Should guidelines on saturated fat consumption recommend lowest intake possible?

Although current dietary guidelines in the United States recommend people limit their intake of saturated fat to less than 10% of their daily calories, potential risks and benefits associated with saturated fat consumption has led to considerable debate as to whether future guidelines should recommend people reduce saturated fat intake as much as possible.

Experts debated the topic at Nutrition 2020, which was held virtually after initially being canceled because of concerns about COVID-19.

The debate compliments three papers published in the American Journal of Clinical Nutrition, one of which presents evidence in favor of this recommendation, another with evidence of why the recommendation should not be made and a third that gives a consensus of the evidence and offers suggestions for future research.

Evidence supporting the recommendation

Penny M. Kris-Etherton, PhD, RD, FAHA, FNLA, FASN, CLS, distinguished professor of nutrition at the Pennsylvania State University, argued in favor of national guidelines that recommend lowering saturated fatty acid (SFA) consumption as much as possible.

One reason to support the recommendation involves the effects of SFA on low-density lipoprotein cholesterol (LDL-C), which is a causal factor in heart disease, Kris-Etherton noted.

For instance, she explained that one study showed that LDL-C was lowered when 5% of energy from saturated fat was replaced with 5% of energy from other dietary components, including polyunsaturated fatty acids (PUFAs; –9 mg/dL), monounsaturated fatty acid (–6.5 mg/dL), or carbohydrates (–6 mg/dL).

Kris-Etherton cited two large epidemiological studies that showed replacing saturated fat with other fats, particularly PUFAs, reduced the risk for total mortality and CVD mortality.

A recent review of 15 randomized control trials with 59,000 participants examined reductions in saturated fat intake and CVD, specifically examining overall mortality, cardiovascular mortality and CVD events. Kris-Etherton said the review found that “reducing dietary saturated fat reduces combined cardiovascular events by 21%.”

The meta-regression, she explained, “suggested that greater reductions in saturated fat reflected greater reductions in serum cholesterol, resulting in greater reductions in risk of coronary heart disease events.”

Other studies have shown that high SFA intake induces cellular inflammation, changes vascular function and decreases the richness and diversity of microbiotia in the gut, Kris-Etherton said.

Regarding current recommendations, she explained that the scientific report from the 2015 Dietary Guidelines Advisory Committee stated that there was strong and consistent evidence from both randomized control trials and modeling in prospective cohort studies to show that replacing saturated fats with PUFA reduces the risk for CVD and coronary mortality.

The 2015-2020 Dietary Guidelines for Americans recommends three health eating patterns with less than 10% of energy from saturated fats. Meanwhile, the AHA’s Recommended Dietary Pattern suggests 5% to 6% of energy intake should be from saturated fats.

“It’s unlikely there would be any unintended consequences of a health dietary pattern that provides 5% to 6% of energy from saturated fat, given that these food-based patterns meet nutrient adequacy and all other dietary recommendations for calories, sodium, added sugars and alcohol,” Kris-Etherton said.

Reasons not to set guidelines to lowest possible consumption

Ronald M. Krauss, MD, professor of pediatrics and medicine at the University of California, noted that analyses of major clinical trials have been flawed, which questions the idea that lower SFA intake lowers the risk for CVD.

He explained that in three such randomized control trials, PUFA intake was 13% to 25%, much higher than the current recommended limit of 10% energy intake. Therefore, he said, the possibility that PUFAs provide CVD benefits whereas SFAs have a neutral effect cannot be ruled out.

In addition, prospective cohort studies on the effects of SFAs on CVD cannot determine causality, and it is often challenging to collect accurate dietary information from patients, Krauss said.

Recent observational studies have also failed to provide support for a relationship between saturated fat and CVD. For instance, the PURE study, which involved 135,335 participants from 18 countries, did not identify an association between the two.

Therefore, Krauss said, “there is not a conclusive clinical trial and epidemiologic evidence to support CVD risk reduction that is attributable to lowering SFA intake.”

Krauss explained that recommending people consume the lowest possible levels of saturated fats may also have public health consequences. For instance, some patients may replace saturated fats with sugars or processed carbohydrates, which could lead to adverse effects.

“Promotion of more healthful food choices, which would in and of itself lead to limiting SFA intake — and that, I fully agree with— would make the argument for an SFA guidelines superfluous — why have it at all — and thus eliminate the inconsistencies and confusion that it has generated,” he said.

Consensus on recommendations, needed research

Both Krauss and Kris-Etherton concurred that currently, recommended healthy eating patterns that suggest less than 10% energy consumption of SFAs are not high in SFAs.

In addition, both agreed that advice to reduce SFA intake as much as possible may have unintended consequences if “the implementation is done inappropriately with respect to nutrients and food that are substituted,” Krauss said.

“For example, added sugars in high quantities, or even other kinds of foods in very high amounts, could imbalance the diet and that is really, potentially, an adverse effect,” he added.

They also agreed to recommend decreasing SFA intake to reduce LDL-C levels.

Meanwhile, there were disagreements over whether lowering SFA intake lowers CVD risk, whether or not there is rationale for people to aim for a specific reduction in dietary SFA intake and the extent to which LDL-C reduction with lower SFA consumption predicts CVD risk.

To provide more evidence to support SFA intake recommendations, Kris-Etherton said that further research is needed to assess long-term relationships between healthy diet patterns with different SFA intake levels and morbidity and mortality outcomes. She noted that these studies should consider LDL-C and additional risk factors.

“We can both agree that we really need to identify more reliable surrogates for CVD outcomes than those currently in use, that may minimize the need for these long-term, costly studies on dietary interventions that look at saturated fat and that replenish macronutrients,” she said.