Much of the fatty acids used by the body is supplied by the diet, excessive amounts of carbohydrates and protein obtained from the diet can be converted to fatty acids and stored as triglycerides. Fatty acid synthesis occurs mainly in the liver and mammary glands, and to a lesser extent in adipose tissue and kidney, the process incorporates acetyl CoA carbons into the forming fatty acid chain using ATP and NADPH.

The acetyl portion of acetyl CoA is transported to cytosol as citrate, produced by condensation of oxaloacetate and acetyl CoA, the first reaction of the citric acid cycle, this occurs when the concentration of mitochondrial citrate is high, observed when there is a high concentration of ATP and isocitrate dehydrogenase is inhibited. The increase of citrate and ATP favors the synthesis of fatty acids, since this pathway needs both. Acetyl CoA should be converted to malonyl CoA. Carboxylation is catalyzed by acetyl CoA carboxylase and requires ATP, this reaction is the regulated step in fatty acid synthesis: it is inactivated by products, malonyl CoA and palmitoyl CoA, and activated by citrate, another regulatory mechanism is reversible phosphorylation of enzyme, which makes it inactive due to the presence of adrenaline / glucagon

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