Time-restricted eating is a type of intermittent fasting that I find easy to do. Lots of nutrition, longevity, and medical experts agree on the benefits of intermittent fasting. For one thing, it allows the body to do an internal cleanup cycle known as autophagy that gets rid of damaged components in cells. Research on the mechanisms of autophagy led to a Nobel prize in 2016. It also can be a useful weight loss tool. It is interesting that nutrition experts that disagree on other aspects of eating agree that intermittent fasting is beneficial. For example, low-carb advocates and whole-food plant-based advocates both agree on intermittent fasting. There is a good review of the science on the benefits of fasting in Ref , available online here. I’ve also discussed some of its benefits previously. There are some caveats about it, for one thing it can be a bad idea for people with eating disorders. I’d definitely recommend doublechecking with your Dr. before trying it if you have any doubts.
Fasting sounds pretty extreme, and there certainly are versions of it that are, but in it’s mildest form you can eat 3 meals a day, but just don’t eat dinner too late and don’t snack after dinner. I first got into this by accident because I would snack at night and get acid reflux at bedtime. So I stopped snacking at night, but still would have a problem if dinner was a heavy meal. Then I made dinner a lighter meal and the problem was solved. My wife and I eat breakfast about 8 AM and are done with dinner by about 6 AM, so with no evening snacking I’d accidentally blundered into time-restricted eating, with a “fast” from dinner to breakfast of 14 hours. Lots of cultures around the world emphasize eating heavier earlier in the day and lighter later.
In addition, I’ve also done a longer fast by not eating breakfast immediately on arising for some time, but I usually only do it a couple of days a week, when I’m planning a long easy workout. This helped me to achieve a good level of fat adaptation. I had some concern about doing it on days when I worked out harder because there is some talk on the internet about it causing muscle loss. I hadn’t done enough research on the science, it turns out muscle loss is easily avoidable, which I’ll revisit below.
But what really made we want to look into skipping breakfast (or, equivalently, replacing breakfast and lunch with brunch) every day instead of a couple of days a week was reading the inspiring book The Health Experiment: My Intermittent Fasting Story, by Cheryl Gremban. She is a retired nurse, who was overweight (based on her BMI, medically in the obese category), despite having tried various attempts at healthier eating, including Weight Watchers. The book starts while she was still active in her hectic career. She had recently become a nurse supervisor, and as a kind-hearted person was working long hours supporting both her patients and staff. She was too exhausted to exercise after her shifts.
In her sixties, she reached the point of giving up after meticulously counting calories for a month, using her medical training to do it scientifically. Calories in, calories out. Guaranteed to work, right? She gained a pound during the month.
At this point she heard about time-restricted eating from a friend, and after doing research convincing herself there was sound science behind it, gave it a try. The results after 30 days were encouraging so she kept going. The book chronicles her odyssey, which led her to normal weight and much improved health. What really caught my eye was her extremely healthy blood testing results. She ended up retiring from nursing and having a much more active lifestyle towards the end of the journey. In part two of the book she gives her tips on following time-restricted eating as a lifestyle.
Implementing Time-restricted Eating
There are various ways of implementing time-restricted eating. As I mentioned above the easiest is just not eating dinner too late and avoiding evening snacks. This can easily result in a 14 hour fast. Longer fasts usually comes down to skipping at least one meal. Some people eat a hearty breakfast and lunch but don’t eat dinner, while some skip breakfast and eat lunch and dinner. The latter is what works well for me, and is also what Cheryl follows in the book. I found that once I became reasonably fat adapted, I’m just not that hungry on arising and can easily postpone eating till lunchtime. That was driven home for me the last time I had to do bloodwork, and was not able to get an early morning appointment so had to go, in the fasted state, at 11:30. In the past I would have dreaded making it through that morning without eating, but now it was not a problem.
The idea is that your “window” of eating be restricted to at most 10 hours. Most people do better if it’s somewhat less, Mine is a little under 7 hours, while through most of the book Cheryl follows an 8 hour window, although she was experimenting with tightening it towards the end. As an example, for a dinner-skipper, if you have breakfast at 7:00 am, and finish lunch by 1:00 pm, your eating window is only 6 hours, so you are fasting for 18 hours. If you are a breakfast-skipper, and eat lunch at noon and finish dinner by 7:00 pm, you have a 7 hour eating window so are fasting for 17 hours. It can be pushed farther than this, there are even people who swear by a one meal a day version, with a fast of as much as 23 hours, but 8-10 hours is probably a good place to start.
We have been taught that breakfast is the most important meal of the day, so the idea of regularly skipping it may raise alarm bells. However, the science behind this can be a bit misleading, because it does not take fat adaptation into account. For example, I’ve seen studies where people who are normally accustomed to eating breakfast are asked to skip it, and later in the morning show impaired performance on cognitive tests compared to a control group that’s allowed to eat breakfast. What we need is comparison with a third group of people that are used to not eating breakfast and have become fat adapted. Many people that are used to it actually report improved mental clarity in the fasted state. But again, when in doubt, check with you Doc. Also, breakfast maybe your favorite meal and you have no desire to start your day without it. In that case you could just do the milder three meal a day version, or have dinner be the meal you skip.
Cheryl gives valuable tips on healthy eating during your “window”. The most important, for me, is not grazing continuously during your hours of eating. Think of it as two good meals and maybe one snack in between. Also this is not a license to eat junk, it is still beneficial to stick to healthier foods. She emphasizes, however, that she was able to get away more often with treats, as long as they weren’t her trigger foods.
From my experience and what I’ve read from others, there can be a be a transition period before time-restricted eating is comfortable. As I’ve mentioned, it is easier me, because I am already fat-adapted, which I achieved by exercising at a comfortable pace for longer sessions a couple of times a week before breakfast (I discussed that in detail here). If you try fasting and are not fat adapted, you might struggle through cravings until your body adjusts. So here are some tips:
- Try the exercise before breakfast a couple of times a week first.
- Start with the easier three meal a day version and only try a shorter eating window after you a used to that (or simply keep on with the three meal a day version).
- Try minimizing ultra-processed foods or anything that’s a trigger food for you.
It’s important that outside the eating window no calories at all are consumed, even milk or cream or a little sugar in coffee. Cheryl and other authors I’ve read have also emphasized not consuming artificial sweeteners outside the eating window, as there is some evidence it can fool the brain into releasing insulin and interfere with fat adaptation.
Also I want to emphasize that this is not a quick weight loss tool. It can, combined with good eating habits (like avoiding junk), lead to steady sustainable weight loss. But don’t be discouraged if weight loss does not occur rapidly, or even at all at first, there are various other benefits besides weight loss.
Time-restricted Eating And Exercise
For the most part, exercising while fasting is supposed to add to the benefits, for example, exercise can also trigger cellular cleanup (autophagy). But there is the concern of muscle loss, especially if you do strength training. I found a good discussion of that here. It turns out not to be a problem as long as you eat a meal shortly after the exercise session. So I do have to modify my strength training days a bit. Usually I do strength training part at the beginning of an exercise session after a short warmup. Doing it in the fasted state, I’ll modify it so I postpone strength training till later in the morning, right before lunch. This appears to be only necessary for strength training. For lower intensity cardio, and even for high intensity interval training, it seems to be ok, even beneficial, to exercise earlier while fasting, and not eat right away afterwards.
I’ve started a 30 day experiment of doing the two meal a day version of time-restricted eating every day, a couple of days ago. I’ll report back in a month how it goes. Unfortunately I don’t have any blood testing planned in the future, so I won’t be able to see effects on that, but I can report on things like weight management and how energetic I feel.
- Longo, V, and Mattson, M, “Fasting: Molecular Mechanisms and Clinical Applications”, Cell Metab. 2014.