I was struck today by the juxtaposition of two recent articles here at ScientificAmerican.com. In “Thin Body of Evidence,” John Horgan expresses his skepticism about journalist Gary Taubes’s claims that carbohydrates, not fat, are the cause of obesity, heart disease and other health problems faced by many Americans. In “Mummy Says Princess Had Coronary Disease,” scientists who performed a CT scan on a 3,500-year-old Egyptian mummy express their puzzlement that this ancient princess had advanced atherosclerosis (hardened arteries) despite her civilization’s “healthy” diet that included wheat, barley, bread and beer—and only small amounts of meat.

Atherosclerosis is linked to high blood levels of triglycerides (a type of fat molecule) and low levels of HDL cholesterol, the “good” cholesterol. Eating a lot of carbohydrates (such as wheat, barley, bread and beer) is well known to raise triglycerides and lower HDL. Eating fat (such as found in meat) counteracts these effects, raising HDL and lowering triglyceride levels. The Egyptian princess’s diet, therefore, is the perfect recipe for high triglycerides and low HDL—and for atherosclerosis.

These facts about diet and blood lipid levels are not controversial—they have been known for decades and verified repeatedly by scores of studies. So why were the anthropologists surprised by the mummy’s atherosclerosis? And why is Horgan resistant to the idea that carbohydrates cause obesity and desease? The answer lies in two all-too-human tendencies: over-reliance on personal experience and resistance to information that contradicts our beliefs.

Horgan and the anthropologists who studied the mummy are falling victim to their preconceived notions about nutrition—that whole grains are healthy and animal fats are dangerous. They can hardly be blamed; those ideas have been trumpeted as truths for three decades in this country. But those notions were never based on good science, and now evidence is mounting that they are just plain wrong. Taubes details that evidence masterfully in Good Calories, Bad Calories (Knopf, 2007) and Why We Get Fat (Knopf, 2010).

Yet even with such a large body of research pointing to carbohydrates as the root of many medical evils, the Horgans out there can’t see past their own experience. Their high-carb diets never caused them to get fat; therefore, carbs must be fine. I don’t need to point out to the readers of this site how unscientific it is to hold up one individual’s experience—a case study, if you will—as a refutation of carefully controlled studies. Besides, the health effects of a high-carbohydrate diet often are not visible as weight gain—that Egyptian princess, no doubt thin as a rail (have you ever seen a fat mummy?), had a level of atherosclerosis that today would have doctors scrambling for a bypass operation. I have a hunch that if Horgan compared his blood lipid profile to Taubes’s, he would not be so quick to write off Taubes’s diet as “gross.”

I am not trying to single out Horgan—on the contrary, I think he is just one of many, many people who are struggling to make sense of the fact that what they have believed about diet and health for most of their lives is measurably wrong. And he’s in very good company. I stumbled on a survey a few months ago that found that most doctors don’t know which dietary component—protein, fat or carbohydrate—raises blood levels of triglycerides, and thus increases the risk of heart disease. It’s carbohydrates, of course. But like so many other findings that contradict the idea that whole grains are heart-healthy, it has been forgotten or ignored.

In the interest of full disclosure, I must admit that I started delving into diet and health studies in an attempt to battle my own obesity, which had plagued me my whole adult life. My reading led me to believe that sugars and grains in my diet were the culprit and, sure enough, once I cut those out and increased the amount of animal fats in my diet, I lost 50 pounds. (I always had and continued to eat a lot of vegetables, too.) I have never felt more energetic or clear-headed.

So, yes, my personal experience tells me Taubes is correct, just as Horgan’s experience tells him Taubes is incorrect. But, importantly, I would not have had my experience if I had not read the nutrition literature with an open mind. I look forward to the day when everyone, even those without pressing health concerns, can take their blinders off, relegate personal experience to second fiddle, and accept what the research is really saying. Only then will we be able to reverse the skyrocketing rates of obesity, diabetes and heart disease in this country.

Image courtesy of iStockPhoto / barol16