Few questions polarize people like the one about why are we fat. The answer is complex, but the most common explanation is that eating more calories than we burn leads to weight gain. While that's true, it's not the whole story.
Scientists have found that genes and other factors influence how our bodies change food into energy and store fat. Certain genetic conditions, such as Prader-Willi syndrome, can also make it harder to lose weight.
Our bodies use calories to grow and maintain cells, move the body, and heat it. When they have extra calories, our bodies store them as fat in specialized cells called adipose tissue. The excess fat cells shrink when we consume fewer calories or exercise more, which lowers the overall body weight.
Some of this extra fat is needed to protect the body's organs and skeleton, but much of it is simply unnecessary. In fact, a growing number of studies suggest that being overweight is actually associated with a lower risk of disease and death, particularly heart disease and stroke.
The main type of fat in our diets is saturated, which comes from animal products such as beef and pork; high-fat dairy foods such as butter, lard, cream, and cheese; and baked goods and desserts made with full-fat ingredients. The healthier fats are monounsaturated and polyunsaturated, which come from plant oils such as olive, peanut, safflower, sesame, and canola. These fats tend to be "softer" and more liquid than saturated fats.