For decades, we have been advised to steer clear of saturated fats. Several research papers published in the early 1950s implicated dietary fat as a key player in the development of heart disease. By 1961, the American Heart Association (AHA) published dietary guidelines that included reduction of saturated fats and in 1982, the Nutrition Committee of the AHA recommended no more than 10% of daily calories from fat.

So what are saturated fats? They are usually solid at room temperature and found in the foods we tend to like the most, that is, meat, cheese, ice cream, butter, and other dairy products. A few plant-based oils, such as coconut and palm oils, also contain saturated fats.

Scientists have recently revisited the role of saturated fats in cardiovascular disease and, as it turns out, the early studies may have been wrong. Authors of one paper published in 2010 and another in early 2014 analyzed data from a number of previous studies. The authors indicate that there is no relationship between dietary saturated fat and heart disease risk and, furthermore, the evidence does not support our current dietary guidelines that encourage “low consumption of saturated fats.” In fact, authors of a separate study found that a “low-carbohydrate diet was more effective for weight loss and cardiovascular risk reduction than a low-fat diet.”

Nina Teicholz, an investigative journalist, recently authored a book entitled The Big Fat Surprise (released in March of 2014) that corroborates the recent findings regarding saturated fats. Ms. Teicholz spent eight years sifting through previous research on the connection between heart disease and saturated fats. According to her, the research that was the basis for our current dietary guidelines was severely flawed.

The primary author, Ancel Keys, was a physiologist at the University of Minnesota in the 1950s. The story goes that Keys became interested in heart disease when he observed that American businessmen were experiencing high rates of heart attacks, Europeans had lower death rates from coronary heart disease when food supplies were low following World War II, and then-President Eisenhower himself had a heart attack, bringing cardiovascular disease to the medical forefront. Following a series of smaller studies, Keys developed his theory that fat, particularly saturated fat, caused heart disease, which came to be known as the diet-heart hypothesis.

In 1953, Keys published a very influential paper where he purported a “remarkable relationship” between fat and heart disease.  He presented data from the United States, Canada, Australia, England and Wales, Italy, and Japan supporting his hypothesis that consumption of fat causes heart disease.  Several years later, Jacob Yerushalmy, a biostatistician at the University of California at Berkeley, noted in a separate paper that, although the countries Keys selected supported the diet-heart hypothesis, data were available for 22 countries.  As it turned out, when data from all countries were analyzed, the causal relationship between dietary fat and heart disease disappeared.

Keys launched what came to be known as the ‘Seven Countries’ study in 1958.  He collected data on dietary habits and heart attack rates in the United States, the Netherlands, Finland, Yugoslavia, Italy, Greece, and Japan.  As a result, Keys reported that greater consumption of animal fat led to a higher rate of heart attacks. There were a few problems with his data, however.  Keys visited Greece during Lent when people abstain from eating meat, which would have skewed his data.  Additionally, the correlation between animal fat and heart attacks was not observed in Finland, Greece, and Yugoslavia.  Keys also intentionally left out countries such as Holland and Norway where residents eat a lot of fat but experience little heart disease.

In spite of the flaws, Keys’ research received a great deal of media attention and he ultimately persuaded both the AHA and the U.S. government that saturated fats were the bad boys that caused not only heart disease but played a major role in the development of obesity and cancer as well. What followed are the national dietary guidelines that are still accepted today.

Dariush Mozaffarian, MD, at the Harvard School of Public Health, is one of many researchers who now believe that our current dietary guidelines need to be revisited. He says that “we can’t judge the healthfulness of a food [only] by how many grams of saturated fat it has.” Other experts aren’t buying the new findings. Walter Willett, MD, Chair of Nutrition and Mozaffarian’s colleague at the Harvard School of Public Health, says the conclusions of recent studies should be disregarded.

What does all of this mean for us? It is unknown when or if the current dietary guidelines will change and it will take more research and discussion to alter a long-held belief. If you have questions regarding these new findings and wish to revisit your own nutritional habits, please to talk to your doctor and/or a dietitian.

– Holly Hough, PhD

Please consult with your doctor before making any dietary changes.

References: American Heart Association; The Journal of Nutrition; Annals of Internal Medicine; American Journal of Clinical Nutrition; British Columbia Medical Journal; WebMD; Dr. Frank Lipman: Interview with Nina Teicholz; NBC News

Images by Flicker users Yamashita Yohel and Anne Hornyak, via CC

Click to read Holly’s post, A Spoonful of Sugar…Not So Nice After All