The Interrelationships of Carbohydrate and Lipid Metabolism

SummaryThis paper attempts to review the current state of knowledge on the interrelationships of carbohydrate and lipid metabolism in the domestic fowl. The aspects of metabolism reviewed include— 1. Pathway of carbon in de novo lipogenesis from carbohydrate substrates.2. Hyperlipogenesis from fructose.3. The effects of dietary lipid on lipogenesis and carbohydrate metabolism.4. The effects of feeding “carbohydrate-free” diets on metabolism.5. Changes in metabolism in relation to the pattern of food intake.6. Carbohydrate and lipid metabolism in relation to physiological state.Lipogenesis in the domestic fowl is very similar to that in the mono-gastric mammal except that in the fowl the liver, and not the adipose tissue, is the major site of lipogenesis. The effects of variation of the amounts and type of carbohydrate and lipid in the diet on the interrelationships of carbohydrate and lipid metabolism are largely what would be expected from the results of similar studies with mammalian species. There are however interesting quantitative differences in some metabolic steps between birds and mammals. The effects of the pattern of food intake on carbohydrate and lipid metabolism are similar in both avian and mammalian species. With the onset of sexual maturity and commencement of egg laying in the pullet there are great changes in the physiology of the bird. These physiological changes are accompanied by increases in the blood and liver lipid content. There is some evidence that hepatic lipogenesis from carbohydrate sources increases, when the bird comes into lay, to meet the requirement for lipid for egg production. However it has also been reported that the rates of hepatic lipogenesis in laying hens, cockerels and immature pullets are similar. The importance of lipogenesis from glucose in the laying hen requires further investigation.