Dietary Guidelines Experts Again Condemn Saturated Fats, Ignore Rigorous Evidence
By Nina Teicholz
Last week, the USDA released its draft conclusions for the 2020 Dietary Guidelines for Americans (DGA), and the cap on saturated fats looks likely to stay firmly in place. The evidence linking saturated fats to heart disease was judged to be “strong,” not only for adults, but also, for the first time, children. These were the conclusions of the Subcommittee on Dietary Fats and Seafood, part of the larger DGA Advisory Committee.
The draft conclusions are not surprising, given that the five-person Subcommittee is one-sided and unbalanced, according to an analysis by the Nutrition Coalition. The group includes one of the staunchest foes of saturated fats and not a single person to oppose her. The conclusions are also unsurprising given that advice to limit saturated fat has been in place for 40 years. These views are entrenched in government agencies, university nutrition departments and are supported by many food and pharmaceutical interests.
Yet scientific justification for a continuation of these caps is lacking, and the Subcommittee presented weak evidence to make its case. The past decade has seen a thorough reconsideration of saturated fats, and now, there are close to 20 review papers reexamining the evidence. These have near-universally concluded that saturated fats have no effect on cardiovascular or total mortality, and there are very few findings of any kind of cardiovascular events (heart attacks, MIs, etc). The effect of saturated fats on LDL-cholesterol, which is often cited, must be considered irrelevant when there is so much higher-level evidence on more definitive outcomes.
In addition, there is a growing view that restricting the natural foods containing these fats causes harm by reducing access to the full complement of nutrients essential for human health. For instance, the U.S. Dietary Guidelines, with its current 10% cap on saturated fats, fails to meet nutrient targets for, among other things, iron and choline, which are most easily obtained by eating regular meat and dairy—foods that also happen to contain saturated fats.
Recent thinking on saturated fats has also come to embrace the idea that there are many different saturated fatty acids, each with differing effects. Treating them as single entity is widely viewed as simplistic.
The Subcommittee ignored this evolving science, however. It’s draft conclusions are:
ON ADULTS, there is:
- “Strong and consistent evidence from randomized controlled trials shows that replacing saturated fatty acids with unsaturated fats, especially polyunsaturated fatty acids, significantly reduces total and low-density lipoprotein [LDL] cholesterol.”
Grade: Strong - Strong evidence demonstrates that replacing saturated fatty acids with polyunsaturated fatty acids in adults reduces the risk of coronary heart disease events and cardiovascular disease mortality.
Grade: Strong
The conclusion on LDL-cholesterol immediately raises questions.
Why Look at Cholesterol when More Definitive Data Exist?
It is unclear how the committee can justify looking at intermediary, or “surrogate” endpoints, such as total and LDL-cholesterol, when the Institute of Medicine, in a 2010 report, stated that neither LDL- or HDL-cholesterol were reliable markers for cardiovascular disease in interventions involving food [1]. LDL-cholesterol is especially unreliable in trials involving saturated fats, since it has been known for years that LDL comes in different particle sizes and that saturated fats increase only the kind of LDL particle (large, and ‘buoyant’) that is associated with less cardiovascular risk.
Citing surrogate endpoints is also hard to justify when far more definitive, “hard” outcome data exists. Hard outcomes are events like heart attacks and death. Death is especially reliable, as it’s hard to dispute, whereas a diagnosis of a heart attack is subject to variability across time and place. These, more rigorous outcome data on heart attacks and mortality, are extensive for saturated fats, and they come from randomized, controlled clinical trials on some 50-75,000 people, depending on which trials one counts. In all these studies, saturated fats were replaced by unsaturated fats—the direct comparison that the Subcommittee addresses—and they conclude that saturated fats have no effect on cardiovascular or total mortality.
Our list of the nearly 20 review papers is here.
Subcommittee Ignores the Rigorous Data
The Subcommittee had two options to examine the original clinical trial data on those 50-75,000 people, which date from the 1960s and 70s—and have never been directly reviewed by any DGAC committee. Either the Subcommittee could have reviewed the trials directly, or it could have reviewed the many review papers of these trials. It did neither.
Whether this was a decision made by the Subcommittee or by USDA officials is unknown. USDA staff frequently say that all decisions are up to the expert committee, yet it frequently becomes obvious that USDA officials themselves are making key decisions on methodology, protocols, and the USDA conducts all the systematic reviews. In the case of the Birth-to-24-months work, for instance, the USDA completed all the reviews before the 2020 Committee even convened.
Regarding saturated fats, any expert in the field knows about the plethora of recent papers reflecting shifting views on this subject. Since Subcommittee members were theoretically chosen for their expertise in the subject, they could have insisted on a protocol that would have allowed consideration of this new science. The Subcommittee also should have been guided by a law stating that that the DGA must be based on the science “that is current at the time.”
Even if the Subcommittee were somehow unaware of the most recent science in this field, it had been amply informed, via thousands of public comments on the subject, including more than one by The Nutrition Coalition.
More importantly, an esteemed group of scientists, including two former members of previous DGACs and the former chair of the 2005 DGAC, submitted more than one public comment about the missing data. Members of this group also sent a letter to the Secretaries of USDA and HHS.
“Strong” Grade for Cardiovascular Events, Mortality Not Supported by the Evidence
The Subcommittee gave a “strong” grade to the link between saturated fats and cardiovascular events/mortality. Normally, a “strong” grade is granted only when there are multiple, controlled clinical trials supporting a hypothesis. As we’ve seen, however, rigorous clinical trials on 50-75,000 people show no effect on cardiovascular or total mortality. This is a large and rigorous body of contrary evidence.
What evidence did the Subcommittee use to justify its “strong” conclusion? According to my search, the list of studies it reviewed included no clinical trials on saturated fats that looked at outcomes of cardiovascular events or mortality. [2]
The Subcommittee included only eight trials on saturated fats. None reported on the outcomes of cardiovascular events or mortality:
- The “DIVAS” study. Outcomes: lipids (#198 on the list of “included studies” starting at p. 34);
- Three trials on meat. Outcomes: mainly lipids (#4, 23, 44);
- A trial on high saturated fat + high protein. Outcomes: insulin sensitivity, lipids (#42);
- A trial on low saturated fats + low glycemic index. Outcome: liver fat (#197);
- The “Canola Oil” study. Outcome: Serum-Mediated Cholesterol Efflux from THP-1 Macrophages (#122).
- A trial comparing saturated fats to monounsaturated fats, refined carbohydrates. Outcomes: inflammatory markers, lipids. (192)
It’s important to note that saturated fats did not have clearly adverse effects in a majority of these trials. For instance, in trial #192, the conclusions state that replacing saturated fats with either monounsaturated fats or refined carbohydrates did not improve cardiovascular risk factors and that refined carbohydrates worsened them.
The remaining studies examined by the Subcommittee on saturated fats were all epidemiological. These included six studies with outcomes on cardiovascular disease (#119, 116, 161, 228, 162, 212) and two on mortality (#29, 220). However, this is a type of study design that can only demonstrate association. Very rarely can these studies be used to demonstrate causation.
More on epidemiology: it is a type of science used to generate hypotheses, the 1st step in science before conducting a clinical trial (Step #2), which can more definitively establish cause-and-effect. In the case of saturated fats, we’ve already been through Step #1 of hypothesis generation, back in the 1950s. Step #2, the clinical trials, have also been done—on a massive scale—in the 1960s and 70s, as described above. Thus, it makes no sense to ignore the Step #2 science and go back to Step #1, as if the clinical trials never existed. The more rigorous data are from the clinical trials. These cannot be ignored in favor a fundamentally weak type of science, to try to substantiate a “strong” recommendation on saturated fats.
A final note. It’s possible that the 2020 Subcommittee is simply rolling forward the “strong” recommendation from the 2015 DGAC review on this topic. That review was not systematic; it was instead an ad hoc selection of review papers that were not accurately summarized, as documented here. It is therefore not be a solid foundation for the 2020 review.
ON CHILDEN:
ON CHILDREN, the Subcomittee stated that there is:
Strong evidence demonstrates that diets lower unsaturated fatty acids and cholesterol during childhood result in lower levels of total blood and low-density lipoprotein cholesterol throughout childhood, particularly in boys.
Grade: StrongIn making this conclusion, the Subcommittee looked at only three clinical trials, all on surrogate outcomes— with the same limitations of the data as described for adults, above. Use of surrogate endpoints for children is even more problematic, since cholesterol levels in childhood have never reliably been correlated with heart disease later in life.[3] The studies are:
The “DISC” study, on 300 children aged 7-10. This trial included only children with unusually high LDL-cholesterol (in the 80th to 98th percentile) and therefore were not a typical population. In other words, these children could very well have had familial hypercholesterolemia, the genetic condition that causes heart disease through a metabolic defect, which is entirely different from the way that cholesterol is altered by diet. According to the Subcommittee’s exclusion criteria, which disallows studies “that exclusively enroll participants with high blood lipids, (e.g., TC, LDL, HDL, or triglycerides),” this study should have been excluded from consideration. Moreover:
Subcommittee member Linda Van Horn was a DISC study leader, a conflict of interest that did not appear to be managed;
Children on the DISC diet suffered nutritional deficiencies: they ended up consuming less than two thirds of the RDAs for calcium, zinc, and vitamin E. They also got less magnesium, phosphorus, vitamin B12, thiamin, niacin, and riboflavin than did children in the control group. These problems speak to the serious issues involved in limiting foods that contain these nutrients. Children, especially, need these nutrients for healthy growth and development.
The “STRIP study in Finland involved babies as young as 7 months up to age 3. They were given vitamin supplements to remediate any nutrients lacking in the dietary intervention, which was low in saturated fats. No particular benefit was seen, although no harm, either. (#143, 146, 165)
A study on 60 obese adolescents that used a multifactorial intervention, including changes in nutrition, psychology, physical exercise and clinical therapy. Due to the multifactorial nature of this study, outcomes cannot be attributed to saturated fats alone. (#126)
The Subcommittee’s “strong” recommendation on children is therefore based on very slim data: children under the age 3 receiving supplements (showing no benefit), a few hundred children with abnormally high cholesterol, and adolescents receiving a multi-factorial intervention that fails to isolate saturated fats. These are hardly the data that one would want to justify a population-wide recommendation for all children in America. [4]
It is a tragic situation when deeply entrenched, status-quo views cannot be illuminated by the best and most rigorous science. It’s not just science that loses but the American public, which will yet again receive antiquated advice, based on weak science, that will quite likely cause harm.
[1] Institute of Medicine. 2010. Evaluation of Biomarkers and Surrogate Endpoints in Chronic Disease. Washington, DC: The National Academies Press. https://www.dietaryguidelines.gov/sites/default/files/2020-04/DFSSC_DF-CVD_Final_Protocol_4.20.2020.pdf, p. 133
[2] Note that for all the results here, I searched only the term “saturated.”
[3] ”The Pathogenesis of Atherosclerosis— An Update,” New England Journal of Medicine 295 (1986): 488–500; Canadian Paediatric Society and Health Canada, Joint Working Group, Nutrition Recommendations Update: Dietary Fat and Children (Ottawa, Ontario: Health Canada, 1993).
[4] For more detail on these trials, see Teicholz, The Big Fat Surprise, pp. 152-156. I don’t know of any other critical readings of these trials, but I encourage you to recommend other analyses in the comment section, below.