According to the Centers for Disease Control, two-thirds of Americans are overweight or obese. From 2003 to 2004 alone, estimated obesity rates in America increased by 0.8 percent. In other words, 3 million more people became obese in one year. Some scientists believe that the reason that Americans can't lose the weight has to do with the number of fat cells they generated growing up.
The Fat Cell Theory
It should be no surprise that our most important physiological developments happen when we're children. Fat cells (or "adipocytes") proliferate in three stages: in the first two years of life; when the child is about 7 years old; and in adolescence. The Fat Cell Theory explains that once we finish growing, we no longer produce more fat cells. When adults gain weight, their fat cells simply grow. Adults who were leaner as children will have fewer fat cells to expand than those who were overfed during the crucial fat-cell-growth years.
Researchers headed by Dr. Kristy Spalding at the Karolinska Institute in Sweden first established that children and adolescents produce new adipocytes, but adults' numbers stayed constant. To find out whether adults could eliminate fat cells in extreme circumstances, Spalding measured the number of fat cells in severely obese patients who underwent gastric binding surgery. Although the gastric binding patients lost huge quantities of weight, their numbers of fat cells stayed the same as before surgery.
Hyperplastic and Hypertrophic Fat Cells
When a child eats too much food, his fat cells swell until they are filled to capacity. When his adipocytes can hold no more, he begins to produce more fat cells. A high number of fat cells is known as "hyperplastic obesity." Even if this child loses weight before he is fully grown, he is stuck with the extra fat cells--and thus a greater capacity to store fat--forever. Since adults who become obese can't produce more fat cells, their adipocytes simply expand to house the extra calories. The condition of having enlarged fat cells is known as "hypertrophic obesity" ("hypertrophy" means "excessive growth").
Criticism of the Fat Cell Theory
Not all scientists buy into the Fat Cell Theory. The idea that fat children make fat adults is too simplistic and doesn't explain why some people gain weight later in life, according to some scientists. The interpretation that your body fat is predetermined discourages personal responsibility to follow a sensible diet and exercise program. Since Spalding's research 30 years ago, little research has been done to confirm her findings.
Whether the Fat Cell Theory is accurate or not, it is still possible to shrink your fat cells (and your waistline) through a combination of proper diet and exercise. Humans evolved to hold onto fat for protection from cold and starvation, so it will take patience and lifestyle changes to override biology and permanently lose fat. That being said, many Americans have managed to lose large amounts of weight and keep it off with hard work. Talk to your doctor to find a weight loss program that works for you.