Macronutrient Ratio Modification in a Semi-Purified Diet Composition: Effects on Growth and Body Composition of Juvenile Zebrafish Danio rerio

The interaction of dietary macronutrients in the control of growth, body composition, health, and longevity has received renewed attention. The protein leverage hypothesis proposes an inverse relationship between dietary protein levels and obesity development (low protein promoting high obesity), although the majority of laboratory studies have utilized a design modulating the protein amount within a single dietary protein source composition. We investigated whether varying the levels of dietary protein amount and sources would have impacts on growth and body composition using the Zebrafish Danio rerio model. At 28 d postfertilization, Zebrafish were fed 1 of 12 dietary treatments for 12 weeks. Diets contained different protein sources (fish protein hydrolysate [FPH], soy protein isolate [SOY], casein [CAS], or a mixture of all three sources including wheat gluten [MIX]). Sources were formulated at three protein concentrations (18, 33, or 48% as fed, substituted with wheat starch for caloric balance). Body length, height, and weight were measured over time and at termination. Contributions of macronutrients to growth and body fat outcomes were estimated by LASSO (least absolute shrinkage and selection operator) regression. Male and female length, height, and weight increased significantly in response to increasing dietary protein. Male and female fish fed SOY or FPH had the highest amount of body lipid at all protein concentrations relative to those fed CAS or MIX. Relative body lipid was highest in fish that were fed the lowest protein concentration. These data suggest an important role of macronutrient balances, including dietary protein amount and source, in relation to the protein: energy (carbohydrate and lipid) ratio on growth and body composition outcomes. These outcomes may ultimately reflect metabolic alterations that can lead to confounding interpretations of health and disease status. Furthermore, these data reinforce the need to consider and report dietary composition in establishing rigorous and reproducible nutritional guidelines for Zebrafish.