Egg Consumption, Cholesterol Research, And Study Funding
The effect of diet on health indicators, such as cholesterol levels, is a trending topic that is also somewhat controversial. Research has reported conflicting findings, suggesting that future researchers should try to better understand the impacts of variables such as the type of research design (e.g., experimental vs. correlational), the variables that were statistically controlled (e.g., demographics characteristics, and behavioral patterns of participants), and the characteristics of the study (e.g., funding sources). The purpose of this study was to examine the hypothesized increasing trend of industry-funded research, as well as to examine the potential impact of industry-funding on the objectivity of the reported findings.
Cholesterol is a major contributor to cardiovascular disease, a leading cause of death in the general population. As such, cholesterol is an important variable to consider when making food-related choices. However, prior research has resulted in conflicting narratives about the role that food choices (egg consumption in particular) have on cholesterol, making it difficult to determine the true effect. To further complicate things, a preliminary review of prior research indicated that 10 out of the 12 studies reviewed were funded by the egg industry. This finding should obviously raise concern, given the potential conflict of interest.
In an attempt to better understand the relationship between funding source and reported research findings, the authors conducted a study where they examined historical research published in the PubMed and Cochrane Central Register of Controlled Trials electronic databases. The authors used search terms such as “egg” and “cholesterol” when selecting articles, and they searched for articles that were published through March 8, 2019. In addition, they limited their search to research conducted with human participants. The authors identified additional studies via the reference list of the secured studies from their literature search. The final list of studies that were used in the analysis included those that reported effect sizes associated with the relationship between egg consumption (eggs or products containing egg yolk) and total or LDL cholesterol concentrations in the blood, plasma or serum. However, studies with low validity were excluded from the analysis — low validity would include studies with a duration of fewer than 24 hours, or studies with confounding variables not controlled.
In total, the authors identified 977 studies. After removing duplicates and those that did not meet the study criteria, a total of 211 studies remained (27 observational, 172 intervention-based, 3 case studies, and 9 systematic reviews). For each study included in the analysis, the three primary variables of interest included type of funding (industry-funded or not), the reported effect size (denoting the relationship between egg consumption and cholesterol levels), and the concordance rate between the author’s conclusions and the reported statistical findings. Studies that reported financial support from any industry that could benefit from the promotion of eggs were coded as industry funded. The effect size was determined by the net increase or decrease in cholesterol levels based on a comparison using a baseline and/or control group. Only situations with significant net increases or decreases in LDL were considered significant effects; changes in total cholesterol alone were not sufficient. Finally, comparisons were made between those studies that were funded by industry and those that were not in terms of their concordance rate.
The study found that the proportion of articles identified as industry-funded has increased at a statistically significant rate. Interestingly, of those studies that were industry-funded, 85% included the use of appropriate controls in comparison to 66% of non-industry funded studies. However, industry-funded studies resulted in a 49% discordance rate compared to 13% for non-industry-funded studies. Specifically, industry-funded articles were more likely to report neutral or favorable results with regard to the effect of egg consumption on cholesterol levels. Given these results, consumers should consider funding types when evaluating the credibility of the results of this type of research. Likewise, animal advocates should be aware of these possible weaknesses in industry-funded research when doing their advocacy.