Both Dietary Ratio of n-6 to n-3 Fatty Acids and Total Dietary Lipid Are Positively Associated with Adiposity and Reproductive Health in Zebrafish

Abstract

Background: Controversial findings have been reported in human and animal studies regarding the influence of n-6 (ω-6) to n-3 (ω-3) fatty acid ratios on obesity and health. Two confounding factors may be related to interactions with other dietary lipid components or sex-specific differences in fatty acid metabolism.

Objective: This study investigated main and interactive effects of total dietary lipid, ratio of n-6 to n-3 fatty acids, and sex on growth, adiposity, and reproductive health in wild-type zebrafish.

Methods: Male and female zebrafish (3 wk old) were fed 9 diets consisting of 3 ratios of n-6 to n-3 fatty acids (1.4:1, 5:1, and 9.5:1) varied within 3 total lipid amounts (80, 110, and 140 g/kg) for 16 wk. Data were then collected on growth, body composition (determined by chemical carcass analysis), and female reproductive success (n = 32 breeding events/diet over 4 wk). Main and interactive effects of dietary lipid and sex were evaluated with regression methods. Significant differences within each dietary lipid component were relative to the intercept/reference group (80 g/kg and 1.4:1 ratio).

Results: Dietary lipid and sex interacted in their effects on body weight (P = 0.015), total body length (P = 0.003), and total lipid mass (P = 0.029); thus, these analyses were stratified by sex. Female spawning success decreased as dietary total lipid and fatty acid ratio increased (P = 0.030 and P = 0.026, respectively). While total egg production was not associated with either dietary lipid component, females fed the 5:1 ratio produced higher proportions of viable embryos compared with the 1.4:1 ratio [median (95% CI): 0.915 (0.863, 0.956) vs 0.819 (0.716, 0.876); P < 0.001].

Conclusions: Further characterization of dietary lipid requirements will help define healthy balances of dietary lipid, while the sex-specific responses to dietary lipid identified in this study may partially explain sex disparities in the development of obesity and its comorbidities.

Keywords: body composition; diet-induced obesity; dietary lipid composition; reproductive health; zebrafish.

FIGURE 1

Main and interactive effects of TDL and RFA on terminal body mass and body composition in male and female zebrafish. Contour plots: (A) male body mass; (B) female body mass; (C) male total lipid mass; and (D) female total lipid mass. Table values represent parameter estimates from regression analysis. ^*,**Significant change from reference group (80 g/kg TDL or 1.4/1 RFA): *P < 0.05, **P < 0.01. NS, P > 0.05. adj., adjusted; RFA, ratio of n–6 to n–3 fatty acids; TDL, total dietary lipid.

FIGURE 2

Effects of total dietary lipid and ratio of n–6 to n–3 fatty acids on reproductive success in female zebrafish. (A, C) Boxplots for total egg production. (B, D) Boxplots for embryo viability (ratio of viable eggs/total eggs produced). Data are from successful breeding events and represent counts from individual events. Boxes represent the IQR of values (bottom, lower quartile/25th percentile; center bar, median value/50th percentile; top, upper quartile/75th percentile). Upper/lower whiskers signify values within 1.5 IQR of the upper/lower quartiles. Outliers (closed circles) and mean values (diamond markers) are also shown on plots. Differences from the reference group within each dietary lipid component were evaluated with zero-inflated regression analysis. ***Different from 1.4:1 ratio, P < 0.001. NS, P > 0.05.