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Dietary fat content affects energy intake and weight gain independent of diet caloric density in rats.

Recent considerations of high-fat diet hyperphagia have focused on fat's relatively high energy density as the critical variable which promotes overeating. However, a high-fat (HF) diet has been shown to enhance intake and weight gain relative to a high-carbohydrate (HC) diet when both energy density and palatability are equated [Am. J. Physiol. 269 (1995) R30]. The present studies investigated the generality of this finding across manipulations of diet caloric density, diet physical form, and chow availability. Separate groups of male rats were fed HF or HC at either 2.3 or 1.15 kcal/ml for 16 days; HF feeding enhanced weight gain relative to HC across both levels of energy density. HF hyperphagia also occurred when diets were presented in semisolid (gelled) form, and when chow was available in addition to liquid diet. These findings are consistent with previous observations that an HF diet can enhance daily kilocalorie intake and weight gain at least partly via a mechanism that is unrelated to caloric density.

Animal Feed↗

Central melanocortin system modulates energy intake and expenditure of obese and lean Zucker rats.

Melanocortins play a critical role in appetite and body weight regulation, because manipulations of this pathway can lead to the development of obesity in several animal models. The purpose of this study was to use a melanocortin receptor agonist and antagonist to evaluate the involvement of melanocortins in feeding, energy metabolism, and body weight regulation in lean and obese Zucker rats. Central administration of a melanocortin receptor antagonist (SHU9119) elevated food intake and body weight of lean Zucker rats but had little effect in obese Zucker rats. In contrast, the melanocortin receptor agonist MTII reduced food intake in both lean and obese rats but was more potent in the obese Zucker rats. These data indicate the existence of functional melanocortin receptors in both lean and obese Zucker rats but suggest that obese Zucker rats have reduced endogenous melanocortin tone. In addition to its effects on food intake, MTII infusion elevated oxygen consumption and decreased respiratory quotient dose dependently during the light cycle. Our data suggest that a melanocortin receptor agonist can induce weight loss by increasing energy expenditure and promoting body fat utilization in addition to its inhibitory effects on food intake in both obese and lean Zucker rats.

Animals↗

Stimulation of energy intake and growth by saccharin in rats.

Rats fed wet diets containing saccharin consumed 12-14% more energy and gained 24-55% more weight than rats fed the same diets without saccharin. Saccharin-induced stimulation of intake was usually not so pronounced during the first week as during subsequent weeks of each experiment. Similar results were obtained using diets high in starch and fat. However, these effects could be obliterated by simply exposing the rats to unsweetened (plain) diet or to saccharin in water for several days before the sweetened diets were introduced. Furthermore, although stimulation of intake by saccharin was observed with diets containing 80% water, no such effect was observed with a diet containing 60% water. Rats given low-energy sweetened water in addition to their 80% water diet consumed substantially more fluid but not more or less energy than rats given unsweetened water. Preference tests suggest that saccharin increases diet palatability only very slightly; this finding is one of several observations suggesting that stimulation of intake by saccharin cannot be interpreted in terms of increased diet palatability. These results suggest that dietary hyperphagia results from the interaction between innate and learned responses to the taste of foods. Osmotic factors did not seem to exert a major influence in these experiments.

Analysis of Variance↗

Restricted energy intake and elevated calcium and phosphorus intake for boars during growth. II. Foot and leg measurements and toe and soundness scores.

Boars were assigned at 5 wk of age in a 2 X 2 factorial arrangement to two energy (ad libitum and 75% of ad libitum) and two Ca and P levels (100 and 150% of the National Research Council daily recommended amounts) to determine the effect of reduced growth rate and elevated Ca and P intake on foot and leg measurements, pad and horn incidence and severity of lesions, and structural soundness. There were 20 boars/treatment; 15 boars from each treatment were necropsied at 10 +/- 2-d intervals from 80 to 220 d of age (45 to 185 d on test), with the remaining five boars in each treatment being necropsied at 220 d of age. Feet and leg measurements were taken and toe pads and horns were scored initially and after 78 and 131 d on when necropsied. Boars remaining after 130 d on test were scored for overall structural soundness. Toe size and circumference and length of limbs increased as boars grew, with larger values for ad libitum-fed compared with limit-fed boars when observed at a constant age. However, when these values were corrected for body weight, the effect of energy was generally removed and, in some cases, reversed. Limit-fed boars appeared to have fewer pad and horn lesions, but the effects were inconsistent. In general, Ca and P levels had little or no effect on toe and limb sizes and pad and horn lesion scores, whether or not the values were expressed on a constant age or corrected body weight basis. A comparison of inside and outside toes on the front and hind feet revealed that outside toes were larger than inside toes, with the magnitude of the difference much larger for the hind foot than for the front foot. The hind inside toes had fewer pad and horn lesions. Structural soundness scores were more desirable in ad libitum-fed compared with limit-fed boars; but, elevated Ca and P levels had no effect. Thus, these data do not support a hypothesis that structural soundness can be improved by reducing the growth rate of developing boars or by feeding an elevated level of Ca and P.

Animals↗

Having it all: historical energy intakes do not generate the anticipated trade-offs in fecundity.

An axiom of life-history theory, and fundamental to our understanding of ageing, is that animals must trade-off their allocation of resources since energy and nutrients are limited. Therefore, animals cannot "have it all"--combine high rates of fecundity with extended lifespans. The idea of life-history trade-offs was recently challenged by the discovery that ageing may be governed by a small subset of molecular processes independent of fitness. We tested the "trade-off" and "having it all" theories by examining the fecundities of C57BL/6J mice placed onto four different dietary treatments that generated caloric intakes from -21 to +8.6% of controls. We predicted body fat would be deposited in relation to caloric intake. Excessive body fat is known to cause co-morbidities that shorten lifespan, while caloric restriction enhances somatic protection and increases longevity. The trade-off model predicts that increased fat would be tolerated because reproductive gain offsets shortened longevity, while animals on a restricted intake would sacrifice reproduction for lifespan extension. The responses of body fat to treatments followed our expectations, however, there was a negative relationship between reproductive performance (fecundity, litter mass) and historical intake/body fat. Our dietary restricted animals had lower protein oxidative damage and appeared able to combine life-history traits in a manner contrary to traditional expectations by having increased fecundity with the potential to have extended lifespans.

Animals↗

A high-protein, high-fat, carbohydrate-free diet reduces energy intake, hepatic lipogenesis, and adiposity in rats.

The aim of this work was to determine the effects in rats of ingesting 1 of 3 diets with normal or high protein concentrations and various carbohydrate:lipid ratios on weight gain, body composition, and the development and metabolism of white adipose tissue (WAT). For this purpose, male Wistar rats were fed for 20 or 42 d a high-carbohydrate, low-fat, normal-protein diet (76, 10, and 14% of energy as carbohydrate, lipid, and protein, respectively, carbohydrate:lipid ratio (C/L) = 7.6), a normal-carbohydrate, low-fat, high-protein diet (35, 10, and 55% of energy as carbohydrate, lipid, and protein respectively, C:L = 3.5), or a carbohydrate-free, high-fat, high-protein diet (45 and 55% of energy as fat and protein, respectively, C:L = 0). Growth, food intake, body composition, WAT cellularity, and several markers of lipogenesis including fatty acid synthase and lipoprotein lipase activities were measured in adipose tissue and liver. Lowering the C:L ratio reduced the development of WAT, weight gain, body fat mass, and adipocyte size, and in rats fed the carbohydrate-free diet (C:L = 0), the total number of adipocytes in subcutaneous WAT. These reductions in adipose tissue development with decreases in the C:L ratio of the diet seemed to be due primarily to reduced hepatic lipogenesis.

Adipose Tissue↗

Neuroendocrine profiles associated with energy intake, sleep, and stress in the night eating syndrome.

CONTEXT: Night eating syndrome (NES) is characterized by evening hyperphagia and frequent awakenings with ingestion of food. It is associated with obesity and depressed mood. Greater understanding of hormonal influences on NES is desirable. OBJECTIVE: Our objective was to evaluate 25-h profiles of hormones involved in energy balance, sleep, and stress in NES. DESIGN: Blood assays for glucose, insulin, ghrelin, leptin, melatonin, cortisol, TSH, and prolactin were sampled repeatedly among NES and control subjects. Food intake and depressive symptoms were assessed. SETTING AND PARTICIPANTS: Fifteen NES and 14 matched control participants stayed three nights in a General Clinical Research Center. MAIN OUTCOME MEASURES: We assessed differences between NES and control participants in the 25-h profiles of eight hormones. RESULTS: Nocturnal food intake was higher among NES participants, although their daily calorie intake was similar to that of controls. Reflecting their increased nocturnal intake, insulin (P < 0.001) and glucose levels (P = 0.07) among NES participants were higher than those of controls. Ghrelin levels were significantly lower in NES participants than in controls from 0100-0900 h (P = 0.003). Levels of plasma cortisol, melatonin, leptin, and prolactin did not differ between groups, but there was a trend for TSH levels (P = 0.07) to be higher during the 25 h in NES. NES participants had greater depressive symptoms than controls (P < 0.001). The differences in the levels of glucose, insulin, and ghrelin between NES and controls are closely associated with nocturnal food intake.

Adult↗

Food intake and energy expenditure of Nigerian female students.

Twenty apparently healthy and normal Nigerian female students, resident at the University of Ibadan campus, were studied for seven consecutive days to assess their food energy intake and energy expenditure during sedentary and physical activities. The mean age (years) of the group was 20.05 (SD 3.44, range 16-29), mean height (m) 1.62 (SD 0.07, range 1.47-1.74) and body-weight (kg) 51.28 (SD 3.21, range 46-58). The food intake of each subject was obtained by direct weighing, and the energy value determined using a ballistic bomb calorimeter. Daily activities were recorded and the energy cost of representative activities was determined by indirect calorimetry. Activities mainly involved sitting, mean (min/d) 354 (SD 84, range 253-475). Personal domestic activities took a mean of 162 (SD 73) min/d. Sleeping took a mean of 451 (SD 62) min/d. The mean energy intake of the group was 8480 (SD 1316) kJ/d or 167 (SD 30.6) kJ/kg body-weight per d. This value is lower than that recommended by the Food and Agriculture Organization/World Health Organization (FAO/WHO) (1973) as the energy requirement for adult women engaged in light activities (9205 kJ/d), but it is higher than the FAO/WHO/United Nations University (UNU) (1985) recommended value of 8326 kJ (1990 kcal)/d for a housewife in an affluent society. It is lower than the recommended intake of 9350 kJ/d for rural women in developing countries (FAO/WHO/UNU, 1985). The mean energy expenditure (kJ/d) of the female subjects was 6865 (SD 214, range 6519-7222). Mean energy expenditure was lower than mean energy intake. The energy intake and expenditure values indicated that the subjects participating in the present study were not physically very active. It is suggested, for health reasons, that they might undertake more physical activity.

Adolescent↗

Creatinine and inulin clearance at the different nitrogen and energy intake in sheep.

1. Renal creatinine and inulin clearances were compared between sheep fed (a) high nitrogen and high energy diet; (b) low nitrogen and high energy diet and (c) low nitrogen and low energy diet. 2. Inulin clearance was significantly lower in sheep on both low nitrogen diets vs the group with high nitrogen intake. Differences were not ascertained between the groups on low nitrogen diets. 3. No significant differences were found in the creatinine clearance. The creatinine inulin clearance ratio was higher when animals were fed low nitrogen diets, vs the group on a high nitrogen diet. 4. Results suggest that the endogenous creatinine is not suitable for the GFR measurement in sheep under the different conditions of nutrition.

Animals↗

Dietary fat and the control of energy intake: evaluating the effects of fat on meal size and postmeal satiety.

Three separate experiments in lean subjects confirmed that a 1.52-MJ (362-kcal) carbohydrate supplement at breakfast suppressed appetite 90 min later but had no effect on a test meal given after 270 min. A 1.52-MJ (362-kcal) fat supplement produced no detectable action on measures of appetite at any time point. Therefore, fat and carbohydrate do not have identical effects on the appetite profile. In a further study in obese subjects, a novel experimental design was used to assess the satiating efficiency and compensatory response of fat. Eating from a range of either high-fat or high-carbohydrate foods, obese subjects voluntarily consumed twice as much energy from the fat items, thereby indicating a weak action of fat on satiation. In turn, this large intake of fat exerted a disproportionately weak effect on satiety. These studies suggest that the appetite-control system may have only weak inhibitory mechanisms to prevent the passive overconsumption of dietary fat. The results indicate how this action could induce a positive energy balance and lead to a gradual upward drift in body mass index.

Analysis of Variance↗

Effects of aerobic conditioning at intensities corresponding to lactate threshold plus reduced energy intake in college-age females.

The effects of a 15-wk aerobic conditioning (4.2 +/- 1.3 d/wk) plus energy restriction (25 kcal/kg/d diet) program on anthropometric and physiologic attributes were studied in 16 obese women between the ages of 18 and 24. The women were divided into either an experimental (E, n = 10) group or a control (C, n = 6) group. The exercise + diet (E) group demonstrated significant reductions in body weight, both absolute and relative body fat, Katsura index, and serum triglycerides, and increases in oxygen uptake relative to lactate threshold (LT), maximal oxygen uptake, and the ratio of high-density lipoprotein cholesterol to total cholesterol. In the C group, none of the variables measured in this study remained unchanged. Thus the benefits of weight reduction without any change in fat free weight following the program were pronounced in the female university-age group that we studied. In conclusion, the highly structured aerobic conditioning at intensities corresponding to LT together with a proper dietary regimen is considered optimal with respect to favorable changes in various anthropometric and physiologic attributes. The feasibility of treating obese individuals with manifestation of medical and/or psychological problems in a school setting should be a significant matter in future research.

Adolescent↗

Energy intake, body composition and reproductive performance of the gilt.

The relationship between age, live weight, body composition and energy status on the onset and maintenance of reproductive activity in females is reviewed. When possible, swine studies have been employed, although, of necessity, much data are drawn from other species. The relationship between age, weight and puberty is controversial. However, from the available data we conclude that neither age nor weight are reliable indices of reproductive development, but that minimum threshold values for these characteristics must be achieved before puberty can occur. Human data provides a strong indication that a minimum adipose to lean tissue ratio is a prerequisite for puberty onset. Limited data from swine support this contention and indeed it may be a superior measure of reproductive development than either age or weight. However, the value of this ratio remains to be defined in pigs, and again it is minimum threshold level, the attainment of which is necessary, but not in itself sufficient, for puberty onset. A positive energy balance seems to be necessary for puberty onset and the maintenance of estrous cycles in some species, but this has not been investigated in swine. The mechanisms whereby adiposity and energy status influences reproduction are discussed. Human studies demonstrate a negative correlation between energy status, body fatness and plasma gonadotrophin levels. Also, adipose tissue has the ability to metabolize sex steroids, aromatizing androgens to estrogens and changing the direction of estrogen metabolism to produce more or less biologically potent estrogens.

Adipose Tissue↗

The role of fat, fatty acids, and total energy intake in the etiology of human colon cancer.

A high correlation between national per capita disappearance of fat and national rates of colon cancer led to the hypothesis that consumption of fat, especially from animal sources, increases risk for colon cancer. Over the past two decades, this hypothesis has been tested in numerous case-control and cohort studies. In general, neither case-control nor cohort studies find that the total fat composition of the diet increases risk of colon cancer. Case-control studies frequently find that total energy consumption is related to a higher risk of colon cancer, but this result is difficult to interpret because physical activity appears to be protective whereas obesity increases risk. In contrast with the results for total fat, epidemiologic data regarding the role of specific fatty acids are sparse. Nonetheless, useful information regarding major fatty acids may be inferred from the numerous studies that have examined major source of various fats in relation to colon cancer. Intake of red meat or beef has been related to colon cancer risk in most case-control and cohort studies, whereas dietary fat from sources other than red meat, including dairy, poultry, and vegetable oils, does not increase risk of colon cancer. The apparent influence of red meat does not appear to be mediated through its total lipid content, suggesting that other factors such as heterocyclic amines formed during cooking may be critical. Mechanisms whereby fat or red meat may influence colon carcinogenesis are discussed, although none appear compelling.

Colonic Neoplasms↗