We all associate overweight people with low energy, and there’s a good reason for this. But it’s not the reason you think. People don’t get fat because they don’t move much; they don’t move much because they are getting fat. The energy they could use to be active is being diverted to storage as fat. The culprit is insulin, which is released mostly in response to eating carbohydrate, much less so in response to eating protein or fat.
When you are a parent, this lethargic behavior is extremely frustrating. I remember vividly once when Juliana was about 9 and we were on vacation and she didn’t move from the couch all day. I actually remember wondering what was wrong with her. She wasn’t sick, but she didn’t look like she felt well. At 3 in the afternoon I insisted that she go outside and do something, anything. She didn’t want to. I had to really push her, and I was trying to hide my anger as I did it. Eventually she did so, reluctantly.
Now I know that going outside and moving was actually a huge effort for her, because she didn’t have much energy for motion. It was mostly being stored in fat cells.