Untrending: Does Intermittent Fasting Really Work?
Surprisingly, this is one fad that has (some) evidence to back it up.
In Untrending, we side-eye the latest fads so we know what we’re getting ourselves into — and what (if anything) we’re getting out of them.
Do you know how your best friend’s brother dropped a ton of weight before his wedding? Intermittent fasting. How your coworker’s auntiji reversed her diabetes? Intermittent fasting. How your dad’s business partner’s wife’s cousin beat Alzheimer’s and ran a marathon? Intermittent fasting. Intermittent fasting. Intermittent fasting!
It’s everywhere these days, with claims that border on the miraculous. But does intermittent fasting really work? Is it really worth it? And for whom?
Some people advocate a 5:2 or 6:1 regimen, that is, fully abstaining from food one to two of the seven days in a week; some swear by an every-other-day approach that alternates eating and fasting; while others restrict their eating to a handful of hours in a day, eating within a eight hour period, say, and fasting for the remaining 16 hours in a day (also known as not snacking). Regardless, the premise is the same: that a regular amount of short-term abstention from food will promote weight loss and yield health benefits.
It’s not rocket science, but it does fly in the face of previous research that has found fasting slows down metabolism in a way that counters weight loss efforts and good health. But that research, argue advocates of intermittent fasting, is based on fasting for extended periods of time. Intermittent fasting is intended to last no more than 48 hours at a time — tops.
(As an aside, before we get started, this article is only examining intermittent fasting as a method of health and weight management; fasting for religious purposes is something else entirely, and no one here is making a case for or against it.)
Studies of intermittent fasting show something quite different — though it should be noted that intermittent fasting is a fairly new area, if not in practice, at least in research. So, the first conclusion about intermittent fasting should be: while initial explorations of its effects are encouraging, a lot more research needs to be done to conclusively establish its benefits.
That said, let’s take a look at the benefit with the most evidence behind it: Intermittent fasting appears to work for preventing diabetes in at-risk individuals. A large-scale 2018 review of research into intermittent fasting’s effect on the body name-checked 10 independent studies to conclude intermittent fasting “regimens ranging in duration from 8 to 24 weeks have consistently been found to decrease insulin resistance.”
Further, intermittent fasting has “been found to decrease fasting glucose levels by 3 to 6% in individuals with prediabetes.” This has big implications for South Asians, who have an ethnic predisposition to insulin resistance — an innate risk factor for metabolic syndrome, which includes conditions like diabetes and obesity. (That said, intermittent fasting is not a lifestyle change that should be embarked upon without consulting a doctor, especially if you already have a metabolic disorder.)
Intermittent fasting also appears to work for weight loss. Studies suggest intermittent fasting boosts metabolism, making it an effective method of weight loss. That said, it’s not particularly more effective than restricting calories. A 2015 review of existing research found alternate-day fasting over the course of three to 12 weeks, and single-day-per-week fasting over the course of 12 to 24 weeks, reduced body weight by 3 to 9 percent in normal-weight, overweight and obese participants. And a 2016 small-scale study of 34 men concluded that while intermittent fasting and calorie restriction “are equally as effective in decreasing body weight and fat mass,” intermittent fasting dieters had a slight edge in that they saw less muscle loss in the process than calorie counters.
The benefits of intermittent fasting may also include improved cardiovascular health. The same 2015 study that pointed to weight loss benefits also found sharp drops in total cholesterol and triglyceride (markers of metabolic and cardiovascular problems) levels. Further, animal studies suggest intermittent fasting affects heart rate and blood pressure in a way akin to endurance exercise, but so far, there’s not much proof to back up this claim in humans.
Finally, intermittent fasting has been touted as having other benefits — such as boosting cognitive and physical performance, and reducing chronic inflammation — but there is far less evidence for these effects, most of which have been observed in animals, not humans. For the time being, until research accumulates, these claims are marginally better than hopeful thinking and pointers to where future research should be focused.
So, is intermittent fasting worth it? It depends. First, there is the type of regimen: “There is evidence to suggest that the circadian rhythm fasting approach, where meals are restricted to an eight to 10-hour period of the daytime, is effective,” said Dr. Deborah Wexler, director of the Massachusetts General Hospital Diabetes Center and an associate professor at Harvard Medical School, in 2018. (Though she adds that it’s mostly about finding a regimen that you can sustain.)
Ultimately, per the 2018 research review, intermittent fasting works best for: older adults who are unhealthily overweight, but are any way prone to losing muscle mass with age and should minimize its further loss in the process of fat loss; and people with or at-risk for metabolic disorders or cardiovascular problems. It might also be useful for people who are otherwise healthy, but want to lose some weight and who can’t be bothered with counting calories.
Like all lifestyle changes, the biggest obstacle to intermittent fasting working is compliance. So, the bottom line is, if you’re looking to lose weight or manage your blood sugar, intermittent fasting might be worth consideration — but only if it feels like something you can commit to.
Liesl Goecker is The Swaddle's managing editor.