Intermittent Fasting is trendy; does it actually work?

During my recent trip to India I discussed eating habits and mealtimes with many people I met, as well as with Ayurveda doctors and practitioners.

Religious traditions and spiritual pursuits guide many of the people I interviewed in India to fast intermittently or to eat only one or two meals a day. Ayurveda, which is an ancient healing tradition that originated in the Indian subcontinent and is practiced today by certified Ayurvedic doctors, subscribes personalized holistic advice not only regarding what to eat, but also about when to eat your meals. Ayurveda regimens may include intermittent fasts, which are usually short-term, and not compete fasts, and generally counsels a long break between dinner and breakfast, smaller dinners, and lunch and breakfast as the larger meals.

Intermittent Fasting (IF) is trending back at home – as a weight loss and fitness regimen. There are dozens of books and plans out there, many different patterns of cycling between the days of fasting and those on which you can eat. Fasting isn’t a new idea, but Intermittent Fasting is now popping up as the solution we’ve all been waiting for; success stories from celebrities make it seem like beauty and a svelte figure are all about the distribution of food over time.

Could the old practice of giving your digestive system a rest – for whole days or part of the day ­– be the key to sustainable weight loss? Is Intermittent fasting more than just a way to cut caloric intake?

Can intermittent fasting help you lose weight?

Intermittent fasts vary in regimen, and can be anything from food restrictions on one to several days a week, with food restrictions that can be anything from a total fast to a severe cut in daily intake.

The short answer is yes. Intermittent fasting for weight loss usually results in weight loss.

But – and here’s the big but – most weight loss diets work. You can lose weight on practically any regimen, from the Grapefruit Diet to Paleo to Keto to Weight Watchers, as long as you cut caloric intake.

Intermittent fasting as a weight-loss diet should be tested against other diets.

A recent review that included 11 randomized controlled trials with at least one fast day a week demonstrated similar weight loss results when compared to regular continuous calorie restricted diets, and similar metabolic benefits (weight loss, no matter how you achieve it, improves glucose tolerance, lipid profile and blood pressure parameters.) Several other reviews comparing intermittent fasting to continuous calorie restriction show similar results: a comparable weight loss of 4-8 percent body weight with no clear winner.

The real test of any weight loss diet is weight maintenance. Keeping weight off long term and preventing a rebound is the real challenge for all weight loss diets. In the short term, intermittent fasting works because it controls caloric intake, but it’s the long term that really matters, and long-term trials of intermittent fasting are lacking.

Time restricted eating vs. intermittent fasts 

Time restricted eating is often lumped together with Intermittent Fasting. Time restricted eating is the practice of consuming daily meals within a limited time window that can range anything from 3 to 14 hours. If the eating time window narrows to just 3 hours this does resemble a intermittent fasting regimen, but when the window is 10-14 hours it actually resembles what life used to be like for most of humanity until very recently. In my childhood, which wasn’t all that long ago, and my kids’ childhood, which was just about yesterday, dinner usually ended at around 7, and there was no food from then until breakfast on ordinary days.

It’s called breakfast because the morning meal used to break a fast.

People used to have large breaks between meals – meals interspersed with snacking and grazing occasions are a relatively new phenomenon, at least evolutionarily – and at least 12 hours with no food overnight.

Several studies show that limiting mealtimes to 10-12 hours a day, and longer nighttime food abstinence, can lead to an involuntary and effortless cut in calories and to weight loss.

In a 2-week study that limited eating to 6am to 7pm, with no additional food limitations, young healthy men  lost about a pound each week.

A longer term controlled study of obese people using a narrower eating time window of 10am to 6pm resulted in 7 pounds lost in about 3 months.

A recent study in Cell Metabolism found that overweight people, at high risk of developing type 2 diabetes, who gave themselves a 14 hour break from food overnight for 3 months, lost 3 percent of body weight and had improvements in blood pressure, cholesterol, insulin and glucose levels. What’s most interesting is that the participants in the study weren’t asked to change what they ate, but nevertheless reduced caloric intake – spontaneously.

How does this work? Eating within a certain timeframe led to eating fewer calories in these studies. Late night eating, as we all know, is famous for poor food choices – people rarely order salad deliveries at midnight.

But does giving your body a break from food specifically when it’s dark outside play a role?

It might. We’re not machines that can be fueled anytime. We, like any other animal, have inner clocks that have a complex interaction with food, and these clocks, our circadian rhythm, organizes our body’s functions, including our hormonal and metabolic pathways on a time-of-day dependent basis. Even our gut microbes show circadian variation.

Intermittent fasting as a weight loss diet scheme may be as good as any other – provided you choose healthy foods, don’t overdo it, and can sustain this kind of regimen.

Timed eating, however, at its most gentle form, as in 10-14 hours window without food overnight, is just common sense, and the way our recent ancestors got humanity to thrive so far.

And it’s really a simple thing to try in 2020.

Dr. Ayala