Turning surplus carbohydrate into fatty acids
De novo lipogenesis is the synthesis of new fatty acids from non-fat precursors, mainly carbohydrate. When glucose is abundant, glycolysis and the pyruvate dehydrogenase reaction generate acetyl-CoA in the cytosol via citrate export. Acetyl-CoA carboxylase (ACC) converts acetyl-CoA to malonyl-CoA, the committed step, and fatty acid synthase (FAS) then assembles malonyl units into palmitate, a 16-carbon saturated fatty acid.
Palmitate can be elongated, desaturated, and esterified with glycerol into triglycerides for storage. Insulin and the transcription factors SREBP-1c and ChREBP upregulate this pathway when carbohydrate intake is high.
How large a role it plays in humans
In people eating typical mixed diets, de novo lipogenesis usually contributes only a small fraction of stored body fat; most dietary fat is stored directly. The pathway becomes more active under sustained carbohydrate surplus or overfeeding. This is general educational information about metabolism, not dietary advice; nutrition decisions should account for total energy balance and individual context.