[jyl]

Here is a question on weight gain and aging. Kind of a follow on to some recent discussions on obesity and diabetes.

Is it natural to gain weight as you age? Is it inevitable?

Some information I found.

A study in the UK of 1200 men and women. The average man gained between 10 and 20 lb per decade, starting at age 39. This is just average joes, not fitness buffs.

A study in the US of 4000 male runners from 18 to 50. The average runner gained 3.3 lb per decade.

Information I found on boxers. I went looking for this because boxers are weighed for each fight, and they need speed and mobility. A sample of lighter weight (not heavyweights, who can be kinda pudgy) professional boxers gained 30-40 lb during their careers. One of the boxers who gained the least was Sugar Ray Leonard. He went from 140 lb in 1976 (Olympic champion light welterweight) to 165 lb in 1988 (won super middleweight title).

Then I looked for information on the fittest athletes of all, in the most grueling sport by far, that is incredibly weight sensitive. You can guess what that is - professional cycling. Unfortunately, cyclists' weights aren't reported consistently and fluctuate during the TdF, when they can lose 10 lb despite eating 10,000 calories/day. Lance Armstrong appears to have maintained roughly 165 lb for his career.

So my conclusion was that, unless you are a genetic and athletic freak like Lance, you will tend to gain weight as you age. From 3-4 lb per decade if you run seriously, to 20 lb per decade if you're on the porkier side of average Joe-Dom.

My question is, does this match up with what we know about human physiology? What part of the body inherently gets heavier with age? We know that after 30, muscle mass and tone tends to go downhill, but even if converted to fat, that should weigh less not more.

So why do people, even very fit people, get heavier as they get older?

Does this happen with other animals? Not sturgeon and such species who never stop growing, or housecats who get fat and lazy like their owners. I mean like wild lions, eagles, orcas.