Age-related increase in food spilling by laboratory mice may lead to significant overestimation of actual food consumption: implications for studies on dietary restriction, metabolism, and dose calculations

Abstract

It is widely accepted that food consumption in humans declines with advanced age; however, data from mice remain controversial. Based on our previous observation that mice spill a considerable amount of food while eating, we hypothesized that increased food spillage in old mice masks actual food intake. To investigate whether mice exhibit age-associated declines in food consumption, we evaluated the actual food consumption of C57BL/6 mice at various ages by measuring both the amount of food in the food receptacle and the amount dropped to the cage bottom during feeding. We found that old mice dropped significantly more food (36% ± 8%) than young mice (18% ± 5%), which led to overestimations of food consumption, particularly in old mice. Although actual food consumption decreased in very old mice, food intake per body weight did not significantly change. These findings suggest that caution should be taken to accurately quantify food consumption by aged animals.

Figure 1.

Food dropped to cage bottom. Representative picture showing that old mice (20–21 months old) drop more food to the cage bottom than mature adult mice (5–7 months old). Mice were housed individually, and photograph was taken 24 hours after mouse was placed in a new cage.

Figure 2.

Basic parameters measured daily for mice at various ages (adolescent 2 months, n = 9; mature adult 5–7 months, n = 13; middle-aged 11–13 months, n = 10; old 20–21 months, n = 10; and very old 29 months, n = 7) over a 5-day period. (A) Body weight. (B) “Apparent food consumed” is the amount of food that disappeared from the food receptacle in a 24-hour period. (C) “Food dropped” is the amount of powdered food dropped through the wire bottom, which accumulated on the cage floor in a 24-hour period. Indicates statistically significant difference compared with 2-month-old mice. Indicates statistically significant difference compared with 5- to 7-month-old mice. #Indicates statistically significant difference compared with 11- to 13-month-old mice. §Indicates statistically significant difference compared with 20- to 21-month-old mice. *Indicates statistically significant difference as compared with all other groups. One, two, or three symbols indicate p < .05, .01, and .001, respectively.

Figure 3.

Actual food consumption of mice at various ages. (A) “Actual food consumed” is the amount of food that was actually eaten by the mouse in a 24-hour period. It is calculated by subtracting the food dropped from the apparent food consumed. Indicates statistically significant difference compared with 2-month-old mice. Indicates statistically significant difference compared with 5- to 7-month-old mice. #Indicates statistically significant difference compared with 11- to 13-month-old mice. §Indicates statistically significant difference compared with 20- to 21-month-old mice. One, two, or three symbols indicate p < .05, .01, and .001, respectively. (B) Actual food consumed per body weight per day is the actual food consumed adjusted for body weight. ***Indicates statistically significant difference as compared with all other groups (p < .001).

Figure 4.

Ratio of actual food consumed versus food dropped by mice at various ages; 100% equals apparent food consumed. ***Indicates statistically significant difference (p < .001) as compared with 2-, 5- to 7-, and 11- to 13-month-old mice for food dropped (black-colored symbols) and actual food consumed (white-colored symbols). For each age group, apparent food consumed and actual food consumed were significantly different (p < .01).

Figure 5.

Food consumption pattern of dietary-restricted mice. Mice (20 months, n = 5) on 20% dietary restriction do not eat all of the dropped food; 100% equals apparent food consumed. For each feeding group, apparent food consumed and actual food consumed were significantly different (p < .01). No significant (NS) difference was observed for food dropped or apparent food consumed between DR- and AL-fed mice on wire bottom or bedding, respectively. AL = ad libitum; DR = dietary restriction.