Effects of nutrition on male reproductive health and ageing

Abstract

In this thesis, in Chapter 2 I presented a systematic review of studies that use the Nutritional Geometry Framework (NGF), revealing a lack of studies using NGF to investigate nutritional effects on male reproductive traits in mammals at different life stages. To address this knowledge gap, I conducted studies using NGF design in male C57BL/6J mice (Chapter 3 and 4). In Chapter 3, mice were fed 1 of 10 isocaloric (energy content: 14.7 MJ/kg) diets with different macronutrients ratios from 5 weeks of age. After 16-19 weeks of diet, mice were culled, and their body composition and reproductive characteristics were assessed. Sperm motility and antioxidant capacity were found to be positively correlated with the amount of dietary fat. In Chapter 4, the same treatment diets were used but not commenced until 12 weeks of age and male reproductive traits were assessed after 1, 6, 12, and 18 months of dietary treatment. Nutritional effects on male reproductive traits were found to change over time and differed from Chapter 3 where mice had been fed treatment diets during adolescence. In Chapter 5, calorie restriction (CR) was performed to investigate the effect of energy intake on male reproductive health across the lifespan. Three diet treatments with identical macronutrient ratios (64% carbohydrate, 21% protein and 15% fat) were used: control (ad libitum fed, energy density 14.7 MJ/kg), 20% CR (CR-F, 80% ration of control diet) and CR dilution (CR-D, ad libitum fed, energy density 10.5 MJ/kg). Mice were fed for the same time periods as Chapter 4. Although body composition and adiposity were significantly lowered by CR, male reproductive traits (sperm concentration, motility and testicular antioxidant capacity) were not significantly affected by CR, although age-related decline was observed. Overall, the findings of this thesis underscore the importance of considering macronutrient balance in studies examining dietary impacts on male reproductive health across the lifespan.