WASHINGTON--Controversial headlines claiming that eggs don't raise cholesterol levels could be the product of faulty industry-funded research, according to a new review published in the American Journal of Lifestyle Medicine.
Researchers with the Physicians Committee for Responsible Medicine examined all research studies published from 1950 to March of 2019 that evaluated the effect of eggs on blood cholesterol levels. The researchers examined funding sources and whether those sources influenced study findings.
The results show that prior to 1970, industry played no role in cholesterol research. The percentage of industry-funded studies increased over time, from 0 percent in the 1950s to 60 percent in 2010-2019.
"In decades past, the egg industry played little or no role in cholesterol research, and the studies' conclusions clearly showed that eggs raise cholesterol," says study author Neal Barnard, MD, president of the Physicians Committee for Responsible Medicine. "In recent years, the egg industry has sought to neutralize eggs' unhealthy image as a cholesterol-raising product by funding more studies and skewing the interpretation of the results."
Overall, more than 85 percent of the studies--whether funded by industry or not--showed that eggs have unfavorable effects on blood cholesterol. Industry-funded studies, however, were more likely to downplay these findings. That is, although the study data showed cholesterol increases, study conclusions often reported that eggs had no effect at all. Approximately half (49 percent) of industry-funded intervention studies reported conclusions that were discordant with actual study results, compared with 13 percent of non-industry-funded trials.
For example, in one 2014 study in college freshmen, the addition of two eggs at breakfast, five days a week over 14 weeks, was associated with a mean LDL cholesterol increase of 15 mg/dL. Despite this rise in cholesterol, investigators concluded that the "additional 400 mg/day of dietary cholesterol did not negatively impact blood lipids." The cholesterol change did not reach statistical significance, meaning that there was at least a 5 percent chance that the cholesterol rise could have been due to chance alone.
"It would have been appropriate for the investigators to report that the cholesterol increases associated with eggs could have been due to chance. Instead, they wrote that the increases did not happen at all. Similar conclusions were reported in more than half of industry-funded studies," adds Dr. Barnard.
These studies have even influenced policymakers. In 2015, the U.S. Dietary Guidelines Advisory Committee reported that "available evidence shows no appreciable relationship between consumption of dietary cholesterol and serum cholesterol...." After reviewing the evidence, however, the government did not carry that statement forward in the final Guidelines, which called for eating "as little dietary cholesterol as possible."
"The egg industry has mounted an intense effort to try to show that eggs do not adversely affect blood cholesterol levels," adds Dr. Barnard. "For years, faulty studies on the effects of eggs on cholesterol have duped the press, public, and policymakers to serve industry interests."
Several meta-analyses have concluded that egg consumption does raise cholesterol levels. According to a 2019 meta-analysis, eating an egg each day raises low density lipoprotein (LDL, or "bad") cholesterol by about nine points. The study, published in the American Journal of Clinical Nutrition, combined the findings of 55 prior studies, finding that every 100 milligrams of added dietary cholesterol (approximately half an egg) raised LDL ("bad") cholesterol levels by about 4.5 mg/dL. A 2019 JAMA study of nearly 30,000 participants found that eating even small amounts of eggs daily significantly raised the risk for both cardiovascular disease and premature death from all causes.
Of 153 studies analyzed in the American Journal of Lifestyle Medicine report, 139 showed that eggs raise blood cholesterol (68 of these reached statistical significance, meaning the results were very unlikely to be due to chance). No studies reported significant net decreases in cholesterol concentrations. Non-significant net cholesterol decreases were reported by six non-industry-funded and eight industry-funded studies.