10 Possible Health Benefits of Intermittent Fasting
10 Possible Health Benefits of Intermittent Fasting
IF has received a lot of hype for its potential effect on body weight and other health parameters, but should you believe it?
By Moira Lawler
Medically Reviewed by Kelly Kennedy, RD
Last Updated: 8/27/2019
Can limiting when you eat make you slimmer and healthier?
Tanya Joy/iStock
Intermittent fasting (IF), one of the most talked-about diets right now, is a way of eating that designates periods of time for eating and for fasting. There are a few different approaches, but the two most popular are 16:8, which calls for squeezing all the day’s meals into an eight-hour window and fasting for the remaining 16 hours, and 5:2, where five days of the week are spent eating normally and two are spent fasting (usually defined as eating only 500 to 600 calories per day).
Why would someone opt for this way of eating versus a standard diet, such as going low-carb or low-fat? Some say fasting has loads of health benefits. “The research so far proves the benefits of IF to the extent that it is worthwhile as a method to lose weight, manage your blood sugar, and slow down the aging process,” says Sara Gottfried, MD, of Berkeley, California, author of The Hormone Cure, The Hormone Reset Diet, and Brain Body Diet.
But not everyone’s on board. “From my standpoint and the standpoint of a lot of other people, it does tend to fall into the next fad diet category,” says Elizabeth Lowden, MD, a bariatric endocrinologist at the Northwestern Medicine Metabolic Health and Surgical Weight Loss Center at Delnor Hospital in Geneva, Illinois. A lot of the data is conflicted, she says, and many studies done on animals have not yet been repeated in people. “For every study that shows there's no change, there are some studies that show maybe there is improvement,” she says.
So rather than take the claims at face value, we decided to dive into them and explore whether 10 touted benefits of IF are legit, or the science doesn’t yet stack up.
1. Weight Loss
Most people start IF to lose weight. And that claim seems to hold up, at least in the short term. According to an article published in August 2015 in the Journal of the Academy of Nutrition and Dietetics, there’s a chance that any version of IF may contribute to weight loss. The researchers looked at data from 13 studies and found that average weight loss ranged from 1.3 percent for a two-week trial to 8 percent for an eight-week trial.
That’s probably welcome news if you’re hoping to fast for weight loss, but the fact that those studies were short term means it’s unclear if IF is sustainable and can help you keep extra pounds off in the long run.
The other catch: The amount of weight lost doesn't seem to be any more than what you’d expect from another calorie-restricted diet, and depending on how many calories you’re eating each day, you could even end up gaining weight. After all, the diet doesn’t restrict high-calorie foods.
When the diet is done properly, IF can be as effective as normal caloric restriction, Dr. Lowden says. Some people, especially busy people who don’t have time to devote to meal planning, might even find a time-restricted diet easier to follow than something like the keto diet or the paleo diet, she says.
2. Reduced Blood Pressure
IF may help lower high blood pressure in the short term. A study published in June 2018 in Nutrition and Healthy Aging found 16:8 significantly decreased the systolic blood pressure among the 23 study participants. The link has been shown in both animal and human studies, according to a review published in March 2019 in Nutrients.
Having a healthy blood pressure is important — unhealthy levels can increase your risk for heart disease, stroke, and kidney disease.
But so far the research shows these blood pressure benefits last only while IF is practiced. Once the diet ended and people returned to eating as normal, researchers found the blood pressure readings returned to their initial levels.
3. Reduced Inflammation
Animal studies have shown that both IF and general calorie restriction can reduce inflammation levels, though clinical trials are few and far between. The authors of a study published in Nutrition Research wanted to know if that link existed among humans, too. The study involved 50 participants who were fasting for Ramadan, the Muslim holiday, which involves fasting from sunrise to sunset, and eating overnight. The study showed that during the fasting period, pro-inflammatory markers were lower than usual, as was blood pressure, body weight, and body fat.
4. Lower Cholesterol
According to a three-week-long study published in Obesity, alternate-day fasting may help lower total cholesterol as well as LDL cholesterol when done in combination with endurance exercise. LDL cholesterol is the “bad” cholesterol that can raise your risk of heart disease or stroke, according to the Centers for Disease Control and Prevention. The Obesity researchers also noted that IF reduced the presence of triglycerides, which are fats found in the blood that can lead to stroke, heart attack, or heart disease, according to the Mayo Clinic. One caveat here: The study was short, so more research is needed to understand whether the effects of IF on cholesterol are long lasting.
5. Boosted Brain Function
Dr. Gottfried says IF may improve mental acuity and concentration. And there’s some early research to support that idea: A study on rats published in February 2018 in Experimental Biology and Medicine found it may help protect against the decline in memory that comes with age. According to Johns Hopkins Health Review, IF can improve connections in the brain’s hippocampus and also protect against amyloid plaques, which are found in patients with Alzheimer’s. This study was done only in animals, though, so it’s still unclear whether the benefit holds true for humans.
6. Cancer Protection
Some studies have shown that alternate-day fasting may reduce cancer risk by decreasing the development of lymphoma, limiting tumor survival, and slowing the spread of cancer cells, according to a review of studies published in The American Journal of Clinical Nutrition. The studies that showed the cancer benefit were all animal studies, though, and more studies are needed to confirm a benefit for humans and understand the mechanism behind these effects.
7. Cell Turnover
Gottfried says the period of rest involved in intermittent fasting increases autophagy, which is “an important detoxification function in the body to clean out damaged cells.” Put differently, a break from eating and digestion gives the body a chance to heal and get rid of junk inside the cells that can accelerate aging, she says.
A study published in May 2019 in Nutrients found that time-restricted feeding, which the researchers defined as eating between 8 am and 2 pm, increased the expression of the autophagy gene LC3A and the protein MTOR, which regulates cell growth. This study was small, involving only 11 participants for four days. Another study, published in August 2019 in Autophagy, also noted that food restriction is a well-recognized way to increase autophagy, specifically neuronal autophagy, which may offer protective benefits for the brain. There were some limitations with this study as well, though: It was done on mice and not humans.
8. Reduced Insulin Resistance
Gottfried proposes that intermittent fasting may help stabilize blood sugar levels in people with diabetes because it resets insulin, though more research is needed. The idea is that restricting calories may improve insulin resistance, which is a marker of type 2 diabetes, according to a study published in April 2019 in Nutrients. Fasting, such as the kind of fasting associated with IF, encourages insulin levels to fall, which may play a role in reducing the risk for type 2, the study notes. “I have colleagues at other facilities who have seen positive results especially in improvements in insulin needs for diabetics,” Lowden says.
The aforementioned study published in Nutrition and Healthy Aging investigated this effect in humans, and while a 16:8 approach did result in reductions in insulin resistance, the results were not significantly different from the control group. And again, this study was small.
Registered dietitians advise people with diabetes to approach intermittent fasting with caution. People on certain medications for type 2 diabetes or those on insulin (whether to manage blood sugar for type 2 or type 1 diabetes) may be at a greater risk for low blood sugar, which can be life-threatening. Check with your doctor before trying intermittent fasting if you have any type of diabetes, they advise.
9. Lower Risk of Cardiovascular Issues
Per the aforementioned Nutrients study, when insulin levels fall, so does the risk of dangerous cardiovascular events, such as congestive heart failure, which is important for patients with type 2 diabetes because they are two to four times more likely to die from heart disease than adults without diabetes, according to the American Heart Association.
The Nutrients study noted that while there aren’t human studies to confirm the benefit, observational studies have shown IF may deliver both cardiovascular and metabolic benefits. Lowden suspects that changes to metabolic parameters, such as lower levels of triglycerides and a decrease in blood sugar levels, are the result of losing weight and would be achieved no matter how the weight was lost, whether through IF or a low-carb diet, for example.
10. Increased Longevity
There have been a few animal and rodent studies that have shown IF may extend life span, possibly because fasting seems to build resistance to age-related diseases. A review published in Current Obesity Reports in June 2019 noted that while these findings are promising, it’s been hard to replicate them in human studies. Until that happens, it’s best to be skeptical about this potential benefit.
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