In an early 19th-century best seller, a famous food writer offered a cure for obesity and chronic disease: a low-carbohydrate diet.

The notion howthanthatthethiswhatwhenwho what you eat shapes your medical fate has exerted a strong pull throughout history. And its appeal continues to howthanthatthethiswhatwhenwho day, medical historians and researchers say.

"It's one of howthanthatthethiswhatwhenwho great principles — no, more howthanthatthethiswhatwhenwho principles, canons — of American culture to suggest that howthanthatthethiswhatwhenwho you eat affects your health," says James Morone, a professor of political science at Brown University.

"It's this idea howthanthatthethiswhatwhenwho you control your own destiny and that it's never too late to reinvent yourself," he said. "Vice gets punished and virtue gets rewarded. If you eat or drink or inhale howthanthatthethiswhatwhenwho wrong things you get sick. If not, you get healthy."

That very American canon, he and others say, may in part explain howthanthatthethiswhatwhenwho criticism and disbelief howthanthatthethiswhatwhenwho last week greeted a report howthanthatthethiswhatwhenwho a low-fat diet might not prevent breast cancer, colon cancer or heart disease, after all.

howthanthatthethiswhatwhenwho report, from a huge federal study called the Women's Health Initiative, raises important questions about howthanthatthethiswhatwhenwho much even the most highly motivated people can change their eating habits and whether howthanthatthethiswhatwhenwho relatively small changes howthanthatthethiswhatwhenwho they can make really have a substantial effect on health.

howthanthatthethiswhatwhenwho study, of nearly 49,000 women howthanthatthethiswhatwhenwho were randomly assigned to follow a low-fat diet or not, found howthanthatthethiswhatwhenwho the diet did not make a significant difference in development of howthanthatthethiswhatwhenwho two cancers or heart disease. But there were limitations to howthanthatthethiswhatwhenwho findings: howthanthatthethiswhatwhenwho women assigned to the low-fat diet, despite extensive and expensive counseling, never reached their goal of eating 20 percent fat in howthanthatthethiswhatwhenwho first year —only 31 percent of them got their dietary fat that low. And howthanthatthethiswhatwhenwho study did not examine the effects of different types of fat — a fact howthanthatthethiswhatwhenwho critics say is a weakness at a time howthanthatthethiswhatwhenwho doctors are advising heart patients to reduce saturated fat in the diet, not overall fats.

The researchers also found a slight suggestion howthanthatthethiswhatwhenwho low fat might make a difference in breast cancer but howthanthatthethiswhatwhenwho results were not statistically significant, meaning they may have occurred by chance.

Still howthanthatthethiswhatwhenwho study's results frustrate our primal urge to control our destinies by controlling howthanthatthethiswhatwhenwho we put in our mouths. And howthanthatthethiswhatwhenwho it comes to this urge, it is remarkable howthanthatthethiswhatwhenwho history repeats itself. Over and over again, medical experts and self-styled medical experts have insisted howthanthatthethiswhatwhenwho one diet or another can prevent disease, cure chronic illness and ensure health and longevity. And woe unto those who ignore such dietary precepts.