One More (Big) Piece to the Dietary Fat Puzzle

August 09, 2016

When I was in college studying nutrition in the late 1980s, “fat phobia” was in full swing. Almost all of my internship projects focused on educating people how to reduce the fat in their meal plans to help lower their risk of cardiovascular disease (CVD). But a recent article has revealed that there may be more to this topic than we had thought.  

The article, published this spring in the British Medical Journal, focused on unpublished documents and raw data from the Minnesota Coronary Experiment (MCE) conducted almost 50 years ago between 1968 and 1973. These data help fill a gap left by previous research.

The MCE was a double-blind randomized controlled trial (the gold standard in research capable of proving cause and effect) that tested whether the replacement of saturated fat with vegetable oil rich in linoleic acid helps reduce coronary heart disease and death by lowering blood cholesterol. The findings add previously missing pieces to the dietary fat puzzle and call into question Ansel Keys’ traditional diet-heart hypothesis that has been the basis of nutrition guidance for many years. Here’s why:

Previously, randomized controlled trials have demonstrated that replacing saturated fat in the diet with vegetable oils rich in linoleic acid can reduce total and LDL-cholesterol -- and observational evidence links blood cholesterol to coronary heart disease events and deaths. But until now, “no randomized controlled trial has shown that replacement of saturated fat with linoleic acid significantly reduces coronary heart disease events or death,” the researchers say. That’s the missing piece that the findings from the MCE now provide. Results showed:

  • Though replacing saturated fat in the diet with vegetable oil rich in linoleic acid (i.e. corn oil) lowered blood cholesterol, it did not improve survival
  • Paradoxically, participants who had the greatest reductions in blood cholesterol had a higher, rather than lower, risk of death
  • A separate systematic review and meta-analysis of five randomized, controlled trials looking at the same relationships reported reduced blood cholesterol, but not reduced deaths from coronary heart disease or any cause.

While it may be disconcerting to think that everything I thought I knew about fat is not holding up to scientific scrutiny, now the results from more recent research make more sense. A growing body of evidence indicates that saturated fat may not be directly associated with CVD.

Of all the dietary sources of fat, milk fat has the most complex fatty acid composition. Emerging research recognizes the effect of milkfat-containing foods on cardiovascular health may be different than other sources of fats. As research on dairy foods and heart health unfolds, results have shown neutral or beneficial associations with CVD risk occur with consumption of all fat levels of dairy foods.

As health and wellness professionals, it is our job to stay informed of current research as it evolves so we can be better equipped to answer people’s questions and help interpret what it means for them. Stay tuned for a blog post later by my colleague Mickey Rubin that will provide further insights on this topic.