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Influence of Intermittent Fasting or Protein-free Feeding on Lipid Metabolism in Young Cockerels¹

Laboratory of Nutritional Biochemistry, Department of Animal Science, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801

The influence of intermittent fasting or protein-free feeding on several aspects of lipid metabolism was studied in young cockerels. Birds were subjected to one of three treatments: 1) feeding a protein-adequate diet ad libitum; 2) feeding a protein-adequate diet for 2 days followed by a protein-free diet for 1 day; 3) feeding a protein-adequate diet for 2 days followed by fasting for 1 day. Cockerels maintained on these schedules for 3 weeks were used to study liver lipid levels, in vitro fatty acid synthesis from acetate-1-¹⁴C and from glucose-U-¹⁴C, cholesterol synthesis from acetate-1-¹⁴C, and the activities of citrate cleavage enzyme and malic enzyme. The effect of these treatments on plasma cholesterol levels was also ascertained. The birds in treatment groups 2 and 3 generally had higher hepatic lipogenic capacities (except for birds in group 3 following the day of fast), enzyme activity levels and plasma cholesterol levels. The liver fat level was increased after ingestion of the protein-free diet for 1 day in birds of group 2 and after the first day of refeeding following the day of fast in group 3. The activity of malic enzyme changed significantly from day to day in cockerels of group 2. Following the ingestion of protein-free diets malic enzyme activities almost sevenfold higher than ad libitum control values were observed which dropped to about twice control values prior to the next period of protein-free feeding. The data presented suggest that hepatic fatty acid synthesis is regulated at two points: 1) in the conversion of glucose to acetyl CoA and 2) in the conversion of acetyl CoA to fatty acids. The conversion of glucose to acetyl CoA appears to be the more important point of regulation.

KEY WORDS: • chicken • fatty acid synthesis • liver • enzyme adaptation • periodicity of eating

¹ Supported in part by U. S. Public Health Service Research Grant no. HE-13245 from the Heart and Lung Institute and by the Illinois Agricultural Experiment Station.

² Present address: Department of Food Science and Human Nutrition, Michigan State University, East Lansing, Michigan 48823.

³ Present address: Department of Chemistry, Utah State University, Logan, Utah 84321.

Manuscript received 11 November 1971.