Effects of meal frequency and snacking on food demand in mice

Abstract

Ad libitum feeding patterns in mice show substantial differences between laboratories, in addition to large individual and time-of-day differences. In the present study, we examine how mice work for food when access to food is temporally restricted and so they are forced to take discrete meals. In a first experiment, separate groups of ICR:CD1 mice were given access to food for 4, 8 or 16 opportunities or meals per day, with the duration of access at each opportunity adjusted reciprocally so that the total time of availability was 160 min per day in all three conditions. During the periods of availability, mice were able to earn food pellets by nose poke responses, according to an incrementing series of fixed unit prices (FUP: 2,5,10,25) with each schedule in force for 3-4 days. Total food intake was similar in all three groups, indicating that mice generally were able to adjust their intake to a range of temporal availabilities. In each group, food demand fell as FUP increased. In the 8 and 16 meal groups, no food was eaten in many of the opportunities. Within an opportunity, the rate of intake generally declined with time, indicative of satiation. At low FUPs, later opportunities in each day were associated with smaller meals than earlier opportunities; in contrast, at high FUPs the first opportunity was also a small meal. Collectively, these results show that mice eat less at higher costs but not because of time constraints of the schedule: instead, they exhibit an elective anorexia. In the second experiment, we examined whether snacking between imposed meals would affect subsequent meal(s). Mice were adapted to the foregoing 8 opportunity protocol. Then, half the mice received free snacks of sugar cubes after the 3rd, 4th and 5th meal opportunities and the intakes of sugar and pellets were examined at low and high unit costs for pellets (FUP 2 and 25). At FUP2, mice decreased demand for pellets and compensated energetically for the sugar they consumed. At FUP25, mice also decreased demand, but by less than the energy obtained from sugar. These data show that choice for pellets over a free palatable snack, and subsequent compensation of energy intake, is modified by effort and demand.

Eating Frequency, Food Intake, and Weight: A Systematic Review of Human and Animal Experimental Studies

“…For the five studies, the number of feeding occasions in the EF manipulations varied greatly, ranging from 1 to 24 feeding occasions per day, and the experimental period ranged from 3 to 28 days ( 35 – 39 ). Of the three studies reporting on intake, all found no significant difference in consumption between EF conditions ( 36 , 37 , 39 ). Of the four studies reporting on body weight, three found no significant difference between EF conditions, and one found significantly less body weight gain in the higher EF condition ( 35 , 36 , 38 , 39 ).…”

“…Of the three studies reporting on intake, all found no significant difference in consumption between EF conditions ( 36 , 37 , 39 ). Of the four studies reporting on body weight, three found no significant difference between EF conditions, and one found significantly less body weight gain in the higher EF condition ( 35 , 36 , 38 , 39 ). Cardiometabolic/hormonal measures taken varied between studies, but insulin and insulin-like growth factor-1 were measured in two studies, with inconsistent outcomes found (one study found significantly higher insulin in the higher EF condition, while the other study found significantly lower insulin in the higher EF condition; one study found significantly higher insulin-like growth factor-1 in the higher EF condition, while the other study found no difference among the EF conditions) ( 38 , 39 ).…”

“…As a whole, the reviewed experimental studies provide little support that increasing EF influences intake or body weight. Out of the 13 studies that reported on a measure of consumption, 8 (61.5%) found no significant effect of EF ( 20 , 23 , 26 , 28 – 30 , 32 , 36 , 37 , 39 , 40 , 42 , 43 ). Seventeen studies reported on body weight or BMI, with 11 studies (64.7%) finding no significant effect of EF ( 21 , 22 , 24 – 27 , 31 , 33 – 36 , 38 – 42 , 44 ).…”

The motivation for exercise over palatable food is dictated by cannabinoid type-1 receptors

“…Although such an exposure always occurred during the active phase of the nycthemeral cycle, it by no means fully recapitulates the human condition where reward choices are permanent. One means to circumvent this limit might consist of housing the animals in operant chambers (46) with permanent choices between wheel running and feeding. Our future experiments, aimed at focusing on this paradigm, will surely help to refine the present results.…”

Effects of Incentives and Genetics on Food Choices and Weight Phenotypes in the Neuroendocrine Gene Tubby Mutant Mice

“…Also, as with operant chamber studies from other investigators, a similar "N" was used, with similar statistical power (e.g. [43,44]). We furthermore found results in the mouse model very consistent with what has been observed in human populations.…”