Our bodies are very confusing machines, but we can explain gaining or losing weight in terms of calorie intake. Each of us has a specific number of calories we need to eat each day to not gain or lose any weight. It depends on a lot of things, like being a boy or a girl, or how much you exercise. Let’s say for example that for Joe, it is 2000 calories. If Joe eats more than 2000 calories in a day, he will gain weight, but if he eats less, like 1700 calories, he will lose weight. So if Joe eats 3000 calories every single day, it will add up and he will deposit more fat onto his body. His body doesn’t know what to do with all the extra energy, so it stores it!

Most of what makes us who we are comes from 2 places - our heredity [our genes] and our environment .

Our heredity gives us our different body shapes - mine has sort of thin arms and legs and is sort of big around the middle. Our environment gives us some of the details - the people I knew who lived in a vegetarian yoga community were almost all skinny. The food we eat does a lot to make us fatter or thinner. I've read that fat people can get that way by hanging out with fat friends [and eating with them, too, I'm sure!]

Eating more helps you grow bigger. My older granddaughter is too skinny, and her almost-chubby sister, 3 yrs younger, is almost as tall as her older sister is.

Food is so nice that it's usually hard to eat enough less to lose weight.

This depends on the person, really. There are a lot of different possible reasons. Some people don't burn enough calories, others eat too many, etc.