Limits to sustained energy intake XXVIII: Beneficial effects of high dietary fat on lactation performance in mice

Maximal animal performance may be limited by the ability of animals to dissipate heat; the heat dissipation limitation (HDL) theory. Since diets vary in the incidental heat produced during digestion (specific dynamic action, SDA), the HDL theory predicts lactating female mice consuming diets with lower SDA should have increased reproductive performance. Dietary fat has a lower SDA than dietary carbohydrate. Female mice were fed low (LF), medium (MF) or high fat (HF) diets (10%, 45% and 60% energy from fat respectively) from days 4-18 of lactation. HF and MF-fed mice weaned significantly heavier litters than LF mice. This was because they not only consumed more energy (metabolisable energy intake, E mei ; HF:306.5±25.0, MF:340.5±13.5 kJ d-1) at peak lactation, but also delivered more milk energy to their pups (milk energy output, E milk : 203.2±49.9, 229.3±42.2 kJ d-1 respectively) than the LF-fed mice (E mei =266.7±4.5, E milk =164.60±30.59 kJ d-1). This effect was greater than predicted from the SDA of the different diets combined with a mathematical model based on the HDL theory. Fatty acid profiles of the diets, milk and pups, showed significant correlations between the profiles. Besides reduced SDA, HF and MF-fed mice were probably able to directly transfer absorbed dietary fat into milk, reducing the heat production of lactogenesis, and enabling them to perform better than expected from the HDL model. In summary, HF and MF diets had beneficial effects on reproductive performance compared to the LF diet because they enabled mice to generate milk more efficiently with less incidental heat production.