Cows, like humans, produce insulin-like growth factor in response to growth hormones and release it into the blood, and the protein makes its way into their milk.

The group's analysis points to a connection between calorie intake and a protein called Insulin-like Growth Factor (IGF) -1, with obesity increasing and calorie restriction decreasing levels of IGF-1.

Several studies have found that insulin promotes the growth of bone through the over-expression of a bone-building protein known as insulin-like growth factor 1 (IGF-1).