Saturated Fats Should Not Be Replaced With Refined Carbs or Sugar

Adela Hruby PhD Adjunct Instructor, Friedman School of Nutrition Science and Policy Research Fellow, Harvard School of Public Health Fellow, Oak Ridge Institute for Science and Interview with:
Adela Hruby PhD

Adjunct Instructor, Friedman School of Nutrition Science and Policy
Research Fellow, Harvard School of Public Health
Fellow, Oak Ridge Institute for Science and Education

Medical Research: What is the background for this study?

Dr. Hruby: There were several reasons for conducting this study. While dietary quality and nutrient content in relation to cardiometabolic disease are long-standing interests of the investigators at the Department of Nutrition at the Harvard T.H. Chan School of Public Health, we were also motivated to lend clarity to some findings of a couple meta-analyses published in the last few years that had concluded – with the accompanying news headlines, most notably “Butter is Back” (Bittman, NY Times) – that saturated fat intake is benign with respect to risk of heart disease. We were also partly motivated by the Scientific Report of the Dietary Guidelines for Americans Committee, which were released earlier this year, which continue to support the existing upper limit of 10% of energy intake from saturated fat.

Medical Research: What are the main findings?

Dr. Hruby:  Our main observation is that saturated fat intake is not benign when it comes to heart disease. It only looks benign when it’s compared to refined carbohydrate and sugar intake, or when compared to trans fat intake.

Replacing saturated fat in the diet with polyunsaturated or monounsaturated fats, or with high-quality carbohydrates, was associated with 9-25% lower risk of incident heart disease. In addition, replacing refined carbohydrates and sugars with saturated fat was also not associated with lower risk of heart disease, while replacing the refined carbohydrates and sugars with polyunsaturated fat or carbohydrates from whole grains was associated with 11-22% lower risk of heart disease.

It is our view that the headline-making meta-analyses of the last few years regarding saturated fat’s “non-association” with heart disease, while generally well-conducted, failed to adequately consider the replacement nutrient. Through the 80s and 90s, most folks, when reducing saturated fat intake, ended up replacing the fat with refined starches/sugars, rather than with healthful fats and carbohydrates. This was the evident trend in our own cohorts as well. In addition, many trials of saturated fat reduction used placebos or control diets that were defined as “usual diet” – typically low in fat and/or high in refined carbohydrates – rather than a placebo or control consisting of more healthful fats or carbohydrates. Thus, the aforementioned meta-analyses failed to consider the potential impact of saturated fat’s comparator, i.e., they did not explicitly ask the question, ”compared to what?” The replacement nutrient matters. People do not drop calories (e.g., from saturated fat) without replacing them with something else.

Our findings are consistent with most studies that did consider the quality of the nutrient replacing saturated fat, for example the trials in which polyunsaturated fats replaced saturated fats in relation to cardiovascular endpoints and/or risk factors. In fact, a 2010 meta-analysis of trials that did ask the question, “compared to what?” found significant heart disease risk reduction when polyunsaturated fats replaced saturated fats in interventions. As for monounsaturated fats, the PREDIMED study in Spain is among the most notable to have shown their beneficial effects in the primary prevention of cardiovascular disease.

Importantly, we considered fats as entire classes (e.g., saturated, polyunsaturated, monounsaturated, trans) rather than as individual dietary fatty acids, or their food sources, for two primary reasons: first, the aforementioned meta-analyses addressed their hypotheses in terms of these classes, rather than as individual fatty acids or foods rich in these fats, per se; second, the Dietary Guidelines also generally refer to these classes of fats, and to energy from these fats, rather than to individual fatty acids. That said, it is possible and there is some evidence that individual fatty acids, even saturated fatty acids, have differing effects on heart disease risk and/or risk factors, but these hypotheses were not investigated in the current study.

Medical Research: What should clinicians and patients take away from your report?

Dr. Hruby:  Limiting saturated fat intake has been a long-standing recommendation from many professional, government, and international organizations, as one way of lowering risk of heart disease, and these recommendations should continue to be adhered to. It is not enough to advise patients to lower saturated fat intake; patients should be advised that saturated fats should not be replaced with refined carbohydrates or sugars, since these replacements will not contribute to lowering their heart disease risk. Rather, healthful replacements should be emphasized, namely foods with unsaturated fats and carbohydrates from whole grains. By way of a practical example, butter – in cooking or as a spread – can be replaced with extra-virgin olive oil, which is a common practice in Mediterranean countries. Other vegetable oils, such as canola oil, are also an option. Another example, this one of snack choice: if an individual is used to reaching for potato chips or candies, perhaps they might try reaching for walnuts, almonds, or peanuts instead. Swapping refined-grain carbohydrates for whole-grain carbohydrates is today a relatively straightforward switch, since whole-grain products, such as whole-grain breads, cereals, and pasta, are now nearly as common on grocery store shelves as are refined-grain versions of these products. While behavior change is undeniably challenging, these relatively simple dietary swaps can help individuals reduce their risk of heart disease. Patients might also be referred to Registered Dietitians for nutrition education, which would better their understanding of nutrition labels, dietary needs, and healthy cooking.

Medical Research: What recommendations do you have for future research as a result of this study?

Dr. Hruby: There are several interesting directions which this research area will likely take. One is that the totality of the evidence (such as that provided in meta-analyses) may be reconsidered with an eye on the quality of the replacement nutrient. We may also consider the roles of individual fatty acids on risk of heart disease, as well as their food sources, to better understand and generate hypotheses about the etiology of heart disease. Mechanistically, we can continue to investigate the effects of fatty acids on the precursors to and, ultimately, incidence of heart disease.


Li Y, Hruby A, Bernstein AM, et al. 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.2015;66(14):1538-1548. doi:10.1016/j.jacc.2015.07.055.

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Adela Hruby PhD (2015). Saturated Fats Should Not Be Replaced With Refined Carbs or Sugar