Consider All Evidence in
Diet-Health Controversy
With regard to "conventional wisdom" about how diet affects our health and well-being, there appears to be room for healthy skepticism. Making news recently were the results of a review of multiple scientific studies showing no evidence that eating beef causes cancer. That doesn't necessarily negate the results of other research where findings suggest there may be a connection. However, conflicting results do show that any causal association between beef and cancer has not been proven.
You wouldn't know that if you listen only to the diet gurus and health professionals claiming that, for several reasons, red meat is bad for your health. Most of them argue that science has "proved" it. The problem is that contradictory research often doesn't attract much attention. If a study doesn't support the researchers' hypotheses, the results may simply be ignored.
That's the contention of award-winning science writer Gary Taubes. As a contributing correspondent to Science magazine and numerous other publications, Taubes has focused his writing on controversial science. He has authored several books, including Good Calories, Bad Calories, which questions current dietary dogma. For several years, Taubes's writings have raised questions about the science pointing to dietary fat as a probable cause of heart disease and a major contributor to an obesity epidemic in America.
Fat and heart disease
The primary question Taubes asks is whether the low-fat, high-carbohydrate diets we've been told to eat for the past 30 years are not only making us heavier but are contributing to other chronic diseases as well.
"Consider, for instance, that most reliable evidence suggests that Americans have indeed made a conscious effort to eat less fat, and particularly less saturated fat since the 1960s," Taubes says. "According to the USDA (U.S. Department of Agriculture), we have been eating less red meat, fewer eggs and more poultry and fish; our average fat intake has dropped from 45% of total calories to less than 35%, and National Institutes of Health (NIH) surveys have documented a coincident[al] fall in our cholesterol levels."
Taubes cites a 40% decline in hypertension among Americans between 1976 and 1996, and a 28% decline in the number of individuals with chronically high cholesterol levels.
"But the evidence does not suggest that these decreases have improved our health," he adds.
Deaths due to heart disease definitely have dropped, Taubes admits, but studies of heart disease mortality suggest the decline is largely due to more successful methods of treatment for patients with heart disease. He says there is little evidence that the incidence of heart disease has declined, as might be expected if eating less fat made a difference.
Taubes says Ancel Keys, who launched a crusade against heart disease in the late 1940s, successfully promoted the idea that a fatty diet led to heart disease and blood cholesterol levels could serve as a predictor. By 1952, while admitting his theory was based more on speculation than data, Keys argued for reduction of fat in the diet. After studying several small populations of people in several countries, Keys claimed the data revealed a strong association between blood serum cholesterol levels, rates of heart disease and high amounts of fat in the diet.
Critics of his "Seven Countries Study" accused Keys of cherry-picking the data. They pointed out how the evidence waned as available data from other countries were added to the mix. Despite his detractors and conflicting evidence, Keys convinced many of his colleagues and much of the American public that reducing the amount of fat, and particularly animal fat, in the diet would reduce the likelihood of developing heart disease.
According to Taubes, Laurence Kinsell and Edward Ahrens then demonstrated that the crucial factor in controlling cholesterol was not whether fat was from animal or vegetable, but its degree of "saturation." From that, came the notion that all animal fats are bad saturated fats and all good unsaturated fats are found in vegetables and fish.
"The reality is that both animal and vegetable fats and oils are composed of many different kinds of fats, each with its own chain length and degree of saturation, and each with a different effect on cholesterol," Taubes says. "Half of the fat in beef, for instance, is unsaturated, and most of that fat is the same monounsaturated fat as in olive oil. Lard is 60% unsaturated; most of the fat in chicken fat is unsaturated as well."
In 1957, says Taubes, the American Heart Association (AHA) opposed Keys on the diet-heart issue, due to insufficient evidence. In 1960, without any new evidence, the AHA issued a report supporting Keys's hypothesis and suggesting Americans could reduce their risk of heart disease by reducing fat in their diets and replacing saturated fats with polyunsaturated fats. The report spawned a Time magazine cover story carrying Keys's recommendation for a heart-healthy diet, which included nearly 70% of calories from carbohydrates and 15% of calories from fat.
An alternative hypothesis
The scientific community was split, and researchers then set out to test Keys's hypothesis. According to Taubes, the press played a major role by consistently siding with proponents. And proponents argued that any research that did not support their belief had been misinterpreted or was based on questionable data.
"There are dozens of examples, over time, where evidence refuting the hypothesis was ignored and the results were never published," Taubes states.
Based on his investigation of the literature available, Taubes maintains that the "eat less fat and live longer" mantra was based on ambiguous data interpreted with selection bias. Nonetheless, it is the basis for the kind of nutritional wisdom promoted by a majority of nutrition and health care professionals.
Taubes advocates an alternative hypothesis, suggesting that obesity and perhaps a variety of diseases, including diabetes, are caused by the excessive consumption of calories from refined carbohydrates and starches. He challenges the scientific research community to rigorously test this hypothesis. Taubes says the scientific obligation is to "establish the cause of obesity, diabetes and the chronic diseases of civilization beyond reasonable doubt," with due consideration of all evidence.
Editor's Note: Gary Taubes was a guest speaker at the 2008 Feeding Quality Forum sponsored by Certified Angus Beef LLC.