cardiovascular disease, diabetes, and cancer. However, most of these effects are due to the leanness and lack of body fat that results from a calorie-restricted diet when used long-term. If you eat properly, ingest sufficient nutrients, and exercise, you can probably get 99% of all the benefits of a calorie-restricted diet with the notable advantage of not feeling constantly tired, cold, and hungry, as well as looking as if you just escaped from a prisoner of war camp.

But why do people tend to overeat as they get older? A study published six years ago supplies a probable answer to this mystery. In a study led by Zane Andrews, a neuroendocrinologist at Monash University . . .