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. But remember, genes are not everything.

. And that somewhere else is our

The Tech Museum of Innovation Share Stanford at The Tech Museum Home About Genetics Ask a GeneticistCategories Submit a Question Video Gallery Online Exhibits Genetics in the News Books Sponsors When Will Broccoli Taste Like Chocolate Click here to order our latest book, When Will Broccoli Taste Like Chocolate? Error message Notice: Undefined index: und in __lambda_func() (line 2 of /srv/www/genetics.thetech.org/htdocs/sites/all/modules/views_php/plugins/views/views_php_handler_field.inc(202) : runtime-created function). Notice: Undefined index: und in __lambda_func() (line 2 of /srv/www/genetics.thetech.org/htdocs/sites/all/modules/views_php/plugins/views/views_php_handler_field.inc(202) : runtime-created function).

behavior

If 40-80% of BMI comes from genes, then 20-60% comes from somewhere else

possibly tell how much of someone's weight is due to genes? And how much is due to life style choices? One way scientists try to pick apart genetic and environmental causes is to study sets of identical twins. Identical twins have the same DNA but can be put in different environments. This lets scientists directly tell what is due to genetics and what is due to genes. For example, in one study of obesity, sets of identical twins were fed extra food and forced to behave similarly (same amount of exercise, eating, etc.). During the study both twins in an identical twin pair gained about the same weight. But there were huge differences in the amounts of weight gained between sets of twins. This kind of study tells us that the tendency to gain more or less weight is in our genes. But twin studies can also show that some aspects of weight have to do with behavior too. For instance, scientists looked at identical twin pairs that exercised different amounts. As expected, the twin that exercised more weighed less. This shows that weight is not just genetic and that behavior is not all genetic. The fact that the twins had different exercise patterns definitely suggests that what we weigh has a large environmental component. So how much we weigh has to do with both our genes and our behavior. Just because someone's parents are heavy that does not mean their children will be heavier too. But it might mean that they will have trouble keeping the weight off. Good exercise habits and eating healthy foods can help maintain a normal weight. The opposite is also true. Your genes can predispose you to be normal weight. But if you eat too much food and do not exercise enough to use up the extra energy, then you will gain weight and eventually become overweight. Weight is really just a product of energy taken in (food you eat) minus energy used (for exercise, for heating our bodies, for helping digest our food, etc). So to lose weight, all you have to do is use more energy than you eat. And to gain weight, you just have to eat more food than you use up. Sounds simple, right? But of course it isn't--partly because of genes. Our genes can affect the amount of weight lost from dieting and exercise. They can also affect how much weight is gained when we eat too much. Our genes make proteins that work together to control everything from how often we get hungry to how we use energy from food. They even control how much exercise we can do at a time. Because our genes tell our bodies how to handle the food we eat, it's often hard for us to achieve a certain target weight. But what we weigh isn't only due to our genes. Katie Cunningham More Information How identical twins can look different even with the same genes.Obesity genesAppetite genes Back to Conditions Search Ask a Geneticist His parents were probablyoverweight. But notnecessarily.Identical twin studies showthat our weight is partgenetic and part en