October 3, 2024 – Ethan WeissMD, was already a believer in intermittent fasting when he began looking into it.
For seven years, the cardiologist practiced a type of fasting generally known as time-restricted eating. He ate whatever he wanted from noon to eight p.m. every single day and fasted for the remaining 16 hours.
But when he began looking into the subject, his pondering modified.
The University of California San Francisco researcher and his colleagues published a 12 weeks Study that found no significant difference in weight loss between individuals who practiced time-restricted eating and those that ate a standard breakfast, lunch, and dinner.
At this point, Weiss now not followed the weight loss program and stopped encouraging others to make use of it.
“It worked out pretty well for me at first,” he said. But his family, he added, “were very happy that I quit. “I'm nicer now.”
In the past Quarter century as obesity rates rose, intermittent fasting has become one of the most popular diets in the United States, thanks in part to research touting its exceptional weight loss and health benefits. Just this week, a study made headlines by finding that time-restricted eating combined with nutritional counseling led to greater reductions in body fat and better blood sugar control than nutritional counseling alone in adults with metabolic risk factors such as abdominal fat and high blood pressure. In a current survey, About 13% of Americans who diet reported using intermittent fasting.
The appeal is clear. You don't have to count calories, eat carbs, or eat like someone from a bygone era. In fact, you can eat whatever you want as long as you consume it within a limited daily window.
“People like it because it’s so easy to incorporate into your lifestyle,” he said Krista VaradaPhD, Professor of Nutrition at the University of Illinois Chicago, who has been studying intermittent fasting since 2005.
Their research shows that people who practice intermittent fasting typically eat less overall. In their study from 2024 People with obesity Reduce about 200 to 550 calories per day – without counting a single one.
This can lead to serious weight loss, which often leads to significant consequences Health improvements.
However, other recent research shows mixed results.
An August study found that a increased risk of cancer cell growth in mice when they were fed again after fasting.
A poster presentation at a scientific conference was reported earlier this year more common diseases of the heart and blood vesselsThese are people whose eating habits were similar to intermittent fasting.
Does this mean fasting diets are dangerous? That's a hard no, and we'll explain why in a moment. But despite what enthusiasts have long argued, they may not be particularly effective for weight loss and disease prevention either.
Fasting and weight loss
Fasting's weight-loss and health-promoting reputation was built on studies in mice.
Varady's research also began there. But she and her colleagues quickly moved on to studying intermittent fasting in humans.
“Mice are just not good role models for fasting,” she said. “They have really high metabolic rates. Fasting a mouse for a day is like fasting a human for a week.”
At first, Varady viewed intermittent fasting as an improvement over more traditional dieting approaches. “What I noticed was that people really hated constantly tracking their calories,” she said. “They also didn’t like having to restrict themselves every day.”
Varady and her colleagues tested the effects of fasting on the second day – eating about 25% of their normal diet one day and eating anything they wanted the next day.
“But then we started to realize that people hate this diet too,” she said. At this point, her research turned to the 16:8 approach – 16 hours of fasting and 8 hours of eating. “It seemed like a natural progression to study what people actually do.”
The results of these studies, which have now included thousands of people, show a consistent pattern: improvements in health indicators and reductions in disease risk come from people eating less and losing weight.
“If you don’t lose weight, you don’t see any health benefits,” she said.
Possible health risks
So what about recent reports linking intermittent fasting to health risks??
The first was a poster presentation at a scientific conference sponsored by the American Heart Association. (In other words, it wasn't a published study in a peer-reviewed journal.) It examined self-reported dietary data from a large sample of American adults and identified a very small group – just 414 out of more than 20,000 – who said they had all of them Meals eaten within an 8 hour window.
Compared to people who reported eating in 12- to 16-hour windows, they were 91% more likely to die from heart disease during the follow-up period of at least 8 years.
No one could say whether they accurately reported what and when they ate, whether they were demographically different from other people in the data set, or whether their eating behavior was a conscious choice.
Despite these limitations, the American Heart Association promoted the results of the presentation in one Press releaseleading to comprehensive reporting and a devastating reaction by 34 nutritionists, including Varady.
The study that linked intermittent fasting to a higher risk of cancer was very different.
Scientists at the Massachusetts Institute of Technology found that in mice Many of the health benefits don't actually come from fasting– but rather from refeeding after fasting. When mice resumed eating after fasting, their bodies activated stem cells to repair and regenerate damaged tissue. This repair process, which includes: Removal of damaged or dysfunctional cellsis considered a major advantage of intermittent fasting.
However, there is a potential downside: Cancer cells were more likely to proliferate during the refeeding period – at least in mice that were genetically engineered to be more susceptible to cancer.
How does this apply to a person who eats for a limited time or fasts every other day?
That is not the case.
“You can find links to almost everything good and bad on any diet,” Weiss said. But he hasn't seen any evidence of this yet Intermittent fasting is harmful.
On the contrary, previous animal studies have shown that a lower risk of cancer associated with fasting.
And preliminary human studies suggest so Improvements in metabolic health and brain function with 5:2 intermittent fasting – eat normally for 5 days and limit yourself to a single meal on the other 2 days.
This study compared people in the fasting group with a matched group who ate what the authors called “healthy living nutrition” 7 days per week for 8 weeks. Both groups achieved the identical metabolic advantages, while the 5:2 fasting group performed barely higher on tests of pondering skills.
Fasting myths
A challenge with any weight loss program is separating myths from facts.
Proponents of fasting, for instance, often say this go without food for a long time was a natural a part of human evolutionary history. That's true, and that's why our bodies are the way in which they're today metabolically flexible – We can survive on almost any style of food or without food.
However, it doesn't follow that folks, ancient or modern, act routinely selected abstaining from food, beyond certain religious practices.
Professor of Anthropology at Duke University Hermann PontzerPhD, spent a variety of time on it Hadzaa standard hunter-gatherer community in Tanzania.
“My observations are inconsistent with the idea that prolonged fasting is a normal part of life,” Pontzer said. “It’s very rare that there’s nothing to eat.”
On the opposite side of this coin is the concept that fasting is so unnatural that it causes harm. Varady is typically asked to comment false narratives.
“The main issue that really bothers me and is getting a lot of attention online is that intermittent fasting messes with people's reproductive hormones, especially women,” she said. “I don’t know how this started, but there are literally no human studies showing clinically significant changes in a hormone like estrogen.”
It is a component of a bigger challenge facing nutritionists in addition to physicians, nutritionists and other practitioners.
“The only thing people really listen to is random influencers on social media and what they think about intermittent fasting,” Varady said.
Another myth: Fasting gives people permission to eat unhealthy foods while they eat.
The idea seems intuitive, especially for more extreme versions of intermittent fasting. For example, if someone has just fasted for twenty-four hours or their eating window is simply 4 hours per day, you'd expect them to run to the drive-thru the moment the window opens.
“Interestingly, that is not the case,” Varady said. “People don’t want to replace all the food in their pantries. So you eat the same foods, but less of them. We are not seeing an increase in sugar or saturated fat intake.”
How to do Istop Lenten be just right for you
If you choose to present it a try, Varady recommends 16:8 intermittent fasting.
“The 8-hour window is a good start,” she said. “It results in some of the most beautiful weight loss we've ever seen, and it's one of the easiest to incorporate into a person's lifestyle.”
It also helps to approach it with realistic expectations.
“Intermittent fasting results in mild weight loss,” Varady said — mainly what you'd expect from any weight loss program. “It just helps people eat less. It’s not magical.”