December 01, 2020

How much do your genetics influence your weight?

Q: I'm pretty thin and my cousin is overweight. We tease each other about it — he says I got the "thin" genes, and I counter that he eats too much. How much do genes influence your weight?

A: Your weight is determined by a complex interplay of many factors. These include many body processes — how full you feel as you eat, your appetite levels, how your body uses and burns energy, and how quickly food passes through your digestive system — each of which has a genetic component. Environmental factors, including where you live or your income level, and diseases you have or medications you take can be factors, too. There are also behavioral factors such as your food choices, calorie consumption, physical activity, smoking and the quality and quantity of sleep. Even the types of bacteria in your gut and stress levels play a role.

In fairly simple terms, genes do appear to play a role in your weight and body mass index (BMI), which uses weight and height to estimate body fat. Studies of twins who were raised together or apart — and of adopted children — suggest that genetics or heritability accounts for perhaps 30% to as much as 70% of why you have the BMI level you do.

That's substantial, but that also means 30% to 70% of your BMI level is related to nongenetic variables. Among the most important on that list is being mindful of how much you eat and the amount of energy you expend.

A diet that focuses on minimally processed plant foods, lean protein sources and healthy fats such as olive oil — and portion control — can help keep calorie intake in check. So does avoiding sugary drinks, high-calorie...