Viewpoint Cite This: J. Agric. Food Chem. 2017, 65, 9931-9933
pubs.acs.org/JAFC
Do We No Longer Need To Worry about Dietary Cholesterol? Hanyue Zhu and Zhen-Yu Chen* Food & Nutritional Sciences Programme, School of Life Sciences, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, People’s Republic of China When elevated LDL cholesterol and its oxidized LDL cholesterol circulate in the blood, they cause the endothelial dysfunction by activating a number of scavenger receptors, promoting the growth and migration of smooth muscle cells, adhering to monocytes/macrophages and fibroblasts, causing atherosclerosis, narrowing the artery, and blocking the blood flow. As stated by the American Heart Association, high LDL cholesterol is still one of the major controllable risk factors for CHD, heart attack, and stroke. The five clinical trials following the National Cholesterol Education Program Adult Treatment Panel III Guidelines indicate a 1% reduction in LDL cholesterol leads to a 1% reduction in the risk of major CHD events,3 while the Atherosclerosis Risk in Communities (ARIC) Study and the Four Prospective American Studies demonstrate that a 1% increase in HDL cholesterol is associated with up to a 3% reduction in the risk of cardiovascular diseases.4,5 One fundamental question is whether dietary cholesterol raises plasma cholesterol and LDL cholesterol. The answer is ecommendation on reducing cholesterol intake to yes; however, the effect is not as significant as we thought. As decrease the risk of coronary heart disease (CHD) has summarized in the report on the previous clinical studies by been on dietary guidelines for many years. CHD is the most McNamara,6 100 mg of dietary cholesterol increase plasma TC common cause of death in the world. Hypercholesterolemia, only by 2.2−2.5 mg/dL, with LDL being increased by 1.9−2.1 characterized by a high level of cholesterol in the blood, is one mg/dL and HDL cholesterol being increased by 0.40−0.44 of the major risk factors for CHD. For years, it has been mg/dL, so that the ratio of LDL/HDL remains unchanged. A recommended by government authorities to avoid highmajor source of dietary cholesterol among adults in China is cholesterol foods to maintain a normal blood cholesterol from egg (∼55%), pork (∼20%), and fish and shellfish (∼9%). concentration, but those days may be coming to an end. In Because eggs are relatively high in cholesterol and low in 2015, the recommendation on the dietary cholesterol limit was saturated fat and contain no trans fat, they have served as a removed from the American Dietary Guidelines and the vehicle for delivering cholesterol in many clinical trials. Results Japanese Dietary Guidelines. In 2016, the Chinese Dietary of these trials have proven that consumption of 1−2 eggs per Guidelines also dropped the recommendation on the day (200−400 mg of cholesterol) has little or slight effect on plasma cholesterol and is unlikely to have substantial overall cholesterol intake limit. Such withdrawals of the dietary impact on the risk of CHD or stroke among healthy men and cholesterol limit have caused serious concern among both the women.7,8 However, among individuals with type 2 diabetes, public and scientific community. Do we no longer need to increased egg intake is associated with CHD risk.9 worry about cholesterol in our diet? To address this question, Why does dietary cholesterol have a slight effect on plasma this viewpoint will briefly discuss (i) the relationship between cholesterol? First, humans synthesize most cholesterol, almost blood cholesterol and cardiovascular diseases and (ii) the effect up to 3 times the amount from diet. In adult humans of dietary cholesterol and major dietary components on plasma consuming a typical Western diet, about 800−900 mg of cholesterol. cholesterol is synthesized daily, while about 300 mg comes The higher the concentration of plasma total cholesterol from the diet (Figure 1).10 Second, the pathway for (TC), the greater the risk of CHD. This positive link between synthesizing cholesterol is well-regulated by a feedback plasma TC and CHD has been supported by numerous animal 1,2 inhibition mechanism on 3-hydroxy-3-methylglutaryl coenzyme and clinical studies. Because cholesterol is insoluble, it is A (HMG-CoA) reductase, which catalyzes the rate-limiting step transported in plasma by carriers known as lipoproteins. There of cholesterol biosynthesis. Hepatic HMG-CoA reductase is are two main types of lipoproteins, namely, high-density efficiently downregulated by dietary cholesterol. Thus, the body lipoprotein (HDL) and low-density lipoprotein (LDL). HDL can maintain cholesterol homeostasis by up- or downregulating cholesterol is referred to as a “good” cholesterol (reference hepatic HMG-CoA reductase to synthesize much or less value of >50 mg/dL), because it helps to remove excess cholesterol from the arteries and other tissues back to the liver. LDL cholesterol is referred to as a “bad” cholesterol (reference Received: October 17, 2017 Published: November 14, 2017 value of
