Straight talk on intermittent fasting
Despite a lack of research proving it aids weight loss, it’s been wildly popular
Sometimes it seems as if the diet world is nearly as polarized as the political sphere.
Especially when it comes to intermittent fasting (IF). I wrote a piece about it last year and, almost immediately, saw people sub-tweeting me to complain about promoting an eating disorder in the name of wellness.
That’s a pretty stock response to the mere mention of IF in some circles.
On the other end of the spectrum are the die-hard devotees of this popular weight-loss plan, which places more emphasis on when people eat than what they eat.
Last fall, when Dr. Ethan Weiss, a cardiologist and researcher at the University of California, San Francisco, published results from a study that cast doubts on the efficacy of IF, he got an earful.
“I certainly had a mix of responses, either on email or social media,” Weiss recalls. “There were some people who were super cool and really interested, but there were some people who were extremely unhappy. I got a lot of comments from people like, ‘You idiot, how can you tell me that this form of restricted eating doesn’t work when it worked for me?’ ”
In fact, fasting worked for Weiss, too, who lost weight over the six years he was on the regimen, so he’s likely the last person who would have said that IF can’t work. And, indeed, he never said it didn’t work. What the researcher did say was that he conducted a randomized control study where the research subjects on IF were told to eat whatever they wanted so long as it was only in an eighthour window, and they failed to lose a significant amount of weight — only two pounds in 12 weeks.
So, does it work? Or not? The study flew in the face of a lot of anecdotal evidence from individuals who have had success, including Weiss himself. He expected his research to confirm that this was an effective way to lose weight and was rather surprised by the results.
Intermittent fasting is wildly popular and famously used (in some form or another) by everyone from the GOOP set to Silicon Valley tech bros. Part of its appeal is that it’s simple, since there are no cards to count or foods to weigh. And, although most people who follow it reduce their intake of processed carbohydrates, fasting isn’t an elimination diet — you don’t have to give up an entire food group.
In addition, it’s been championed by Toronto’s own Dr. Jason Fung, nephrologist and founder of the Metabolic Clinic in North York, with a self-reported high success rate in reversal of diabetes and weight loss. The idea behind it largely revolves around insulin, which controls our blood glucose levels. When we eat, our insulin levels go up. The theory has it that, if we let our insulin flatline instead, we’ll burn off our stored energy — a.k.a. fat.
Conversely, Fung argues that, failing to regulate insulin can raise your risk for other health problems, including Type 2 diabetes, obesity and breast and colorectal cancer, the latter two of which are explored in his new book, “The Cancer Code: A Revolutionary New Understanding of a Medical Mystery.”
“The World Health Organization has classified 13 different types of cancer as obesity-related,” says Fung. “So the key is that, if you are overweight — and that’s affecting more and more people — it’s important to bring that weight down. And if you have type 2 diabetes, which is becoming a bigger and bigger problem over these last 10 years, reversing it will reduce your risk of those associated cancers.”
All of this sounds simple enough, right? There are a lot of potentially complicating factors, however, starting with the issue that there’s no peer-reviewed research at this point to prove the theory.
And, although fasting isn’t new (Fung points out that it’s a component of several traditional practices in well-established religions), we don’t know how sustainable a long-term fasting regimen is, especially when it comes to the more extreme fasts that some advocates have endorsed. It’s one thing to skip breakfast, but entirely another to embark on a 36-hour fast.
In fact, the length of the fast is one thing Fung thinks went wrong with the aforementioned University of California study. The design had been based on a study that showed rats lost weight when restricted to an eight-hour eating window. Rats, however, have a much faster metabolism and the human equivalent to a 16-hour rat fast is more like 24 or 36 hours, he explains.
So, letting a rat eat anything it wants over eight hours is not at all the same as telling humans to load up on all the good things in their eating windows.
“So the problem is, if you say, ‘Eat whatever you want,’ and they’re eating pizza and french fries all throughout the eight hours and then not eating for the rest of the day, they’re not going to do very well,” says Fung.
“I know that. I mean, I see that all the time and it’s simply not a powerful enough fast for a lot of people.”
Here’s where things get tricky though. People doing more extreme fasts at the Metabolic Clinic are supervised by Fung and his team. But when diet gurus in the wild west of the wellness world advise DIY extreme fasts, there is a danger of self-harm. For example, I did a seven-day detox program last year for the sake of journalism and concluded that, first of all, it was a starvation diet and, second of all, starvation diets aren’t my thing.
“Fasting is a tool and you have to know when to use it and, yes, you could do great harm if you use it badly,” says Fung. “Almost everything we do in medicine could cause great harm if you don’t use it correctly. But taking the tool away is like saying knives are bad because you could cut yourself. But, if I want to cut my steak, I need a knife, right?”
I keep coming back to the University of California study and wondering about the definition of insignificant weight loss. If you lost two pounds every 12 weeks, that’d be more than eight pounds a year. Nobody aiming to become the “biggest loser” would be satisfied with that, but a lot of people might be quite happy to imagine themselves being eight pounds lighter this time next year. If you did that for a few years …
If it works, that is. And the peer-reviewed research simply isn’t there at this point, so we can’t really say with any certainty. All we know for sure is that fasting for 16 hours isn’t a licence to graze for the intervening eight.
Which is also kind of common sense, right?
Science takes time, especially dietary science, because it’s hard to do large control studies and be sure that people are sticking to their experimental regimen for weeks at a time. We will eventually get more answers, perhaps even some from University of California’s Weiss, who, even though he’s given up fasting himself, hasn’t written off the regimen completely.
“I’m very intrigued by the interaction between meal timing and diet composition, particularly when it comes to macronutrients,” he says. “So, I’m hoping to do a study in the future where we would look at the potential interaction of the two variables together.”
So, stay tuned. We’ll know who’s right eventually. And on the need for more research, everyone agrees — especially Fung. There’s no need for polarization.
Instead, we need to do more of the thing that seems the hardest for humans — to be patient. Especially when it comes to weight loss.