The Glycemic Index and Fasting
The best approach to eating is a low-glycemic diet, and one that is centered on wholesome, nutritious foods. A low-glycemic diet is any diet aimed at controlling blood sugar. Even though fasting may reduce the effects of poor eating habits, it's not a powerful enough mechanism to completely prevent or reverse the ailments brought about from an unhealthy diet.
When considering a low-glycemic diet, make sure you consider these two factors:
Glycemic index: The glycemic index tells you how quickly your blood sugar rises after eating a certain food. Foods that have a high glycemic index, such as sugary foods, tend to spike insulin levels and raise blood sugar very quickly.
Glycemic load: The glycemic load tells you how much a food spikes your insulin and raises your blood sugar overall, regardless of time. Typically, the more carbs a food contains, the higher the glycemic load, but not necessarily the glycemic index. For example, whole grains, because they're digested slowly, typically have a lower glycemic index, but because they're carb heavy, they tend to have a higher glycemic load.
So, if you want to eat for health and leanness, then your aim must be to focus your diet around foods that are low glycemic — that is, foods that have both a low glycemic index and low glycemic load.
These foods include lean protein sources (such as chicken and turkey), fatty protein sources (such as a grassfed steak), healthy fat sources (such as nuts, seeds, or extra-virgin olive oil), most vegetables (such as broccoli, cauliflower, and so on), and some fruits (such as blueberries and blackberries).