This story was originally published in 2013. Since then, evidence for the benefits of fasting has mounted. See here, here, and here. But so many questions still remain. What is clear? Dieting is hard. For example, this study, which examined an every-other-day-fast regimen and a more traditional calorie-restriction diet, lost 31% of its participants.
A couple of weeks ago I found myself in a beautiful rural home that belongs to my parents’ friends, a slim and sophisticated couple who enjoys bird watching and international travel. I was meeting this pair—let’s call them George and Marsha—for the first time. I’m inherently nosy, so while the rest of the group chatted, my eyes scanned the room. On the fridge, I noticed a slip of paper that looked to be George and Marsha’s weekly dinner menu. That night they’d be having polenta and pork roast. The other days had meals written next to them too, all except for Monday and Wednesday. Next to those two days, Marsha (or George) had scrawled “Fast.”
Fast as in not eat? Marsha and George didn’t seem like the type to fall for juice cleanses or fad diets. My parents said the couple had probably seen the same documentary they had. The show follows Michael Mosley, a BBC journalist and former physician, on his quest to become slimmer and healthier through fasting.
I’ve never heard of Michael Mosley, but I’m not sure how I missed him. Lately Mosley is everywhere — on the BBC, on PBS, in the news. In January he launched a bestselling diet book co-authored by journalist Mimi Spencer. Here’s the approach they’re advocating: To lose weight and improve health, dieters should fast two days each week. On fasting days, women should consume no more than 500 calories. Men are allowed 600. The other five days dieters have no restrictions.
In the BBC documentary my parents referenced, a chubby, unhealthy, middle-aged Mosley seeks the secret to weight loss and health. He starts his journey by visiting Joseph Cordell, a lawyer who practices calorie restriction. Individuals who follow this diet, known as CRONies, generally cut their caloric intake by 25%. So a woman who typically eats 2,000 calories a day would consume just 1,500. There’s lot of science to support the benefits of calorie restriction. I wrote about a few studies here. But there’s no doubt it has drawbacks, hunger being among them. Emily Yoffe, who tried caloric restriction back in 2007, had this to say: “Each meal I ate now had the poignancy of a Shakespeare sonnet: how much I longed for each bite, how aware I was of how few there would be.”
Mosley wasn’t convinced he could adopt calorie restriction as a lifestyle. “What I really want to do is try to understand the ways in which calorie restriction works,” Mosley said in the documentary. “Then hopefully I can get all the delicious benefits without actually having to do it.”
In other words, Mosley wanted what the entire human race has always wanted — a shortcut.
Mosley’s search for a shortcut leads him to fasting. Not all fasts are created equal, and Mosley flirts with various forms. He first tries a painful three-day fast. But he wants something a little less intense, so he visits Krista Varady at the University of Illinois. She’s studying alternate day fasting. Participants in her studies fast every other day and on those days Varady’s subjects eat a single meal that’s about 400-600 calories. The other days they can eat whatever they want. Varady has found that alternate day fasting can help participants shed pounds and lower their cholesterol and blood pressure.
“I am now starting to be won over by the idea that a simple pattern of feast and fast can be powerful,” Mosley says after his visit with Varady. “It seems to have an impact which goes beyond simply eating less. And I think it could work for someone like me.”
But Mosley doesn’t adopt alternate day fasting. In the book, he writes that fasting every other day “can be socially inconvenient as well as emotionally demanding.” Instead he chooses to fast two days a week, eating 600 calories those days and a normal diet the other days. And it seems to work. In three months, Mosley loses 19 pounds. His body mass index falls from 26.4 to 24, and his body fat drops from 28% to 21%.
“The results have been absolutely fantastic for me. But that doesn’t mean that intermittent fasting will work for everyone. It’s really important that they do more trials on humans to find out if, in the long term, it is safe and effective,” Mosley says in the documentary.
Yet, early this year, Mosley launched a diet book that advocates the exact diet that he once said needs more research. The book description includes this line: “Is it possible to eat normally, five days a week, and become slimmer and healthier as a result? Simple answer: yes.”
I can’t decide whether to high five Mosley or shake him. On one hand, obesity and the health problems it begets are rampant in the US and Europe. So kudos to Mosley for developing a somewhat simple diet plan that’s rooted in science. But there are still so many unknowns. Fasting can be dangerous. And Mosley’s evidence for the effectiveness of the diet relies heavily on anecdote. And who’s to say that intermittent fasting will be less painful than the tried and true dieting strategy of eating slightly less each day?
On its Web site, Britain’s National Health Service notes that “compared to other types of weight loss programmes the evidence base of the safety and effectiveness of the 5:2 diet [five days of normal eating, two days of fasting] is limited.”
One thing is clear: Mosley’s diet probably isn’t right for me. Limiting myself to 500 calories in a day would leave me very very hangry. I might lose some weight, but I’d also likely lose a husband. Others seem to be struggling too.
5-2 has worked for me, mainly because it’s only two days a week, and I can do that. I lost 20 pounds five years ago and kept it off until late last year when I had surgery. I gained 10 pounds from sitting around doing nothing and letting myself eat what ever I wanted because recovery was enough “sacrifice”. I have since lost five of the ten pounds and have resumed the 5-2 routine.
I don’t think any diet will work unless it’s something the dieter can accept and adapt to. It gets complicated if you have non-supportive family members (I am lucky not to be in that situation). It gets difficult if you can’t just “be with” your hunger periodically over the day. Keeping physically active during the fast day pretty much makes the hunger go away as long as you are moving about. Learning to experience hunger without panicking about where your next bite will come from is also valuable (it’s kind of a “zen-like” acceptance of the situation–and it’s only 24 hours).
All I can say is that nothing else worked for me over numerous gain/loss episodes during the seven decades so far of my life. I found this routine, I can stick to it, I can eat whatever I want on the 5 off-days without feeling guilty, and except for the unusual situation of recovery from surgery I have not had to spend a second worrying about my weight for the last five years. In addition, when I had pre-op exams all the medical people were amazed how healthy I am, and the surgeon said the main reason I recovered swiftly is because I’m really healthy. I don’t know if I can scientifically credit the 5-2 diet for that, but I sure can credit it anecdotally.