In February 2015, the US Dietary Guidelines Advisory Committee reported that dietary cholesterol was no longer a “nutrient of concern.” According to the Committee’s report, “available evidence shows no appreciable relationship between consumption of dietary cholesterol and serum cholesterol….” In the ensuing media tempest, some food writers saw a green light for indulgence in eggs, sausage, and other high cholesterol foods. Others went further, exonerating high blood cholesterol levels, and patients began asking their physicians whether cholesterol matters.
It does, and here is why:
Despite cholesterol’s essential functions—it is a part of cell membranes and a raw material for bile acids and certain hormones, such as testosterone and estrogens—plasma cholesterol concentrations are strongly associated with cardiovascular disease risk.
Yes, plasma cholesterol levels are driven upward by saturated fat intake—on average, a one percent increase in energy from saturated fat increases LDL cholesterol concentration about two percent. But they are also influenced by dietary cholesterol. Beginning in the 1950s, Ancel Keys, Mark Hegsted, and other researchers found that dietary cholesterol boosts blood cholesterol in a roughly linear relationship within normal intake levels, with a diminishing effect at the higher intakes used in some research studies.
Since then, the relationship between dietary cholesterol and circulating cholesterol has been repeatedly reaffirmed. A 1988 National Institutes of Health conference arrived at the same conclusion as Hegsted, and a meta-analysis published in 1992 and two more published in 1997 agreed: cholesterol you eat raises cholesterol levels in your blood.
In 2002, the Institute of Medicine reviewed the evidence, concluding that cholesterol consumed in foods clearly raises blood cholesterol levels. The Food and Drug Administration agreed as it weighed the question of whether cholesterol content should be reported on food labels in the Federal Register of 3 March 2014.
So how did the Dietary Guidelines Advisory Committee arrive at its not-guilty verdict? The committee wrote that its finding of no relationship between dietary cholesterol and serum cholesterol was “consistent with the conclusions of the AHA/ACC report,” citing a 2014 report by the American Heart Association and American College of Cardiology.
However, the AHA/ACC report did not actually reach this conclusion. It summarized evidence published after 1998—that is, after the most recent meta-analyses were published—and called for more research, but did not suggest that there was no relationship between dietary cholesterol and serum cholesterol. Of course, the issue may be largely theoretical, because most cholesterol-containing foods also contain saturated fat—and both raise LDL cholesterol concentrations.
In dismissing the risks of dietary cholesterol, the committee may have inadvertently further confused an already bewildered public, many of whom do not differentiate dietary cholesterol from blood cholesterol, or cholesterol from saturated fat.
What is to be done? The 2010 Dietary Guidelines for Americans recommended that cholesterol intake be limited to 300 mg/d, or 200 mg/d for persons with or at high risk for cardiovascular disease or type 2 diabetes. Given the evidence, it would be prudent not to disregard those limits, but rather to strengthen them. The optimal cholesterol intake may well be zero.
When it comes to cholesterol, caution is advisable.
Competing interests: The authors have no conflicts of interest to declare.