The Low-fat House of Cards

Are we hypocrites if we criticize observational trials that don't support our beliefs, but we promote ones that do?

That's a tough question.

If we promote nutritional epidemiology that supports our beliefs as high-quality evidence, then yes, we would be hypocrites. Nutritional epidemiology is still very weak evidence, whether it supports our beliefs or not.

(See our Guide on Observational versus Experimental Studies)

But when the foundation of our faulty concept of "healthy nutrition" and our misguided nutritional guidelines are based on these flawed observational studies, it makes sense that we should promote all available contrary information.

A recent analysis from Lipids in Health and Disease provides us that opportunity. This is a new meta-analysis of 63 underlying observational trials that reported on dietary fat intake and risk of cardiovascular disease. To be included, the study had to compare the highest level of fat intake to the lowest level of intake and compare the rates of cardiovascular disease events.

Lipids in Health and Disease: Dietary total fat, fatty acids intake, and risk of cardiovascular disease: a dose-response meta-analysis of cohort studies

According to the study's results, trans fat intake was the only variable associated with an increased risk for cardiovascular disease, and it was a weak association at that with a hazard ratio of only 1.14.

Notably, both higher total fat intake and saturated fat intake had no association with increased cardiovascular risk. In fact, in the Asian populations, higher saturated fat consumption appeared to be associated with a lower risk of cardiovascular disease (again a weak association at 0.84).

Monounsaturated fat and polyunsaturated fat intake likewise showed no positive or negative association with cardiovascular disease. When only looking at studies lasting longer that 10 years, higher polyunsaturated fatty acid consumption had a very weak association with reduced cardiovascular risk at 0.95.

The authors point out how the "diet heart" hypothesis is based on selective evaluation of observational studies, or on studies using LDL as a surrogate endpoint rather than measuring true endpoints such as heart attacks, strokes and death. Thus it is important to promote nutritional epidemiology studies such as this one that contradict prevailing beliefs about the dangers of dietary fat and saturated fat. How can individuals and societies who promote the dangers of saturated fat explain the multiple studies showing absolutely no association with cardiovascular risk? In truth, they cannot, other than to admit this is a very low quality of evidence and there is no true consensus.

We need to be careful not to promote these studies as "proving" that saturated fat is harmless. These studies cannot prove anything. But we certainly should highlight them to show how our fear of fat is based on a house of cards that comes tumbling down when we understand the quality of evidence behind it. It's time to demand higher quality evidence for advice promoted by our dietary guidelines. It's time to retire the true fad diet that lacks scientific support - the low-fat and low-saturated-fat diet.

For a more detailed discussion about saturated fat, see our guide:

Thanks for reading,
Bret Scher, MD FACC

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