Regulation of Macronutrient Intake—Carbohydrate, Fat and Protein

Appetite regulation and energy balance

The decision to begin eating or to stop eating is a complex process. Hunger is primarily driven by hunger signals, like ghrelin and neuropeptide Y, originating from the gastrointestinal tract and from the hypothalamus. The hunger signals stimulate the seeking of food and the eating, being activating for the body and mind. Thirty minutes after the start of eating, satiety signals arise from the intestinal tract and, in between meals, from the adipose tissue and liver. Satiety signals are sedative and arrest the processing of food in the intestine, hence leading to termination of eating. One problem with overeating today is the ready access to palatable food, such as sucrose and fat. The palatable food works by weakening the satiety signals and activating the hunger signals. The reward system with endogenous opiates may also be activated.

CONCLUSIONS

Food and drinks rich in sucrose and fat should be given in a restricted way to children, since there is no biological control feedback to regulate the intake of such products.

Plasma enterostatin: identification and release in rats in response to a meal

OBJECTIVE

To discover a possible absorption and/or secretion of enterostatin into the circulating blood, as well as to compare the levels of circulating enterostatin after high-fat feeding and low-fat feeding.

RESEARCH METHODS AND PROCEDURES

Using a specific enzyme-linked immunosorbent assay, plasma enterostatin levels were determined after feeding a high-fat, a high-fat/-sucrose, or a low-fat meal to Sprague-Dawley rats deprived of food overnight.

RESULTS

The enterostatin levels were increased by all diets; the response to the high-fat and the high-fat/-sucrose meals was greater in magnitude and duration than that to the low-fat meal. In addition, enterostatin levels correlated with the intake of dietary fat. Plasma enterostatin levels after high-fat feeding were found to be similar to those after intravenous administration of exogenous enterostatin known to inhibit high-fat food intake. Gel chromatography of pooled postprandial plasma extracts followed by high-performance liquid chromatography analysis showed that plasma enterostatin was identical to synthetic enterostatin. Affinity cross-linking of plasma proteins with 125I-enterostatin on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, followed by autoradiography, revealed a single band with a molecular weight of about 66 kDa, indicating the presence of a potential enterostatin-binding protein in plasma.

DISCUSSION

The measurements of plasma enterostatin may be a sensitive indicator for the measurement of fat intake.

Mitochondrial ATP synthase--a possible target protein in the regulation of energy metabolism in vitro and in vivo

The increasing prevalence of obesity in the Western world has stimulated an intense search for mechanisms regulating food intake and energy balance. A number of appetite-regulating peptides have been identified, their receptors cloned and the intracellular events characterized. One possible energy-dissipating mechanism is the mitochondrial uncoupling of ATP-synthesis from respiratory chain oxidation through uncoupling proteins, whereby energy derived from food could be dissipated as heat, instead of stored as ATP. The exact role of the uncoupling proteins in energy balance is, however, uncertain. We show here that mitochondrial F1F0-ATP synthase itself is a target protein for an anorectic peptide, enterostatin, demonstrated both after affinity purification of rat brain membranes and through a direct physical interaction between enterostatin and purified F1-ATP synthase. In insulinoma cells (INS-1) enterostatin was found to target F1F0-ATP synthase, causing an inhibition of ATP production, an increased thermogenesis and increased oxygen consumption. The experiments suggest a role of mitochondrial F1F0-ATP synthase in the suppressed insulin secretion induced by enterostatin. It could be speculated that this targeting mechanism is involved in the decreased energy efficiency following enterostatin treatment in rat.