It?s Not the Carbs, Stupid

Researchers are finding that constant exposure to fat and sugar can cause some humans to crave them as they do an addictive drug

By Ellen Ruppel Shell

NEWSWEEK

Aug. 5 issue ? In the mid-19th century, William Banting first popularized the low-carbohydrate weight-loss plan that has once again grabbed the media?s collective attention. Banting was a well-meaning London undertaker who grew so fat in middle age that he could not descend a staircase face first, for fear of being toppled by his copious paunch.

HIS FRIEND AND physician, the noted British aural surgeon William Harvey, prescribed a regimen focused on meat, small amounts of fruit and liberal lashings of Claret, sherry and madeira, which helped Banting drop 35 pounds in 38 weeks. Delighted by this result, Banting printed the diet at his own expense and distributed 2,500 free copies. The diet was so popular that when he died in 1878 nearly 60,000 additional copies had been sold at sixpence apiece. ?Bantingism? became synonymous for dieting, ?bant? common usage for losing weight, and Bantinga legend.


Banting?s plan has resurfaced in many forms over the years, more than a few of them best sellers. Most recently the Dr. Atkins Diet Revolution?a 30-year-old scheme?has gotten the buzz. Atkins?s claim is that carbohydrates, not fat, are to blame for the ballooning of Americans. But this theory loses credibility when one considers that while Atkins?s book was selling 10 million copies, obesity blossomed into a full-blown epidemic.

The discovery of the obesity gene in humans half a decade ago offered evidence that chronic weight gain is at its heart biological, the consequence of a mismatch between nature and nurture. Simplistic explanations, such as blaming obesity on a drop in fat consumption, ignore scientific reality. In countries like India and China, obesity was virtually unknown until the introduction of a high-fat, Western-style diet.

One well-known reason for this is that dietary fat converts to body fat more efficiently than does protein or carbohydrate, but recently scientists have uncovered what appears to be an equally important factor. Peter Havel, of the University of California, Davis, and Michael Schwartz, of the University of Washington, Seattle, are investigating the possibility that high levels of fat and fructose are mucking up our brain chemistry, and thereby muting the signals that would normally tell us to put down the fork. These signals are produced by peptides, which are regulated by a number of hormones, namely insulin, leptin and ghrenlin. Under normal conditions these hormones help maintain a stable body weight by adjusting levels of the peptides that control eating. But a diet loaded with fat and fructose hampers the regulation of these hormones. Complicating matters still further, Schwartz says, is that the brain loses its ability to respond to these hormones as body fat increases?so the obese are doubly penalized.

Other researchers are finding evidence that constant exposure to fat and sugar can cause some humans to crave them as they do an addictive drug. A Princeton University psychologist recently showed that rats fed a high-sugar diet were, when the sugar was removed, thrown into a state of anxiety similar to that seen in withdrawal from morphine or nicotine. Sarah Leibowitz, a neurobiologist at Rockefeller University, believes that frequent exposure to fatty foods may configure the brain to crave still more fat. She has shown in animal studies that galanin, a brain peptide that simulates eating behavior and decreases energy expenditure, increases when the animal eats a high-fat diet.

There are many factors contributing to the explosion of obesity in the United States, and the world, but the radical changes in the composition of our diet are first among them. While scientific work in this arena is in its infancy, it?s already clear that varying the amount of fat and other nutrients in the diet affects brain chemistry by activating certain genes, and this in turn directs our dietary preferences. By submitting ourselves to a steady dose of highly processed, sweet, high-fat foods, we have unwittingly entered into a dangerous experiment, the long-term consequences of which are only now beginning to surface.

Shell is author of ?The Hungry Gene: The Science of Fat and the Future of Thin,? to be published this fall by Atlantic Monthly Press.

© 2002 Newsweek, Inc.

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