by Beth Janes
The notion of fasting for better health has all the hallmarks of a fad diet or passing overhyped trend: Claims that sound almost too good to be true, celebrity followers, rigorous guidelines at odds with the way even the healthiest people eat, and, of course, deprivation. (Remember the cabbage soup diet? Or the Master Cleanse, a juice fast that consisted of drinking a lemon juice, cayenne pepper, and maple syrup concoction?)
Yet fasting — which is generally defined as going with little or no food for a period of anywhere from about 12 hours to several days — has one thing going for it that many other trendy programs don’t: Solid preliminary research.
What the Science Says
Some of the most promising recent science has come out of the Longevity Institute at the University of Southern California Leonard Davis School of Gerontology. In 2014, researchers there found that a three-day fast involving less than 200 calories per day could help revitalize the immune system on a cellular level.
Reporting their findings in the journal Cell Stem Cell, the study authors observed that when cells went without standard fuel from regular meals, the body switched to survival mode and ended up killing off old, damaged white blood cells to conserve energy.
While that may not sound groundbreaking, what happened after is noteworthy: Once provided with food and nutrients again, the body’s stem cells kicked into gear and restocked the immune system with a fresh batch of (healthier) cells.
Additional preliminary research by the same group and others, including some experts at Johns Hopkins University and MIT, suggests even more benefits of putting the body into a type of temporary survival mode via short-term fasting, including:
- An increase in the number and activity of stem cells in other areas and organs, such as the gut and brain. That may lead to positive changes that could improve memory and learning, and also help protect against diseases like Alzheimer’s.
- A lowering of risk factors for heart and other diseases by helping the body shed visceral fat — the most dangerous kind that collects around the midsection.
- Reduced symptoms of multiple sclerosis, gained by killing off some autoimmune cells and replacing them with healthy ones.
- Some protection against the toxic effects of chemotherapy, which in turn allows the immune system to better work with traditional therapies to fight cancer cells.
One finding many of these fasting studies share is that the body has to first use up its stored glycogen (the storage form of glucose), and start burning fats instead — a metabolic state called ketosis. A potential explanation: Stem cells may function better on a diet of fat versus carbs or stored glycogen.
Reaching that fat-burning state, however, isn’t easy — it can take more than 12 hours with no or few calories. And if you’ve ever gone that long or longer without food (say, to prep for a medical test), you know it can be unbelievably hard to do, says Bill Rawls, MD, medical director of Vital Plan.
So given that the findings listed above are still preliminary, the question remains: Is short-term fasting worth it?
Is Fasting Right for You?
While the research is promising, some experts are withholding final judgment until more and larger studies are done to support the benefits of fasting in bigger groups of people and to ensure long-term safety. Still, fasting isn’t a new phenomenon. Various religions have a long history of incorporating it in their practice.
Right now, in fact, Muslims around the world are fasting from sunrise to sunset for the month of Ramadan. Our hunter-gatherer ancestors also probably went without food for prolonged periods. The benefits that today’s researchers are discovering may even have evolved because of our ancestors’ habits.
“I think there can be a lot of value in fasting,” Dr. Rawls says. “At a basic level, it takes some of the pressure off your gastrointestinal system.” He notes that digesting food requires a lot of energy, and any break from eating — or even just eating less — can temporarily lighten the burden on your GI tract. And that offers a break to the 70 percent of your immune system housed in the gut, allowing it to redirect resources elsewhere.
If you’re interested in fasting, though, you should consult with your doctor first. It’s likely not safe for those with diabetes, and it may not be recommended for anyone who takes medications for blood pressure or other conditions.
“I think for people with serious medical conditions, who are trying to recover from a chronic illness, or who have poor gut function and are nutritionally deprived, it could be too much of a hardship,” Dr. Rawls says. He adds that even if you’re generally healthy, “it can be a stress on the body.” What’s more, hunger disrupts sleep, which can have negative effects on the immune system.
Consider, too, the practical realities: “Fasting for three days is not easy or fun,” Dr. Rawls says. “You feel this gnawing hunger every minute for the first two days or so; it’s not pleasant.”
It’s also inconvenient. Many people experience debilitating headaches, and often lack the energy to exercise or do other everyday activities. “You don’t really have the capacity to do very much when fasting, but life is busy,” says Dr. Rawls. “I find it hard to take that time out.”
Fortunately, there are other, less severe alternatives to a full-on, three-day fast, such as reducing your “eating window” to 12 hours or so. For example, you might only eat between the hours of 8am and 6pm or 8pm, allowing for a 12- to 14-hour mini fast.
The key to this approach, though, is to not binge during the hours you do eat. “One of the values of fasting is that it can be an opportunity to start embracing a better diet,” Dr. Rawls says. He notes that simply following his basic three rules for a nourishing diet can have far-reaching immune benefits as well:
- Eat more vegetables than anything else.
- Make the vast majority of your food free of labels (e.g. fresh and unprocessed).
- Choose the healthiest protein sources, including eggs and fish, especially salmon.
While reducing your eating window has its benefits, if your immune system is in need of extra support, the payoff of embracing the challenges of a more traditional fast might be worth the time lost and temporary discomfort. And it can be the perfect excuse to lay low and make space in your life for recuperation. Keep reading if you’re ready to give fasting a try.
3 Fasts to Consider
The science-backed protocols below may make the experience a little more palatable than quitting food cold turkey for two or three days straight. They’re still not easy, but they are easier.
1. Fasting Mimicking Diet
The researchers at USC who reported that three days of fasting can regenerate the immune system were looking for ways to make fasting more tolerable while maintaining results. They discovered that a five-day program low in protein and calories done every month or every other month seems to mimic the effects of a stricter protocol.
Called a fasting mimicking diet (FMD), it involves eating 1,100 calories the first day, with half of those calories coming from vegetables and the other half from plant-based, high-fat foods like nuts and olive oil. Then for the next four days, you’re allowed 800 calories a day — again, made up of half veggies, half healthy fats. Other guidelines include taking a multivitamin and drinking unsweetened tea. (Find more information on the diet and science in the book The Longevity Diet, by Valter Longo, Ph.D., director of USC’s Longevity Institute and developer of the FMD.)
2. Alternate-Day Fasting or the 5:2 Diet
A form of intermittent fasting, this protocol involves limiting yourself to 500 or fewer calories every other day or on two nonconsecutive days a week. On all of the remaining days, you eat a normal, 2,000- to 2,500- calorie diet.
This approach was studied by Mark Mattson, Ph.D., professor of neuroscience at Johns Hopkins School of Medicine and chief of the Laboratory of Neurosciences at the National Institutes on Aging. He and his team found benefits on brain function, and on the brain’s ability to help increase neurons’ resistance to injury.
3. Time-Restricted Feeding
Another type of intermittent fasting, time-restricted feeding involves consuming all your calories within a short window of time each day, usually 6 or 8 hours. Early research on this type of fasting is positive, suggesting that it may help lower risk of cancer and metabolic disorders, as well as ward off weight gain and increase fat loss. One recent study also showed it may help reduce inflammation by impacting white blood cells.
With both time-restricted feeding and the 5:2 or alternate-day programs, consider gradually working your way up to the full fasting periods, especially if you’re used to eating frequently. And talk to your doctor for guidance. He or she may suggest starting first by going for 10 or 12 hours without food or limiting calories only one day a week, and then gradually reducing your calorie intake every week.
Regardless of your approach, be sure to reintroduce food gradually once you’ve finished a fast — especially after a longer one like the FMD. After going without nutrients, you want the first foods you take in to be especially nourishing. They should also be easy to assimilate and digest, so your body doesn’t have to expend too much energy to replenish its nutrient stores.
Eat lightly, focusing first on whole foods and complex carbohydrates such as fruit, vegetables, and brown rice before adding fish, dairy, and other foods. And, of course, try to avoid the common pitfall of “rewarding” yourself for fasting by overloading on calories, meat and dairy, processed carbs, sugar, and fat.
Otherwise, unless you have a medical condition, the potential for long-term or serious harm from fasting is pretty low, Dr. Rawls says. His only other guideline is more subjective: “If it feels really bad, don’t do it.”
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