The BMJ (fomerly the British Medical Journal) is publishing a terrfic new study that mines 40-year old data about the effects of eating saturated fats on mortality and heart disease rates. The research was a double blinded, parallel group, randomized controlled dietary intervention trial done in Minnesota in the late 1960s and early 1970s in which 9,000 participants were fed either diets that contained saturated fats (meat, milk, cheese) or diets with polyunsaturated fats (corn oil chiefly). The participants were more than 9,000 men and women over age 20 admitted to either a nursing home or one of six state mental hospitals in Minnesota. The experiment lasted from 41 to 56 months. The researchers were seeking to find out what effects a diet low un saturated fats would have on cholesterol levels, heart disease, and overall mortality.
Eating plant-based oils did reduce cholesterol levels in participants assigned to that diet. While original researchers back in the 1970s did not find any effect on heart disease trends, they believed that had their experiment gone on that the benefits from lowering cholesterol would have eventually emerged. The results of the study were never fully published, although the researchers reported some of their preliminary results at a American Heart Association conference 1975.
So why were the results of a such rigorous study not published widely? The BMJ study also cites biostatistician Steven Broste, who used the Minnesota data in his master's thesis back in 1981, which found no significant difference in mortality rates in the saturated fats versus unsaturated fats cohorts. According to the Washington Post, Broste suggests …
…that at least part of the reason for the incomplete publication of the data might have been human nature. The Minnesota investigators had a theory that they believed in — that reducing blood cholesterol would make people healthier. Indeed, the idea was widespread and would soon be adopted by the federal government in the first dietary recommendations. So when the data they collected from the mental patients conflicted with this theory, the scientists may have been reluctant to believe what their experiment had turned up.
"The results flew in the face of what people believed at the time," said Broste. "Everyone thought cholesterol was the culprit. This theory was so widely held and so firmly believed — and then it wasn't borne out by the data. The question then became: Was it a bad theory? Or was it bad data? … My perception was they were hung up trying to understand the results."
The BMJ data recovery and reanalysis now finds that the vegetable oil diet did lower cholesterol, but did not lower mortality or heart disease rates. In fact, for participants over age 65, lower cholesterol led to higher, rather than lower risks of death. In addition, the BMJ researchers comprehensively reviewed other controlled trials and report that they "do not provide support for the traditional diet heart hypothesis."
The BMJ study is another in a growing line of research* that undermines the "heart-healthy" dietary guidelines from the federal government and that American Heart Association. The AHA still warns:
There's a lot of conflicting information about saturated fats. Should I eat them or not? The American Heart Association recommends limiting saturated fats – which are found in butter, cheese, red meat and other animal-based foods. Decades of sound science has proven it can raise your "bad" cholesterol and put you at higher risk for heart disease.
The more important thing to remember is the overall dietary picture. Saturated fats are just one piece of the puzzle. In general, you can't go wrong eating more fruits, vegetables, whole grains and fewer calories.
When you hear about the latest "diet of the day" or a new or odd-sounding theory about food, consider the source. The American Heart Association makes dietary recommendations only after carefully considering the latest scientific evidence.
There is less and less conflicting evidence, so perhaps a careful reconsideration is in order. See Reason TV's "How the Government Makes You Fat: Gary Taubes on Obesity, Carbs, and Bad Science."
*See my February 2015 item, "The Red Meat, Eggs, Fat and Salt Diet" for links to several relevant studies.