Body fat increases by enlarging existing fat cells (fat cell hypertrophy) or increasing the number of fat cells (fat cell hyperplasia).

Until recently, scientists thought that the number of fat cells was fixed in adults, but could be influenced by exercise and diet during childhood.

Now, we realize that things aren’t that simple. Scientists discovered that overeating combined with decreased physical inactivity can trigger increased fat cell production.

This makes people more prone to obesity, because they have more places to store fat.

Scientists have long known that yo-yo dieting – repeated weight-loss dieting followed by overeating – increased the risk of obesity. Yo-yo exercising (periods of exercise followed by weeks of physical inactivity) has the same effect.

The best strategy for weight control is to maintain a long-term, sensible diet and exercise plan that you can do for a lifetime. [sources: Journal of Applied Physiology, Fitness RX]