Studies with rats have shown that Leptin resistance (in combination with insulin resistance and weight gain) is seen in rats after they are given unlimited access to palatable, energy-dense foods. This effect can be reversed when the rats are again fed a better diet and are not given unlimited access to the food. This suggests the value of human beings moving toward a balanced intake of foods that are unrefined along with appropriate portion control. Interestingly, this approach is what is mirrored in the Longevity Lifestyle Matters program. Studies in 2008 (led by Shapiro) and in 2010 (led by Oswal) suggest that that the main role of leptin is to act as a starvation signal when levels are low and to help maintain fat stores for survival, rather than a satiety signal to prevent overeating. Leptin levels signal when an animal has enough stored energy to spend it in pursuits besides acquiring food.