To Your Health
with Dr. David Katz

Not All Body Fat Is Created Equal

You probably already know that not all body fat is created equal. For instance, excess fat around the middle is much more likely to contribute to diabetes and heart disease risk than fat accumulated in the lower limbs, buttocks, and thighs. The so-called apple pattern of central obesity, more common in men, is more dangerous than the pear pattern, more common -- at least until after menopause -- in women.

That’s where the timing of weight gain enters the picture. Obesity researchers have long known that there are two basic ways to accumulate an excess of fat tissue: store more fat in the cells you already have, or make more cells.

When obesity is the result of over-stuffed fat cells (adipocytes), it is referred to as “hypertrophic obesity.” When adults gain weight, this is what tends to result- a notion reinforced by the new study in Nature. When weight fluctuates in adults, it mostly represents fat cells changing size.

The story is quite different in children. Among other things, children specialize in growth, and are much more adept than adults at increasing the cell count in their bodies. Doing so, in fact, is a defining characteristic of childhood. When growth stops, adulthood cannot be far off.

Unfortunately, this ability of children to make cells extends to fat cells. So when children take in more calories than they need and put the excess into storage in the form of body fat, they tend to increase the population of fat cells in their bodies, not just the supply of fat in the cells they have. When obesity results from the accumulation of too many fat cells, it is referred to as “hyperplastic obesity.”

For any kind of cell, there is a normal size range. Getting cells to vary within this range might require some effort, but usually can be done. Getting cells to move outside that range is invariably much tougher.

In the case of fat cells, they have a mechanism to tell the appetite center in a part of our brain called the hypothalamus whether or not they are satisfied with the calories they are being sent. When fat cells fill up, they release a hormone called leptin into the blood stream. When it reaches the hypothalamus, it suppresses the release of yet another hormone, neuropeptide Y, and our appetite declines.

But alas, this communication works just as effectively in reverse! When fat cells feel they are being starved, they in essence stop talking to the hypothalamus in protest. Leptin relsease slows or stops, leptin levels fall, and neuropeptide Y levels rise. The end result of this passive aggression by our adipocytes is that we wind up feeling hungry all the time, until we feed them, and ourselves.

Any adult who has attempted weight loss knows it's tough, even if the weight was gained AS an adult. But if overweight first occurs in adulthood, weight loss will involve shrinking enlarged fat cells down to size. They will be reluctant, but they can be compelled to make that trip.

If overweight begins in childhood, however, weight loss will be an attempt to reduce the number of fat cells. The only way to do that is to starve adipocytes to the point where some of them commit a form of cellular suicide known as apoptosis. Pushing them that far is possible, but very, very difficult.

The rate of childhood obesity is soaring, with some studies suggesting increasing rates of overweight even during the first year of life. As tough as it is for anyone to lose weight and keep it off, it will be that much tougher for kids subject to early-onset obesity to do so. The Nature study reveals that those fat cells they accumulate early in life will hang in there, even after significant weight loss.

But of course, we know how to prevent those fat cells from developing in the first place. When calories consumed don’t exceed calories burned, excess body fat need not accumulate. An array of strategies, policies, programs, and attitudes that help kids get physically active, and eating well, at home, in school and everywhere they go is the answer.

The best way to address childhood obesity is to prevent it. Never has the classic adage about ounces of prevention and pounds of cure been more apt, since the failure to prevent those initial gains of excess body fat measured in ounces may well result in excess pounds that are excruciatingly hard to cure.