Dynamic effects of dietary protein restriction on body weights, food consumption, and protein preference in C57BL/6J and Fgf21‐KO mice

Abstract

Single‐case experimental designs (SCEDs) are rarely used in behavioral neuroscience despite their potential benefits. The current study used a SCED to evaluate the effects of dietary protein restriction in C57BL/6J and Fgf21‐knockout (KO) mice on body weight, food consumption, and protein preference and changes in those outcome measures were quantified using multilevel linear models. In C57BL/6J mice, rate of weight gain was lower and food consumption and protein preference higher during periods of low (4% kcal) protein diet feeding compared to periods of normal (18% kcal) protein diet feeding. In Fgf21‐KO mice, who do not produce the liver‐derived hormone FGF21, rate of weight gain and protein preference were not substantially affected by diet although food consumption was slightly higher during periods of low protein diet than periods of normal protein diet. These results demonstrate that protein restriction dynamically regulates physiological and behavioral responses at the individual mouse level and that FGF21 is necessary for those responses. Further, the current results demonstrate how a SCED can be used in behavioral neuroscience research, which entails both scientific and practical benefits.

Persistent Behavioral and Physiological Effects of Dietary Protein Restriction

“…Figure 2A depicts the average grams of each solution consumed on each day of each preference assessment in the Torres et al (2022) study. In the group of mice that started on the normal protein diet (Figure 2A, left panel, non-shaded area), mice consumed 4.6 – 7.1 grams of casein and 5.4 – 8.3 grams of maltodextrin solution across days of the first and second assessments, indicating a slight preference for maltodextrin.…”

“…We identified three studies in which preference for a protein vs. carbohydrate solution was evaluated during exposure to a normal protein diet and during exposure to a low protein diet in the same animals (Chiacchierini et al, 2021; Naneix et al, 2020; Torres et al, 2022). In the Torres et al (2022) study, one group of mice was exposed to 21 days with a normal protein (18% casein, by weight) diet (D11051801, Research Diets Inc, New Brunswick, NJ) followed by 28 days with a low protein (4% casein, by weight) diet (D11092301, Research Diets Inc). A second group of mice received 21 days exposure to the low protein diet followed by 28 days exposure to the normal protein diet.…”

“…Data from Dibattista and Holder (1998) and Naneix et al (2020) were extracted using the free PlotDigitizer web application ( PlotDigitizer ). Previously published data from our laboratory (Torres et al, 2022, Cohort 2) were re-analyzed and re-plotted to show amounts, in grams, of protein (casein) and carbohydrate (maltodextrin) solution consumed during each of four preference assessments. Data from Chiacchierini et al (2021) were downloaded from the corresponding author’s publicly available repository (McCutcheon, 2021) and converted into csv files using the Python programming language.…”

“…Data from DiBattista and Holder (1998) and Naneix et al (2020) were not analyzed statistically because individual animal data cannot be extracted from the relevant figures. Data from Torres et al (2022) were analyzed using a linear multilevel model in which amount of solution consumed, in grams, was the dependent variable and Solution (casein or maltodextrin; categorical, dummy-coded with casein as reference level), Diet (Low Protein or Normal Protein; categorical, dummy-coded with Normal Protein as the reference level), Group (Low Protein First or Normal Protein First; categorical, dummy-coded with Normal Protein First as the reference level), and Assessment number (1 or 2 within each diet; continuous) were used as predictors with all possible interactions included. Solution and Diet were also included as random effects at the individual mouse level.…”

“…For rodents, a balanced diet contains around 15-20% protein, by weight. Moderate dietary protein restriction to around 5-10%, by weight, induces physiological and behavioral changes including decreased body weight, increased energy expenditure, increased expression of Fgf 21 and increased circulating FGF21, increased consumption of low protein food, and increased preference for and consumption of protein-rich food sources (Chaumontet et al, 2019; Chiacchierini et al, 2021; Hill et al, 2017; Hill et al, 2019; Hill et al, 2020; Laeger et al, 2014; Murphy et al, 2018; Naneix et al, 2020; Torres et al, 2022; Volcko & McCutcheon, 2022; White et al, 2000a, 2000b; Zapata et al, 2019). Robust behavioral and physiological adaptations to dietary protein restriction are consistent with the idea of protein leverage, in which animals prioritize protein intake and will overeat other macronutrients to reach a protein target (Raubenheimer & Simpson, 2019; Simpson & Raubenheimer, 2005).…”