Study Questions Link between Saturated Fats and Heart Disease

Dr Rajiv Chowdhury, Senior Research Associate in Global Cardiovascular Health at the University of Cambridge in England, is a qualified physician who was trained in Cardiovascular Epidemiology at the University of Cambridge with the support of a prestigious Gates Cambridge scholarship.

Following completion of his PhD in 2013, he embarked on his current position of Senior Research Associate in Global Cardiovascular Health within this department. He was elected a Fellow of the UK Royal Society for Public Health in 2011.

In an interview, Dr Rajiv explains the findings of a study which indicate that all saturated fats may not be created equal when it comes to coronary heart disease (CHD).

1. Your study in the Annals of Internal Medicine generated a lot of interest. Can you explain the findings of the study?

Our meta-analysis, published in the Annals in March 2014, investigated how levels of fatty acids consumption or circulating composition might be related to future risk of CHD.

In our analyses, we included estimates from observational studies that measured ‘total’ fatty acids from dietary intake; observational biomarkers studies that looked at ‘individual’ fatty acid subtypes; and randomised controlled trials of fatty acid supplementation. Taken together, this quantitative review combined data from 72 unique studies comprising over 600,000 participants from approximately 20 countries.

First, we considered results on dietary total fatty acid intake from 32 prospective studies (with 512,420 participants). We found essentially null associations for total saturated, monounsaturated and omega-6 polyunsaturated fatty acids with CHD, whereas intake of long-chain omega-3 polyunsaturated fatty acids was associated with lower CHD risk and intake of trans fatty acids was associated with higher CHD risk.

Second, we considered results on individual circulating fatty acid subtypes from 17 prospective biomarker studies (with 25,721 participants). We found a significant inverse association between margaric acid and CHD, and non-significant positive associations of palmitic and stearic acids with CHD. We found some evidence that circulating levels of eicosapentaenoic and docosahexaenoic acid (the two main types of long-chain omega-3) and arachidonic acid were each associated with lower CHD risk.

Third, we considered 27 randomised controlled trials of fatty acid supplementation or replacement (with 105,085 participants). In aggregate, these trials have not suggested clear benefits after supplementation with alpha-linolenic acid or with long-chain omega-3 fatty acid, or replacement of saturated fats with omega-6 polyunsaturated fatty acid.

2. Could you explain the findings in layman’s terms?

In our review, by combining data from published population-based studies, we found no significant association for total or composite saturated fats in diet with the risk of heart disease. However, when we examined subtypes of saturated fats in blood, different individual subtypes seemed to associate differently with risk, indicating perhaps all saturated fats may not be created equal when it comes to their health effects.

Additionally, we, observed a strong association for higher trans (or artificial) fats with high risk of heart disease. We also found specific polyunsaturated fats to be beneficial in observational studies; however, these findings were less consistent with those in the trials.

More research is needed to examine the food sources and health effects of specific fatty acid subtypes.

3. What was your motivation for looking into this area of interest?

Since the landmark Seven Countries Study report was published by Dr Ancel Keys back in the 1960s, a significant number of epidemiological and interventional studies have investigated the intriguing association between fatty acids and cardiovascular risk.

This large body of evidence has shaped nutritional guidelines worldwide, which generally encourage low consumption of saturated fats, high consumption of omega-3 polyunsaturated fatty acids from fish or plant sources, and avoidance of trans fats, particularly those from partially-hydrogenated fat.

We, however, noted considerable inconsistencies in the pre-existing evidence. For example, many prior prospective observational studies had questioned whether there really are significant associations between saturated fats intake and cardiovascular disease.

Nonetheless, these conventional dietary observational studies were limited by potential misclassification in the self-report questionnaires used to capture fat consumption, and importantly, by their inability to compute intake of specific fatty acid subtypes. This latter more specific assessment is, however, essential since fatty acid composite groups (such as total saturated fats) have many subtypes that vary greatly in their food sources and subsequent health effects.

Fatty acid biomarker studies, in this respect, may provide more accurate assessment of fatty acid consumption and metabolism, and opportunity to assess risk by individual subtypes. While several studies assessed biomarkers of individual fats in relation to CHD risk, they were generally small studies and were never systematically reviewed and meta-analysed.

Finally, we noted that, with respect to randomised trials of fatty acid supplements for preventing coronary disease, interpretation of results has been complicated by the differences in participant-level or study-level circumstances. Therefore, to help clarify these uncertainties in both available observational and intervention studies, we conducted our comprehensive meta-analysis.

MPOC