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Q. What is the best fasting method for weight loss?
A. We talk about intermittent fasting like it’s one thing, but it’s actually an umbrella term that refers to several different eating patterns that restrict eating in some way. The way that each style restricts calories differs. In some styles of fasting, you avoid all food for a day, others have you shrink the amount of time in which you can eat your meals into a small window, and there are plans that have you eat every day—just small quantities some days and regularly other days. These plans are sometimes called fasting-mimicking diets.
Although it’s reached peak popularity in the past few years, fasting has actually been around a long time. I believe fasting comes from religion, and you may already know about some religious traditions involving fasting such as Ramadan. In the past few years, I’ve seen a lot of talk on blogs about all the purported health benefits of fasting, from aiding weight loss to helping you live longer. But even though there is research done on fasting, it’s important to remember that it’s mostly preliminary, and blogs don’t always portray the clinical trials correctly. A lot of the studies are done on animals. The human studies are small, mostly 20-30 people, and rely on self-reported data from participants—which is known to be at least slightly inaccurate.
Types of intermittent fasting
My research focuses on alternate-day fasting, but there are many different kinds. If you’re considering them for weight loss, the overall method for achieving that is the same no matter which style you choose. Fasting may help you shrink the number of calories you consume without counting calories. The idea is that these fasting windows create a calorie deficit that is almost impossible to make up during eating windows. It’s the calorie deficit that leads to weight loss. There’s nothing inherently magical about fasting.
Although there’s a lot of talk about how periods of fasting can improve your metabolic health, that’s simply untrue. Like any other diet, fasting may reduce your body weight. When you lose weight, your metabolism decreases. There is some indication that fasting may help you hold onto more muscle and maximize fat loss, but that’s as a percentage of the weight you lose. Fasting doesn’t help you lose more weight than any other plan that lowers calorie intake.
It’s also worth noting that most people struggle a little for a period of time, generally the first ten days, when starting an intermittent fasting plan. We’re all accustomed to eating some way, and we don’t deal well with the change. “Hanger” is a real thing. But past the 10-day point, people seem to get used to fasting and actually many of them report feeling less hunger, increased fullness, and even a surge of energy.
16/8 method or Leangains protocol
This is the most popular breakdown of hours for time-restricted feeding. This fasting diet is exactly what it sounds like: you refrain from eating for 16 hours of the day and eat all of your meals during the remaining eight hours. The idea of this plan from a weight loss perspective is the same as other plans: Theoretically, you’re creating a large enough caloric deficit during the fasting periods that you cannot get your calorie intake high enough to undo during your smaller eating window.
Although there are a lot of different variations of fasting getting their own books, this is one of the most popular. This plan requires you to complete a 24-hour fast once or twice a week. The remaining days, you go back to eating as you normally do. Many people may find this plan difficult compared to the other variations on fasting because they’re going for a longer amount of time without food.
The 5:2 Diet is very similar to eat-stop-eat, except you eat food every single day. Instead of full days of fasting, this plan has you on very low calories—typically 500 calories for women and 600 calories for men—two days of the week. The other five days of the week, you eat normally.
There are two variations of alternate-day fasting (ADF). For one, you fast completely on one day, and the next day you return to eating normally. The other version allows you to eat 500 calories on fasting days but, again, you return to your normal caloric intake the next day.
The Warrior Diet
Although there’s some crossover with this one between fasting and the Paleo community, the concept is the same as time-restricted feeding. Think the 16/8 method, but with longer daily fasting. On this fasting diet, you fast all day and eat one large meal—generally in the evening.
Spontaneous meal skipping
There’s some debate as to whether this counts as actual fasting. I’d say there’s little point in skipping a meal if the aim is to reap the health benefits of fasting if the gap you’re creating between meals is less than 12 hours. So it may make sense to skip breakfast, especially if you’re not hungry in the morning, but skipping lunch and having an afternoon snack may not create this 12-hour window.
Which intermittent fasting method is best for me?
I always tell people to try whichever plan is closest to their current lifestyle. If you’re someone who isn’t hungry in the mornings, then the 16/8 method may work well for you. You may even find that it’s easy to follow the alternate-day fasting plan because you’re not hungry until later. Like anything, you need to be consistent to see results and get the health benefits of any plan that you follow. If you lose weight following a fasting diet, but then go back to the non-fasting diet you were on before, you’re likely to gain all the weight back. Specifically, with the alternate-day fasting, ideally a person fasts for a day, feasts the next day, and continues this cycle for the rest of their lives.
But there’s nothing magical about fasting. We don’t have enough research done in humans to say that many of the health benefits you see in blogs or heard repeated actually happen for most people. Much of the research is done in animal models. We do see that different styles of intermittent fasting can help people lose weight. But if you’re someone who likes to eat small meals every two or three hours, fasting likely isn’t for you, and there’s no evidence that people lose more weight fasting than they do on any other weight loss plan as long as the calorie restriction is the same.
And there’s simply no intermittent fasting plan that we can say is safe for pregnant women, children, or seniors. No form of fasting is suggested for people with a history of eating disorders, either. Before trying any methods of intermittent fasting, people on prescription medication should consult their healthcare provider. Dosage for some medications, like those that help control blood sugar, may need to be altered. Any eating plan that decreases body weight may require changes to your medication regimen.