Dr. Jason Fung says that we have failed to perceive the profound and wide-reaching health benefits of a very simple practice: fasting.
In The Complete Guide to Fasting: Heal Your Body Through Intermittent, Alternate-Day, and Extended Fasting, Dr. Fung argues that it is a key tool for maintaining optimal health, losing weight and sustaining the loss, controlling Type 2 diabetes, improving heart health, preventing cancer, and fighting aging.
As a kidney specialist, Dr. Fung spends most of his time with patients who suffer from obesity and diabetes. Most have been treated with insulin for the diabetes and for obesity given “calories in, calories out” advice, meaning they are merely told, “eat less, exercise more.”
Since completing his medical training in 2001, Dr. Fung has gone through several shifts in his approach to diabetes and obesity. A major breakthrough came when he realized that both Type 2 diabetes and obesity are an insulin resistance problem. The body actually has plenty of insulin but it’s not working right. It requires more and more insulin to manage a diabetic’s blood sugar. Dr. Fung says giving insulin to these patients is like “fighting the fire with gasoline” and that they will eventually be overwhelmed by diabetes and obesity.
Once Dr. Fung began to focus on insulin resistance, he realized that diet can either exacerbate the body’s insulin problem or help heal it. In the 2000s, he began to follow the story of low-carb dieting’s promise for helping obesity, an idea that increasingly gained traction in the medical literature. As is typical for doctors, Fung had almost zero instruction on nutrition and diet in nine years of medical training, and he was very skeptical at first. Gradually he made the shift, though, and in 2012 he founded the Intensive Dietary Management Program to help his patients through diet and nutrition.
There was one more shift to come in Dr. Fung’s thinking, however. He discovered that, even though diet can effectively treat obesity and diabetes, it is extremely difficult to achieve dietary change and maintain it. Long-term studies show that less than 1 percent of people stick with dietary changes. However, when Dr. Fung began to prescribe fasting—an extremely simple idea to understand and practice—his patients made breakthroughs and maintained health. He saw much greater success with maintaining weight loss and reversing Type 2 diabetes.
Dr. Fung maintains that diet is important and a ketogenic diet—high fat, low-carb, adequate protein—is preferred for addressing insulin resistance, but diet is not his focus. He does not insist patients adopt any macronutrient balance model—whether that’s low-fat, or low-carb, Atkins, the Zone, or any other fad that comes along. It’s just too complex for most people to understand and put into practice, so he keeps it simple. He encourages people to avoid anything that comes in a package or is highly processed. Eat real food, whether broccoli or beef, he says. And practice fasting, which allows you to make some mistakes and occasionally indulge without worsening your insulin resistance.
The Complete Guide to Fasting is a nicely designed book presenting the history and science of fasting, explanations of different types of fasting, practical strategies for how to fast, a recipe section of foods and meals to be eaten in coordination with fasting, and many testimonials of both patients and health experts who have benefited greatly from fasting.
Biochemistry of eating and fasting
Dr. Fung explains that when we eat, insulin regulates whether the energy we take in will be used up or stored in the liver and in fat. If we have insulin resistance, our energy regulation is dysfunctional: There is a vicious cycle of storing too much energy and the insulin resistance gets worse and worse. In order to improve our insulin sensitivity and energy regulation, we must keep our insulin levels consistently low somehow. Fasting is the answer. It is much simpler and more powerful than difficult-to-follow diets for reducing insulin, Dr. Fung says.
Many people mistakenly assume that the cure of fasting must be worse than the disease. They think they’ll be starving, tired, and miserable, but Dr. Fung is quick to point out that just the opposite is true. Many people report that it is relatively easy to fast and they even feel great while doing so.
There is plenty of scientific evidence to show the body quickly adjusts to fasting. Adrenaline increases and stimulates our metabolism. Human Growth Hormone increases availability of fats for fuel. There are hunger waves, but the body is fueled by ketones and appetite is suppressed. Many people report long periods of absence of hunger and increased mental clarity while fasting. Drinking water, tea, coffee, or bone broth also helps the body get through hunger waves.
How to fast for health
The Complete Guide to Fasting is packed full of information about various methods of fasting, but there are two main categories: intermittent fasting and longer fasts. “Intermittent” refers to fasts done at irregular intervals, and it has become very popular in health circles in the last few years. A common way to fast intermittently is simply to not eat from after dinner until lunchtime the next day. This results in a 14- to 18-hour fast, and it can be done a few times a month or a few times a week. Dr. Fung says many people see significant benefits from this simple practice.
Sometimes intermittent fasting is not enough to help a patient breakthrough, but a longer fast of 24, 36, or 48 hours often does it. And many people do longer fasts of several days, and for various reasons. It could be for spiritual reasons or trying to overcome a nagging health problem. Some athletes even say that fasting resets their body and helps them reach peak performance.
Of course, some people such as expectant mothers and children should not fast, and others, such as those with diabetes or serious health conditions, should only fast carefully under a doctor’s supervision.
The promise of fasting
Perhaps the most interesting chapter of the book is the one on fasting for Type 2 diabetes, which has become an epidemic. The incidence has quadrupled since the 1980s. Dr. Fung reports that “in 2012 14.3 percent of American adults had diabetes and 38 percent had pre-diabetes, for a total of 52.3 percent.” Dr. Fung reviews forgotten medical history in this chapter and argues that fasting has “been known to cure type 2 diabetes for over a hundred years.”
The chapters on anti-aging and heart health also contain fascinating information. During World War II, some prisoners forced to go without food experienced astonishing increases in mental abilities, such as learning languages effortlessly and memorizing entire books. Science is only beginning to understand fasting’s effects on the brain, but there are indications it could help with Parkinson’s and Alzheimer’s diseases. Fasting is known to stimulate “autophagy,” the process by which cells replace themselves and renew tissues. When it comes to heart disease, Dr. Fung says that fasting reduces triglycerides released from the liver, and that is much more important than cholesterol in the blood, which still gets the blame for heart disease despite the notion being debunked for decades.
Caveat and conclusion
One caution for Christian readers of this book is that Dr. Fung does not share a Christian worldview. He notes that all religious traditions see spiritual benefits in fasting but doesn’t focus on that. (See previous articles if you are looking for resources on the spiritual dimensions of fasting.) Several times Dr. Fung mentions in passing the theory that fasting must work because sometime in the deep evolutionary past man had to adapt to a lack of food, which is an unnecessary premise for his thesis.
Overall, though, this book is a comprehensive and ground-breaking resource on fasting. The claims are carefully supported by Dr. Fung’s clinical practice, medical literature, and the many detailed and engaging testimonials included in the book. He makes a compelling case that fasting is a powerful but overlooked remedy for whatever ails us, and that we could all benefit from fasting in one way or another.
This article is for educational purposes only and not meant as medical advice.