Physiology& Behavior,Vol. 49, pp. 639--642.©PergamonPresspic, 1991. Printedin the U.S.A.
0031-9384/91 $3.00 + .00
BRIEF COMMUNICATION
Effects of Treadmill Exercise on Weight Cycling in Female Mice P. E. WAINWRIGHT, J. R A N D A L L SIMPSON, R. CAMERON, L. H O F F M A N - G O E T Z , D. W I N F I E L D , D. M c C U T C H E O N A N D M. MACDONALD
Department of Health Studies, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada Received 14 M a y 1990
WAINWRIGHT, P. E., J. RANDALL SIMPSON, R. CAMERON, L. HOFFMAN-GOETZ, D. WINFIELD, D. McCUTCHEON AND M. MACDONALD. Effects of treadmill exercise on weight cycling in female mice. PHYSIOL BEHAV 49(3) 639--642, 1991.--Weight cycling increases food efficiency and rate of weight regain. This study induced weight loss in adult female B6D2FI mice via dietary energy restriction and exercise to determine whether the weight loss regimen influenced rate of weight regain. Four groups of animals were studied: RES, restricted (food restricted); EX, exercised(treadmill exercised); SC, sham control (treadmill exposure, not exercised); LC, /ab chow control (appropriately aged control). Both EX and SC voluntarily reduced food intake to the level of the RES animals. The RES group showed increased food efficiency and rate of weight regain relative to the LC group; this effect was attenuated in both the EX and SC groups. These findings demonstrate that a) the cycling phenomenon occurs in mice, and b) stressors such as forced exercise or exposure to a novel environment can modify the pattern of food efficiency and rate of weight regain engendered by dietary restriction. Obesity
Weight cycling
Forced treadmill exercise
Metabolic efficiency
'WEIGHT cycling' or 'yo-yo dieting' in humans refers to the observation that chronic dieters regain weight more easily and lose weight with more difficulty with successive cycles of weight loss and gain (3,9). Repeated cycles of weight gain and loss have been studied most rigorously using animal models. Rats, cycled through two sessions of caloric restriction and refeeding, develop increased food efficiency which impaired weight loss and enhanced weight regain (4). The increased food efficiency is not a function of age (2), but is rather a consequence of alterations in physiological processes (4). Specific factors may include decreased metabolic rate (9) and alterations in body mass and composition (6). Previous animal studies have induced weight loss through food restriction. Hence, weight loss per se and food restriction have been confounded. Exercise which increases basal metabolic rate [reviewed in (10)], and changes body composition (1), may counteract some of the effects of food restriction. This study explored differences in the effects of weight loss by forced treadmill exercise vs. caloric restriction. We hypothesized that weight loss based on exercise would result in lower food efficiency and slower weight regain than that based on dietary restriction.
Psychological stress
male B6D2F 1 mice (Charles River Breeding Laboratories, Quebec), which had borne one litter at four months of age. They were housed under standard conditions [described in (12)].
Des~n There were four experimental groups and three phases: phase 1 (weight gain), phase 2 (weight loss), and phase 3 (weight regain). Initially the animals were assigned randomly, in the ratio of 3:1, to either the weight gain condition or the lab chow control condition. After six weeks on an obesity-promoting diet (phase 1), the percent obesity of the former group {[(obese weight -
initialwt)/initialwt] x I00}, was calculated.Animals 20%--65% obese were stratifiedby percent obesity and assigned randomly, by stratum, to one of three groups, resulting in animals being matched by percent obesity across groups. The groups were: 1) RES (food restricted), 2) EX (exercised on treadmill), 3) SC (sham control, i.e., treadmill exposure, but no exercise). Following weight loss (phase 2), these groups were allowed to regain weight (phase 3). At this point the lab chow control group, 4) LC, underwent an initial period of weight gain, thereby providing an age-matched, untreated control group. LC animals which had lost any weight at the end of phase 1 were excluded from the study; during phase 3 those remaining gained weight to the levels attained in the cycled groups, supporting a comparable selection of animals in all groups. Body weight was measured throughout;
METHOD
Subjects Subjects were genetically homogeneous, seven-month-old re-
639
640
WAINWRIGHT ET AL,
TABLE 1 BODY WEIGHTCHANGESAND FOOD INTAKEOF B6D2F~ FEMALEMICE DURINGPHASE 2 (LOSS)AND PHASE 3 (REGAIN)* RES n=ll
EX n=ll
SC n=9
Weight change (adj) (g) Phase 2 (Loss) Phase 3 (Regain)
9.5 "x _ 0.6 9.2 a - 0.5
9.0 a • 0.6 8.5" _+ 0.5
7.9 ay ± 0.6 6.8 b --- 0.6
Days (adj) Phase 2 (Loss) Phase 3 (Regain)
26.1 --_ 2.9 16.8a __ 4.4
32.6 _+ 2.9 26.6 ~ - 4.4
---
Rate (g/day) Phase 2 (Loss) Phase 3 (Regain) Food intake (adj) Phase 2 (Loss) (Daily Av. % of LC kcal) Phase 3 (Regain) (kcal/day) Efficiency (g wt. gain/kcal)
0.37 -+ 0.02 0.84 a -+ 0.14
0.36 _-. 0.06 0.45 b _ 0.11
0.32 __. 0.06 0.36 b _-. 0.07
58.1 a __ 2.6
63.0
--- 2.6
67.7 b --- 2.9
20
19
-+ 1
20
__ 1
0.04 a __ 0.006
0 . 0 2 b -- 0 . 0 0 4
• 1
0.02 b -- 0.003
LC n=ll
---+ 0.6 9.2 a --- 0.5 0.2 b
-39.9 b -- 4.4
0.23 b -+ 0.02
19
-- 1
0.01 b -- 0.001
*Values represent means -~ SEM, (adj) = values adjusted using percent obesity as covariate. Means with different superscripts in a row are significantly different (/7
0031-9384/91 $3.00 + .00
BRIEF COMMUNICATION
Effects of Treadmill Exercise on Weight Cycling in Female Mice P. E. WAINWRIGHT, J. R A N D A L L SIMPSON, R. CAMERON, L. H O F F M A N - G O E T Z , D. W I N F I E L D , D. M c C U T C H E O N A N D M. MACDONALD
Department of Health Studies, University of Waterloo, Waterloo, Ontario, N2L 3G1, Canada Received 14 M a y 1990
WAINWRIGHT, P. E., J. RANDALL SIMPSON, R. CAMERON, L. HOFFMAN-GOETZ, D. WINFIELD, D. McCUTCHEON AND M. MACDONALD. Effects of treadmill exercise on weight cycling in female mice. PHYSIOL BEHAV 49(3) 639--642, 1991.--Weight cycling increases food efficiency and rate of weight regain. This study induced weight loss in adult female B6D2FI mice via dietary energy restriction and exercise to determine whether the weight loss regimen influenced rate of weight regain. Four groups of animals were studied: RES, restricted (food restricted); EX, exercised(treadmill exercised); SC, sham control (treadmill exposure, not exercised); LC, /ab chow control (appropriately aged control). Both EX and SC voluntarily reduced food intake to the level of the RES animals. The RES group showed increased food efficiency and rate of weight regain relative to the LC group; this effect was attenuated in both the EX and SC groups. These findings demonstrate that a) the cycling phenomenon occurs in mice, and b) stressors such as forced exercise or exposure to a novel environment can modify the pattern of food efficiency and rate of weight regain engendered by dietary restriction. Obesity
Weight cycling
Forced treadmill exercise
Metabolic efficiency
'WEIGHT cycling' or 'yo-yo dieting' in humans refers to the observation that chronic dieters regain weight more easily and lose weight with more difficulty with successive cycles of weight loss and gain (3,9). Repeated cycles of weight gain and loss have been studied most rigorously using animal models. Rats, cycled through two sessions of caloric restriction and refeeding, develop increased food efficiency which impaired weight loss and enhanced weight regain (4). The increased food efficiency is not a function of age (2), but is rather a consequence of alterations in physiological processes (4). Specific factors may include decreased metabolic rate (9) and alterations in body mass and composition (6). Previous animal studies have induced weight loss through food restriction. Hence, weight loss per se and food restriction have been confounded. Exercise which increases basal metabolic rate [reviewed in (10)], and changes body composition (1), may counteract some of the effects of food restriction. This study explored differences in the effects of weight loss by forced treadmill exercise vs. caloric restriction. We hypothesized that weight loss based on exercise would result in lower food efficiency and slower weight regain than that based on dietary restriction.
Psychological stress
male B6D2F 1 mice (Charles River Breeding Laboratories, Quebec), which had borne one litter at four months of age. They were housed under standard conditions [described in (12)].
Des~n There were four experimental groups and three phases: phase 1 (weight gain), phase 2 (weight loss), and phase 3 (weight regain). Initially the animals were assigned randomly, in the ratio of 3:1, to either the weight gain condition or the lab chow control condition. After six weeks on an obesity-promoting diet (phase 1), the percent obesity of the former group {[(obese weight -
initialwt)/initialwt] x I00}, was calculated.Animals 20%--65% obese were stratifiedby percent obesity and assigned randomly, by stratum, to one of three groups, resulting in animals being matched by percent obesity across groups. The groups were: 1) RES (food restricted), 2) EX (exercised on treadmill), 3) SC (sham control, i.e., treadmill exposure, but no exercise). Following weight loss (phase 2), these groups were allowed to regain weight (phase 3). At this point the lab chow control group, 4) LC, underwent an initial period of weight gain, thereby providing an age-matched, untreated control group. LC animals which had lost any weight at the end of phase 1 were excluded from the study; during phase 3 those remaining gained weight to the levels attained in the cycled groups, supporting a comparable selection of animals in all groups. Body weight was measured throughout;
METHOD
Subjects Subjects were genetically homogeneous, seven-month-old re-
639
640
WAINWRIGHT ET AL,
TABLE 1 BODY WEIGHTCHANGESAND FOOD INTAKEOF B6D2F~ FEMALEMICE DURINGPHASE 2 (LOSS)AND PHASE 3 (REGAIN)* RES n=ll
EX n=ll
SC n=9
Weight change (adj) (g) Phase 2 (Loss) Phase 3 (Regain)
9.5 "x _ 0.6 9.2 a - 0.5
9.0 a • 0.6 8.5" _+ 0.5
7.9 ay ± 0.6 6.8 b --- 0.6
Days (adj) Phase 2 (Loss) Phase 3 (Regain)
26.1 --_ 2.9 16.8a __ 4.4
32.6 _+ 2.9 26.6 ~ - 4.4
---
Rate (g/day) Phase 2 (Loss) Phase 3 (Regain) Food intake (adj) Phase 2 (Loss) (Daily Av. % of LC kcal) Phase 3 (Regain) (kcal/day) Efficiency (g wt. gain/kcal)
0.37 -+ 0.02 0.84 a -+ 0.14
0.36 _-. 0.06 0.45 b _ 0.11
0.32 __. 0.06 0.36 b _-. 0.07
58.1 a __ 2.6
63.0
--- 2.6
67.7 b --- 2.9
20
19
-+ 1
20
__ 1
0.04 a __ 0.006
0 . 0 2 b -- 0 . 0 0 4
• 1
0.02 b -- 0.003
LC n=ll
---+ 0.6 9.2 a --- 0.5 0.2 b
-39.9 b -- 4.4
0.23 b -+ 0.02
19
-- 1
0.01 b -- 0.001
*Values represent means -~ SEM, (adj) = values adjusted using percent obesity as covariate. Means with different superscripts in a row are significantly different (/7
