Calories homeostasis

SIRTl belongs to the mammalian sirtuin family of NAD -dependent histone deacetylases (HDAGs) [198, 199]. Targets known to be deacetylated by SIRTl include histone 4 (H4), NFkB, and p53 [198, 199]. Through its deacetylase activity, SIRTl is considered to control cellular metabolic homeostasis, and to play important roles in the regulation of gene expression, cell proliferation, differentiation, survival, and senescence [198, 199]. SERTl activation has been considered to play a crucial role in calorie-restriction-induced longevity in several species [200]. 

Contrary to previous beliefs, altering the amount of cholesterol ingested has only a minor effect on total plasma cholesterol concentration in most people. A study performed on over 80,000 female nurses found that increasing cholesterol intake by 200 mg for every 1000 calories in the diet did not appreciably increase the risk for heart disease. Because the body is well equipped with compensatory mechanisms to maintain cholesterol homeostasis, if a decrease in dietary cholesterol intake occurs, the biosynthesis of cholesterol increases, almost to a level to fully compensate for the decrease in cholesterol intake in contrast, when body has excess cholesterol, cholesterol biosynthesis decreases with a concomitant increase in cholesterol excretion pathways through biliary cholesterol and bile acids. 

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