Fasting- can literally starving yourself break the obesity code?
Updated: Apr 3, 2022
The Complete Guide to Fasting: Heal Your Body Through Intermittent, Alternate-Day, and Extended Fasting- Jason Fung (2016)
The Obesity Code: Unlocking the Secrets of Weight Loss- Jason Fung (2016)
These two books on diet and fasting contradict much of the traditional advice regarding weight loss, making claims that the ancient practice of fasting is a great way to trick your body into weight loss. Reading them, my bullshit detector flashed yellow, because much of what they claim runs so contrary to what I originally thought.
Jason Fung is a Canadian doctor who started a diabetes and obesity program in Toronto and splashed into the diet debate with these two books. The Obesity Code came out a bit earlier, and it is a traditional look at his research into fasting. The Complete Guide to Fasting came out later in the same year, and is a much more reader-friendly book, with tons of colorful charts and personal stories from people who've tried fasting for weight loss.
Both books center on insulin, a hormone that the body releases immediately after eating to help it absorb sugar. Diabetics and obese people become resistant to insulin because of their dietary habits, with the result that the insulin stops working and blood sugar spikes, causing damage all through the body, as well as weight gain.
This theory doesn't so much focus on what you eat, but when you eat it. Snacking and frequent meals are more common now that food and temptation is everywhere you go. Because we eat so frequently, our insulin levels spike all day, only going down while we're sleeping. While insulin is high, our body gets the message to store fat, and when it dips lower we burn fat.
Fasting takes insulin levels even lower by skipping meals, or entire days of eating. Our bodies evolved in periods of intermittent feasts and famines, and is more able to deal with food shortages than we think. During fasts, our bodies stop storing fat in the liver and start burning it, which is how you lose weight. The fasts can last anywhere from 12 hours to 14 days (some have gone much longer, but this books don't go there).
Dr. Fung covers a lot of the objections that people might have to fasting, including muscle loss, energy levels, and nutrient deficiencies, debunking claims that fasting is unsafe. He points out who shouldn't try fasting- underweight people, pregnant and nursing women, children, and people who have certain medical situations.
The advantages from fasting seem almost too good to be true.
- Increased mental clarity and memory
- Weight loss
- Lower blood sugar
- Lower cholesterol
- Prevention of Alzheimer's and dementia.
- Extending lifespan
- Decreasing inflammation
Possibly the most shocking part of the book is his look at the failures of the traditional diet advice- eat less and move more. He uses charts and graphs from the Biggest Loser season 8 and other failed diets to show how initial good results are followed by eventual weight gain in most (not all) cases. The process is this:
1- People cut calories and exercise more, resulting in weight loss down to a plateau level where they stop losing.
2- During this low-calorie regime, the body starts to think it's starving, and if the diet lasts long enough, it adjust the metabolic rate (BMR) downward. This means that during the day as you do your routine activities, your body burns fewer calories than it did before. In the case of the Biggest Loser contestants, their BMR went down from 200 to 800 calories per day.
3- Now that the body has reset to this lower metabolic rate, when the dieters resume normal eating with healthier foods, they gain much of the weight back. Even though they may be eating better than they did before, the weight thermostat on their bodies has been reset by the diet, and their bodies burn fewer calories than they did before. (Even with increased exercise!)
How to get around this terrible trap? To reset the weight thermostat you need to control insulin resistance. Dr. Fung uses the example of a refrigerator in your kitchen and a freezer in your basement. The fat freezer represents all the fat stored in your body that you need to burn off. The refrigerator represents the short-term energy stored in your liver. In order to get at the fat stores, you need to first use up all the easy energy. But to get to the fat down in the basement, you need to reduce insulin levels to let the body get access. And this is best done by fasting.
When we eat, our insulin levels go up, gradually dropping as the time between meals gets longer. When we snack, insulin levels stay up all the time. When we fast, however, insulin levels drop enough that the body can finally start burning off fat, without messing with the weight thermostat. With low insulin levels the body's metabolic rate goes down a bit, but not nearly as much as it does when insulin is high. So there is no reset of the weight thermometer. This is complicated stuff, but it finally made sense as I kept reading.
Since these books were published, even more fascinating research has come about related to fasting. Eating, especially with processed foods common in today's diet, exposes the body to a myriad of toxins and sugars. Digesting and processing these materials takes up a lot of energy from the brain and body. Once the food is gone after 8 hours, the brain can actually perform better, with improvements in memory, thinking, and sensations. After a large meal, it's not uncommon to go into a "food coma", where we get physically and mentally tired as our bodies struggle to process the stuff we've just ingested.
There is also a profound switch that happens when our bodies stop digesting glucose and starts looking for other things. The body starts to break down fatty acids for energy once the easy glucose fuel from a big meal or snack disappears. For mysterious reasons, this triggers stem cell rejuvenation, where these powerful cells can help rebuild and strengthen aging organs and increase longevity. These stem cells can perform miracles on aging or damaged bodies, but they only seem to be triggered after fasts of 16 to 48 hours.
During fasts people are supposed to hydrate with water, tea, and coffee and little else. Fasting for more than one day can be difficult because after the liver stores run dry, hunger pangs can increase. Supposedly after the second day it gets much easier, and the author has some interesting suggestions on how to deal with hunger. Drink lots of water, keep busy, remove temptations, and don't binge after a fast ends are ways to make fasts more manageable.
I have tried 24-hour fasts myself, and it was easier than I expected. One of my biggest problems was the lifelong habits that tell me when I'm supposed to eat, tied to the people around me who also expect to eat at those times. We don't have to do three meals a day all the time, but our minds are trained to expect them. And thinking about eating makes us hungrier. It's best to have a plan of an alternative activity that takes the place of the missing meal, such as a noontime walk or morning exercise routine. And any intermittent fasting regime must take into account healthy, balanced meals for the time periods when one is not fasting.
I'm still not totally sold on the concept of fasting, but these books state the case very well. The concept of fasting has been showing up a lot more since these books came out, but I doubt that it will become widespread because of the addictive quality of salt, sugar, and fat laden foods that are just about everywhere. I could see problems for people with eating disorders like anorexia or bulimia, but as long as one feels in control of their eating habits, it looks relatively safe.