Genetic variation in the murine lifespan response to dietary restriction: from life extension to life shortening

Chronic dietary restriction (DR) is considered among the most robust life-extending interventions, but several reports indicate that DR does not always extend and may even shorten lifespan in some genotypes. An unbiased genetic screen of the lifespan response to DR has been lacking. Here, we measured the effect of one commonly used level of DR (40% reduction in food intake) on mean lifespan of virgin males and females in 41 recombinant inbred strains of mice. Mean strain-specific lifespan varied two to threefold under ad libitum (AL) feeding and 6- to 10-fold under DR, in males and females respectively. Notably, DR shortened lifespan in more strains than those in which it lengthened life. Food intake and female fertility varied markedly among strains under AL feeding, but neither predicted DR survival: therefore, strains in which DR shortened lifespan did not have low food intake or poor reproductive potential. Finally, strain-specific lifespans under DR and AL feeding were not correlated, indicating that the genetic determinants of lifespan under these two conditions differ. These results demonstrate that the lifespan response to a single level of DR exhibits wide variation amenable to genetic analysis. They also show that DR can shorten lifespan in inbred mice. Although strains with shortened lifespan under 40% DR may not respond negatively under less stringent DR, the results raise the possibility that life extension by DR may not be universal.     

Diminished satiation in rats exposed to elevated levels of endogenous or exogenous cholecystokinin

Rats maintained on a high-fat (HF) diet exhibit reduced sensitivity to the satiation-producing effect of exogenous CCK. Because more CCK is released in response to HF meals than low-fat (LF) meals, we hypothesized that increased circulating CCK associated with ingestion of HF diets contributes to the development of decreased CCK sensitivity. To test this hypothesis, we implanted osmotic minipumps filled with either NaCl or CCK octapeptide into the peritoneal cavity. Subsequently, we examined the effect of intraperitoneal NaCl or CCK (0.5 microg/kg) injection on 30-min food intake. CCK significantly reduced 30-min food intake less in rats implanted with CCK-releasing minipumps compared with those with NaCl-releasing minipumps. Because dietary protein is a potent releaser of endogenous CCK, we hypothesized that rats adapted to a high-protein (HP) diet might also exhibit reduced sensitivity to exogenous CCK. Therefore, in a second experiment, we examined CCK-induced reduction of food intake in rats maintained on LF and rats maintained on HF or HP. Ingestion of LF stimulates very little endogenous CCK secretion, whereas both HF and HP markedly increase plasma CCK concentrations. Both doses of CCK reduced food intake significantly less in HF and HP rats compared with LF rats. There were no differences in 24-h food intake, body weight, or body fat composition among LF-, HF-, and HP-fed rats. These results are consistent with the hypothesis that sustained elevation of CCK either by infusion of exogenous CCK or by dietary-induced elevation of plasma CCK contributes to the development of reduced sensitivity to exogenous CCK.     

Orchiectomized Fischer 344 male rat models body composition in hypogonadal state

The hypogonadal state in men is accompanied by substantial decreases in muscle and bone mass and by an increase in adiposity. Most of the strains of orchiectomized (ORX) rat that have been used to model this state display substantial losses in bone, but only subtle changes in adiposity and muscle mass. In order to identify a rat model displaying a robust catabolic response to ORX, we studied three strains: Fischer 344 (F344), Brown Norway and Wistar. ORX caused a significant and sustained decrease in weight gained by F344, but only a trend toward reduced weight gain in Brown Norway rats and a modest reduction weight gain in Wistar rats that was significant only after 56days. ORX suppressed food intake in F344 rats, and to a lesser degree in Brown Norway and Wistar rats. ORX reduced muscle mass significantly in F344 rats, but not in Brown Norway or Wistar rats. ORX increased adiposity moderately in F344 rats and substantially in Wistar rats. ORX caused a marked reduction in prostate mass and increase in bone resorption in all three strains. Thus, F344 was the only strain in which ORX produced substantial decreases in food intake, body weight and muscle mass with increased adiposity and increased bone resorption. We conclude that the F344 rat displays a broad range of catabolic effects following ORX and is the best rat model for studying the androgenic pathway and strategies for reversing catabolic changes induced by hypogonadism.     

Measures of body size and growth in rhesus and squirrel monkeys subjected to long-term dietary restriction

Although many studies have reported the robust effects of dietary restriction (DR) in retarding numerous aging processes in rodents, little is known about the outcomes of reducing caloric intake of a nutritious diet on aging in primates. Most primate studies have concerned the effects of malnutrition. We hypothesized that DR influences aging processes in primate species as it does in rodents. In the present study, 24 male rhesus (Macaca mulatta) monkeys (ages 0.6–5 years) and 25 male squirrel (Saimiri sp.) monkeys (ages 0.3–10 years) were provided diets formulated differently for each species but both fortified with vitamins and minerals (40% above recommended levels) as controls (approximating ad libitum levels) or experimentals (about 30% below the level of diet provided controls of comparable age and body weight). The results reported here concern the hypothesis that DR imposed during various developmental stages in these two primate species would affect morphometric parameters obtained at different occasions during the first 5 years of the study. Groups of older monkeys (rhesus: 18–25 years, n = 3; squirrel: 10–15 years, n = 4) were also included as controls for comparative purposes. Among groups of rhesus monkeys begun on DR prior to 6 years of age, growth in body weight and crown-rump length was reduced about 10–20% beginning after 1 year on the diet, with estimated food intake being reduced about 30–35% over this period. Measures of skin-fold thickness and various body circumference measures were also reduced in experimental groups of rhesus monkeys. In contrast, the DR regimen involving a different diet produced little impact on comparable measures in squirrel monkeys, with the estimated food intake being reduced only about 20–25% over this period. However evidence of divergence in some morphometric parameters in squirrel monkeys was beginning to emerge in young groups (<5 years(after 3 yers on the diet. © 1995 Wiley-Liss, Inc.     

Modulations by dietary restriction on antioxidant enzymes and lipid peroxidation in developing mice.

The effects of dietary restriction (DR) on the activities of liver superoxide dismutase (SOD), catalase (Cat), and glutathione peroxidase (GPX) and the level of lipid peroxidation (LP) in developing mice were investigated in this study. Male and female Kunmin mice were fed a standard rodent diet ad libitum (AL), 80% of AL food intake (20% DR), or 65% of AL food intake (35% DR) for 12 or 24 wk. Both 12 and 24 wk of DR resulted in retarded body weight gain in male and female mice. The activities of SOD, Cat, and GPX and the content of LP in DR male and female mice were not different (P > 0.05) from those in controls after 12 wk of DR. However, the SOD activity was increased at 24 wk in 20% DR (P < 0.05) and 35% DR (P < 0.01) male, but not in DR female, mice. The Cat activity was elevated at 24 wk in both DR male (P < 0.05 for 20% DR, P < 0.01 for 35% DR) and female (P < 0.01) mice with a greater increase in DR female (P < 0.05) than in DR male animals. GPX activity was also increased at 24 wk in DR male (P < 0.01) and female (P < 0.01) mice with a greater elevation in DR females (P < 0.05) than in DR males. Furthermore, LP was decreased at 24 wk in both DR male (P < 0.01) and female (P < 0.01) animals with a greater reduction in DR females (P < 0.01) compared with DR males. These findings indicated that 24 wk, but not 12 wk, of DR led to differential effects on liver SOD, Cat, and GPX activities and LP content in male and female mice during development, suggesting sex-associated modulations of DR on antioxidant systems in developing animals.     

Curcumin Mimics the Neurocognitive and Anti-Inflammatory Effects of Caloric Restriction in a Mouse Model of Midlife Obesity

Dietary curcumin was studied for its potential to decrease adiposity and reverse obesity- associated cognitive impairment in a mouse model of midlife sedentary obesity. We hypothesized that curcumin intake, by decreasing adiposity, would improve cognitive function in a manner comparable to caloric restriction (CR), a weight loss regimen. 15-month-old male C57BL/6 mice were assigned in groups to receive the following dietary regimens for 12 weeks: (i) a base diet (Ain93M) fed ad libitum (AL), (ii) the base diet restricted to 70% of ad libitum (CR) or (iii) the base diet containing curcumin fed AL (1000 mg/kg diet, CURAL). Blood markers of inflammation, interleukin 6 (IL-6) and C-reactive protein (CRP), as well as an indicator of redox stress (GSH: GSSG ratio), were determined at different time points during the treatments, and visceral and subcutaneous adipose tissue were measured upon completion of the experiment. After 8 weeks of dietary treatment, the mice were tested for spatial cognition (Morris water maze) and cognitive flexibility (discriminated active avoidance). The CR group showed significant weight loss and reduced adiposity, whereas CURAL mice had stable weight throughout the experiment, consumed more food than the AL group, with no reduction of adiposity. However, both CR and CURAL groups took fewer trials than AL to reach criterion during the reversal sessions of the active avoidance task, suggesting an improvement in cognitive flexibility. The AL mice had higher levels of CRP compared to CURAL and CR, and GSH as well as the GSH: GSSG ratio were increased during curcumin intake, suggesting a reducing shift in the redox state. The results suggest that, independent of their effects on adiposity; dietary curcumin and caloric restriction have positive effects on frontal cortical functions that could be linked to anti-inflammatory or antioxidant actions.     

Reduced anorexic effects of insulin in obesity-prone rats fed a moderate-fat diet

Rats prone to develop diet-induced obesity (DIO) have reduced central sensitivity to many metabolic and hormonal signals involved in energy homeostasis. High-fat diets produce similar defects in diet-resistant (DR) rats. To test the hypothesis that genotype and diet exposure would similarly affect central insulin signaling, we assessed the anorectic effects of 8 mU third ventricular (iv3t) insulin before and after 4 wk intake of a 31% fat, high-energy (HE) diet intake in outbred (OutB) rats. Rats were retrospectively designated as DR or DIO by their low or high weight gains on HE diet. Before the HE diet, iv3t insulin reduced 4-h and 24-h chow intake by 53% and 69% in DR rats but by only 17% and 27% in DIO rats, respectively. Also, the anorectic response to iv3t insulin in OutB rats was inversely correlated (r = 0.72, P = 0.002) with subsequent 4-wk weight gain on the HE diet. Similarly, in selectively bred (SB) chow-fed DR rats, 8 mU iv3t insulin reduced 4-h and 24-h intake by 21% and 22%, respectively, but had no significant effect in SB DIO rats. Four-week HE diet intake reduced 4-h and 24-h insulin-induced anorexia by 45% in OutB DR rats and completely abolished it in SB DR rats. Reduced insulin responsiveness was unassociated with differences in arcuate nucleus insulin receptor mRNA expression between DIO and DR rats or between rats fed chow or HE diet. These data suggest that DIO rats have a preexisting reduction in central insulin signaling, which might contribute to their becoming obese on the HE diet. However, since the HE diet reduced central insulin sensitivity in DR rats but did not make them obese, it is likely that other brain areas are involved in insulin's anorectic action or that other pathways contribute to the development and maintenance of obesity.     

Reduced feeding response to neuropeptide Y in senescent Fischer 344 rats

The anorexia of aging syndrome in humans is characterized by spontaneous body weight loss reflecting diminished food intake. We reported previously that old rats undergoing a similar phenomenon of progressive weight loss (i.e., senescent rats) also display altered feeding behavior, including reduced meal size and duration. Here, we tested the hypothesis that blunted responsiveness to neuropeptide Y (NPY), a feeding stimulant, occurs concurrently with senescence-associated anorexia/hypophagia. Young (8 mo old, n = 9) and old (24-30 mo old, n = 11) male Fischer 344 rats received intracerebroventricular NPY or artificial cerbrospinal fluid injections. In response to a maximum effective NPY dose (10 microg), the net increase in size of the first meal after injection was similar in old weight-stable (presenescent) and young rats (10.85 +/- 1.73 and 12.63 +/- 2.52 g/kg body wt (0.67), respectively). In contrast, senescent rats that had spontaneously lost approximately 10% of body weight had significantly lower net increases at their first post-NPY meal (1.33 +/- 0.33 g/kg body wt (0.67)) than before they began losing weight. Thus altered feeding responses to NPY occur in aging rats concomitantly with spontaneous decrements in food intake and body weight near the end of life.     

Protective effects of long term dietary restriction on swimming exercise-induced oxidative stress in the liver, heart and kidney of rat

In this study, we evaluated the hypothesis that long term dietary restriction would have beneficial effects on the oxidative stress and antioxidant enzyme systems in liver, heart and kidney in adult male rats undergoing different intensities of swimming exercise. Sixty male, Sprague-Dawley rats were assigned as either dietary restricted on every other week day (DR) or fed ad libitum (AL) groups, and each group was further subdivided into sedentary, endurance swimming exercise training (submaximal exercise) and exhaustive swimming exercise (maximal exercise) groups. Animals in the submaximal exercise group swam 5 days/week for 8 weeks, while maximal exercise was performed as an acute bout of exercise. In parallel with the increase in the intensity of the exercise, the degree of lipid peroxidation and protein oxidation were increased in both the DR and AL groups; however the rate of increase was lower in the DR group. Reduced glutathione (GSH), glutathione peroxidase (GSH-Px) and glutathione reductase (GR) enzyme activities were lower in the DR group than in the AL group. In parallel with the increase in exercise intensity, GSH and GR enzyme activities decreased, whereas an increase was observed in GSH-Px enzyme activity. In conclusion, the comparison between the DR and AL groups with the three swimming exercise conditions shows that the DR group is greatly protected against different swimming exercise-induced oxidative stress compared with the AL group.     

Exercise training attenuates diet-induced reduction in metabolic rate

The combined influence of exercise training and dietary restriction on daily energy expenditure was evaluated by exposing 48 male Sprague-Dawley rats to one of three food intake conditions [ad libitum (AL), moderately restricted (MR), or severely restricted (SR)] and to one of two exercise conditions [treadmill exercised (E) or cage confined (CC)]. After 10 wk of exercise and dietary restriction, the MR-CC and MR-E rats weighed 84 and 86%, respectively, of AL-CC, whereas the SR-CC and SR-E rats weighed 66 and 68% of AL-CC. Dietary restriction and subsequent weight loss produced significant reductions in both total and resting daily energy expenditure. Exercise partially reversed this effect, but the extent of this reversal diminished as the severity of dietary restriction was increased. These results raise the distinct possibility that inconsistencies in the current literature concerning the effects of exercise on whole body metabolism during periods of dietary restriction might be reconciled by an appreciation and an understanding of the influence that duration of exercise training and severity of food restriction have on this measure.     

Effects of different diets and dietary restriction on perinatal endogenous DNA adducts. Time dependence of oxidative and presumptive nonoxidative lesions

Type II I-compounds (indigenous DNA adducts) denote a class of bulky oxidative DNA lesions that are detectable by 32P-postlabeling and represent useful biomarkers of DNA damage induced by oxidative stress. Their levels are increased in tissue DNA under pro-oxidant conditions, for example, as previously shown, in newborn rat organs. Here we have investigated whether the maternal diet affects perinatal type II I-compound levels. Pregnant F344 rats were fed Purina-5001 natural-ingredient or AIN-93G purified diet from day 11 of gestation. Type II I-compounds were measured in liver DNA at three different developmental stages, i.e., fetus, and 24 h and 9 days postnatally. Higher adduct levels were detected in the Purina-5001 group at each stage. In a second experiment, pregnant F344 rats were subjected to dietary restriction (DR) (by 40%; Purina-5001) from day 12 of gestation. At 24 h postpartum hepatic type II I-compound levels were decreased compared to parallel ad libitum (AL) fed controls. As an unrelated observation, fetal lung, but not liver, kidney, and skin DNA contained a different pattern of nonpolar, apparently nonoxidative adducts, which were not diet-dependent. These spots were not detectable 24 h after birth and were observed at much reduced levels and only in a few samples at 9 days. The main results show for the first time that the maternal nutrition modulated levels of oxidative lesions in fetal and neonatal DNA, but the underlying mechanisms (e.g., differences in metal or caloric content of the diets) still need to be determined. The dietary effects were apparently transmitted through both placenta and the mother's milk.     

Repeated light-dark shifts speed up body weight gain in male F344 rats

This study is aimed at verifying the causal relationship of chronic circadian desynchronization and changes in body weight control. Eight male albino F344 rats aged between 12-15 wk were subjected to twice weekly 12-h shifts of the daily light-dark (LD) cycle for 13 wk (3 mo). Continuous circadian phase shifts consisting of intermittent phase delay and advance and reduced circadian amplitudes were consistently displayed in all five experimental rats implanted intraperitoneally with heart rate, body temperature, and activity transponders. The experimental rat maintained a greater body weight during LD shifts and even after 10 days of recovery than that of the age-matched control rat, which was maintained on a regular LD cycle. Body weight gain was greater in the first 2 mo of LD shifts in the experimental rat than in the control rat. Relative to the baseline, food intake and activity percentages were increased and reduced, respectively, for the experimental rats. Features of these results, such as increased body weight gain and food intake, and reduced activity, suggest a causal relationship of chronic circadian desynchronization and changes in body weight control in male albino F344 rats.     

Effects of dietary calorie restriction or exercise on the PI3K and Ras signaling pathways in the skin of mice

Weight control by exercise and dietary calorie restriction (DCR) has been associated with reduced cancer risk, but the underlying mechanisms are not well understood. This study was designed to compare the effects of weight loss by increasing physical activity or decreasing calorie intake on tumor promoter-induced Ras-MAPK and PI3K-Akt pathways. SENCAR mice were randomly assigned to one of the following five groups: ad libitum-fed sedentary control, ad libitum-fed exercise (AL+Exe), exercise but pair-fed at the amount as controls (PF+Exe), 20% DCR, and 20% DCR plus exercise (DCR+Exe). After 10 weeks, body weight and body fat significantly decreased in the groups of DCR, DCR+Exe, and PF+Exe when compared with the controls. AL+Exe did not induce weight loss due to, at least in part, increased food intake. Plasma IGF-1 levels reduced significantly in DCR and DCR+Exe but not PF+Exe. The protein H-Ras and activated Ras-GTP significantly decreased in TPA-induced skin tissues of DCR-fed mice but not exercised mice. PI3K protein, phosphoserine Akt, and p42/p44-MAPK were reduced, however, in both DCR and PF+Exe groups. Immunohistochemistry demonstrated that the significantly reduced H-Ras occurred in subcutaneous fat cells, while the reduced PI3K and PCNA took place only in the epidermis. Plasma leptin decreased in PF+Exe, DCR, and DCR+Exe, while the caspase-3 activity increased in DCR+Exe only. Genomic microarray analysis further indicated that the expression of 34 genes relevant to PI3K and 31 genes to the MAPK pathway were significantly regulated by either DCR or PF+Exe treatments. The reduced PI3K in PF+Exe mice was partially reversed by IGF-1 treatment. The overall results of this study demonstrated that DCR abrogated both Ras and PI3K signaling, which might inhibit TPA-induced proliferation and anti-apoptosis. Selective inhibition of PI3K by PF+Exe but not AL+Exe seems more attributable to the magnitude of the caloric deficit and/or body fat loss than diet versus exercise comparison.     

Effect of dietary restriction on estrous cyclicity and follicular reserves in aging C57BL/6J mice

Restricting the food intake of female mice by alternating days of feeding and fasting delayed the age-related loss of estrous cycling potential and retarded the rate of follicular depletion, as determined after reinstatement of ad libitum (AL) feeding. During the period of food restriction (FR; 3.5-10.5 mo), food intake and body weight were about 80% of AL values. Mice were acyclic and predominantly in a state of diestrus during FR, but after reinstatement of an AL diet at 10.5 mo all FR mice resumed cycling regularly. By contrast, 80% of AL controls had become acyclic by this age, and the cycles of the remaining mice were significantly longer than those of the reinstated FR mice. Follicular reserves of 12.5-mo-old FR mice were twice those of age-matched AL controls. Cycling performance of reinstated FR mice, measured by cycle length and the proportion of mice still cycling, was equivalent to that of AL mice when the latter were 2-5 mo younger. Ovarian age, measured by the size of the follicular reserve, was similarly retarded in FR mice. Based on these data and previous evidence that follicular depletion plays a major role in the cessation of cyclicity in this strain, we hypothesize that the delayed loss of estrous cyclicity in aging FR mice is mediated at least in part by the retarding effect of dietary restriction on the rate of follicular depletion.     

Effect of dietary restriction and/or exercise on 23-h metabolic rate and body composition in female rats.

This study examined the effects of three levels of dietary intake [ad libitum fed (AL), moderately severe (MSR), and severe restriction (SR)] and two levels of exercise [cage confinement (CC) and exercise training (E)] on 23-h resting metabolic rate (RMR) and body composition in 47 female Sprague-Dawley rats. At the end of the 9-wk study, the MSR and SR groups weighed approximately 81 and 61%, respectively, of the AL-CC group. RMR was depressed for the MSR and SR groups compared with the AL-CC group. This was true whether expressed on an absolute (ml/min) or relative (ml.min-1.kg-0.75) basis. On a relative basis, which accounts for changes caused by weight loss alone, the RMR decreased by approximately 12 and 19%, respectively, for the MSR and SR groups compared with the AL-CC group. Although E resulted in significant differences in fat mass, percent fat, percent water, and heart mass between the AL groups, there were no significant differences between E and CC groups at either the MSR or SR level of dietary intake for any of the variables measured (i.e., body composition, muscle mass, RMR). Thus E does not appear to affect the composition of lost weight or RMR during diet-induced weight loss for female rats of normal weight.     

Nutritional requirements for maintenance of body weight and fat deposition in the long-distance migratory garden warbler, Sylvia borin (Boddaert)

Intake of food, protein, fat and carbohydrates and their fecal output and the birds' weights were recorded during different feeding trials with specific nutrient reduced diets in the old-world long-distance migratory garden warbler. The birds' body weights were affected by low dietary protein as well as low dietary fat levels. Low dietary protein and fat levels were associated with significant changes in daily gross and net food intake and in the efficiency of food and nutrient utilization. Birds fed on diets with low nutrient levels for an extended length of time recovered in weight after an initial weight loss. They obviously compensated the restricted nutrient levels primarily by increasing the daily food intake and by changing the efficiency of food and nutrient utilization. Effects of restricted dietary nutrient levels on body weight and adaptation depended on the previous composition of the food. The average daily net fat intake was much higher than the average daily net protein intake, both for maintenance of a constant body weight and for successful regain of weight. The data were further discussed with respect to the role of a fruit diet in omnivorous passerine birds.     

The influence of food restriction versus ad libitum feeding of chow and purified diets on variation in body weight, growth and physiology of female Wistar rats

Ad libitum (AL) supply of standard chow is the feeding method most often used for rodents in animal experiments. However, AL feeding is known to result in a shorter lifespan and decreased health as compared with restricted feeding. Restricted feeding and thus limiting calorie intake prevents many health problems, increases lifespan and can also increase group uniformity. All this leads to a reduced number of animals needed. So-called standard chows are known to be prone to variation in composition. Synthetic foods have a more standard composition, contributing to group uniformity which, like diet reduction, may decrease the number of animals necessary to obtain statistical significance. In this study, we compared the effects of AL versus restricted feeding (25% reduction in food intake) on standard chow versus synthetic food of three different suppliers on body weight (BW), growth, several blood parameters and organ weights in growing female Wistar rats over a period of 61 days. Diet restriction led to a decreased growth and significantly reduced variation in BW and growth as compared with AL feeding. AL feeding on synthetic diets caused a significantly higher BW gain than on chow diets. Due to experimental design, this same effect occurred on food restriction. Blood parameters and organ weights were affected neither by diet type nor by amount. Incidentally, variations were significantly reduced on food restriction versus AL, and on synthetic diets versus chow diets. This study demonstrates that food restriction versus AL feeding leads to a significantly reduced variation in BW and growth, thereby indicating the potential for reduction when applying this feeding schedule.     

The effect of various dietary zinc concentrations on the biological interactions of zinc,copper, and iron in rats

Three groups (14 rats each) were fed one of the following diets for 8 wks: a control purified basal diet containing 12 ppm zinc, 5 ppm copper, and 35 ppm iron; the basal diet with less than 2 ppm zinc; or the basal diet supplemented with 1000 ppm zinc. Rats fed the zinc-deficient diet had decreased weight gain, moderate polydipsia, and intermittent mild diarrhea. The zinc-supplemented rats had a cyclical pattern of food intake and weight loss from weeks 5 to 8. Tissue concentrations suggest that zinc and copper were not mutually antagonistic with chronic dietary imbalances. If tissue element concentrations reflected intestinal uptake, then competition and/or inhibition of intestinal uptake occurred between zinc and iron. The fluctuations in tissue element concentrations that occurred with increased duration of the study were at variance with previous studies of shorter time periods. The dietary proportions of zinc, copper, and iron appear to influence zinc, copper, and iron metabolism at the intestinal and cellular transport levels over a given period of time.     

Gender-specific prandial response to dietary restriction and oxidative stress in Drosophila melanogaster

Drosophila melanogaster is ideal for studying lifespan modulated by dietary restriction (DR) and oxidative stress, and also for screening prolongevity compounds. It is critical to measure food intake in the aforementioned studies. Current methods, however, overlook the amount of the food excreted out of the flies as feces or deposited in eggs. Here we describe a feeding method using a radioactive tracer to measure gender-specific food intake, retention and excretion in response to DR and oxidative stress to account for all the ingested food. Flies were fed a full, restricted or paraquat-containing diet. The radioactivity values of the food in fly bodies, feces and eggs were measured separately after a 24-hr feeding. Food intake was calculated as the sum of these measurements. We found that most of the tracer in the ingested food was retained in the fly bodies and < 8% of the tracer was excreted out of the flies as feces and eggs in the case of females during a 24-hr feeding. Under a DR condition, flies increased food intake in volume to compensate for the reduction of calorie content in the diet and also slightly increased excretion. Under an oxidative stress condition, flies reduced both food intake and excretion. Under all the tested dietary conditions, males ingested and excreted 3-5 fold less food than females. This study describes an accurate method to measure food intake and provides a basis to further investigate prandial response to DR and prolongevity interventions in invertebrates.