Most of the cholesterol in the body is synthesized by the liver. Cholesterol synthesis is affected by various factors such as excessive fat & cholesterol intake, fat structure & composition, lack of dietary fiber, postprandial glucose levels, etc. Consumption of eggs was also positively associated with elevated cholesterol in the past. However, American Heart Association (2000) suggests that contrary to the popular belief, 1 or 2 eggs per day, as part of a balanced diet, do not contribute to high cholesterol levels. This was echoed by a small study conducted by Njike et al (2010) who also concluded that daily consumption of eggs did not affect serum cholesterol or other lipid profiles in a negative way.Five common dietary factors contributing to high cholesterol:-
1. Refined carbohydrates
As refined carbohydrates are rapidly digested to glucose, this provokes a high insulin response, which in turn, activates the synthesis and activity of an enzyme HMGCoA Reductase, involved in cholesterol synthesis (Ness & Chambers 2000 Benyon et al 2007).
2. Lack of fibre
Fibre-rich foods such as beans, lentils, vegetables, seeds, nuts, etc. are a good source of plant sterols & stanols, also known as phytosterols, which are plant cell membranes compounds with chemical structures similar to cholesterol. Consumption of plant sterols inhibit the intestinal absorption of cholesterol and can decrease LDL cholesterol (Malinowski & Gehret 2010).
3. Lack of oily fish in the diet
Oily fish (salmon, trout, sardines, mackerel, herring, anchovy, etc.) are rich in Omega 3 fatty acids, which help to lower LDL cholesterol by inhibiting triglycerides (TGCs) production (Holub 2009). Increased triglycerides are associated with greater formation of LDL cholesterol, as TGCs provide higher availability of Acetyl-CoA, a substrate for cholesterol synthesis (Bradley-Hillgartner et al 1995).
4. High saturated fats
Animal studies show that diets high in saturated fats (e.g. red meat & dairy products) also activate the liver enzyme HMG-CoA Reductase (Bradley-Hillgartner et al 1995), thus contributing to high cholesterol levels.
5. Trans fats
Trans fats (e.g. in processed foods such as crisps, cakes, biscuits, pastries, etc.) increase the synthesis of LDL cholesterol and lower HDL cholesterol twice as much as saturated fats (Clifton et al 2004). This makes trans fats particularly hazardous. A 2% increase in energy intake from trans fat has been associated with a 23% increase in cardiovascular risk (Remig et al 2010).
References:
American Heart Association (2000) An eating plan for healthy adults The new 2000 guidelines Our American Heart Association Diet Dallas TX
Benyon S Roach JO Lim MY (2007) Metabolism and Nutrition (3rd edition) Mosby
Bradley-Hillgartner F Salati LM Goodridge G (1995) Physiological and molecular mechanisms involved in nutritional regulation of fatty acid synthesis Physiological Reviews 75 47 -76
Clifton PM Keogh JB Noakes M (2004) Trans fatty acids in adipose tissue and the food supply are associated with myocardial infarction The Journal of Nutrition 134 7 1848
Holub BJ (2009) Docosahexaenoic acid (DHA) and cardiovascular disease risk factors Prostaglandins, Leukotrienes and Essential Fatty Acids 81 2-3 199-204
Malinowski JM Gehret MM (2010) Phytosterols for dyslipidemia American Journal of Hospital Pharmacy 67 14 1165-73
Ness GC Chambers CM (2000) Feedback and hormonal regulation of hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase: the concept of cholesterol buffering capacity Proceedings of the Society for Experimental Biology and Medicine 224 1 8-19
Njike V Faridi Z Dutta S Gonzalez-Simon AL Katz DL (2010) Daily egg consumption in hyperlipidemic adults-effects on endothelial function and cardiovascular risk Nutrition Journal Jul 2 9:28
Remig V Franklin B Margolis S Kostas G Nece T Street JC (2010) Trans fats in America: a review of their use, consumption, health implications, and regulation Journal of the American Dietetic Association 110 4 585-92
