Last week, some local hospital sponsored a health fair where I work. Employees who wanted the free cholesterol test were told to fast overnight. At an early afternoon meeting later that day, one of my co-workers struggled to explain something, then apologized with “Sorry, I can’t think straight. I haven’t eaten since last night, and I haven’t had time to grab lunch yet.”
Heh-heh … I hadn’t eaten since dinner the previous night either, and wasn’t planning to eat until 7:00 p.m. or so. I wasn’t hungry, or tired, or mentally foggy. That’s because I’m used to it. Most Mondays and Thursdays, I don’t eat until dinner. Those are my 24-hour intermittent fasts.
If you haven’t tried intermittent fasting, I’d recommend it. I’d also recommend you educate yourself first by picking up a copy of The Complete Guide to Fasting by Dr. Jason Fung and Jimmy Moore. (Why the heck this thing isn’t called Fasting Clarity is beyond me. I’ll ask Jimmy when he visits us for Thanksgiving week.)
Dr. Fung wrote about the benefits of fasting at the end of his excellent book The Obesity Code. This book is the extended version of those chapters, with an introduction by Jimmy, fasting success stories supplied by some of Dr. Fung’s patients, and commentary by health experts such as Mark Sisson, Abel James, Dr. Thomas Seyfried and Robb Wolf.
In his half of the introduction, Dr. Fung explains that he looked into fasting largely out of frustration. He was treating type 2 diabetics the traditional way, and neither he nor his patients were happy with the results:
Instinctively, most patients knew what we were doing was wrong. They would say to me, “Doctor, you have always told me that weight loss is critical in the treatment of type 2 diabetes, yet you have prescribed me insulin, which has made me gain so much weight. How is that good for me?” I never had a good answer for this. Now I knew why. They were absolutely right; it wasn’t good for them.
As patients took insulin, they gained weight, and when they did, their type 2 diabetes got worse, demanding more insulin. And the cycle repeated: they took more insulin, they gained more weight, and as they gained more weight, they needed more insulin. It was a classic vicious cycle.
We doctors had been treating type 2 diabetes exactly wrong. With the proper treatment, it is a curable disease. Type 2 diabetes, like obesity, is a disease of too much insulin. The treatment is to lower insulin, not raise it. We were making things worse. We were fighting the fire with gasoline. I needed to help my obesity and type 2 diabetes patients lower their insulin levels, but what was the best approach?
Certainly, there are no medications that do this. There are surgical options that help, such as bariatric surgery (commonly called “stomach stapling”), but they are highly invasive and have many irreversible side effects. The only feasible treatment left was dietary: reducing insulin levels by changing eating habits.
The change in eating habits included adding various fasting protocols to a better overall diet. As Dr. Fung emphasizes in the book, intermittent fasting does not give us license to live on a junk diet on non-fasting days.
Jimmy’s half of the introduction describes his own experiences with fasting, ranging from his first attempts at intermittent fasting, all the way through his n=1 experiments with 21-days fasts. He learned a few hard lessons along the way, such as don’t drink diet sodas while fasting, and don’t try to fast when you’re in a period of high stress.
The chapters in Part One describe what fasting is and why it’s good for your health. Part of understanding what fasting is understanding what it isn’t: it’s not starvation, and it’s not living on a permanent low-calorie diet.
Starving and fasting should never be confused with each other, and the terms should never be used interchangeably. Fasting and starving live on opposite sides of the world. It is the difference between recreational running and running because a lion is chasing you. Starvation is forced upon you by outside forces. Fasting, on the other hand, may be done for any period of time, from a few hours to months on end. You may begin a fast at any time of your choosing, and you may end a fast at will, too. You can start or stop a fast for any reason, or for no reason at all.
As later chapters explain more fully, low-calorie diets and fasting produce markedly different hormonal responses. That’s why most low-calorie diets fail. We’re eating less, but still eating. The body still believes it’s supposed to store calories, but there are fewer of them. So the body may respond by slowing the metabolism. Fasting, on the other hand, produces hormones that tell the body it’s time to tap the reserves.
A decreased insulin level is one of the most consistent hormonal effects of fasting. All foods raise insulin to some degree. Refined carbohydrates tend to raise insulin the most and fatty foods the least, but insulin still goes up in both cases. Therefore, the most effective method of reducing insulin is to avoid all foods altogether. During the initial stages of fasting, insulin and blood glucose levels fall but remain in the normal range, maintained by the breakdown of glycogen as well as gluconeogenesis. After glycogen is used up, the body begins to switch over to burning fat for energy. Longer-duration fasts reduce insulin more dramatically. Regularly lowering insulin levels leads to improved insulin sensitivity—your body becomes more responsive to insulin.
And later in the book …
Most people expect that a period of fasting will leave them feeling tired and drained of energy. However, the vast majority of people experience the exact opposite: they feel energized and revitalized during fasting. Partly this is because the body is still being fueled—it’s just getting energy from burning fat rather than burning food. But it’s also because adrenaline is used to release stored glycogen and to facilitate fat-burning, even if blood sugar is high. The increased adrenaline levels invigorate us and stimulate the metabolism. In fact, studies show that after a four-day fast, resting energy expenditure increased by 12 percent. Rather than slowing the metabolism, fasting revs it up.
My hesitation about intermittent fasting (before I read more on the subject and tried it for myself) centered around the belief that I’d lose muscle mass. In a chapter titled Busting The Myths of Fasting, the book explains why that belief is wrong. Unlike low-calorie dieting, fasting actually encourages muscle growth by spurring production of growth hormone – which makes perfect sense if you think about it from a paleo perspective. If an unsuccessful hunt left paleo man weak and slow, he’d be even less likely to bring down prey on the next attempt. As the book explains:
The most potent natural stimulus to growth hormone secretion is fasting. In one study, over a five-day fasting period, growth hormone secretion more than doubled. During fasting, in addition to the usual early-morning spike of growth hormone (pulsatile), there is also regular secretion throughout the day (non-pulsatile). Both pulsatile and non-pulsatile release of growth hormone is increased during fasting. Interestingly, very low-calorie diets are not able to provoke the same growth hormone response. A study of a religious forty-day fast found that baseline growth hormone levels increased from 0.73 ng/mL to peak at 9.86 ng/mL. That is a 1250 percent increase in growth hormone, all done without drugs. And a 1992 study showed a fivefold increase in growth hormone in response to a two-day fast.
Of course, as many of us have learned from experience, fasting is much easier if your daily diet is a good one. That means real food with real fats. The book takes some well-deserved shots at the U.S. Dietary Guidelines, which turned us into a nation of carbivores who are hungry six times per day. But Dr. Fung (I’m assuming this came from him) doesn’t push a strict low-carb diet either:
Relying on macronutrient-based guidelines or calorie limits makes eating far more complicated than it should be. We do not eat a specific percentage of fats, protein, and carbohydrates. We eat foods. Certain foods are more fattening than others. Therefore, the best advice focuses on eating or not eating specific foods, not specific nutrients.
There is nothing inherently unhealthy about carbohydrate-containing foods. The problem arises when we start changing these foods from their natural state and then consuming them in large amounts. The same also applies to processed fats. Processing transforms relatively innocuous vegetable oils into fats that contain trans fats, toxins whose dangers have now been well recognized.
Chapter four summarizes the many advantages of fasting: it’s convenient, it’s free and it’s flexible – you can add fasting to your lifestyle whether you’re a vegan or a confirmed carnivore. Fasting also allows many people to free themselves of fearing every little treat:
Now, I am not saying that you should eat dessert every single day. However, fasting restores the ability to occasionally enjoy that dessert by balancing out the feast. It is, after all, the cycle of life. Feasts follow fasts. Fasts follow feasts. This is how we have always lived. Birthdays, weddings, holidays, and other special occasions have always, throughout human history, been celebrated with feasts. But those feasts should be followed by fasts.
Even if you do live on a low-carb diet, fasting provides additional benefits:
The very low carb diet does remarkably well, providing you 71 percent of the benefits of fasting, without actual fasting. But sometimes low-carb just isn’t enough. I’ve had many patients who limited their carbohydrates but still had elevated blood sugars. How do you get more power? Fasting. Insulin is the main driver of obesity and diabetes. A very low carb diet can reduce insulin by more than 50 percent, but you can go another 50 percent by fasting. That’s power.
The next several chapters go into more detail about using fasting for specific benefits: to treat type 2 diabetes, to slow the aging process, to boost heart health.
Part Two is the how-to section of the book. I know, I know: how much how-to information do we need to learn how not eat for awhile? Well, there’s more to it than you might think. There’s good advice in here on how to avoid common effects like headaches (salty broths help), who shouldn’t fast (kids, pregnant or nursing women, underweight and malnourished people), and various fasting protocols.
There’s no single protocol that’s best for everyone. Some people may find they do best with a four-hour eating window, some may prefer alternate-day fasting, some may prefer the 5:2 plan popularized by Dr. Michael Mosley in the U.K, and some may want go to for extended fasts lasting several days or longer. The book explains each protocol and describes the advantages.
My protocol, in case you’re curious, is to mix Mosley’s 5:2 with 24-hour fasts. In other words, twice per week I don’t eat for 24 hours, then eat one meal of around 600 calories for dinner. I haven’t noticed a shift in weight, but I view the fasting as a health regimen. After seeing Chareva’s father hobbling around our house because of his stroke, I’m more determined than ever to keep the biological machinery from breaking down.
Part Three is the resources section. There are suggested schedules for various fasting protocols, recipes for broths and teas that make fasting more pleasant, and lots of real-food recipes for meals on non-fasting days.
Like The Obesity Code and Jimmy’s Clarity series, The Complete Guide to Fasting is an easy-to-read, consumer-friendly book that passes my Aunt Martha test. The science nerds will also be happy to see that each chapter ends with a list of references to studies.
When the book was released, Amazon ran out of stock within days. There’s a good reason for that: it’s an excellent resource, and word got around quickly. You may have to wait for a copy, but I believe you’ll be glad you added The Complete Guide to Fasting to your library.