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We all have them: friends who can eat anything they want without gaining weight. How do they stay that way? What’s their secret? A resting metabolism on steroids?
Not exactly. The biggest secret of your “naturally slim” friends is that they consume far fewer calories than you think. But they stay slim, not only because of their low-calorie intake, but also because of their lower fat cell number.
Studies have shown that obese and overweight individuals have a greater number of fat cells than "naturally slim” people. When we slim down, fat cells shrink in size, but the number of fat cells we have does not decrease. When fat cells die, like all cells do, the body simply creates new ones in its effort to keep the number constant. So an obese person who loses weight will still have more fat cells than the person who never gained weight.
The greater number of fat cells in formerly obese people may be a factor in their tendency to regain the weight they lost. The same amount of fat is distributed across a larger number of the fat cells versus a small number of fat cells has the same weight and volume. But fatter fat cells produce more of the hormone “leptin,” which puts the body in a fat-burning mode and makes us eat less. So, a smaller number of fatter fat cells protects against weight gain.
When you have a large number of fat cells, you have many fat cells with less fat in each. Smaller fat cells have an increased "fat-filling drive.” They favor fat storage and cause us to feel hungry. So when a person with a large number of fat cells loses weight, this results in less fat in each cell, and this makes the body fight to gain weight.
The number of fat cells you are stuck with can be influenced by genetics. But being significantly overweight at any one time in your life plays a much greater role in increasing your fat cell number than your genetic makeup.
During childhood and adolescence, the number of fat cells can increase or decrease, but after the teen years the body aims at keeping the number of fat cells constant. If you are obese as a teenager or young adult when the body settles on its preferred fat cell number, this is likely to result in a greater number of fat cells in adulthood and a potential life-long weight struggle.
But the number of fat cells can also increase if you gain a lot of weight later in life. There is consensus among researchers, however, that your fat cell number doesn’t normally decrease, not even with prolonged weight loss. So, a one-time weight gain could make you struggle with your weight for the rest of your life.
Modern weight loss techniques like liposuction, which vacuums out chunks of fat from your fat depots, and cryolipolysis, which “freezes” your fat off, remove fat cells. As a result, your fat cell number goes down. But this fat is quickly regained.
Researchers don’t know whether the body regenerates the lost fat cells or increases the size of the remaining fat cells after liposuction and cryolipolysis. It cannot be ruled out that the body reacts to the artificial loss of fat cell the same way it reacts to the natural death of fat cells, which is to make new fat cells to replace the old ones.
Decreasing the number of fat cells long-term might require interfering with the mechanisms in the body that keep the fat cell number constant.
So far the only known way to shake up the body’s set fat cell number is to consume foods or supplements that increase the death rate of fat cells. Various antioxidants have been found to have the potential to reduce the number of fat cells in the body by increasing programmed cell death — for example, the vitamin A metabolite retinoic acid.
Among the most promising is resveratrol, an antioxidant in the skin of red grapes that is becoming increasingly popular as a nutritional supplement. Research has shown that resveratrol may tip the birth-death balance of fat cells when large enough amounts are consumed. When taken as a nutritional supplement, resveratrol may decrease the body’s set fat cell number, making it easier to keep the weight off.
