A New Take on Obesity's Origins

Here's a word that could rock your world: epigenetics.

No, that's not the latest cosmetic treatment for wrinkles, or a cool new weight loss technique — although it does have to do with body weight.

"Epigenetics" means "on or above genetics." And when what's called an "epigenetics mechanism" is at work in a living organism, the genes themselves aren't altered, but how the genes function during the organism's early growth is changed.

This is starting to sound too much like a science class, so let's back up a bit and put this in more human terms.

You're probably aware that when women are pregnant, they often hear from their doctors the mantra, "Don't gain too much weight during your pregnancy." What constitutes "too much" has probably changed over the years, but doctors don't find that old "eating for two" excuse as cute as the rest of us might. In fact, doctors are also advising women who want to become pregnant to get to a healthy weight before doing so.

This isn't just the typical medical "tut-tut-ing," as it turns out. Studies funded by the Agricultural Research Service (ARS) are giving us a new and somewhat startling look at how influences that occur in the womb and perhaps during the first few months of life could affect development of a child's ability to regulate his or her weight, even into adulthood.

Yes, you read that right: If a woman packs on too many pounds during pregnancy, the child's body-weight-regulating mechanism could be harmed by the mom's excess weight. This, in turn, could increase the risk that the child would become an overweight or obese adult, with a higher risk of health problems such as type 2 diabetes or cardiovascular disease.

In the ARS-funded study, scientists looked at weight gains among rat pups whose mothers, called "dams," were either lean or overweight (as a result of deliberate overfeeding in the laboratory) at the time of conception and during pregnancy.

For this study, the scientists mated the lean or overweight female rats with lean males. The pups were nursed only by normal-weight dams to make sure the pups' exposure to their mothers' obesity occurred only in the womb.

All of the rat pups were at a normal weight at birth and at weaning. But when the weaned offspring were given free access to a high-fat ration, the offspring born to overweight mothers gained significantly more weight, and more of that weight as fat, compared to the offspring of the lean mothers. And that's despite the fact that the offspring of the overweight mothers didn't eat any more of the high-fat food than did the pups born to the lean mothers!

What does this mean in real-world terms? The study's results strongly suggest that exposure to the mother's obesity — while in the womb — results in programming of the baby's body-weight-control mechanisms. The factor of the mother's obesity all by itself was enough to significantly increase the baby rats' susceptibility to obesity.

You might be thinking, "Well, maybe those rats were genetically different from each other, so that's why this happened." But the scientists were careful to use only rats that were genetically similar, so that rules out the possibility that genetic differences among the mothers could contribute to the remarkable difference in the baby rats' sensitivity to those high-fat rations.

If this all translates to humans, this study's findings underscore the need for women who want to become pregnant to make sure they're at a healthy weight at conception, and to gain no more than the recommended amount of weight during the pregnancy. Unfortunately, the incidence of obesity or overweight among pregnant women in the United States is on the rise.

What's more, an epigenetics study from 2008 with a population of genetically similar lab mice with a tendency toward obesity showed a "transgenerational amplification of obesity." That means that the overweight mouse mothers gave birth to even heavier baby mice, the females of which gave birth to still heavier baby mice — and on unto the third generation...