“Fasting” diets are all the rage. Even time-restricted eating, where you eat only during a four to eight hour window every day, is now popularly called “intermittent fasting.” There is also the 5:2 Fast Diet, where you eat normally for five days a week and eat only 500 calories for women or 600 calories for men on two “fasting” days–any two, which are usually not consecutive. Another form of short-term fasting is the every-other-day fast, where, predictably, you eat only every other day.
These types of eating restriction have their places. “Intermittent fasting” improves insulin resistance, inflammation markers, and has a positive impact on weight control for people who tend to graze. The 5:2 Fast Diet and every-other-day fasting are both easy weight loss plans for many people, and the 5:2 Fast Diet is able to be transformed without too much difficulty into a permanent lifestyle change without much overhead, and overweight people get all the benefits of weight loss from them.
However, none of these are a prolonged fast. A prolonged fast must be at least three days in duration if a complete water fast and at least four days if there are small amounts of food consumed. A prolonged fast can be dangerous for some people–especially a water-only fast–and so should only be undertaken under the guidance of a doctor. That said, prolonged fasts of three to seven days have benefits that intermittent and single-day fasts can’t match.
Our bodies were shaped in a time when food shortages were common. They not only add fat against times of need, but they also keep around senescent (old) and injured cells and organelles that aren’t functioning very well, as well as letting various fragments of fats, sugars, and proteins hang about–just like you let things slide to the back of the fridge when new, yummier food is in constant supply. When you cut off the supply of new food, though, the body immediately starts rummaging around for things to consume–just like you! Eventually, if no food comes in, it reduces the body to the equivalent of eating grass and leather shoes, and eventually you die. But in between, when there is just a short-term food shortage, the body dips into its version of the pantry and freezer and eats some of its stores there by burning fat, and it also goes into the back of the fridge, where senescent cells are the wilted spinach and intermediate-glycation molecules are the fuzzy furry thing that used to be a take out dinner, and the body recycles into food anything that’s edible and trashes things that aren’t. After a few days, the fridge, freezer, and pantry are neat and clean, with the remaining supplies nicely organized at you’ve gone through everything–and you can start bringing in new food again. This process is called autophagy.
Though this is a metaphor, it’s an amazingly accurate one! The scary, fuzzy things in the back of our body’s fridge don’t just sit there, getting gross. They cause actual, real damage. Without periodic prolonged fasts, our body just doesn’t know what to do with this cellular clutter, and it becomes a heavy contributor to several poor health and aging processes.
This clutter is such an issue that Valter Longo, the Edna M. Jones Professor of Gerontology and Biological Sciences at the University of Southern California, has focused most of his research on the topic over the past several years in his efforts to counter Alzheimer’s disease, cancer, and diabetes through the controlled stress of short-term prolonged fasting and its ability to alter cellular expression. A large percentage of the benefits of fasting that are cited here are found in his body of research that you can read on PubMed.
Prolonged fasts of three days to a week not only decrease body fat: they also selectively decrease the damaging visceral fat to a greater degree, and they preserve both muscle mass and bone density. They aren’t a particularly good weight loss technique because the net loss after any three-day water-only fast is going to be in the range of one to two pounds of fat in people who are not class II obese and above, but they help maintain an ideal body composition in slimmer people as well as fight and sometimes reverse insulin resistance and type II diabetes in larger people. Prolonged fasts have a far better impact on type II diabetes and insulin resistance than normal-paced weight loss, and the effects of fasting are responsible for the reversal of diabetes often found in the first stage of recovery after gastric bypass surgery, when patients are eating an extremely low calorie diet for several weeks. You can have the same effects with fasting alone, no surgery needed!
Beyond the level of mere fat loss, prolonged fasts improve cholesterol, lower blood pressure, and decrease the levels of insulin-like growth factor (IGF). Though bodybuilders are constantly wanting to increase their levels of IGF, when IGF is high without exercise, it is closely linked to aging and inflammation. Your baseline IGF should be very low and should only increase in response to physical activity. Prolonged fasts also dramatically lower CRP and other inflammation markers. It also increases the number of naive T-cells by replacing excess and broken memory T-cells, which is important for a healthily active immune system–rather than a bunch of T-cells trying to hunt down a specific pathogen that may not even exist in your body, naive T-cells are able to respond fluidly to any intruder and then to call for help to identify and kill it.
Prolonged fasts of three to seven days also put you deep into short-term nutritional ketosis. While long-term ketosis has a number of serious drawbacks, including impairing neurological function and creating tissue-level insulin resistance that is very hard to reverse, short-term ketosis is extremely beneficial as the switchover kills some malfunctioning cells and organelles and decreases IGF, among other things.
We also have every reason to believe, based on animal studies, that regular bouts of fasting will lower your chances of dementia, cancer, and atherosclerosis. Finally, perhaps most excitingly, prolonged fasts in humans have been shown to increase stem cell regeneration.
For all of these reasons, I’ve been undertaking periodic prolonged fasts for a little more than the last year, roughly one every two to three months. I would like to do a fast once every two months, regularly, but fasting is psychologically challenging–surprisingly, more to start than to maintain for periods of less than five days! Laziness gets to us all.
Valter Longo has developed an easier, safer protocol than complete water fasting called the Fast Mimicking Diet. In this diet, the fast is prolonged over five days, with an induction day of 1090 calories that is 10% protein, 56% fat, and 34% carbohydrates and four fast-mimicking days that are 725 calories delivered as 9% protein, 44% fat, and 47% carbohydrates. This patented diet plan is delivered through mail-order meals with the company ProLon that Dr. Longo founded after his research began bearing such good fruits. Here are results from his later studies about the effects of his patented diet on various markers of health:
You can order directly from ProLon or go through a doctor. (I am not affiliated with Dr. Longo or ProLon and have never spoken with him, but I’ve admired Dr. Longo’s work for more than a decade.) From personal experience, I don’t recommend cooking while you are fasting! If you don’t use ProLon for your Fast-Mimicking Diet imitation, you should prepare any meals ahead of time.
I usually take a similar approach. On my very first try, I worked out a meal plan using CRON-O-meter online for free that followed the macronutrient proportions of the Fast Mimicking Diet. Honestly, though, I was pretty miserable on this diet. I was starving all the time, and I was also preparing meals while starving. Not a good combination.
For me, personally, eating less was the answer. Instead of 725 calories, I eat less than 400, staying well below the maximum calorie count of every macronutrient in the actual Fast-Mimicking Diet plan. Basically, I grab a few cashews whenever I get really hungry and eat them slowly. When I do this, I end up not really being hungry at all after the first day of a four days of very low calorie consumption. I also still drink tea and zero-calorie electrolyte water. During the first two cycles of fasting, I was absolutely exhausted late in the first extremely low-calorie day as my body went into nutritional ketosis, but now I tend to get a long burst of energy, which doesn’t do much for my sleep!
I have also done a four-and-a-half-day water-only fast when I was having some severe neurological symptoms and my neurologist was stumped about what to do. By the fourth day of water-only fasting, I was having a much harder time than I do on one day of light eating plus four days under 400 calories. On the fifth day, I gave up about five hours short of the mark when the house was full of the smell of delicious food! My neurological symptoms stopped on the second day of my water fast, and they only came back to a much lesser extent about six weeks later, and with a second, gentler mimicking-style fast, they disappeared again, only to reappear about two months later, even less severe than before. Since the last, third fast, they’ve been gone for nearly half a year. I cannot say for certain whether the fasting was the cause, but I took this route based on studies of fasting in multiple sclerosis patients with similar symptoms, and I did not regret it.
On a psychological note, I find that a fast also shakes me out of any bad food habits and restores a healthier, more respectful relationship with food. There are many people who have a near-terror of being hungry and use food as the most reliable source of comfort. For them, a fast could be even more psychologically beneficial, as they would face and conquer their fear and dependency.
I have found that fasting is something that has some immediately noticeable short-term positive effects, which are enough for me to continue even without the long-term promises of better health.
You should never fast if you are pregnant. Therefore, the ideal time to start a fast when you are trying to conceive is during menstruation. In addition, you should not do any kind of strenuous activity while you are fasting, because that can put your electrolytes out of balance, which can make you very ill or, in rare cases, result in death. Always consult with your doctor before starting a fast.
Disclaimer: I am not a doctor, and this is not personal medical advice.