Revision as of 23:44, 17 August 2020

What is Saturated fat?

Saturated vs Unsaturated Fatty Acids

Polyunsaturated Fatty-acids (PUFA)

Mono Unsaturated Fatty-Acids (MUFA)

Trans Fatty-Acids (TFA)

How Do We Know That SFAs Increase Risk Of CVD?

Scientific Consensus

SFAs Increase LDL

Mortality Outcomes

There are over ten systematic reviews and meta analyses of both observational studies and RCTs encompassing millions of people that establish reducing or replacing saturated fat with other nutrients results in significantly decreased CVD morbidity and/or mortality8-20.

While there are also a few additional reviews suggesting that it has no observable effect21,22, along with those that the authors of the JACC review mention2-5, they involve critical flaws that impair their ability to effectively assess the relationship between SFAs and CVD morbidity/mortality, and as such have been heavily criticized. Following is a discussion of each of these trials, their respective pitfalls, and additional comments from other parties where appropriate

Rejection Of Consensus

Epidemiology Denial

Correlation ≠ Causation

SFAs Are Most "Stable"

Common Studies Cited By Saturated Fat Apologists

JACC Review

Recently a “State-of-the-Art” review entitled Saturated Fats and Health:A Reassessment and Proposal for Food-Based Recommendations was published in The Journal of the American College of Cardiology, in which authors presented the argument that current evidence does not support the dietary guidelines recommendations to limit saturated fatty acid (SFA) intake to less than 10% of daily calories on the basis of reducing morbidity and mortality from common chronic diseases, most notably cardiovascular disease (CVD). They remark that although SFAs raise low-density lipoprotein cholesterol (LDL), this is due to increases in large (and not smaller, dense) particles, which aren’t as strongly related to CVD risk. Further, they exclaim that not all sources of fatty acids impart similar effects on health due to differences in their overall structure and the complex matrices of the foods they are found in, specifically emphasizing that dark chocolate, unprocessed meat, and whole-fat dairy are not associated with the risk of CVD and recommendations to limit their intake solely due to their SFA content are unsubstantiated1. Although some of the sentiments they offer are agreeable, and despite their claims otherwise, the totality of the available evidence does not support many of their arguments. Accordingly, their publication will likely cause greater confusion to the american population already struggling to decide who they can trust among the disordered field of nutritional science, and result in more harm than benefit.

The review begins by briefly discussing the history behind the initiation of dietary goals and recommendations to lower saturated fat intake dating back to the 1970s, and details that since the 80s there have been specific goals of reducing saturated fat intake to less than 10% if total calories to reduce CVD risk. The authors declare that their main intention is to answer the question posed by the United States Department of Agriculture and Health and Human Services’ in 2018; “What is the relationship between saturated fat consumption (types and amounts) and the risk of CVD in adults?” by reviewing the effects of saturated fats on health outcomes, risk factions, and mechanisms underlying CVD and metabolic outcomes. Having clearly defined their objective, the question then becomes whether their review provides a sufficient answer that is backed by a solid body of evidence, which will become quickly apparent is far from the case.

In the following paragraph, they say the following:

“The relationship between dietary SFAs and heart disease has been studied in about 400,000 people and summarized in a number of systematic reviews of observational studies and randomized controlled trials (RCTs). Some meta-analyses find no evidence that reduction in saturated fat consumption may reduce CVD incidence or mortality (3–6), whereas others report a significant—albeit mild—beneficial effect (7,8).2-7” 

Based upon this collection of research they conclude that the basis for recommending a low saturated fat diet is unclear and that they intend to propose an evidence-based recommendation for intake of SFA food sources. Right from the start the authors have demonstrated that they aren’t truly reaching their conclusions by considering the totality of the evidence. Despite only mentioning 5 publications that contain about 400,000 subjects, there are actually over ten systematic reviews and meta analyses of both observational studies and RCTs encompassing millions of people that establish reducing or replacing saturated fat with other nutrients results in significantly decreased CVD morbidity and/or mortality8-20. In fact, a couple of the more recent publications on the subject include over double the amount of people they imply this relationship has been studied in17,19. While there are also a few additional reviews suggesting that it has no observable effect21,22, along with those that the authors of the JACC review mention2-5, they involve critical flaws that impair their ability to effectively assess the relationship between SFAs and CVD morbidity/mortality, and as such have been heavily criticized.

Apart from the 4 reviews just discussed, two additional reviews have suggested there may not be an association between saturated fat intake and CVD, one of which the authors of the JACC mentioned in their brief comments on the subject. These two reviews were carried out by Ramsden et al. and Steven Hamley, both including randomized controlled trials focused on determining the potential benefit of replacing saturated fatty acids with mostly polyunsaturated fatty acids. Ramsden et al.’s review included discussion of recovered data from the Minnesota Coronary Experiment (MCE) and also carried out a meta-analysis of an additional 4 RCTs, the Sydney Diet Heart Study (SDHS), the Rose Corn Oil Trial (RCOT), the Los Angeles Veterans Trial (LA Vet), and the Medical Research Council Soy Oil Trial (MRC-Soy), and a sensitivity analysis on the previous 5 in addition to 3 more, the Diet and Re-Infarction Trial (DART), the Oslo Diet Heart Study (ODHS), and the St. Thomas Atherosclerosis Regression Study (STARS).

Taking into account the incredibly large body of high quality evidence from RCTs and observational trials demonstrating the beneficial effect of reducing saturated fat intake on CVD morbidity and mortality, and considering the problematic aspects of reviews suggesting a null effect, it should be incredibly clear the JACC author’s statement that there is a lack of clarity regarding the basis for reducing saturated fat intake is preposterous.

Steven Hamley n-6 PUFA Review

In Hamley’s review of RCTs, he chose to exclude certain trials on the basis of “inadequate control” and other factors that he posits would impact the results, including suspicions that the control group had higher trans fat intake, were exposed to cardiotoxic medications, and had lower vitamin E intake. His meta analysis ended up incorporating the exact same trials as Ramsden et al.’s with the one exception being LA VET, which he replaced with DART. Ironically, this means he included both MCE and SDHS, which exposed the intervention groups to higher trans fat intake, and other small studies underpowered to detect meaningful effects on his chosen endpoints total and major CVD events.

Directly contradicting both of these trials is the recent Cochrane Review on reductions in saturated fat for cardiovascular disease, which was subject to far more rigorous pre-review protocols and analyzed the results of 15 RCTs (even including SDHS) to find that long term reductions in saturated fat intake resulted in significant reductions in the incidence of combined cardiovascular events18.

De Souza et al

Minnesota Coronary

Not only was the MCE flawed in numerous ways that prevented meaningful conclusions being drawn from its results, there were also multiple issues with the other smaller trials included in their analysis (for which MCE ended up being weighed the most). As for the MCE, the high dropout rate (>75%) and subsequently insufficient power to detect effects on mortality, the utilization of a likely trans fat-containing margarine in the intervention group, the fact that the main difference in mortality was observed only in subjects over 65 years of age, and the lack of important metrics such as smoking status, LDL cholesterol, detailed dietary intake data, weight loss, and coronary disease status, were the main problems. The smaller size (and weaker statistical power), exclusion of mortality as a main endpoint, and inclusion of a trans fat based margarine in the experimental group of another trial (SDHS), were further issues that rendered the findings of the analyses unuseful.

Siri-Tarino et al

Chowdhury et al

PURE

Nutrireqs

Harcombe Review

Sydney Diet Heart

Women's Health Initiative

JACC section written by Matt Madore, Aug 16, 2020