A type of intermittent fasting that calls for eating nothing one day, and then whatever a person wants the next, can be done safely for several months and comes with a number of health benefits, a study has found.
Alternate day fasting improved cardiovascular markers, reducing blood pressure and heart rate after four weeks, researchers reported in Cell Metabolism on Tuesday. People who followed the plan for six months also had lower levels of LDL “bad” cholesterol and triglycerides compared to those who ate normally.
Overall, they ate about 37% fewer calories, lost weight and had an “improved fat distribution,” reducing the fat in their trunk and abdomen by about 14% on average.
Researchers saw no adverse effects from alternate day fasting even after six months, concluding the strategy seems to be as beneficial as daily calorie restriction, but easier to stick with.
Humans can easily tolerate skipping food for an entire day, said Dr. Thomas Pieber, one of the study authors and chair of the department of internal medicine at the Medical University of Graz in Austria.
“The truth is that our organism is ready to fast for much longer,” Pieber told TODAY. “Ten thousand or 100,000 years ago, we didn’t have breakfast, lunch and dinner and some cake in-between with our coffee.
“You just have to train your organism to get adjusted to that short-term fasting and after a few days, most people can adjust.”
How it works:
Pieber and his colleagues randomly assigned 60 participants — all healthy, non-overweight adults — to four weeks of either strict alternate-day fasting or to a control group whose members remained on their usual diets.
Alternate day fasting required people to avoid any solid or liquid foods, or any caloric drinks every other day. They could then eat whatever they wanted on the other days. It amounted to 36 hours of fasting and 12 hours of eating.
In addition, the researchers studied a group of 30 people who had already practiced more than six months of alternate-day fasting and compared them to normal, healthy controls who had no fasting experience.
Besides shedding weight and fat, the people who fasted had beneficial cardiovascular changes and showed reduced levels of an age-associated inflammatory marker, the study found.
At the same time, alternate day fasting didn’t cause a decline in bone mineral density or white blood cell count the way continuous calorie restriction has been shown to do in previous studies.
One reason fasting may be so beneficial for the human body is that it can activate autophagy, a mechanism that helps to regenerate cells, Pieber said.
What it feels like to do alternate day fasting:
The first two weeks can be a challenge, but hunger or the lightheadedness that can come with not eating for an entire day actually wasn’t a big issue for the participants after a while, Pieber noted. People often feel “very energetic” on fasting days, he added.
It can take the body 10-14 days to get used to metabolizing food in a different way, said Jamie Baum, director of the Center for Human Nutrition at the University of Arkansas.
“As a nutrition scientist, I’m never pro omitting food for the entire day,” said Baum, who was not involved in the study. “[But] I always say if it works for you… and it’s not eliminating a food group, I’m supportive of it.
Alternate day fasting may be easier to stick with than a normal diet because people know they can eat whatever they want the next day and they don’t have to count carbs or calories, she added.
Other experts weren't so sure.
"I think it would be really difficult for people to follow," said Krista Varady, a professor of nutrition at the University of Illinois, Chicago, who has been studying fasting for 15 years. Previous shorter-term studies found people struggled with zero-calorie alternate day fasting, she noted.
Still, some people find it's easier to just not eat at all because even a small bite of food can cause them to want more, Varady said.
Tips for trying alternate day fasting:
- Always check with your doctor first. This eating regimen may not be right for people with type 2 diabetes or cardiovascular disease, Baum said.
- Try skipping breakfast and lunch, but keeping dinner at first to ease into the regimen, and then expanding to a full 24-hour fast, Pieber recommended.
- Some people prefer a modified version of alternate day fasting where they stick to 500 calories one day, then still eat anything they want the next. In this version, go for at least 50 grams of protein on fasting days to help keep hunger at bay, Varady suggested. A good option may be a salad with beans or some chicken.
- Don’t drink any sweetened beverages on fasting days, even if they contain artificial sweetener, because the sweet taste can cause hunger, Pieber noted. Water is best, though black coffee or tea also works. But don’t overdo it: being hungry and caffeinated can be a terrible combination, Baum cautioned. Hot beverages can help curb hunger, Varady noted.
- Pieber, who fasts himself, doesn’t recommend exercising during the first week people try the plan. But it’s fine after that, he said. “After some weeks, you are even more energetic when you exercise on a fasting day versus the non-fasting day,” he said. But Baum urged caution: If you’re fasting and burning calories during a workout, you could feel weak.
- Be aware that on the days when you’re not eating anything, it may be harder to focus at work or to stay in a positive mood, Baum said. Keep busy, focus on tasks at hand and do things that keep you away from the kitchen and snacks.
- On non-fasting days, focus on eating a healthy diet with lean protein and lots of plant-based foods and whole grains, she recommended.
“There are decades or research showing that eating fewer calories is better for health and living longer,” Baum said. “You need to find something that works. Weight loss is not a one-size-fits-all prescription.”