Through most of history, fasting was done for religious reasons; ancient shamans fasted to reach an altered state, Christians throughout the ages fasted on certain holy days, and other religions have their own traditions. People have probably been fasting for as long as humans have existed. In the last century, however, fasting has usually been done for health-related reasons. And while it’s long been popular in certain circles, in the past few years fasting has really gone mainstream.
This popularity is due in large part to good marketing and a handful of health-conscious celebrities who’ve touted fasting as the cure to a whole range of ills. From the 5/2 diet and other intermittent fasting plans to an endless array of “cleanses,” fasting is everywhere. But is there any truth to the health claims made for fasting? Can fasting, for instance, cure type 2 diabetes?
What is a “fast” anyway?
Strictly speaking, “fasting” is abstaining from all food for a prescribed period of time. It’s where the word “breakfast” comes from; we have dinner, then we abstain from food (in other words, we fast) until we wake up the next day and eat our morning meal—when we “break” our fast. Historically, people might also “fast” from certain foods. For instance, until the mid-twentieth century Roman Catholics “fasted” from meat on Fridays.
The modern definition is a bit more slippery, but generally means to abstain from solid food for a prescribed period of time, usually anywhere from 24 hours to 7 days. Some “fasts” allow fruit juice, tea or coffee. Some fasts ask you to consume smoothies made with special ingredients. A few ask you to abstain from all but one selected food.
Whatever the rules for the specific “fast” you undertake, all forms of fasting do one of two things: they either force you to focus very tightly on what, when, and how you’re eating, or they take food completely out of the picture so that you don’t have to worry about it. The first can be a good thing for anyone with a problem diet—which includes everyone with type 2 diabetes. The second, not so much.
The science behind diabetes reversal through diet
Two types of dietary intervention have been shown to have the potential to reverse type 2 diabetes. These are extreme calorie restriction (a Very Low Calorie Diet or VLCD), and a very low carbohydrate diet, commonly known as a “keto” diet.
In a typical VLCD, total calories are restricted to anywhere between 600 and 800 calories per day. With such limited energy available from food, the body turns from using dietary carbohydrates for fuel and instead begins to use fat for energy—a state known as “ketosis.”
In ketosis (which shouldn’t be confused with ketoacidosis, a medical problem diabetics can face), the body converts fats to something called “ketone bodies” which it then uses for energy rather than glucose derived from carbohydrates. This results in rapid weight loss, beginning with fat in and around the liver and pancreas. This loss of fat in and around theses vital organs is what leads to remission of type 2 diabetes.
In a very low-carb diet, the body also enters ketosis (which is why this type of diet is often referred to as a “keto” diet). In this case, total calories aren’t restricted, but carbohydrates are. The missing carbohydrates are replaced with dietary fat. And without the constant influx of carbs, the body must turn to fat for fuel.
Since fat doesn’t cause the body to produce insulin, insulin levels drop. Fat has little effect on blood sugar, so blood glucose also drops. And since it takes far less fat than carbs to make us feel full, most people eat much less on a keto diet than on the standard carb-filled diet. Not surprisingly, this results in weight loss—including loss of fat in and around the liver and pancreas.
To fast, or not to fast?
The dietary interventions above have been clinically shown to reverse type 2 diabetes in anywhere from 40% to 80% of people. Fasting too restricts calories and carbs. So will fasting have the same effect as these diets? Probably not.
While for a handful of people a fast of five to seven days might be enough to bring fasting glucose levels back into the normal range, that’s only the tip of the iceberg. Studies show that complete reversal through calorie restriction takes roughly eight weeks, and reversal via a keto diet may take anywhere from six to eighteen months. A fast of more than a few days, however, is impossible and in fact is downright dangerous.
The bottom line? You can reverse type 2 diabetes through diet, but fasting is probably not the answer. Instead, look into a VLCD-based program such as the DWD Lifestyle Blueprint or plan your own ketogenic diet. Once you have reversed your diabetes you can revisit the topic of fasting—particularly intermittent fasting—as a tool for maintaining health.