Why is such a huge part of old people overweight?

I'm guessing you're trolling, but I'll bite.

I'm not sure your statement about people being overweight is valid. This .gov site says:

Men often gain weight until about age 55, and then begin to lose weight later in life. This may be related to a drop in the male sex hormone testosterone.

Even if the overweight thing were true, you have attributed this to being a lifestyle choice. But there is a ton of stuff we don't know about how the human body works. One thing studies have shown is that the tendency to be overweight happens in clusters, from which one could infer a person's environment contibutes to their weight.

That might sound like someone not taking responsibility for being overweight, but allow me an analogy: ulcers.

For my entire youth and young adulthood, there were references to ulcers in culture. Stressed out business men in movies and TV shows got ulcers. People had to avoid spicy food because of ulcers. Ulcer medicine commercials were common on TV. Ulcers were a real problem, and were totally attributed to lifestyle.

And that was totally wrong.

Someone figured out that bacteria cause peptic ulcers. The discovers won a Nobel Prize for this.

Could something in our guts (other than the food we eat) contribute to being overweight? Our guts contain a lot of microbes that help us out. Maybe the longer we live, the more of a chance we have to being exposed to something that affects our gut (either getting infected with something bad, or taking a medicine that kills something good).

Just food for thought.

/r/AskOldPeople Thread