Cholesterol controversies

Cholesterol, a lipid involved in the maintenance of cell structures and steroid hormones in the body, has a very controversial history depicted in Figure 1. The organic molecule was first identified in the late 1700s, named^[1] in the early 1800s, and was implicated in heart disease in the mid-1900s^[2]. This implication came to be known as the “lipid hypothesis” and gained much support from the biomedical community with the publication of the Seven Countries Study^[3], an observational study that found a consistent association between blood cholesterol levels and incidences of coronary heart disease in the countries sampled from.

While the validity of these findings has been subjected to much debate^[4], the implication of low-density lipoprotein (a carrier of cholesterol) in coronary heart disease is well accepted in the medical community due to overwhelming evidence from pharmaceutical trials^[5] and genetic studies^[6]. The biggest risk factors associated with hypercholesterolemia (high blood cholesterol) include a diet^[7] high in trans-^[8] and saturated fat, obesity, type 2 diabetes^[9], and genetics^[10]. However, there has been much controversy^[11] over whether or not dietary cholesterol influences blood cholesterol levels.

Early metabolic ward experiments^[12] seemed to support the idea that increased consumption of dietary cholesterol increased serum cholesterol. However, other trials^[13] contradicted these findings. For several decades, medical associations and the dietary guidelines^[14] recommended that Americans limit their consumption of foods high in cholesterol. In 2013, the American Heart Association^[15] stated that there was insufficient evidence to conclude whether there was any cardiovascular benefit to removing or reducing dietary cholesterol. In 2015^[16], the recommendations to limit dietary cholesterol were dropped from the U.S. dietary guidelines.

Yet, many trials^[17] and observational studies^[11] still seem to suggest a notable connection amongst all the controversy. The study under review investigated whether published, high-quality randomized controlled trials supported this connection between dietary cholesterol and blood concentrations of LDL cholesterol and HDL cholesterol.

There is still much controversy surrounding the impact of dietary cholesterol on serum cholesterol. Although many government agencies and medical organizations no longer recommend limiting dietary cholesterol, several clinical trials and observational trials still seem to suggest a connection. The study under review looked at published randomized trials to assess whether dietary cholesterol does impact serum cholesterol and how much.