How It Works: Fast for 14 (women) to 16 (men) hours each day, and then “feed” for the remaining eight to 10 hours. During the fasting period, you consume no calories. However, black coffee, calorie-free sweeteners, diet soda and sugar-free gum are permitted. (A splash of milk in your coffee won’t hurt, either.) Most practitioners will find it easiest to fast through the night and into the morning. They usually break the fast roughly six hours after waking up. This schedule is adaptable to any person’s lifestyle, but maintaining a consistent feeding window time is important. Otherwise, hormones in the body can get thrown out of whack and make sticking to the program harder, Berkhan says.
Fast for 16 hours of the day, and allow yourself a single eight-hour window for eating. This may be a good option for most beginners, because it represents the most subtle change from the standard three-meals-per-day lifestyle. As approximately eight of those fasting hours should be spent getting a good night’s sleep, that leaves only eight hours where participants need to be consciously avoiding food. For many, allowing themselves to eat normally from noon until 8pm gives them a stable meal schedule while also staying in a fasted state for the majority of the time.
Intermittent fasting and the ketogenic diet are two of the top trending eating patterns among dieters and health enthusiasts alike. However, while there are plenty of differences between intermittent fasting vs. keto, they can actually be combined to help amplify results and reach ketosis even faster. In fact, by practicing intermittent fasting on keto, you can take advantage of the unique benefits that both have to offer.
Cons: Even though there is flexibility in when you eat, Leangains has pretty specific guidelines for what to eat, especially in relation to when you’re working out. The strict nutrition plan and scheduling meals perfectly around workouts can make the program a bit tougher to adhere to. (You can learn more about the specifics — as well as when to time these meals — directly from Leangains here and here.)
Perhaps most importantly, intermittent fasting is one of the simplest strategies we have for taking bad weight off while keeping good weight on because it requires very little behavior change. This is a very good thing because it means intermittent fasting falls into the category of “simple enough that you'll actually do it, but meaningful enough that it will actually make a difference.”

What and when you eat during the feeding window also depends on when you work out. On days you exercise, carbs are more important than fat. On rest days, fat intake should be higher. Protein consumption should be fairly high every day, though it will vary based on goals, gender, age, body fat and activity levels. Regardless of your specific program, whole, unprocessed foods should make up the majority of your calorie intake. However, when there isn’t time for a meal, a protein shake or meal replacement bar is acceptable (in moderation).
Every study seems to support cognitive and health benefits for IF. Studies are coming out showing it may help stave off heart disease and it’s even been shown to halt or possibly reverse brain-related diseases such as Alzheimer’s. If in doubt, check out Jason Fung’s youtube videos along with a couple of youtube researchers who do wonderful analytics, an American who lives in Japan who goes by, “Things I’ve Learned” and Thomas DeLauer’s IF material. I’ve been doing IF myself for a few months now and I feel better, more energy, better sleep, and controlled weight.
Jerimiah, the linked study in the article (https://www.sciencedirect.com/science/article/pii/S1550413118302535) specifically studied “eTRF”(Early Time-Restricted Feeding) from 8am – 2pm, and implies that eating earlier is better than later. I haven’t read the study (it’s behind a damn Elsevier pay-wall), so I don’t know how strongly they feel about early vs late, though. For me, personally, 12-8 is doable, and skipping dinner (given the existence of a family and the desire to have dinner with said family) isn’t doable, so I’m pleased to hear from you and April above that it’s working. Just starting!
Another program called the 5:2 Fast Diet involves eating 5 days a week and fasting for the other 2 days, when women can get no more than 500 calories and men no more than 600. That’s a quarter of the amount you likely eat on the days when you don’t fast. Whether you eat those calories in one sitting or spread them across micro-meals throughout the day is up to you.
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