Yet another deep dive into the massive database of the nation’s largest dietary recall study attempts to sell the notion losing a bit of butter a day keeps the cardiologist away.

Many dietary research studies appear to offer conclusive evidence regarding which foods can contribute to the development of various chronic diseases.

Harvard University School of Public Health reports on such studies on a weekly basis, the latest “revelation” being that consuming the saturated fat found in meat and dairy foods is still unhealthy.

Allegedly.

This latest salvo against animal foods appeared in an article in the Harvard newsletter titled, “Butter is not back; Limiting saturated fat still best for heart health.” It was based on a study published in the Journal of the American College of Cardiology last month that analyzed data from the long-running Nurses Health Study, which followed 84,628 women beginning in 1976, and the Health Professionals Follow-up Study, which has tracked 42,908 men since 1986.

According to the researchers, the individuals from those cohorts who were analyzed in this study were free of diabetes, heart disease and cancer at the baseline and were matched by age, body mass index, smoking and physical activity. During the years they were tracked, there were 7,667 recorded cases of coronary heart disease (CHD).

So what do you suppose they determined was the way to mitigate the risk of becoming one of those thousands of CHD patients? By analyzing participants’ diets, the researchers estimated that “replacing 5% of energy intake from saturated fats with equivalent energy intake from either polyunsaturated fats, monounsaturated fats, or carbohydrates from whole grains” would lower the risk of CHD by 25%, 15%, and 9%, respectively.

In contrast, they noted that exchanging 5% of saturated fat calories for the same amount of refined carbohydrates and sugars was not associated with lower CHD risk.

The latter sentence ought to be shared widely, because the significant increase in per-capita consumption of refined carbs is the direct result of USDA’s ill-advised “war on fat” that was launched in the 1980s. Not only did ordinary people cut back on red meat by substituting all kinds of processed foods high in carbohydrates, but food processors reformulated all manner of products to reduce the calories from every kind of fat, not just saturated fat, mostly by replacing them with carbohydrates.

That radical shift in our national nutritional guidance marked the beginning of what the same crowd of professional dieticians are now lamenting as the “obesity crisis.”

The Harvard researchers agreed with that conclusion, although never mentioning the “o-word.”

“Our findings suggest that the low-fat, high-carb trends of the 1980s and 1990s are not effective in reducing risk of CHD,” Yanping Li, co-first author along with Adela Hruby, both researchers in the university’s Department of Nutrition, said in a news release. “It means that individuals should not replace saturated fat with refined carbs or vice versa.”

False and misleading data

After digesting this one piece of sound advice, however, it must be acknowledged that there are two massive flaws with this research.

For one, epidemiological studies that rely on dietary recall are notoriously difficult to analyze. People just don’t accurately record both the portions they consume, as well as the qualitative nature of the food product. Research into recall studies has demonstrated time and again that most people underestimate the calories and overestimate the nutritional value of what they eat—and that’s when they’re recording everything on a daily basis.

In the Nurses and Health Professionals study, people submitted a dietary journal every four years! Yes, the participants are health professionals who should be more knowledgeable about portions and ingredients, but one could just as easily argue that nurses or other health workers might well be motivated to “enhance” their dietary journals so they wouldn’t look like junk food junkies.

Besides, who keeps track of everything they eat for years at a time?

Second, the study’s authors claimed, as all such researchers do, that they controlled for a list of variables, such as amount of physical activity and BMI (body mass index, a ratio of height to weight), meaning that the dietary variables alone were the cause of the differential outcomes. Unfortunately, both BMI and physical activity exist on a spectrum. There are football players, weightlifters and even non-athletes who have a very high BMI — but they’re simply highly muscled. They’re not obese, they have normal body fat percentages, but their BMIs are off the charts.

But many other people with a high BMI are obese. They do have above-average percentage of body fat and they are, in fact, unhealthy.

Bottom line is that BMI is not an absolute measure of anything — certainly not overall health status.

Likewise, “physical activity” can mean anything from strolling around the block a couple times after dinner to high-intensity training in a gym or in one of those “boot-camp” type exercise classes. Having personally conducted surveys asking people about their level of fitness activities, I can testify that a significant majority of people label themselves “active” or even “highly active.”

Yet if you were to drop by their residence on a typical weekday evening, you’d be more likely to find them watching reality TV than sweating along to some workout video.

Point is, researchers can’t control for the many variables that affect health and well-being. So a blanket statement quantifying the risk reduction involved in cutting back 5% on saturated fat is ludicrous.

Not to mention that 5% reduction of a person’s total saturated fat intake — assuming they’re eating the “recommended” diet in which only 10% of total calories come from saturated fat — represents about 12 calories.

Do the math: A standard diet is 2,500 calories a day, 10% of which would be 250 calories of saturated fat. And 5% of 250 is about 12 or 13 calories. Since a teaspoon of butter yields about 110 calories, we’re not exactly talking about a massive reduction.

And yet that’s supposed to reduce one’s risk of heart disease by 25%?

Such a conclusion is as flawed as the methodology used to calculate it.

Dan Murphy is a food-industry journalist and commentator.