Fats – cholestrol
Foods derived from both plants and animals contain sterols (include cholesterol, bile , vitamin D and some hormones), but only animal – derived foods contain significant amounts of cholesterol – meats, eggs, seafood, poultry, dairy products, glandular organs and fats.
There is confusion about dietary cholesterol and blood cholesterol. “Good” cholesterol is not a type of cholesterol found in foods, but it refers to the way the body transports cholesterol in the blood. The human body is not dependent on dietary sources for it’s cholesterol supply. It is synthesized in the liver and other tissues from simple two- carbon compounds such as acetyl coenzyme A.
The liver makes about 800 -1500mg of cholesterol/day, thus contributing much more to the body’s total than does the diet. The daily value of cholesterol from food is 300mg/day. Cholesterol’s harmful effects in the body occur when it ACCUMULATES in the artery walls and contributes to the formation of plaque. These plaque deposits leads to atherosclerosis. Although abnormally large concentrations of cholesterol in the blood are related to atherosclerosis, cholesterol is vital to a wide range of body functions.
Cholesterol is widely distributed in the body, especially in the nervous tissue, blood and bile. It occurs in free form or esterified with fatty acids. Free cholesterol is the chief constituent of gallstones. Cholesterol is the precursor of bile salts, steroid adrenal and sex hormones. In the skin, cholesterol is the precursor of Vitamin D – when the skin is exposed to sunlight, cholesterol is converted to active vitamin D. Cholesterol facilitates the absorption of fatty acids from the intestine and their transportation in the blood ( cholesterol combines with fatty acids, which is more soluble than the free fatty acid molecules).
BIOCHEMICAL ROLE of cholesterol:
Biochemically, it is a sterol and is classed as a steroid. It is closely related to other animal sterols:
7-dehydrocholesterol (precursor of vitamin D); dihydrocholesterol (in tissues); coprosterol (feces). Plantsterols are sitosterol and stigmasterol.
Cholesterol is the precursor of many steroids like: adrenal corticosteroids, vitamin D, saponins, cardiac glycosides, bile acids, male sex hormones and female sex hormones.
Adrenal corticosteroids consist of cortisone, cortisol, aldosterone and derivatives of cortisosterone. Compounds with vitamin D activity are vitamin D2 and D3., which are related to ergosterol and 7- dehydrocholesterol. Saponins are represented by digitonin (plant glycoside of a steroid). An important cardiac glycoside is digitoxigenin, which is related to the two drugs used in the treatment of cardiac disease: digitoxin and digoxin.
Bile acids and bile salts aid in the emulsification and absorption of lipids in the intestine. It also activates the lipase enzyme involved in the digestion of fats. The male sex hormones (androgens) are formed in the testes and develop the secondary sexual characteristics of the male beginning in puberty. The female sex hormones (estrogens and progesterone) are essential for the normal menstrual cycle, the development of the female sexual characteristics in the adult female and the alteration of the menstrual cycle during pregnancy.