Another nail has been driven into the coffin of the diet-heart hypothesis. The Annals of Internal Medicine (the official journal for the American College of Physicians) just published a review article that considered three kinds of studies related to fat and heart disease. (1)
- Studies that evaluated the association between dietary consumption of different kinds of fat and cardiovascular disease (heart attack and stroke)
- Studies that evaluated the association between levels of different kinds of fat circulating in the blood and cardiovascular disease
- Studies that evaluated supplementation with various kinds of fat and cardiovascular disease.
Most importantly, the authors found no statistical association between consumption of saturated fat and cardiovascular disease. I have previously discussed another large meta-analysis published in 2010 with the same finding. (2)
I have discussed the unscientific demonization of saturated fat many times (3,4,5).
This is important because it again speaks against the dietary advice promulgated by the AHA and the USDA to reduce consumption of saturated fat. The low-fat advice has resulted in a proliferation of low-fat high-sugar and high-carbohydrate food products which arguably have contributed to the epidemics of obesity and diabetes in the US.
Similarly, recent studies have correlated dementia with high carbohydrate consumption. (6) If you reduce fat in the diet you must replace it with something else and unfortunately in the US that something else has been sugar and other refined carbohydrates.
Other statistically significant findings in the Annals of Internal Medicine study were an inverse relationship between circulating blood levels of the omega three fats found in seafood (EPA and DHA) and cardiovascular events. The authors pointed out that although higher blood levels of EPA and DHA were significantly associated with lower cardiovascular risk, supplementation with EPA and DHA have had mixed results with many studies showing positive results but some showing no protective effects. My comments on the omega three supplement studies are
- supplementation with fish oil (omega three fats) will not benefit most individuals unless excess pro-inflammatory omega six fats (found in refined vegetable oils) are reduced/eliminated and that side of the equation has not been addressed in any of the published studies. In other words, the studies did not reduce omega 6 fats, they just supplemented with omega 3 fat. If an individual is consuming 30-60 grams of omega six fats per day, trying to balance that with 2-3 grams per day of fish oil will not achieve a healthy ratio.
- many of the fish oil (omega three) supplement studies used very low amounts of fish oil, well below the amounts used in the studies that demonstrated benefit.
I am not suggesting that everyone should take fish oil supplements. Instead, I support eating a whole foods paleolithic diet based on grass-fed meat, free range poultry, free range eggs, fresh wild seafood, fresh vegetables, fresh fruits and nuts.
Finally, the data on trans-fat consumption demonstrated statistically significant correlation with cardiovascular disease. The biochemistry and physiology of manufactured trans-fats demonstrate a disruptive role of these man-made fats and the elimination of these harmful fats from our food supply will likely provide great health benefits.
The authors comment on the complex relationship between fat consumption and circulating levels of specific fats in the blood as demonstrated by Forsythe et al. (6,7) I will discuss this in future posts. For now consider the paradox that high-fat carbohydrate restricted diets result in lower circulating levels of saturated fat compared to high carbohydrate diets. (6,7), Explanation: excess carbohydrates are immediately converted to fat and stored as saturated fat by humans.
2. Siri-Tarino PW, Sun Q, Hu FB, Krauss RM. Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease. Am J Clin Nutr. 2010; 91:535-46.
6. Relative intake of macronutrients impacts risk of mild cognitive impairment or dementia. Journal of Alzheimers Dis. 2012;32(2):329-39. doi: 10.3233/JAD-2012-120862.
7. Forsythe CE, Phinney SD, Feinman RD, Volk BM, Freidenreich D, Quann E, et al. Limited effect of dietary saturated fat on plasma saturated fat in the context of a low carbohydrate diet. Lipids. 2010; 45:947-62. PubMed
8. Forsythe CE, Phinney SD, Fernandez ML, Quann EE, Wood RJ, Bibus DM, et al. Comparison of low fat and low carbohydrate diets on circulating fatty acid composition and markers of inflammation. Lipids. 2008; 43:65-77. PubMed
Bob Hansen MD