“Good cholesterol”, the common name for high-density lipoprotein (HDL) complex, has a mean size of 8–10 nm and a density of 1.063–1.21 g/ml. The HDL particle consists of a central core of esterified cholesterol with a surrounding monolayer of phospholipids, free cholesterol, and apolipoproteins, mostly apoA-I and apoA-II. Importantly, hormones, vitamins, proteins, and microRNAs (miRNAs) can also be incorporated, which may contribute to the health properties of this particle.
HDL acts in prominent pathways that influence atherosclerotic disease development including reverse cholesterol transport, oxidation and inflammation, and endothelial function, immune system modulation, cellular apoptosis, and endothelial progenitor cell homeostasis. HDL is used as a marker by clinicians to help predict cardiovascular risk, but clinical trials using pharmaceutical agents to raise HDL levels have not demonstrated efficacy in cardiovascular disease to date. Measures of the physiological function of HDL, such as cholesterol efflux capacity and HDL inflammatory index, may provide an opportunity for future clinical application.
Exercise and diet have a multimodal effect on cardiovascular disease risk including modifying HDL levels. Studies have shown that exercise can increase HDL levels, however evidence concerning diet is less clear-cut with altered diet regimen modulating HDL in both directions. A new study led by Yung‐Po Liaw of Chung Shan Medical University, Taiwan, published in the journal Medicina, assessed the combined effect of vegetarian diet and exercise on HDL cholesterol levels in an adult Taiwanese cohort from the Taiwan Biobank, which records questionnaire based information on diet and exercise as well as biochemical information.
Overall exercisers had higher levels of HDL than non-exercisers, however there were important differences according to diet. Omnivore exercisers had the highest HDL levels of all groups, whereas exercisers who were pure vegetarians, by contrast, had the lowest HDL levels of all. Exercise produced higher HDL levels than non-exercise only in the omnivore group; former vegetarians, lacto-ovo vegetarians and pure vegetarian non-exercisers had higher HDL than their exercising counterparts. The trend for both exercising and non-exercising vegetarians was lower HDL than non-vegetarians.
The study did not attempt to determine the reasons for vegetarianism combined with exercise leading to lower HDL than non-exercise, however the authors speculated that insufficient fatty acid intake was a possibility. This could not be confirmed as there was no information on the average daily nutrient intake of the participants. If the authors speculation is correct specific dietary supplementation in vegetarians could reverse the trend shown by the study.
“Broadly speaking, we found that (1) HDL‐C levels were higher in exercisers compared to non‐exercisers. (2) Regular exercise in conjunction with strict vegetarian diets led to greater reductions in HDL cholesterol levels. Compared with omnivores, strict vegetarians were associated with lower HDL‐C followed by lacto‐ovo vegetarians. Based on these findings, regular exercise together with strict vegetarian diets might not serve as healthful behaviors to be implemented in everyday life considering the negative impact on HDL‐C,” concluded the authors.