In Chapter 3 of The Complete Guide To Fasting: Heal Your Body Through Intermittent, Alternate-Day, and Extended Fasting, Dr. Jason Fung deals with what he perceives to be the many myths surrounding fasting. He believes that if a person looks at both the anecdotal and scientific evidence he has to offer, that the case against fasting falls to pieces. Let’s take a look at the six myths he addresses.

“Myth #1: Fasting Puts You in ‘Starvation Mode'”

If you’re unfamiliar with the term ‘starvation mode,’ it’s the idea that if the body is put on a tight caloric restriction for a long enough period of time, it will adapt by suppressing metabolic rate. In other words, if you’re not getting enough to eat for days on end, your body will lower its energy needs to compensate. There may be no other self-preservation mechanism the dieter fears more. Just think, cutting calories and passing on dessert…for nothing.

Naturally, one would assume that if cutting back a bit makes for a sluggish metabolism, fasting must surely cause it to bottom out! Dr. Fung argues to the contrary. Though studies do show that cutting calories can indeed negatively impact metabolism, Fung states that such a reduction in a person’s basal metabolic rate does not occur with fasting. How could this be so? He explains that when a person fasts, stored fat provides for all of a person’s energy needs and the body therefore never perceives the deprivation.

“Myth #2: Fasting Makes You Burn Muscle”

Given that the body in a fasting state needs to get nutrients and energy from somewhere, one might assume that muscle loss would be an obvious consequence of fasting. Dr. Fung says this does not actually happen.

Fung begins by arguing that the body is meant to survive periods of fasting and does not turn to muscle as an energy source until body fat drops below 4%. If the body did not fight to preserve muscle, humans would not survive famines and hard times. He mentions one study that backs up his claim; in a study that observed alternate-day fasting for 70 days, body weight decreased by 6%, but fat mass decreased by 11.4% and lean mass (comprised of muscle and bone) did not change at all. This study was conducted with 16 participants in both controlled and non-controlled settings.

He points out that if you are truly worried about muscle loss, exercise should be your top priority as this is the key to building muscle. He says diet and exercise are two separate issues and shouldn’t be confused. A person shouldn’t be concerned that a lack of food (i.e. fasting) would negatively impact muscle mass. Lack of exercise, he stresses, is the real issue.

“Myth #3: Fasting Causes Low Blood Sugar”

To address this concern, Fung begins and ends by reiterating the body’s own protocols for dealing with low blood sugars (first using up stored sugar and then later making new glucose via gluconeogenesis). He mentions no studies or hard data in this section that would demonstrate that fasting does not cause low blood sugars.

“Myth #4: Fasting Results in Overeating”

Fung’s response to this myth is rather short. He notes that while studies do, in fact, show an increase in caloric intake the day after a fast, he emphasizes that this increase is ultimately a moot point given that a person still consumes fewer calories overall than if they had not fasted. He also mentions that, in his own experience working with patients, appetite tends to decrease the longer a person fasts.

(Strangely enough, as I was looking through his citations for this chapter, I noticed one of the studies he references actually contradicts him on this point. In this particular study, 16 men and women were enlisted in an alternate-day fasting protocol over 22 days and the participants lost an average of 2.5% of their body weight and 4% of their fat mass. In addition to these findings, however, the researchers note that at the onset of fasting and for the duration of the study, appetite was shown to increase and remained elevated for every subsequent day of fasting. Hunger did NOT decrease on fasting days over time.)

“Myth #5: Fasting Deprives the Body of Nutrients”

Fung’s response to this “myth” is two-fold. When it comes to vitamin and mineral deficiencies caused by fasting, he says the simple solution is to take a multi-vitamin. Problem solved.

As for macronutrient deficiencies (carbs, protein, and fat), he says the body doesn’t really require any carbohydrate from the diet to begin with. As for protein and fat needs, the body gets thrifty. To deal with the lack of essential amino and fatty acids during a fast, the body both reduces its losses and recycles what it can. However, because we do ultimately need these nutrients from food, he suggests a low-carb diet to increase the percentage of proteins and fats consumed.

As an aside, Dr. Fung reiterates that due to the increased nutrient needs of children, pregnant women, and breastfeeding women, these individuals should not engage in fasting.

“Myth #6: ‘It’s Just Crazy'”

Dr. Fung says this is the last resort response by those who can’t really think of any good reasons not to fast. Whether you think obesity is the result of consuming too many calories, carbohydrates, or fats, fasting is the effective answer in each of these cases. Furthermore, he argues that not only will fasting combat the obesity epidemic, but it also improves health and can be done by (almost) anyone.

While Dr. Jason Fung presents compelling reasons to try a fasting regimen, how do his claims measure up to reality? What is it like to follow an intermittent fasting plan? To answer these questions, I have selected one of the schedules provided in The Complete Guide to Fasting and will follow the plan for an entire week, giving you day-by-day feedback and sharing with you tips to help you succeed, should you decide fasting is something you’d like to try. It’s going to be an eye-opening experience, so stay tuned!