A researchers designing investigation to test what affect eating different types of food we have a blood insulin levels she selected 10 mill subjects were all 25 years of age and in good health day experiment took place over three days ago at 8 AM each day the subject 80 mill consisting of one only type of food they had the blood insulin levels measured as exam in the mail on day one day at a high fat diet on day two day they are high protein diet and I D3 there a horse show sugar daddy what is the manipulative independent variable in this