Have you ever noticed that some people struggle to lose weight while others seem to have no trouble maintaining a healthy body weight? Why is it that some people lack the motivation to exercise while others are can’t seem to stop moving? What about people who appear to have no interest in desserts while others have a “sweet tooth”? Why do overweight parents tend to have children who are also overweight?
The traditional answer is that some people lack willpower which makes it more difficult for them to make healthier eating and activity choices. While motivation and dedicated effort are essential for making healthy choices, genetic research has resulted in the identification of a host of genes that appear to affect physical activity and eating habits, food preferences, and responses to a diet or exercise program.
The link between genetics and obesity is not new. Decades ago researchers found that obesity tends to cluster in families. But is this due to shared genes or a shared environment? The answer is both, but heredity plays an important role. Studies of siblings raised apart show that their body weight and fatness more closely resembled each other than the families they lived with. Other studies show wide variation in body weight among relatives, where some are obese but others are at a healthy weight. This suggests that although genes can predispose people to being overweight, personal behavior can modify this risk.
Genetic variations also explains why people respond to exercise training differently. Much of this knowledge comes from the Heritage Family Study which examined body fatness, fitness, and other health factors in over 700 individuals from 130 families. After completing the same exercise program, some people improved their fitness significantly while others experienced only a minor improvement. The prevailing explanation was that varying degrees of compliance accounted for these differences, but the Heritage study showed that genetic factors were at responsible for 40–50% of the variation in both initial fitness and improvement in fitness.
Your genes can also influence what you eat. Eating habits, including how much you eat as well as food preferences, are at least partly under the control of certain genes. Two separate genes that regulate appetite and the type of food people eat, have been identified. This might explain why some people say they always feel hungry while others are satisfied after a small meal or why some people crave foods that are high in sugar and fat while others do not. Of course, what you eat is a behavior that you can control—you are putting the food in your own mouth, right?—but it is interesting to know that there are genetic factors that make these decisions more challenging for some.
Does this mean that healthy behaviors including eating and exercise are out of your control? Does it give you an excuse for being unhealthy? Absolutely not! Your genes may predispose you to certain health conditions, meaning you are at higher risk, but they do not predetermine your health. The expression of these genes is modifiable by your environment and your behavior. Even though you may be at higher risk for obesity, you still need to eat too much and not be active enough to gain weight. Be aware that “too much” varies greatly among people, so there is no single eating and activity pattern that applies to everyone. But knowing that you have a family history should give you even more motivation to eat a healthy diet and get regular exercise.