Carbohydrate-to-fat ratio affects food intake and body weight in Wistar rats

High-fat diet effects on metabolic responses to chronic stress

CONTEXT

High-fat diets and chronic stress are prevalent risk factors for various chronic diseases in modern societies.

OBJECTIVE

This study investigated the effect of high-fat diet on glucose-related metabolic responses to chronic foot-shock stress.

MATERIALS AND METHODS

Male rats were divided into high-fat diet (containing 54.21% saturated and 44.89% unsaturated fatty acids) and normal diet groups and then into stress and non-stress subgroups. The diets were applied for 5 weeks, and stress was induced during the last week of the diet course. Plasma levels of metabolic parameters, HOMA-IR index, intra-abdominal fat weight, and islets' insulin secretion were assessed.

RESULTS

High-fat diet increased abdominal fat weight and plasma leptin, and insulin levels in response to stress without affecting HOMA-IR index and islets' insulin secretion.

CONCLUSIONS

High proportion of unsaturated fat may not lead to deleterious metabolic responses; however combined with chronic stress has a synergistic and adverse effect on visceral adiposity and results in elevated plasma leptin.

Unlimited access to low-energy diet causes acute malnutrition in dams and alters biometric and biochemical parameters in offspring

Here we analyze the outcomes of unlimited access to a low-energy (LE) diet in dams and their offspring. At 3 weeks’ gestation, pregnant Wistar rats were divided into two groups: (1) the control group received a normoenergetic diet; and (2) the experimental group received the LE diet. In dams, lactation outcomes, food intake, body weight, plasma IGF-1, prealbumin, transferrin and retinol-binding protein levels were evaluated; in offspring, biometric and biochemical parameters and food intake were evaluated. No differences were observed during pregnancy. However, after lactation, dams that received the LE diet demonstrated significant reductions in body weight (P<0.05), plasma IGF-1 (P=0.01), prealbumin and visceral fat (P<0.001). Pups born to dams that received the LE diet demonstrated reduced body length and weight at weaning (P<0.001) and were lighter than the control animals at the end of the experimental period. Pups also demonstrated reduced plasma, low-density lipoprotein (P=0.04), triglycerides (P=0.002) and glucose levels (P<0.05), and differences were noted in visceral fat. These results indicate that feeding dams with LE diet during the reproductive period induces acute malnutrition and impairs the growth and development of offspring, as well as certain metabolic parameters.

Experimental diet based on the foods listed in the Family Budget Survey is more detrimental to growth than to the reflex development of rats

OBJECTIVE: The present study assessed the pregnancy and lactation performances of rats fed an experimental diet based on the foods listed in the Family Budget Survey (Pesquisa de Orçamento Familiar) 2002/2003 and the impact of said diet on the growth and development of the pups until weaning. METHODS: Wistar (n=12) rats were randomly divided into two groups: a control group (control group, n=6) fed a commercial chow (Labina®, Brazil) and an experimental group (n=6) fed the Family Budget Survey diet during the entire pregnancy and lactation period. All animals had free access to food and water during the entire study period. RESULTS: The Family Budget Survey diet increased the duration of pregnancy (control group=21.00±0.00; POFG=21.57±0.55, p=0.025) and made the dams lose weight during the lactation period (control group=27.92±18.47g; POFG=-15.66±16.90g). The Family Budget Survey group presented low food, energy and nutrient intakes during pregnancy, which became even lower during lactation. Pups from Family Budget Survey dams presented lower body weight at weaning (control group=52.38±4.49g; POFG=39.88±2.78g, p=0.001) and lower nose-to-anus length (control group= 117.37±0.64mm; POFG=125.62±0.96mm, p=0.001). However, some physical milestones and reflexes occurred earlier, such as the placing response reflex [control group= 12.00 (9.00-15.00) days; POFG=9.50 (9.00-14.00) days] aerial righting reflex [control group=18.00 (17.00-20.00) days; POFG=16.00 (13.00-18.00) days] and unfolding of the external ear [control group=3.00 (3.00-3.00) days; POFG=2.00 (2.00-3.00) days]. CONCLUSION: The Family Budget Survey diet seems to be more detrimental to the physical growth of the pups than to their brain growth, according to the assessed reflexes and physical milestones and measures. This may be due to the low protein content of the diet for rat reproduction and growth combined with adequate fat and essential fatty acid contents. Providing an adequate amount of protein to the Family Budget Survey diet may normalize pup growth.

An overview on how components of the melanocortin system respond to different high energy diets

High energy diets are used to model the obesity epidemic. Moreover, from a variety of genetic studies, it has become clear that the melanocortin system plays an important role in the regulation of energy metabolism. Since most dietary interventions are not standardized, fat/sugar-induced effects on the melanocortin system vary distinctly among different studies. How components of the melanocortin system are affected by high energy diets remains unclear. Therefore, in this review, we first present an overview of the effects of high energy diets on different elements of the melanocortin system in both mice and rats. The effects of a high energy diet are most consistent for agouti related protein levels which were either not affected or decreased after consumption of a high energy diet, whereas for proopiomelanocortin and the melanocortin receptor expression (and binding) it was difficult to define an overall response to a high energy diet. Because of the complexity of the melanocortin system, it is important to measure more than one element of the system. Only a few studies measured both melanocortin peptide and receptor expression and show that a high fat diet consumed for a longer period of time starting at an early age increases melanocortin signaling, whereas in adulthood a very high fat diet decreases melanocortin signaling. Finally, we review our own data on diet-induced changes in peptide expression and melanocortin binding and show that short term exposure to a free-choice high-fat high-sugar diet also decreases melanocortin signaling which supports hyperphagia observed in this model.