Selective Consumption of Fish Oil at End of the Day Increases the Physiological Fatty Acid Compositions of Eicosapentaenoic Acid and Docosahexaenoic Acid in Mice

Abstract

Diets with high daily fat consumption are associated with excess weight. However, the effects of fat type and consumption timing on excess weight remain unclear. We investigated the selection of a 30% (w/w) fat diet of soybean oil (SOY), lard (LARD), and fish oil (FISH) on the metabolic parameters of mice. Male C57BL/6 mice were divided into the double SOY-box (w-SOY), SOY-box/LARD-box (SOY-vs-LARD), or SOY-box/FISH-box (SOY-vs-FISH) groups and allowed to selectively consume for 8 weeks. The total energy intake was similar for all groups, but the mice selectively chose to consume LARD over SOY and SOY over FISH. Body weight in the SOY-vs-LARD group was significantly higher than that in the w-SOY and SOY-vs-FISH groups. Additionally, minimal but selective consumption of an omega-3 fatty-acid-rich FISH diet at the end of the active period increased the physiological fatty acid compositions of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in the SOY-vs-FISH group; their metabolic parameters were also lower than the SOY-vs-LARD group. In conclusion, selectively consuming small amounts of fish oil at the end of the day may prevent excess weight compared with LARD consumption.

Keywords: high-fat diet; mice; omega-3/omega-6 ratio; overweight; selectivity.

Figure 1

Selectivity for high-fat diets composed of different fat sources in the two-diet-box choice test. Mice were given two diet boxes per cage: either two 30% (w/w) soybean-oil-based high-fat (SOY) diet boxes (w-SOY); a SOY-diet box and a 30% (w/w) lard-based high-fat (LARD) diet box (SOY-vs-LARD); or a SOY-diet box and a 30% (w/w) fish oil-based high-fat (FISH) diet box (SOY-vs-FISH). The mice were permitted free access to deionized water and both diet boxes. (a) Intake of each diet box was measured. (b) Intake from both diet boxes was summed to yield the total daily food intake. Data are shown as the mean ± SD (n = 3). * p < 0.01 vs. SOY diet box.

Figure 2

Effects of selectivity for high-fat diets composed of different fat sources on diurnal food intake rhythms. Mice were given two diet boxes: (a) w-SOY; (b) SOY-vs-LARD; and (c) SOY-vs-FISH. Food intake was averaged every 2 h (n = 3) for 48 h. ○, SOY; ■, LARD; ▲, FISH; dashed line, sum intake. * p < 0.01 vs. SOY diet group.

Figure 3

Effects of selectivity for high-fat diets composed of different fat sources on body weight gain. Mice were given two diet boxes: (○) w-SOY; (■) SOY-vs-LARD; and (▲) SOY-vs-FISH. Data are shown as the mean ± SD (n = 9). * p < 0.01 vs. w-SOY and # p < 0.01 vs. SOY-vs-LARD group.

Figure 4

Effects of selectivity of high-fat diets composed of different fat sources on fatty acid compositions in the plasma (a) and liver (b). w-SOY (□), SOY-vs-LARD (■) and SOY-vs-FISH (■). Data are shown as the mean ± SD (n = 9). * p < 0.01 vs. w-SOY group; # p < 0.01 vs. SOY-vs-LARD group.

Figure 5

Preliminary experiments for checking the protocol used in this study. After 1 week acclimation, two-diet-box choice test was carried out. Mice were given two different boxes per cage: either two 10% (w/w) soybean oil-based low-fat (LF) diet boxes (w-LF); or an LF-diet box and a 30% (w/w) soybean oil-based high-fat diet (SOY) diet box (LF-vs-SOY), and their food consumption (a) and body weight gain (b) were measured for 8 weeks (◇, w-LF group; ◆, LF-vs-SOY group). Data are shown as the mean ± SD (n = 9). No data significantly differed (p < 0.01, Tukey–Kramer test), indicating that our protocol is suitable for evaluation of two-diet-box selection.

Figure 6

Schematic of the experimental design. After 1 week of acclimation using a 10% soybean oil diet (low-fat diet), two-diet-box choice test was carried out. Mice were given two diet boxes per cage: either two 30% (w/w) soybean oil-based high-fat (SOY) diet boxes (w-SOY); a SOY-diet box and a 30% (w/w) lard-based high-fat (LARD) diet box (SOY-vs-LARD); or a SOY-diet box and a 30% (w/w) fish oil-based high-fat (FISH) diet box (SOY-vs-FISH). Food consumption for each cage, which was average of three mice, was measured 3 times per week during the 8-week experimental period. Each diet box was replaced every 3 days. Additionally, diurnal food intake patterns were analyzed at week 7. After 8 weeks of consumption, body mass index, blood biochemistry, organ weights, hepatic lipid levels, and fatty acid composition were analyzed.