Obesity is associated with numerous chronic diseases. Many obese individuals, however, do not display overt disease. This is due to obese people having altered metabolism that does not meet the threshold needed for a clinical diagnosis. Muscle protein turnover appears to be reduced in obesity, where proteins that are damaged and worn out are not replaced as efficiently. However, muscle protein metabolism in obese people has only been measured in situations that do not reflect real-life (i.e. highly controlled laboratory settings with the amino acids being delivered intravenously). The consumption of dietary protein is a well described strategy to stimulate muscle protein synthesis rates in young healthy weight adults. The most effective protein sources to consume to maximize the muscle protein synthetic response generally have a high degree of digestibility leading a high proportion of the dietary protein derived amino acids becoming available into circulation. Animal based protein sources, such as pork, are highly digestible and thus provide a strong stimulatory signal to muscle after their ingestion. Importantly, pork is also rich in the amino acid leucine, which is an important nutrient signaling molecule to muscle.
Thus, the main objectives of this study were 1) determine the impact of consuming high quality protein derived from pork on the synthesis rate of new muscle proteins, and 2) measure the activation of anabolic signals in the muscle after consuming pork in overweight and obese young adults. We also sought to describe the systemic responses in blood glucose and plasma insulin and amino acids to pork ingestion. This was accomplished by measuring muscle protein synthesis before and after eating 6 oz. of lean pork in overweight and obese young adults and comparing their responses to those of healthy-weight controls.
Our findings were:
1) Systemic factors were improved by eating pork in all groups. Specifically, pork ingestion resulted in a large rise in blood amino acids without causing an increase in blood sugar.
2) Anabolic signals in the muscle of overweight and obese adults are hyperactive (~3 times greater) at baseline when compared to the healthy-weight controls. Thus, the ability of blood amino acids to signal to skeletal muscle seems to be diminished with greater fat mass. However, pork ingestion strongly activated anabolic signaling molecules in muscle in healthy weight adults.
3) Muscle protein synthesis in overweight and obese adults is less responsive to pork ingestion than healthy-weight controls. This finding is in agreement with previous reports that used constant amino acid infusions, suggesting that overweight and obese people have intrinsic differences in anabolic signaling that is not overcome by increasing circulating amino acids or insulin by ingesting pork. However, pork ingestion strongly stimulates muscle protein synthesis rates in healthy weight adults and to a degree that is commonly observed after the ingestion of other high quality proteins such as beef, eggs, or milk.
Overall, pork ingestion may have beneficial effects on glucose tolerance in obese people, but intrinsic defects in the muscle of overweight and obese people limit their skeletal muscle anabolic response to food ingestion.