Body mass and behavior in Swiss mice subjected to continuous or discontinuous food restriction and refeeding

Food restriction (FR) is hypothesized to decrease body fat content of an animal and thus prevent obesity. However, the response of energy budget to a continuous (CFR) or discontinuous FR (DFR) remains inconsistent. In the present study, effects of CFR or DFR and refeeding on energy budget and behavior were examined in male Swiss mice. CFR significantly decreased the energy expenditure associated with basal metabolic rate (BMR) and activity behavior, but not sufficiently to compensate for energy deficit and thus resulted in lower body mass and fat content. DFR mice had a significantly higher food intake on ad libitum days and showed increases in BMR and activity after 4 weeks’ DFR, which might resulted in lower body mass and less body fat than controls. After being refed ad libitum, both CFR and DFR mice had similar body mass, BMR, and behavioral patterns to controls but had 95% and 75% higher fat content. This suggested that not only CFR but also DFR would be a significant factor in the process of obesity for animals that were refed ad libitum. It also indicated that food restriction interrupted many times by periods of ad libitum feeding had the same long-term effects like continuous underfeeding.     

The leptin-fat ratio is constant, and leptin may be part of two feedback mechanisms for maintaining the body fat set point in non-obese male Fischer 344 rats.

While plasma leptin and adiposity have been found to be strongly related, the specific nature of this relationship has yet to be clarified. Hence, plasma leptin and three indicators of adiposity were measured in adult male Fischer 344 rats on three different long-term diets: continuous ad libitum feeding; ad libitum feeding until early adulthood, then continuous 60% caloric restriction; and ad libitum feeding until early adulthood, then 60% caloric restriction until 16 months, then ad libitum feeding for 5 months. Body fat was found to be a good linear correlate of plasma leptin, with a zero Y-intercept, and a constant plasma leptin-body fat ratio. The number of adipocytes per rat and % body fat were strong quadratic correlates of plasma leptin. This study is the first to find a zero Y-intercept and constant plasma leptin-body fat ratio, probably because it is the first to simultaneously measure both plasma leptin and body fat accurately, and to account for confounders such as gender, genetic background, age, physical activity, and possibly obesity. The study also explored the effect of switching calorically-restricted rats to ad libitum feeding. This led to a rapid rise, and then synchronized up-down cycles in average daily food intake and body weight, with a steady upward trend toward a new stable body-weight set point. It is hypothesized that this pattern resulted from two simultaneous feedback mechanisms, possibly involving leptin. In conclusion, this study suggests that, under controlled conditions, the plasma leptin-body fat ratio is a constant for a particular mammalian strain, independent of dietary history.     

Influence of caloric restriction and exercise on tumorigenesis in rats

Underfeeding or caloric restriction have been shown to inhibit the growth of spontaneous, transplanted, or chemically induced tumors in rats and mice. At 40% caloric restriction, growth of 7,12-dimethylbenz(a)anthracene-induced mammary and 1,2-dimethylhydrazine-induced colonic tumors is inhibited significantly even when the restricted diet contains twice as much fat as the control diet. Some inhibitory effects become evident even at 10% caloric restriction. In studies involving high fat diets, we find that rats receiving 20% fat ad libitum exhibit significantly higher 7,12-dimethylbenz(a)anthracene-induced mammary tumor incidence, multiplicity, and weight than rats ingesting the same amount of fat daily, but in a diet containing 25% fewer calories. In a study of intermittent ad libitum and restrictive feedings, chemically induced tumorigenicity varies inversely with feed efficiency. Exercise has also been shown to inhibit tumor growth. Sedentary rats fed ad libitum have a 108% higher incidence of 1,2-dimethylhydrazine-induced colon tumors than rats fed ad libitum but subjected to vigorous treadmill exercise. Caloric flux (either reduced intake or increased outflow) appears to reduce tumorigenicity in rodents.     

Sexual Dimorphism in the Response of Adipose Mass and Cellularity to Graded Caloric Restriction

Objective: To investigate the effects of mild to moderate caloric restriction on parameters of body growth, fat mass, and adipose tissue cellularity in female and male Wistar rats. Research Methods and Procedures: Three‐month‐old female and male Wistar rats were subjected to a chronic, mild to moderate caloric restriction paradigm (5%, 10%, or 20% reduction in caloric intake from ad libitum values) for 6 months. This was accomplished using a unique automated feeder system tailored to the food consumption levels of individual rats. Body weight and length, weight of lean organs, regional adipose mass, and adipose cellularity were measured before and after the diet restriction. Results: Caloric restriction produced proportional decelerations in body weight increases in both genders, without significant changes in body length or lean organ mass. Marked and disproportional reductions in regional adipose tissue mass were produced at all levels of food restriction (even at 5% restriction). An unexpected finding was that in response to graded caloric restriction, female rats preserved adipose fat cell number at the expense of fat cell volume, whereas the converse was seen for male rats. Discussion: These studies demonstrate a sexual dimorphism in the response to mild to moderate degrees of chronic caloric restriction. At low levels of caloric restriction, it is possible to affect regional adipose mass and cellularity while preserving lean organ mass.     

Cold acclimation in food-restricted rats

Food intake, body weight and brown adipose tissue (BAT) mass and composition of rats exposed at 6 degrees C either with food ad libitum or food-restricted were compared with those of rats in the thermoneutral zone, with food ad libitum. Cold acclimation with food ad libitum increases food intake and prevents body weight gains. IBAT (interscapular BAT) increases its mass and changes its composition after 3 weeks of cold exposure. Cold acclimation with food restriction produces a progressive decrease in body weight. IBAT mass increases after 3 weeks but changes in composition occur sooner. It is concluded that the overfeeding that accompanies cold acclimation is not necessary for non-shivering thermogenesis in BAT.     

Photoperiod influences the critical caloric intake necessary to maintain reproduction among male deer mice (Peromyscus maniculatus).

The concept of critical day length is well established among rodents; reproductive function is maintained when day lengths are greater than some specific threshold. In addition to day length cues, seasonal breeding in deer mice can also be regulated by food availability. The caloric threshold necessary to support reproduction remains unspecified for seasonally breeding rodents. The present study examined the interaction between photoperiod and food availability on reproductive function in adult male deer mice (Peromyscus maniculatus). A critical caloric intake profile was constructed in long (16L:8D) and short (8L:16D) photoperiods; groups of deer mice in both photoperiods either received food ad libitum or 90, 80, or 70% of their individual ad libitum food intake for 10 wk. At autopsy, paired testes, epididymides, and seminal vesicles were removed and weighed. Body mass, total body fat, and total body water contents were also obtained. Short, as compared to long, day lengths inhibited the reproductive systems of male deer mice. However, food consumption interacted with photoperiod to affect reproductive function. Significant reductions in reproductive organ size as well as spermatogenic activity were observed among short-day mice after a 10% reduction in ad libitum food intake. Long-day animals required a 20% reduction in caloric intake to depress reproductive function. Body mass and total body water content were generally unaffected by either photoperiod or food consumption. Total body fat content was reduced in short- as compared to long-day mice. Individual reproductive responsiveness to short days increased as food availability decreased.(ABSTRACT TRUNCATED AT 250 WORDS)     

食物限制对雄性大绒鼠能量代谢特征的影响

为探讨横断山区大绒鼠适应食物匮乏的适应对策,将成年雄性大绒鼠随机分为自由取食组和饲喂正常摄食量的80% 限食组。测定了自由取食组和限食组雄性大绒鼠的体重、静止代谢率、非颤抖性产热以及体脂含量、血清瘦素含量、肝脏鲜重、褐色脂肪组织重量和消化道形态。结果显示:限食使雄性大绒鼠的体重、体脂含量、静止代谢率、非颤抖性产热、褐色脂肪组织重量和大肠、小肠长度显著降低,使盲肠内容物重量显著增加。血清瘦素含量与体重、体脂含量呈极显著正相关。在限食条件下,大绒鼠主要通过降低体重、基础代谢和产热的能量支出以及动用体内脂肪以应对食物资源短缺的环境条件,瘦素可能参与了能量代谢和体重的适应性调节。     

Leptin prevents obesity induced by a high-fat diet after diet-induced weight loss in the marsupial S. crassicaudata

The aims of this study were to determine in the marsupial Sminthopsis crassicaudata, the effects of leptin on food intake, body weight, tail width (a reflection of fat stores), and leptin mRNA, after caloric restriction followed by refeeding ad libitum with either a standard or high-fat preferred diet. S. crassicaudata (n = 32), were fed standard laboratory diet (LabD; 1.01 kcal/g, 20% fat) ad libitum fo 3 days. On days 4-10, animals received LabD at 75% of basal intake and then (days 11-25) were fed either LabD or a choice of LabD and mealworms (MW; 2.99 kcal/g, 30% fat); during this time, half the animals (n = 8) in each group received either leptin (2.5 mg/kg) or PBS intraperitoneally two times daily. On day 26, animals were killed and fat was removed for assay of leptin mRNA. At baseline, body weight, tail width, and food intake were similar in each group. After caloric restriction, body weight (P < 0.001) and tail width (P < 0.001) decreased. On return to ad libitum feeding in the PBS-treated animals, body weight and tail width returned to baseline in the LabD-fed animals (P < 0.001) and increased above baseline in the MW-fed animals (P < 0.001). In the LabD groups, tail width (P < 0.001) and body weight (P < 0.001) decreased after leptin compared with PBS. In the MW groups, the increase in tail width (P < 0.001) and body weight (P = 0.001) were attenuated after leptin compared with PBS. The expression of leptin mRNA in groups fed MW were greater in PBS than in leptin-treated animals (P < 0.05). Therefore, after diet-induced weight loss, leptin prevents a gain in fat mass in S. crassicaudata; this has potential implications for the therapeutic use of leptin.     

Changes in metabolite concentration in the plasma, liver and muscle of feed restricted Japanese quail exposed to cold.

Quail fed ad libitum and 50% ad libitum were cold exposed for several weeks, during time control quail remained at 21 degrees C. The concentration of plasma glucose, FFA, and uric acid, tissue glycogen and carcass fat content was measured at the end of the cold exposure period. Quail fed ad libitum showed no significant change in the levels of plasma and tissue metabolites, or the carcass fat content, following cold exposure. The feed consumption by the cold exposed quail increased, and the mean body weight showed little variation from that of the controls. Feed restricted quail which were cold exposed lost significantly more weight, and had a lower ranked fat content than their controls. Whereas feed restriction caused a lowering of the liver glycogen concentration in both treatment groups, muscle glycogen levels were higher than in quail fed ad libitum. However, cold exposure was not accompanied by a change in muscle and liver glycogen levels in feed restricted quail. Feed restricted quail at 21 degrees C were hypoglycaemic and hyperlipaemic compared to quail fed ad libitum, but cold exposed feed restricted quail had a much higher plasma glucose concentration than the controls. The ranked carcass fat content was inversely related to plasma FFA level in both control and cold exposed feed restricted quail. It is suggested that both a glycolytic and lipid mobilizing response to cold is obtained in quail whose body reserves are not spared from catabolism by adequate dietary nutrient absorption, and the possibility of gluconeogenesis from precursors produced by proteolysis is indicated.     

Effect of Chronic Caloric Restriction on the Synchronization of Various Physiological Measures in Old Female Fischer 344 Rats

-A variety of physiological and behavioral parameters which relate to metabolism were continuously monitored in 18 month old female Fischer 344 rats which were maintained on either ad libitum or reduced calorie diets. Caloric restriction (CR) stimulated average motor activity per day, the duration of each feeding episode, food consumed per episode, and water consumed per gram lean body mass (LBM). However, CR limited total food consumption, feeding time, number of feeding episodes per day, total eating and drinking time, and the daily ratio of food consumed to water consumed, CR also decreased average body temperature per day, O₂ consumption, CO₂, production, and respiratory quotient. A variety of parameters concerning water consumption were not affected. CR rats ate their food immediately when food was presented during the light span, while ad libitum fed animals ate numerous small meals throughout the entire dark span. An anticipatory response to restricted feeding was also noted. Total motor activity, metabolism, and body temperature increased just prior to scheduled feeding and reached maximum values shortly after feeding, suggesting that these parameters were highly synchronized to feeding. Females and males were found to respond to caloric restriction in a similar fashion. Dramatic changes in respiratory quotient and body temperature suggest rapid shifts between metabolic pathways (glycolysis to giuconeogenesis) to obtain optimal efficiency. Lower body temperature and metabolism may provide protection against DNA damage, thereby increasing the survival potential of restricted rats. These responses may provide insight into the mechanisms by which caloric restriction acts to extend life span.     

Adipose tissue and the effects of fat and calories on breast tumorigenesis in rats

A high fat diet fed ad libitum will promote breast tumorigenesis in rats while caloric restriction of the same high fat diet counteracts this promotional effect. The present study examined the effects of dietary fat and calorie intake on adipose tissue weight and fatty acid composition and on tumor incidence and development. The sites of adipose tissue chosen were the mammary fat pad, representing adipose tissue in the immediate location of the studied tumor, and the abdominal fat depot which in humans has been associated with an increased risk of breast cancer. High (20% corn oil) and low (5% corn oil) fat test diets were offered ad libitum and at 40% restriction levels. In agreement with prior studies, caloric restriction of both high and low fat diets led to marked decreases in tumor incidence (63 to 68% versus 21%), tumor burden (1.84 to 2.05 versus 0.37 to 0.43 tumors/rat), and tumor weight (7.1 to 11.9 versus 1.4 to 2.2 g) at the time of sacrifice (133 days post-DMBA). While final body weights were reduced in proportion to the level of caloric restriction (290 to 291 g versus 184 to 201 g), abdominal fat (8.8 to 9.2 versus 0.9 to 1.6 g), and mammary fat weights (3.1 to 4.1 versus 0.7 to 2.0 g) were reduced markedly in association with the decrease in tumorigenesis. While both tumor and mammary fat were enriched with linoleate reflecting the fatty acid composition of dietary fat, the ratio of arachidonic acid to linoleic acid was higher in tumor tissue than in surrounding normal mammary tissue in both the phospholipid (0.78 versus 0.18) and neutral lipid fractions (0.22 versus 0.03). These observations are consistent with the concept that increases in fat tissue mass in abdominal and mammary fat depots may mediate some of the promotional effects of high fat and high calorie diets. Restriction of dietary fat and calories to reduce body fat and strategies to modify the composition of stored lipids in fat depots may offer nutritional approaches to breast cancer prevention and treatment.     

Reduction of enhanced mammary carcinogenesis in LA/N-cp (corpulent) rats by energy restriction

Restriction of energy intake significantly reduces mammary tumorigenesis in normal rats exposed to carcinogens. Genetically obese LA/N-cp (corpulent) female rats were given 7,12-dimethylbenz[a]anthracene and fed purified diets ad libitum or restricted to 60% of the ad libitum caloric intake. Phenotypically lean littermates were also fed ad libitum. Obese animals developed large mammary tumors more rapidly than genetically normal rats so that 100% of the animals had tumors in less than 16 weeks. Only 21% of the lean animals developed tumors; the energy restricted obese animals had a tumor incidence of 27%. Although obese rats fed the restricted diet weighed significantly less than those fed ad libitum, percent body fat was not reduced, indicating that lean tissue was affected more. Obese animals were markedly hyperinsulinemic (1003 +/- 193 microunits/ml) and energy restriction reduced this to 328 +/- 41; the lean animals had insulin levels of 12 +/- 2. Tumor-bearing rats had higher insulin levels than rats without tumors. These data suggest that body fatness is not directly associated with risk of carcinogenesis. Lean body mass, adipose tissue mass, and their interaction with insulin in its capacity as a growth factor rather than body fatness per se may be determinants of tumor promotion.     

Sexually dimorphic responses to fat loss after caloric restriction or surgical lipectomy

White adipose tissue is the principal site for lipid accumulation. Males and females maintain distinctive white adipose tissue distribution patterns. Specifically, males tend to accumulate relatively more visceral fat, whereas females accumulate relatively more subcutaneous fat. The phenomenon of maintaining typical sex-specific fat distributions suggests sex-specific mechanisms that regulate energy balance and adiposity. We used two distinct approaches to reduce fat mass, caloric restriction (CR), and surgical fat removal (termed lipectomy) and assessed parameters involved in the regulation of energy balance. We found that male and female mice responded differentially to CR- and to lipectomy-induced fat loss. Females decreased energy expenditure during CR or after lipectomy. In contrast, males responded by eating more food during food return after CR or after lipectomy. Female CR mice conserved subcutaneous fat, whereas male CR mice lost adiposity equally in the subcutaneous and visceral depots. In addition, female mice had a reduced capability to restore visceral fat after fat loss. After CR, plasma leptin levels decreased in male but not in female mice. The failure to increase food intake after returning to ad libitum intake in females could be due to the relatively stable levels of leptin. In summary, we have found sexual dimorphisms in the response to fat loss that point to important underlying differences in the strategies by which male and female mice regulate body weight.     

Contribution of Different Mechanisms to Compensation for Energy Restriction in the Mouse

Objective: Restriction of energy intake produces weight loss, but the rate of loss is seldom sustained. This is presumed to be a consequence of compensatory reductions in energy expenditure, although the exact contributions of different components to the energy budget remain uncertain. We examined the compensatory responses of mice to a 20% dietary restriction. Research Methods and Procedures: We measured body mass, body fatness, body temperature, and the components of daily energy expenditure for 50 MF1 mice. Forty mice were then placed on a restricted diet at 80% of their ad libitum intake for 50 days. The remaining 10 mice continued to feed ad libitum. Ten days before the end of the restriction period, the same measurements were taken. Results: There were no significant differences between the control and restricted groups in any parameters before restriction. During the restriction period, body mass increased in both the control and restricted groups, but at a slower rate in the restricted mice. The control group increased in both fat and fat free mass; however, although the restricted group increased fat to the same extent as the controls, fat free mass increased to a lesser extent. The contributions of the different components of the expended energy to compensate for the reduced energy intake were energy deposition, 2.2%; resting metabolic rate, 22.3%; and activity, 75.5%. Discussion: Mice were able to compensate almost completely for the restricted energy intake that was achieved by altering the amount of energy required for each component of the energy budget except digestive efficiency.     

Regional Fat Pad Growth and Cellularity in Obese Zucker Rats: Modulation by Caloric Restriction

Objective : To investigate, in young obese male Zucker rats, the effects of chronic food restriction and subsequent refeeding on: 1) parameters of nonadipose and adipose growth, 2) regional adipose depot cellularity [fat cell volume (FCV) and number], and 3) circulating leptin levels. Research Methods and Procedures : Obese (fa/fa) and lean (Fa/?) male Zucker rats were studied from age 5 to 19 weeks. After baseline food intake monitoring, 10 obese rats were subjected to 58 days of marked caloric restriction from ad libitum levels [obese‐restricted (OR)], followed by a return to ad libitum feeding for 22 days. Ten lean control rats and 10 obese control rats were fed ad libitum for the entire experiment. All rats were fed using a computer‐driven automated feeding system designed to mimic natural eating patterns. Results : After food restriction, OR rats weighed significantly less than did lean and obese rats and showed a significant diminution in body and adipose growth as compared with obese rats. Relative adiposity was not different between obese and OR rats and was significantly higher than that of lean rats. The limitation in growth of the adipose tissue mass in OR rats was due mostly to suppression of fat cell proliferation because the mean FCV in each of the four depots was not affected. Serum leptin levels of OR and obese rats were not different from each other but were significantly higher than those of lean rats. Discussion : Marked caloric restriction affects obese male Zucker rats in a manner different from that of nongenetic rodent models (i.e., Wistar rats). In comparison with the response to caloric deprivation of Wistar rats, these calorically restricted obese male Zucker rats appeared to defend their relative adiposity and mean FCV at the expense of fat cell number. These findings indicate that genetic and/or tissue‐specific controls override the general consequences of food restriction in this genetic model of obesity.     

Effects of yo-yo diet, caloric restriction, and olestra on tissue distribution of hexachlorobenzene

Chlorinated hydrocarbons are lipophilic, toxic, and persistent in the environment and animal tissues. They enter the body in food and are stored in adipose tissue. Loss of body fat through caloric restriction mobilizes stored lipophilic xenobiotics and results in distribution to other tissues. We have studied the reversibility of this process in mice that followed a regimen of body weight cycling. Weight gain was followed by weight loss, a second gain, and a second loss ("yo-yo diet regimen"). We measured the distribution of orally gavaged [14C]hexachlorobenzene, which is sparingly metabolized. We found that weight cycling has different effects in different organs. Continued weight loss resulted in a threefold increase of 14C amount and concentration in the brain. After weight regain, 14C in the brain decreased but then increased again after a second weight loss. Weight loss resulted in an increase in the concentration of 14C in adipose tissue without changing the total amount in that tissue. Weight loss and regain resulted in an increase of 14C in the liver, which reflected an increase of fat in the liver. The regimen of weight gain and loss was repeated in mice gavaged with [14C]hexachlorobenzene, with one group receiving the nonabsorbable fat olestra in the diet. Combined dietary olestra and caloric restriction caused a 30-fold increase in the rate of excretion of 14C relative to an ad libitum diet or a reduced caloric diet alone. Distribution of 14C into the brain resulting from the restricted diet was reduced by 50% by dietary olestra.     

Prevention of mammary tumorigenesis by intermittent caloric restriction: does caloric intake during refeeding modulate the response?

Chronic caloric restriction (CCR) prevents mammary tumorigenesis in rodents, but a protective effect for intermittent caloric restriction (ICR) is less well documented. We recently reported that ICR reduced mammary tumor (MT) incidence of mouse mammary tumor virus-transforming growth factor (MMTV-TGF)-alpha mice to a greater extent than did CCR. Here, we repeated this protocol and obtained serum and tissue samples. Ad libitum (AL) MMTV-TGF-alpha mice were fed AIN-93M diet. Beginning at 10 weeks of age, ICR mice received isocaloric AIN-93M-mod diet (2-fold increases in protein, fat, vitamins, and minerals) at 50% of ad libitum for 3 weeks followed by 3 weeks refeeding with AIN-93M diet. CCR mice were pair-fed AIN-93M:AIN-93M-mod (2:1) matching intakes for restriction/refeeding cycles. Mice were sacrificed for MT size, at 79 (end of 12th restriction) or at 80 (1 week after 12th refeeding) weeks of age. AL and ICR-80 mice had heavier body weights than ICR-79 and CCR mice (P < 0.0001). Cumulative food intakes of ICR and CCR mice were reduced 12% and 15% versus AL mice (P < 0.0001). However, ICR mice consumed significantly (P < 0.0001) more food than did AL mice during refeeding. MT incidence was 84%, 13%, and 27% for AL, ICR, and CCR mice, respectively. MT weight (P < 0.0011) and number (P < 0.01) were higher for AL mice compared with ICR and CCR mice. AL and ICR-80 mice had similar serum IGF-I levels, but only AL values were higher than those of ICR-79 and CCR mice (P < 0.0017). ICR mice had more MT DNA breaks compared with AL and CCR mice, suggesting enhanced apoptosis (P < 0.02). AL mice had higher mammary fat pad ObR and ObRb leptin receptor mRNA expression than did ICR and CCR mice (P < 0.001), but there was no effect on MTs. These results confirm that ICR prevents development of MTs to a greater extent than does CCR, although "overeating" during refeeding may compromise this protection.     

Attenuation of plasma dyslipidemia and oxidative damage by dietary caloric restriction in streptozotocin-induced diabetic rats

Oxidative stress has been proposed as the pathogenic mechanism linking insulin resistance with endothelial dysfunction during diabetes. The present study investigated the attenuation of plasma dyslipidemia and oxidative damage by caloric restriction in experimental diabetes. Forty male Wistar rats were divided into ad libitum and calorie-restricted groups. The calorie-restricted group was subjected to 30% caloric restriction for 63 days before induction of diabetes to 50% of both groups. Caloric restriction significantly (p<0.01) reduced the body weights, reactive oxygen species (ROS), catalase, total cholesterol levels and non-significantly reduced SOD activities in non-diabetic and diabetic rats. Caloric restriction was also found to improve blood glucose levels, glycated hemoglobin, malondialdehyde, triglyceride, oxidized glutathione and reduced glutathione levels and significantly (p<0.05) increased GPx and GR activities in the experimental animals. The non-diabetic rats fed ad libitum had the most significant increases in body weight which could be due to dyslipidemia. These results indicate that dietary caloric restriction attenuates the oxidative damage and dyslipidemia exacerbated during diabetes as evidenced by the significant reduction in their body weights, ROS, total cholesterol levels and the increases in GPx activity and redox status.     

Prevention of Obesity in Middle-Aged Monkeys: Food Intake During Body Weight Clamp

Prevention of obesity and increase in longevity in obesity-prone rodents can be achieved by long-term moderate dietary restriction. In order to examine the likelihood that caloric restriction could have similar salutary effects in humans, rhesus monkeys, after reaching mature adult stature, were placed on a protocol to clamp or stabilize body weight by weekly caloric adjustment Further weight gain was prevented by this caloric titration procedure, and thus middle-age onset obesity, which is very common in this species, was prevented. The present study analyzed daily food intake for six weight-clamped monkeys and six ad libitum fed age-matched animals over a 3- year period, ages 18.5 to 21.5 years. After approximately 9 years of caloric restriction the daily calorie load to maintain stable adult body weight proved to be 40% less than the amount ingested by ad libitum fed animals. Calories per kg body weight did not differ significantly between the groups although the ad libitum fed animals were significantly fatter than the weight-clamped group. Prevention of obesity using this weight clamp protocol has also maintained lower insulin levels and higher glucose tolerance in the restricted animals.