The Cooper Institute

Founded in 1970 by the "Father of Aerobics"
Kenneth H. Cooper MD, MPH


Is Butter Back? Not so Fast!

Posted in
Eat better

Thursday, Jan 14, 2016

As you may already know, there are four types of dietary fat; saturated, monounsaturated, polyunsaturated, and hydrogenated (trans). Because of the longstanding relationship between dietary saturated/trans fats and cardiovascular disease (CVD), current guidelines from world-renowned groups like the the American Heart Association call for limiting saturated fat to less than 7% of total calories and keeping hydrogenated fat intake as low as possible.

In March of 2014, a controversial paper was published in the Annals of Internal Medicine.1 In a technique known as meta-analysis, this paper summarized 76 previously published studies which had examined the relationship between dietary fatty acid intake, circulating levels of fatty acids in the blood, and the subsequent risk of developing coronary heart disease. Surprisingly, the authors concluded that “current evidence does not clearly support cardiovascular guidelines that encourage high consumption of polyunsaturated fatty acids and low consumption of total saturated fats.” This conclusion ignited a firestorm in the scientific community, and the media chimed in with headlines like “Butter is Back!”

Almost immediately, it was determined that the authors had made errors in their manuscript; some scientists even went so far as to say that the paper should be retracted with accompanying press promotion in order to make the public aware of these errors. For example, the authors wrote that a study on omega-3 fats showed that they caused a slight increase in the risk of heart disease, when the study had actually shown a very significant decrease in the risk of heart disease. Another major flaw in the meta-analysis was that it did not address the critical issue of what people who reduced their intake of saturated fats consumed instead. For example, it is well-accepted that replacing dietary saturated fat with simple or highly refined carbohydrate yields no benefit in terms of future risk of CVD. On the other hand, there is growing evidence that replacing dietary saturated fat with polyunsaturated fat does result in a significantly reduced risk of CVD.2

To better answer the question of what happens when people replace dietary saturated fat with unsaturated fats and different types of carbohydrate in relationship to coronary heart disease risk, data from 84,628 women (Nurses’ Health Study) and 42,908 men (Health Professionals Follow-up Study) were tracked over a period of ~27 years3. All subjects were apparently healthy at baseline. A detailed dietary questionnaire was used at baseline, then every 4 years thereafter. During the follow-up period, 7667 cases of coronary heart disease (CHD) occurred. A higher intake of polyunsaturated fats and carbohydrates from whole grains was associated with a significantly decreased risk of CHD. Conversely, a high carbohydrate intake from refined starches and added sugars was associated with a significantly increased risk of CHD. Of major importance, the data showed that replacing 5% of total energy intake from saturated fats with an equivalent number of calories from polyunsaturated fats, monounsaturated fats, or whole grains was associated with a significant decrease in risk of CHD. Conversely, replacing 5% of total energy intake from saturated fats with an equivalent number of calories from highly refined starches and added sugars did not affect CHD risk. These data are summarized below in Figure 1.

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1) Chowdhury, R., et al. 2014. Association of dietary, circulating, and supplement fatty acids with coronary risk: a systematic review and meta-analysis. Ann Intern Med.160(6):398-406.

2) Jakobsen, J., et al. 2009. Major types of dietary fat and risk of coronary heart disease: a pooled analysis of 11 cohort studies. Am J Clin Nutr. 89(5):1425-1432

3) Li, Y., et al. 2015. Saturated fats compared with unsaturated fats and sources of carbohydrates in relation to risk of coronary heart disease: a prospective cohort study. J Am Coll Cardiol. 66(14):1538-1548.