Meal-feeding scheme: twenty years of research in Brazil

Adipose tissue is less responsive to food restriction anti-inflammatory effects than liver, muscle, and brain in mice

High caloric intake promotes chronic inflammation, insulin resistance, and chronic diseases such as type-2 diabetes, which may be prevented by food restriction (FR). The effect of FR on expression of pro-inflammatory and anti-inflammatory genes in adipose tissue, liver, muscle, and brain was compared. Male Swiss mice were submitted to FR (FR group) or had free access to food (control group) during 56 days. The liver, gastrocnemius muscle, brain, and epididymal white adipose tissue (WAT) were collected for analysis of gene expressions. FR attenuated inflammation in the liver, brain, and gastrocnemius muscle but did not markedly change inflammatory gene expression in epididymal WAT. We concluded that adipose tissue was less responsive to FR in terms of gene expression of pro-inflammatory and anti-inflammatory genes.

Ramadan and Its Effect on Fuel Selection during Exercise and Following Exercise Training

Fasting induces short-term physiological adaptations which spare the body's remaining carbohydrate stores and mobilize lipid stores to provide a substitute fuel for many tissues and organs, especially skeletal muscle. Rodent studies show that regular occurrence of fasting then refeeding, stimulates adaptations in muscle which make the animal better placed to withstand a further period of fasting by possessing a better ability to oxidise lipid.This review explores the research describing these adaptations, with an emphasis on Ramadan, a human model of repeated fasting/refeeding. Separately, a single bout of endurance exercise places similar metabolic stress on the body as fasting since the exercising muscle must reduce its use of carbohydrate and utilize lipid more readily as exercise progresses. Not surprisingly therefore, adaptations in muscle to repeated bouts of endurance exercise (endurance training) are similar to those seen with repeated fasting/refeeding. Superimposing the stressors of repeated fasting/refeeding and exercise training, and subsequent adaptations to the muscle and exercise response, are examined by describing the published research which has investigated the situation where athletes continue their training whilst participating in Ramadan.

Insulin sensitivity and liver glucose production in the rat are influenced by lifetime food restriction

In both humans and rats, food restriction leads to increased insulin sensitivity and predisposition to hypoglycemia. We hypothesized that metabolic responses to hypoglycemic episodes could be altered in food-restricted rats. To test our hypothesis, plasma glucose levels and liver glucose production during insulin-induced hypoglycemia were assessed. Rats either had free access to food (FF group) or were food restricted from birth (FR group). As adults, they were subjected to insulin-induced hypoglycemia after an overnight fast. Plasma glucose was measured before (time 0) the intraperitoneal injection of insulin (1 U/kg) and at regular intervals for 300 minutes. Some FF and FR rats received oral glucose (100 mg/kg) 15 minutes after insulin injection, and the same time intervals were investigated. The FR rats showed a larger decrease and slower recovery of plasma glucose than the FF group, and this was not influenced by oral glucose. Liver glucose production from glycogenolysis and gluconeogenesis (ie, before and during the infusion of L-alanine) was higher and lower, respectively, in the FR rats than in the FF rats, either with or without oral glucose before liver perfusion. Preference for glycogenolysis could be a metabolic adaptation for the maintenance of plasma glucose levels during fasting despite lower food availability in the FR rats. However, long-term FR increased the severity of hypoglycemia and impaired plasma glucose recovery. In addition, hypoglycemia could not be prevented by glucose administration. Therefore, food restriction in individuals with intensive insulin therapy should be more rigorously examined.

Patterns of fos activation in rat raphe nuclei during feeding behavior

To analyze the differential recruitment of the raphe nuclei during different phases of feeding behavior, rats were subjected to a food restriction schedule (food for 2 h/day, during 15 days). The animals were submitted to different feeding conditions, constituting the experimental groups: search for food (MFS), food ingestion (MFI), satiety (MFSa) and food restriction control (MFC). A baseline condition (BC) group was included as further control. The MFI and MFC groups, which presented greater autonomic and somatic activation, had more FOS-immunoreactive (FOS-IR) neurons. The MFI group presented more labeled cells in the linear (LRN) and dorsal (DRN) nuclei; the MFC group showed more labeling in the median (MRN), pontine (PRN), magnus (NRM) and obscurus (NRO) nuclei; and the MFSa group had more labeled cells in the pallidus (NRP). The BC exhibited the lowest number of reactive cells. The PRN presented the highest percentage of activation in the raphe while the DRN the lowest. Additional experiments revealed few double-labeled (FOS-IR+5-HT-IR) cells within the raphe nuclei in the MFI group, suggesting little serotonergic activation in the raphe during food ingestion. These findings suggest a differential recruitment of raphe nuclei during various phases of feeding behavior. Such findings may reflect changes in behavioral state (e.g., food-induced arousal versus sleep) that lead to greater motor activation, and consequently increased FOS expression. While these data are consistent with the idea that the raphe system acts as gain setter for autonomic and somatic activities, the functional complexity of the raphe is not completely understood.

Effect of a meal feeding schedule on hepatic glycogen synthesis and gluconeogenesis in rats

We investigated the effect of a meal feeding schedule (MFS) on food intake, hepatic glycogen synthesis, hepatic capacity to produce glucose and glycemia in rats. The MFS comprised free access to food for a 2-hour period daily at a fixed mealtime (8.00-10.00 a.m.) for 13 days. The control group was composed of rats with free access to food from day 1 to 12, which were then starved for 22 h, refed with a single meal at 8.00-10.00 a.m. and starved again for another 22 h. All experiments were performed at the meal time (i.e. 8.00 a.m.). The MFS group exhibited increased food intake and higher glycogen synthase activity. Since gluconeogenesis from L-glutamine or L-alanine was not affected by MFS, we conclude that the increased food intake and higher glycogen synthase activity contributed to the better glucose maintenance showed by MFS rats at the fixed meal time.