Stuck in the past? US dietary guidelines may “lack evidence” for unhealthy saturated fat claims

28 Sep 2021 --- The Dietary Guidelines for Americans (DGA) recently reconfirmed its recommendation to limit saturated fats to 10% or less of total energy intake, despite external reviews that argue these recommendations were not based on sufficient and consistent evidence.

This is according to a new review conducted by various US-based universities, including the University of Texas and the University of California – San Francisco.

Reviewing data
In the past decade, approximately 20 papers reviewing the totality of the data on saturated fats and cardiovascular outcomes have demonstrated the lack of rigorous evidence to support recommendations to limit or replace saturated fatty acids with polyunsaturated fatty acids.

“This review on saturated fats adds to at least 20 others that have all concluded that saturated fats do not affect cardiovascular disease (CVD), cardiovascular mortality or total mortality,” study author Nina Teicholz tells NutritionInsight.

She is also the executive director of The Nutrition Coalition (TNC), a non-profit aiming to ensure that US nutrition policy is based on rigorous scientific evidence.

“This is the latest science on saturated fats, and the conclusion, by different teams of researchers from different parts of the world, is that saturated fats are not a factor driving heart disease. The policy should not be stuck in the past. It should respond to this latest science.”Evidence of the link between saturated fats and cardiovascular disease may be insufficient. 

Researchers explain that the continuation of a cap on saturated fat intake fails to consider the essential effects of the food matrix and the overall dietary pattern in which saturated fatty acids are consumed.

NutritionInsight has contacted the USDA for further comment.

Commercially driven guidelines?
The US dietary guidelines reconfirmed the need to limit saturated fat intake during the 2020 DGA process, despite external evidence that this was not accurate.

There is “a good deal” of evidence of financial conflicts of interest on the expert group that reviews the science for the guidelines, the Dietary Guidelines Advisory Committee, and government staff in the US Department of Agriculture, which oversees this policy USDA itself, comments Teicholz.

“Many food companies represented here produce foods with vegetable oils, which compete with saturated fats. The guidelines currently recommend margarine and soybean oil instead of butter, for instance.”

“All the fats in processed foods, such as cookies, crackers and chips, are some form of vegetable oils. This comprises the backbone of the food industry. Thus, there’s a commercial motivation to keep the limits on saturated fat,” she adds.

In addition to commercial motivation, there is a subtle form of conflict of interest that is “intellectual,” where a member may have spent an entire career trying to show that saturated fats are bad for health, supports Teicholz.

“This was certainly true of the committee reviewing saturated fats for the 2020 guidelines. These conflicts impede the objective, dispassionate evaluation of the most current science.”

Earlier this year, NutritionInsight reported on the industry’s involvement in the DGA. TNC highlighted that the public is unaware of conflicts of interest in the DGA Committee.

Spotlight on saturated fats and CVD
Since introducing the DGA, the national nutrition policy has advised limiting saturated fat consumption as a central strategy for reducing risk for atherosclerotic CVD.

The first limits on saturated fats were suggested by the American Heart Association, in 1961, based on what was the best available evidence at the time, details Teicholz.The DGA may be commercially motivated, argues Teicholz.

“The major study that seemed to support these limits was called the Seven Countries Study, led by a physiologist at the University of Minnesota called Ancel Keys. Keys proposed the diet-heart hypothesis, which suggested that saturated fats and cholesterol cause heart disease. However, the study was observational and therefore provided weak evidence.”

“In the 1960s and 70s, clinical trials were undertaken to try to ‘prove’ Keys’ hypothesis, but the trials did not turn out as hoped,” Teicholz continues. “Specifically, the results did not support the idea that saturated fats and cholesterol cause heart disease. These trial results were largely disregarded as a result.”

In 2010, researchers rediscovered this data and began re-examining it, leading scientists to realize that there was no substantial evidence on the link between saturated fats and heart disease.

In moving forward and taking the following steps to ensure that there is evidence to support claims, “scientists overseeing the review of the science for the next DGA should review the latest papers on saturated fats. All these papers were ignored in the last iteration of the DGA, which was published in late 2020,” adds Teicholz.

Spurring obesity?
In viewing how these guidelines have impacted consumers, Teicholz notes that “it is very likely that having guidelines not based on accurate and most current science has harmed human health.”

The launch of the DGA, in 1980, coincides exactly with the beginning of the US’s obesity epidemic, she flags.

Foods containing saturated fats, such as dairy and meat, are among the most nutrient-rich foods available and the nutrients in these foods are in their most “bioavailable” form. For example, the form of iron in spinach is far less easily absorbed than the type of iron present in red meat, she further explains.

“Encouraging reductions in these foods has led to a diet that is deficient in the basic nutrients needed for human health. The DGA, even if followed perfectly, do not provide all the nutrients that are needed to live healthfully,” concludes Teicholz.

By Nicole Kerr