NPR | Rebecca Hersher | Fasting Studies Clash With Our Desire To Eat What We Want, When We Want It
A new study suggests that skipping meals is difficult.
The study published Monday in JAMA Internal Medicine did not set out to investigate the hardships of abstaining from food. The main question was: Is alternate-day fasting more effective for weight loss and weight maintenance compared with daily calorie restriction?
The answer to that question appears to be "No." The study of 100 people over the course of one year suggests that fasting every other day is no better than restricting calorie intake every day for people trying to lose weight or keep it off.
But the researchers also found that people do not change their eating habits easily. About a third of the study participants who were asked to fast didn't follow the study requirements and ended up dropping out.
The primary finding is in line with other studies of intermittent fasting. As we have reported, previous studies have found potential benefits from fasting for 16 hours each day, or reducing the amount you eat on some days each week, which is the basis for the trendy 5-2 diets.
A 2014 paper in the Proceedings of the National Academy of Sciences argued that modern three-meals-plus-snacks eating patterns are "abnormal from an evolutionary perspective," but nonetheless noted that many people may not want to change their eating habits.
The authors wrote it was "critical" for researchers to study the "long-term adherence of different subject populations" to different fasting schedules.
The paper published Monday is the latest study to, somewhat inadvertently, do just that. Of the 100 participants, most of whom were metabolically healthy, obese women, 69 of them completed the study. Thirty-eight percent of those who were supposed to fast every other day dropped out because they didn't adhere to the diet. Twenty-nine percent of those who were supposed to restrict their calories every day dropped out for the same reason.
That left them with just 33 people in the two fasting groups, which isn't a large enough sample size to lend much weight to the findings.
And they're not alone. Other studies have run into similar issues with participants who struggle to stick with the eating protocols.
Take, for example, Brandie Jefferson, who is a science writer and, currently, a participant in an intermittent fasting program as part of a clinical trial for people with multiple sclerosis.
Just last week, Jefferson wrote for Shots about how difficult it has been to stick with the fasting protocol, which requires that she eat only between noon and 8 p.m. For the remaining 16 hours, she can drink only water, tea or black coffee.
"Over five months, it's been the same nearly every day — I do get a little hungry in the mornings, but I'm thinking about eating more often. I have only eaten any earlier than noon once or twice during the study, like the infamous O'Hare Airport incident when I just couldn't resist that bagel. I still have no regrets.
"My slip-ups tend to be when I'm running late and eat after 8 p.m. I don't think I've screwed up enough to affect the tests, and I've been honest when it comes to food logging."
And it's not just study participants. Jefferson talked to the person running her study, Dr. Ellen Mowry, an associate professor of neurology and epidemiology at Johns Hopkins University.
Mowry explained that when she tries to fast along with participants, she also finds it difficult to stick with the rules. "But often for me," she says, "this is related more to my mental stamina rather than physical."
And as a paper on intermittent fasting published in March notes, "Adherence to diets within trials is notoriously difficult to assess due to missing dietary records and well documented under-reporting [among] overweight subjects."
The authors of that study pointed out earlier work that suggests that allowing people to eat a wider range of foods, even if they are restricting their total calorie intake, could help people stick with a fasting program, but lamented an overall lack of high-quality data for comparing intermittent fasting patterns.
That's because fasting studies generally don't include a large number of participants. For example, the clinical trial that Jefferson is part of has 54 participants, which Mowry says is too small to get particularly useful results.
"The studies are too small to be certain that any change in symptoms is related to the intervention," Mowry says.
Some studies of fasting diets have had more success helping participants adhere to eating plans. A 2015 study of non-obese adults between 19 and 30 years old, for example, found that most of them stuck with the 10-week protocol. But it also was too small to be broadly applicable, since just 24 people participated.