There are many areas in diet and health where the lack of research to pin things down is scandalous. The lack of gold standard research that could settle once and for all whether sugar is seriously bad for health is a good example.
Fortunately, a great deal of research is being done on the health effects of fasting—periods of time with no food. Lisa Drayer’s CNN article “Is fasting the fountain of youth?” is a useful report on some of this research. The best news is that more research results are on the way. For example, she writes:
Clinical trials are currently underway of IF in patients with various diseases such as multiple sclerosis or cancer to determine if fasting can halt progression. "If you hit cancer cells with chemo or radiation, when the individual is in a fasting state, the cells may be more vulnerable to being killed because they use glucose and cannot use ketones [the source of fuel during fasting]," explained Mattson. Researchers are also currently studying how fasting may impact cognitive performance and the risk of Alzheimer's disease in overweight women.
Fasting and Cancer. The background to the explanation that Mark Mattson (chief of the Laboratory of Neurosciences at the National Institute on Aging) gives about the effect of fasting on cancer is that cancer cells are metabolically handicapped—it is easy to damage delicate structures within the mitochondria that produce energy in cells. As a result, while cancer cells can still get quite a bit of energy from sugar and from certain amino acids that are especially common in animal protein, cancer cells have a tough time metabolizing the fat and ketone bodies that are produced from dietary fat and body fat. By contrast, healthy cells do very well taking in and metabolizing any fat and ketone bodies that are circulating in the bloodstream. (See “Good News! Cancer Cells are Metabolically Handicapped” and “How Fasting Can Starve Cancer Cells, While Leaving Normal Cells Unharmed.”) Another likely implication of cancer cells being metabolically handicapped that is important to test is the idea that fasting can be used to prevent cancer. I am betting on this myself: see “My Annual Anti-Cancer Fast.”
Fasting and Autoimmune Diseases. An important mechanism by which fasting could help with autoimmune diseases such as multiple sclerosis is by giving the body a break from aggravating agents in food. If we understood all of the aggravating agents, avoiding certain types of food might do the trick. (See “What Steven Gundry's Book 'The Plant Paradox' Adds to the Principles of a Low-Insulin-Index Diet” for one theory about particular foods that might aggravate autoimmune diseases.) But even without knowing which things in one’s diet might be aggravating an autoimmune disease, eating nothing gives the body a break from those toxins. (I hesitate to use the word “toxins” because of its use by people advocating “cleanses” that include procedures I don’t believe in, but want to work toward reclaiming the word “toxins” for the rest of us. Below, I try to reclaim the word “cleanse” as well.)
Fasting and Dementia. The proposed research about cognitive performance and risk of Alzheimer’s disease is theorizing that insulin resistance—and the resulting high levels of insulin in the bloodstream as the insulin-producing cells compensate—could have bad effects on the brain. Here, the potential benefits of fasting come because periods with no food are the most powerful way to get to the very low insulin levels that might eventually reduce insulin resistance. Fasting is like a drug holiday from the internal drug insulin, that might be able to restore the effectiveness of the drug at low or moderate dosages. (See “Obesity Is Always and Everywhere an Insulin Phenomenon” and “Forget Calorie Counting; It's the Insulin Index, Stupid.”)
Fasting and Longevity. It would take a lot of time and money to see the effects of fasting on how long human beings live, but researchers have shown that mice live longer when they fast periodically. Lisa writes:
Research involving animals has revealed that intermittent fasting can reduce the risk of obesity and its related diseases, including non-alcoholic fatty liver disease, diabetes and cancer. According to Mark Mattson … research from the 1980s revealed that the lifespan of rats increases substantially when they fast every other day, compared to rats who have food available at all times.
A much more recent study, published this month, found that mice who fasted, whether because they were fed all of their calories only once per day or because their calories were restricted, which naturally caused them to eat all of their limited food at once -- were healthier and lived longer compared to mice who had constant access to food.
Trying to tease out whether fasting is simply a form of calorie restriction is very complicated, according to experts. But "in the absence of calorie restriction, and independent of diet composition, fasting mice do better than non-fasting," explained Rafael deCabo, a scientist at the National Institute on Aging and the study's lead author.
Good Health Effects Beyond Weight Loss: Better Blood Sugar Regulation and Less Belly Fat. The good health effects of fasting are not just about weight loss. In two human trials, those who ate less on some days than others had more improvement in regulation of glucose (blood sugar)—a good sign in relation to diabetes—than those who ate somewhat less, but the same amount every day. They also lost more belly fat—a good sign in relation to heart disease. Lisa writes:
The research behind the popular 5:2 diet -- a type of intermittent fasting where people eat whatever they want for five days per week, then limit their diet to 500 calories for two consecutive days, has also revealed health benefits.
"We published two studies with Dr. Michelle Harvie at the University of Manchester; each included 100 overweight women, and the design of both studies was the same," said Mattson. "We divided them into two groups; one group got the 5:2 diet; the other group had three meals per day but we reduced the amount of calories by 20% to 25% below what they normally eat -- so that the weekly calorie intake of both groups would be the same."
Both groups lost the same amount of body weight over a 6-month period, but that was where the similarities ended. "We saw superior beneficial effects of 5:2 diet on glucose regulation (a risk factor for diabetes) and loss of belly fat (a risk factor for cardiovascular disease) compared to the women eating regular meals but restricting calories," said Mattson.
Fasting and Cellular Renewal. When food intake is low enough, the body looks for old cells it can cannibalize for resources. It breaks apart cells that look substandard for parts. Getting rid of the old junker cells can help avoid problems. When is food intake enough for such cleansing cannibalization to get in gear? The production of ketone bodies from body fat seems to be an important indicator. Lisa writes:
According to experts, a critical aspect of fasting -- which is different from simply restricting calories -- is that the body undergoes a metabolic switch from using glucose to using ketones as fuel, a result of the depletion of liver energy stores and the mobilization of fat. (This switch also occurs during extended periods of exercise.)
"If ketones are not elevated, you don't see the beneficial effects," said Mattson. What's more, these metabolic changes that occur during repeated "cycling" from fasting to eating may help to optimize brain function and bolster its resistance to stress and disease, both of which have positive implications for aging.
According to Longo, the presence of ketones in the blood signifies that on the cellular level, the body is "regenerating" itself, which protects against aging and disease.
"We've published many papers, and the main thing we talk about is multisystem regeneration," said Longo. For example, fasting seems to lower the level of damaged white blood cells -- but when you re-feed, stem cells are turned on, and you rebuild and regenerate new, healthy cells, explained Longo. "You get rid of the junk during starvation -- and once you have food, you can rebuild."
"The damaged cells are replaced with new cells, working cells -- and now the system starts working properly," said Longo. This ultimately impacts disease risk, as risk factors for disease decrease when tissues are healthy and functional, explained Longo.
The metabolic switchover during fasting from using glucose (blood sugar) to using ketones as fuel has another likely implication that needs to be more fully tested. Based on my own experience and the experience of others I know, going entirely without food is much less painful if before beginning the fast one was eating in a lowcarb, highfat way. (See “A Barycentric Autobiography.”) In the first few hours of fasting, a big reason is avoiding what I called the “carb rebound effect” in “Obesity Is Always and Everywhere an Insulin Phenomenon” and more accurately the “insulin backlash” in “Using the Glycemic Index as a Supplement to the Insulin Index.” But experientially, there seems to be some suffering later on in a period of fasting when one has been eating highcarb. The best hypothesis I can see for this is that a rough switchover from being all set up to metabolize glucose to metabolizing fats and ketones accounts for a lot of that suffering. My notion is that the more one’s body is set to be metabolizing dietary fats rather than carbs when one does eat, the smoother the transition to subsisting off of one’s own body fat during fat. As far as I know, this claim that there is more suffering during fasting for those who are eating highcarb or otherwise high on the insulin index), has not been tested. But it is worth testing. If people’s perception of fasting as very difficult is just a side effect of eating highcarb or otherwise high on the insulin index, then periodic fasting might be a more sustainable practice for more people if it is combined with low-insulin-index eating. (The perception of fasting as very difficult—in a context where most people are eating highcarb—is reflected in researchers’ use sometimes of a “fasting mimicking diet” in which for five days out of a month, people eat between 800 and 1,100 calories.)
In my own experience, fasting in the context of generally low-insulin-index eating is easy enough that an eating window of four hours—implying on average 20 hours of fasting a day—seems relatively easy. And occasionally going an entire day without food beyond that—implying at least 30 hours of fasting even if one eats late in the day before the fast and early in the day after—is not that bad. When fasting becomes as easy as it is when one is generally eating low on the insulin index, then it can easily be used as a tool to enhance health in many ways.
Don’t miss my other posts on diet and health:
I. The Basics
II. Sugar as a Slow Poison
III. Anti-Cancer Eating
IV. Eating Tips
V. Calories In/Calories Out
VIII. Debates about Particular Foods and about Exercise
Julia Belluz and Javier Zarracina: Why You'll Be Disappointed If You Are Exercising to Lose Weight, Explained with 60+ Studies (my retitling of the article this links to)
IX. Gary Taubes
X. Twitter Discussions
XI. On My Interest in Diet and Health
See the last section of "Five Books That Have Changed My Life" and the podcast "Miles Kimball Explains to Tracy Alloway and Joe Weisenthal Why Losing Weight Is Like Defeating Inflation." If you want to know how I got interested in diet and health and fighting obesity and a little more about my own experience with weight gain and weight loss, see “Diana Kimball: Listening Creates Possibilities” and my post "A Barycentric Autobiography.