How Can Someone Eat So Much & Still Be Skinny?

We all have that friend that we love to hate: the friend who seems to eat whatever she wants yet never gains any weight. You may wonder that her secret is. The answer is complex, and lies in your friend's metabolism, eating habits and her level of activity.

Genetics

• Metabolism, or your body's rate of converting the foods you eat into usable energy, plays a large role in how much you can eat without gaining weight. Metabolism is partly genetic. Some people are born with naturally fast metabolisms, whereas some have slower metabolisms. James O. Hill, director of the Center for Human Nutrition at the University of Colorado Health Sciences Center, states that 30 percent of your metabolism is due to genetics. Certain inherited health conditions can affect metabolism as well, such as thyroid problems.

Diet

• People who maintain a healthy weight also tend to eat differently. They focus on filling, nutrient-dense foods that add bulk to the diet but not a lot of calories. For example, a person with a healthy weight may eat a salad at a buffet before he indulges in a slice of pizza. The salad serves to fill him up so he eats less of the unhealthy foods. As a result, although the person is eating a lot of food, the bulk of the foods he is eating are not as unhealthy, allowing him to eat more food without gaining weight. People with healthy weights also tend to stop eating when they are full.
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Level of Activity

• People with healthy weights can often eat more because they burn more calories through physical activity. Modest amounts of physical activity, such as walking for 45 minutes a few times per week, may not be enough to have a noticeable effect on your metabolism. However, distance runners, weightlifters and others who participate in vigorous physical activity may be able to eat a lot more than the average person who only engages in moderate or no physical activity.

Caveats

• Being thin may not necessarily be healthy. Some people who appear to eat anything they want yet remain thin may have an eating disorder, such as bulimia. Taking certain illegal drugs, such as amphetamines, may also cause you to lose weight in an unhealthy manner. In addition, some who appear thin may be eating in an unhealthy way, such as skipping meals or engaging in questionable fad diets that allow them to overindulge in certain types of foods while strictly limiting others.