Obesity is a major health concern, affecting nearly one-third of adults in the United States alone. It has been established that obesity contributes to many pathologies including cardiovascular disease and altered metabolism. Researchers recently observed that obesity diminishes protein metabolic turnover in skeletal muscles following a protein-rich meal. In other words, excessive fat accumulation diminishes muscle sensitivity to dietary protein intake and results in decreased protein synthesis following meal ingestion. Health care providers should focus on restoring sensitivity of muscles to ingested proteins by encouraging physical exercise prior to meal intakes.
Obesity is a major health concern, affecting one-third of the adults in the United States alone. It has been well established that excessive accumulation of body fat contributes to the development of a variety of pathologies, including cardiovascular disease and metabolic disorders. Furthermore, it has been proposed that the skeletal muscle, a primary regulator of the basal metabolic rate, has impaired protein metabolism in obese and overweight individuals. It is thought that the impaired metabolic activity is a result of improper protein turnover or the lack of sensitivity to protein-rich meals. In other words, individuals with excessive fat accumulation tend to react differently, metabolically, following a protein-rich meal compared to healthy individuals.
A group of researchers compared protein synthesis response, in skeletal muscles, following a protein-rich meal in healthy, overweight, and obese adults. They hypothesized that ingestion of protein-rich meal would stimulate the skeletal muscles in all participants, and thus result in similar postprandial (after meal) protein synthesis rates. A total of thirty participants were recruited including ten healthy adults, ten overweight adults, and ten obese adults. The participants in the three groups were balanced for age and sex. At baseline, each participant’s glucose tolerance, blood pressure, body weight, and height were measured. On the day of experimentation, following a starvation period, the participants were given 170 g lean pork loin as a meal. The meal was representative of the typical protein amount consumed by adults in the United States at dinner, and was enough to stimulate protein synthesis.
The researchers demonstrated that blood glucose levels were similar for all three groups following meal consumption. However, insulin concentrations were much higher in obese participants in comparison to overweight and healthy individuals. Hyperinsulinemia, a condition with elevated insulin levels in the blood, has been associated with many metabolic diseases and pathological conditions. Additionally, researchers demonstrated that protein synthesis in skeletal muscles was similar at baseline between all three groups. Following the meal, however, healthy individuals had a significant increase in protein synthesis, whereas no increased synthesis was observed in overweight and obese individuals. This was true despite having all three groups demonstrating an increase in amino acid content following the protein-rich meal. The researchers also investigated molecular mechanisms, including the mTORC1 protein, which responds to nutrition intake and regulates metabolic activity. It was discovered that mTORC1 protein and phosphorylated mTORC1 were elevated in obese and overweight participants. The researchers proposed that this elevation may contribute to the inability of skeletal muscles to respond to a protein-rich meal in obese and overweight individuals.
In conclusion, researchers observed a diminished protein synthesis response in obese and overweight individuals following a protein-rich meal. In other words, excessive fat accumulation may contribute to defective metabolic signaling in skeletal muscles, as a result of an impaired sensitivity to dietary proteins following a protein-rich meal. Promoting strategies like physical activity before eating can improve sensitivity of muscles to dietary proteins, and should be a therapeutic focus in obese and overweight individuals.
Written By: Haisam Shah, BSc