Comparison of energy expenditure in genetically obese mouse strains using data expressed per mouse or adjusted for body weight (BW) or fat-free mass (FFM). The data shown are from studies performed by the Pennington Biomedical Research Center using indirect calorimetry (Columbus Instruments). The numbers in parentheses in
A indicate the number of animals used per genotype. Data were analyzed by two-way ANOVA, testing for significance of sex, genotype, and interactions.
A: Body composition (fat-free mass) of male and female wild-type (WT),
Mc4r−/− (Mc4r), and
Lepob/Lepob (Ob) mutant mice on the C57BL/6J background was measured using nuclear magnetic resonance (Bruker Minispec) (61). The effects of genotype were highly significant (*
P < 0.0001 between all groups); sex did not alter the effect of genotype on obesity. Fat-free mass was affected by genotype (
P < 0.0001) and sex (
P < 0.0001), with
Mc4r−/− mice having significantly more fat-free mass than wild-type and
Lepob/Lepob mice (#
P < 0.01), while male mice had greater fat-free mass irrespective of genotype. □, fat mass;

, fat-free mass.
B: When expressed per animal, TEE was increased by obesity (effect of genotype, *
P < 0.0001 vs. wild type; effect of sex,
P = 0.27).
C: Normalization of TEE by body weight or lean mass yielding different results. TEE expressed per gram of fat-free mass is significantly increased relative to control mice. ■, wild-type B6; ▨, B6.
Mc4r−/−; □, B6.
Lepob/Lep ob.