Final answer:
Chronic high blood insulin (hyperinsulinemia) primarily promotes fat storage in the body, leading to an increase in body fat. It does not enhance muscle growth or improve insulin sensitivity.
Step-by-step explanation:
Chronic high blood insulin, known as hyperinsulinemia, impacts body composition primarily by promoting fat storage. Insulin is a hormone responsible for regulating blood glucose levels by promoting the absorption of glucose into the liver, fat, and muscle cells, where it's either used for energy or stored for future use. Elevated insulin levels enhance the liver's conversion of glucose into glycogen and increase the synthesis of triglycerides in adipose cells, leading to an increase in body fat. Despite its role in the breakdown of stored glycogen into glucose and the stimulation of muscle protein synthesis, chronic hyperinsulinemia does not enhance muscle growth or improve insulin sensitivity; rather, it creates an environment conducive to fat accumulation.