Moatt Joshua P, Hambly Catherine, Heap Elizabeth, Kramer Anna, Moon Fiona, Speakman John R, Walling Craig A
School of Biological Sciences Institute of Evolutionary Biology University of Edinburgh Edinburgh UK.
Institute of Biological and Environmental Sciences University of Aberdeen Aberdeen UK.
Ecol Evol. 2017 Oct 22;7(23):10056-10065. doi: 10.1002/ece3.3529. eCollection 2017 Dec.
Diet is an important determinant of fitness-related traits including growth, reproduction, and survival. Recent work has suggested that variation in protein:lipid ratio and particularly the amount of protein in the diet is a key nutritional parameter. However, the traits that mediate the link between dietary macronutrient ratio and fitness-related traits are less well understood. An obvious candidate is body composition, given its well-known link to health. Here, we investigate the relationship between dietary and body macronutrient composition using a first-generation laboratory population of a freshwater fish, the three-spine stickleback (). Carbohydrate is relatively unimportant in the diet of predatory fish, facilitating the exploration of how dietary protein-to-lipid ratio affects their relative deposition in the body. We find a significant effect of lipid intake, rather than protein, on body protein:lipid ratio. Importantly, this was not a result of absorbing macronutrients in relation to their relative abundance in the diet, as the carcass protein:lipid ratios differed from those of the diets, with ratios usually lower in the body than in the diet. This indicates that individuals can moderate their utilization, or uptake, of ingested macronutrients to reach a target balance within the body. We found no effect of diet on swimming endurance, activity, or testes size. However, there was an effect of weight on testes size, with larger males having larger testes. Our results provide evidence for the adjustment of body protein:lipid ratio away from that of the diet. As dietary lipid intake was the key determinant of body composition, we suggest this occurs via metabolism of excess protein, which conflicts with the predictions of the protein leverage hypothesis. These results could imply that the conversion and excretion of protein is one of the causes of the survival costs associated with high-protein diets.
饮食是与健康相关性状的重要决定因素，包括生长、繁殖和生存。最近的研究表明，蛋白质与脂质的比例变化，尤其是饮食中蛋白质的含量，是一个关键的营养参数。然而，介导饮食中宏量营养素比例与健康相关性状之间联系的性状却鲜为人知。鉴于身体组成与健康之间的众所周知的联系，一个明显的候选因素是身体组成。在这里，我们使用淡水鱼三刺鱼的第一代实验室群体，研究饮食和身体宏量营养素组成之间的关系。碳水化合物在掠食性鱼类的饮食中相对不重要，这便于探索饮食中蛋白质与脂质的比例如何影响它们在体内的相对沉积。我们发现，脂质摄入量而非蛋白质摄入量对身体蛋白质与脂质的比例有显著影响。重要的是，这不是由于按照饮食中宏量营养素的相对丰度吸收它们的结果，因为鱼体蛋白质与脂质的比例与饮食中的不同，通常身体中的比例低于饮食中的比例。这表明个体可以调节摄入的宏量营养素的利用或摄取，以在体内达到目标平衡。我们发现饮食对游泳耐力、活动或睾丸大小没有影响。然而，体重对睾丸大小有影响，体型较大的雄性睾丸也较大。我们的结果为身体蛋白质与脂质比例偏离饮食比例的调节提供了证据。由于饮食中脂质摄入量是身体组成的关键决定因素，我们认为这是通过过量蛋白质的代谢发生的，这与蛋白质杠杆假说的预测相矛盾。这些结果可能意味着蛋白质的转化和排泄是与高蛋白饮食相关的生存成本的原因之一。
