Aging is the primary cause of decreased insulin sensitivity, surpassing obesity and genetics.
"What's the number one cause of decreased insulin sensitivity? Yeah, obesity is a big deal. Yeah, genetics are a big deal. But number one, the biggest deal is growing old." (said at 1:06:15)
Published physiological studies using gold-standard hyperinsulinemic-euglycemic clamps demonstrate that chronological aging itself is not the primary driver of decreased insulin sensitivity. Rather, age-associated declines in insulin sensitivity are predominantly driven by increased adiposity (especially visceral/ectopic fat) and physical inactivity. When older and younger individuals are matched for body composition and fitness levels, or when older adults undergo endurance training, insulin sensitivity remains largely preserved across age groups, directly contradicting the assertion that aging surpasses obesity and genetics as the primary cause.
- contradicts: Physical inactivity and obesity underlie the insulin resistance of aging. (Diabetes care 2009)
"Insulin sensitivity was not different in younger endurance-trained athletes versus older athletes, in younger normal-weight subjects versus older normal-weight subjects, or in younger obese subjects versus older obese subjects. Regardless of age, athletes were more insulin sensitive than normal-weight sedentary subjects, who in turn were more insulin sensitive than obese subjects. CONCLUSIONS Insulin resistance may not be characteristic of aging but rather associated with obesity and physical inactivity." (abstract, results and conclusions, passage verified)
pubmedfull study (doi)