[Thermogenesis from the breakdown of a ketogenic diet in an experimental model using swine]

A respiration calorimetry experiment with 10 matures sows was conducted to study the effect of a ketogenic diet on heat production and energy utilization. The ketogenic diet contained no carbohydrates and 85% of its energy as fat. The control diet was a mixed diet with most of its energy as carbohydrates. Both diets provided the same daily protein intake, which was slightly below the calculated protein requirement. The level of energy intake was adjusted to a moderate positive energy balance. Both diets were allocated to the same animal for three weeks each according to a crossover design. Seven-day collection periods and 48-hours measurements of the gaseous exchange (carbon-nitrogen balance method) were conducted on individual sows per diet. The ketogenic diet substantially increased the energy losses in faeces, which resulted in a energy digestibility of 75% compared to 93% with the mixed diet. The methane production was also significantly depressed. In contrast, the urine energy excretion was not influenced by the extremely high fat diet. The nitrogen balance showed lower faecal nitrogen losses and a higher urine nitrogen excretion in the animals with the high fat diet. Because of this compensative response no difference in nitrogen retention was observed between the two dietary treatments. The ketogenic diet caused no detrimental effects on thermogenesis or energy utilization. The results of both criteria could be fully explained by the well accepted ideas of the efficiency of utilization of the energy from fat under balanced nutrition conditions. Overall the results demonstrate that a high fat diet has no regulatory effect on the usually diet-induced thermogenesis.