Increased Food Efficiency Research Articles

Weight cycling — a ‘new’ risk factor?

Weight cycling — a ‘new’ risk factor?

Dietary obesity and weight cycling: effects on blood pressure and heart rate in rats.

The overconsumption of rich and palatable foods and "yo-yo" dieting are feeding patterns involved in obesity and possibly hypertension in humans. We therefore examined the effects of diet-induced obesity and weight cycling on the blood pressure and heart rate levels of 60-day-old male normotensive Sprague-Dawley (S-D) and spontaneously hypertensive (SHR) rats. Six months on a high-fat and high-sucrose diet (HF/M) produced a greater obesity in S-D rats than in SHR rats. The caloric intakes of S-D rats fed the HF/M diet were greater than the caloric intakes of pellet-fed controls, whereas those of SHR rats were similar. The obesity of both strains was associated with hyperinsulinemia, heavier white (retroperitoneal) and brown (interscapular) fat pads, heavier heart weights, and tachycardia. Despite these changes, diet-induced obesity failed to increase systolic blood pressure obtained under light ether anesthesia or mean arterial pressure in the conscious state. Paradoxically, the blood pressures of SHR rats fed HF/M diet were reduced perhaps as a result of the high polyunsaturated fat component of the diet. A second S-D dietary obese group was alternated between 2-wk periods of unrestricted HF/M diet and 50% restricted pellet chow. Although their body weights were similar to pellet-fed controls, three cycles of weight loss and weight regain resulted in the consumption of increased dietary fat, increased food efficiency, heavier fat pads, and hyperinsulinemia. Heart rate and to some extent blood pressure fluctuated with diet, being elevated during HF/M feeding and reduced during restricted pellet feeding. Although weight cycling intensified the physiological responses to food ingestion, we found that weight cycling in dietary obese S-D rats did not elevate blood pressure levels.

Body composition in mice maintained with cyclic periods of food restriction and refeeding

The effect of cyclic periods of underfeeding and overfeeding on body composition and energy efficiency was investigated in adult female CD1 Swiss mice. Four groups of mice were studied for 8 weeks: 1) Controls, fed stock diet ad libitum, 2) Overfed, fed stock diet plus a varied selection of highly palatable human foods (cafeteria feeding), 3) Cyclic-fed, given restricted amounts of stock diet (80% of controls) and cafeteria diet on alternate weeks, and 4) Restricted, fed 80% of the food consumed by the controls. The restricted mice had lower body weight, carcass energy content and energy expenditure than the other groups. The overfed mice had increased energy intake, energy expenditure, food efficiency, carcass fat and energy stores. The cyclic-fed mice had higher food intake than the controls but lower intake than the overfed mice. The cyclic-fed mice had increased food efficiency, increased carcass fat and carcass energy compared to the controls but values were less than for the overfed mice. Carcass energy was 224±8 kJ, controls; 314±18 kJ, overfed; 277±14 kJ, cyclic-fed and 173±9 kJ, restricted mice. Carcass energy was highly correlated with total energy consumed (r=0.592, p<0.001). Both regular and periodic consumption of an energy dense diet did increase energy intake, energy efficiency and carcass energy stores. However, there was no evidence that repeated periods of food restriction and refeeding increased body fat stores.

Dietary obesity and neonatal sympathectomy. I. Effects on body composition and brown adipose.

The effect of neonatal sympathectomy with guanethidine (50 mg/kg for 3 wk) on the development of diet-induced obesity (DIO) was assessed by raising guanethidine-(G) or saline-treated (S) Sprague-Dawley rats in small litters (4-5 pups/dam) and feeding a high-calorie diet from weaning (n = 29-30) or by raising similarly treated rats in normal litters (10 pups/dam) and feeding chow from weaning (n = 29-30). Sympathectomy depleted norepinephrine (NE) levels 65-98% in all organs except the adrenals and brain but had no statistically significant effect on weight gain, food intake, food efficiency, body composition, plasma glycerol, insulin, or glucose, or on basal rectal temperatures in either diet group; there was a tendency toward increased adiposity in sympathectomized rats. Despite 95-98% depletion of NE in interscapular brown adipose tissue (IBAT), sympathectomy affected only the percentage of multilocular cells that was decreased 46-69%. Rats from small litters in both treatment groups (S and G) became obese without increased food intake (increased food efficiency), had heavier IBAT pads with bigger cells and more lipid, and were also hyperlipidemic, hyperinsulinemic, and hyperglycemic compared with controls. Therefore neonatal sympathectomy was not as significant in the subsequent development of DIO as were diet and litter size.

Effects of early cold adaptation on food efficiency and dietary-induced thermogenesis in the adult rat

The food intakes of male and female rats (Harvard strain) adapted to cold (5°C) starting at weaning were studied in the cold and during reacclimation to 25°C. Following 24 hr food deprivation, the male rats regained the weight they had lost without making up for the food they had missed (increased food efficiency), while the female rats ate 75% more food than they had missed in regaining their body weights (decreased food efficiency), independent of the temperature at which the animals were housed. On a high fat diet, both cold groups gained less weight than did the two control groups. However, each female group gained significantly less weight than its same temperature male group. Dietary-induced thermogenesis was significantly enhanced in male cold adapted rats 3 months after reacclimation to the zone of thermal neutrality but not in cold adapted female rats. Sex and strain differences are discussed. These data indicate that early chronic cold exposure results in both immediate and long-term changes in food efficiency and metabolism in adult rats, but the effects vary with the sex of the animal.

Growth stimulating effect of picolinic acid added to rat diets.

Rats fed either a soybean protein-based diet or a casein-based diet supplemented with picolinic acid gained significantly more weight than rats fed unsupplemented diets. The zinc concentration of the kidneys from the rats fed the diets supplemented with picolinic acid was significantly greater than that of the rats fed the unsupplemented diets. Rats fed a pyridoxine-free diet formulated with vitamin-free casein and supplemented with picolinic acid gained significantly more weight than rats fed an unsupplemented pyridoxine-deficient diet. The zinc concentration of the kidneys from the rats fed the pyridoxine-deficient diet supplemented with picolinic acid was significantly greater than that of the rats fed the unsupplemented diet. Dietary zinc absorption and food efficiency were increased when rats were fed supplemental picolinic acid. The results suggest that picolinic acid may increase the bioavailability of dietary zinc and perhaps other divalent cations which results in increased food efficiency.

Influence of a Liquid Diet and Meal Pattern on Body Weight and Body Fat in Rats

Rats weighing 110 to 150 g or 250 g initially were utilized in five experiments to determine the effect of the form of the diet (dry versus liquid) and the pattern of feeding (meal-feeding, force-feeding, nibbling, or ad libitum) on body weight gain and on body fat. A high-carbohydrate, 20% casein or 20% lactalbumin diet was fed for 4 to 8 weeks. Consumption of a diet mixed with an equal weight of water increased weight gain in one of three experiments. Body fat content of the rats was not influenced by addition of water to the diet. Neither force-feeding nor meal-feeding influenced body fat gain provided the respective control rats were pair-fed during the initial adaptation period. Likewise, when rats were pair force-fed to ad libitum fed rats without an initial adaptation meal frequency did not influence body fat gain. When meal-fed rats were switched to ad libitum intake their food intake increased to equal that of rats which had been continuously fed ad libitum; however, the rats which had been switched gained more body fat than did rats continuously fed ad libitum. These results suggest that meal frequency may have a minimal influence on body fat accumulation, but that a shift to a higher level of food intake may cause an increased food efficiency and greater rate of fat deposition than in rats continuously fed the higher level of intake.