LEP and Insulin resistance: A review of studies that made use of a high fat diet (typically in young animals) documented several physiological changes with the following being most common11: weight gain of 10-20% over standard chow-fed rats, insulin resistance after as little as 2 weeks on a high fat diet, moderate hyperglycemia after prolonged exposure to high fat diet, elevated leptin levels, hepatic steatosis and changes to pancreatic β cells and insulin secretion.