The glycemic index (GI) is an indicator of how quickly your body’s blood sugar will rise after eating a particular food. No matter what you eat, your blood sugar will temporarily increase as your pancreas secretes insulin into the bloodstream. However, how much your blood sugar increases (and you don’t want it too spike too much) depends on what kinds of foods you eat, particularly carbohydrates. Foods that are mostly fat or protein don’t raise the blood sugar as much (and don’t have as high of a glycemic index) as carbohydrates do so the GI mostly pertains to carb-heavy foods, such as grains and fruits.
In the GI, each food gets a score out of 100. You want to stick to food choices that have a score of less than 50. Foods with a score of less than 50 take longer to digest and don’t induce as much insulin to be released into the bloodstream, which is especially pertinent on fasting days, if you’re adhering to either the 5:2 Diet or the Warrior Diet as you eat some food during the fast. Your fast will be incredibly difficult to successfully complete if you experience a spike in blood sugar.
Typically, foods made from grains come with a high GI score. Dairy can also be problematic, particularly if you’re lactose-intolerant or have difficult digesting dairy. Because fasting and the Paleo Diet complement one another nicely, you should completely cutting grains and dairy from your diet and focus on getting your carbohydrates (and the nutrients you typically get from grains and diary) from fruits, vegetables, and some carb-rich nuts, such as cashews.
Be careful with how much fruit you consume. Although fruit is bursting with nutrients, some fruits are also quite sugar dense, and some high glycemic, such as pineapple and melon. Stick to vegetables and lower glycemic fruits, such as berries.
You can find a glycemic index chart online by typing “glycemic index chart” in your favorite search engine.