Why some people can eat a lot and stay thin

It can be frustrating to have a close friend or family member who seems to be able to eat an endless amount of food and stay thin while you are carefully watching what you eat and still gain weight! It is easy to wonder what their secret is, but it unfortunately it is not that easy. There are many different factors that may be in play here and contribute to their lack of weight gain.

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For starters, things may not be exactly as you see it. Your friend may be eating a rather large amount while you are in their company, but their eating habits may be drastically different when they are not with you. Or maybe you are under the assumption that they are not very active but in fact they are burning a large amount of calories throughout the day. If your thin friends are extremely active, they will have more lean muscle tissue which is linked to a faster metabolism.


If perhaps it is your partner or a close family member where you do in fact see what their daily diet usually consists of, another answer to why they don’t seem to be putting on weight may come down to genetics. There are studies in their infant stages that are suggesting that 60-70% of our body weight is determined by our genes. Also a child’s weight may be determined by the age, weight and diet of the mother during pregnancy.

There are also some who burn a high amount of calories throughout the day through Non-exercise activity thermogenesis (NEAT). Calories may be burned through small activities such as pacing while talking on the phone, chopping up vegetables while cooking or twiddling your thumbs while waiting in line. This supposedly can increase one’s metabolism by up to 50% according to the American Council on Exercise.


In 1967 there was a famous experiment done by medical researcher Ethan Sims whereby he gathered volunteer inmates to participate. If they gained 25% of their body weight through increasing their caloric intake, they would get early release from prison. Surprisingly enough there were many who found it extremely hard to nearly impossible to put on any significant weight. So in many cases it may have nothing to do with what you are putting in your body but rather your DNA.

In conclusion, it is a mix of genetics and environment. Even if your DNA isn’t looking too great, there are ways to be fit and healthy. Talk with a nutritionist and see what would work for you and your lifestyle.

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