Meta-analysis: No conclusive link between saturated fats and CV risk
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A meta-analysis of observational, prospective and randomized trials did not conclusively find any significant association between dietary saturated fat and risk for CVD, CHD, CV events or death.
According to the meta-analysis published in the European Journal of Preventive Cardiology, these findings do not support the position of “diet-heart hypothesis” that diets high in saturated fat confer increased risk for CVD and CV mortality.
“For decades, the conventional wisdom has been that the consumption of saturated fat undermines cardiovascular health, clogs the arteries, increases CVD risk and leads to heart attacks. This misconception, vilification and condemnation of saturated fat arose from the most comprehensive epidemiological population study, the Seven [Countries] Study by physiologist Ancel Keys, PhD, who claimed that saturated fat was the cause of CHD,” Reimara Valk, PhD, MA, MSc, assistant professor of management at American University in Dubai, United Arab Emirates, and colleagues wrote. “This ‘fat is deadly’ message propagated in the media spread around the world, and fat, particularly saturated fat, was demonized since the Seven Countries Study. This misguided public health message led to confusion and doubt among patients, their physicians and the public.”
The Seven Countries Study
The Seven Countries Study was the first long-term study to assess the effect of diet, lifestyle and other risk factors on CVD, across the former Yugoslavia, Japan, Greece, Italy, Finland, the Netherlands and the U.S.
In a Seven Countries Study subanalysis published in Preventive Medicine, researchers concluded that dietary saturated fat, trans fat and cholesterol were associated with 25-year CHD mortality.
Therefore, researchers conducted the present meta-analysis of four observational studies, three prospective epidemiologic studies and 25 randomized controlled trials published from 2010 to 2021 to better understand the association between saturated fats and CVD risk.
Saturated fat and CVD risk
Upon review of contemporary evidence, Valk and colleagues determined that intake of saturated fats was not significantly associated with CVD risk, CV events or death.
The researchers’ review of epidemiolocal and observational studies indicated either no increased risk or a neutral effect of dietary saturated fats on CHD, thus contradicting the diet-heart hypothesis.
The findings were similar after review of randomized controlled trials.
In a randomized trial that evaluated the effect of cooking with coconut oil compared with sunflower oil on CV risk factors over 2 years in patients with stable CHD, researchers observed that coconut oil, despite being higher in saturated fat, had no impact on lipid-related CV risk factors and events compared with sunflower oil.
Results were similar in systemic reviews and meta-analyses evaluating the impact of high saturated fat diets on risk for CVD, such as high-dairy diets. In these trials, researchers observed that total dairy intake had no association with risk for CHD. Other analyses demonstrated neutral associations between CHD and high-fat dairy diets compared low-fat dairy diets, according to the researchers.
“This review shows consistency across studies and coherence of epidemiologic and experimental scientific evidence, providing powerful evidence for absence of observed cardiovascular harm of saturated fat,” the researchers wrote. “Collectively, neither observational and epidemiologic studies or randomized controlled trials or systematic reviews and meta-analyses have conclusively established a benefit of reducing dietary saturated fat on CVD risk, events, outcomes and mortality. The evidence refutes the ‘diet-heart hypothesis’ and implies that it is timely that scientists, clinicians and the public reconsider this hypothesis.”
References:
- Keys A. J Am Med Assoc. 1957;doi:10.1001/jama.1957.62980170024007e.
- Kromhout D, et al. Prev Med. 1995;doi:10.1006/pmed.1995.1049.
- What is the Seven Countries Study? www.sevencountriesstudy.com. Accessed Sept. 7, 2022.
Perspective
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Kim A. Williams Sr., MD, MACC, FAHA
Most research in this area compares one harmful diet with another, with few exceptions, limiting the usefulness of this type of research to improve human health through nutrition. PREDIMED (Estruch R, et al. N Engl J Med. 2018;doi:10.1056/NEJMoa1800389) did not show any — though widely misquoted — decrease in cardiac risk or reduction in CV or total mortality, only decreased stroke risk.
The comparison should be with foods that reduce gastrointestinal dysbiosis, like a plant-based diet, as in PREDIMED (Martínez-González MA, et al. Am J Clin Nutr. 2014;doi:10.3945/ajcn.113.071431).
Any analysis of nutrition going forward needs to be cognizant of effects on obesity, diabetes, lipids, inflammation and hypertension, all of which are influenced or determined by the microbiome.
Nowadays, people generally don’t eat saturated fat, but rather food that contains saturated fat. The positive or negative effects of those foods can vary widely — bacon and coconut meat both have saturated fat, but the former is associated with hypertension (sodium), diabetes, heart disease, stroke, cancer and HF, while the latter is not.
Lastly, saturated fat comes largely from animal product consumption, which is not safe from the perspective of planet sustainability.
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