I often get questions about diet fads. Here’s an email exchange I had recently about if intermittent fasting is beneficial.

Question:

Hi Peter, I was looking for some guidance. I'm felling good and making progress. I just watched videos on keto and felt like I should get some advice from someone who has experience.

Right now I go Fit 4 Less. I do a full body workout with 20 mins cardio in the morning and I do another 20 mins of cardio in the evening. I only eat once in a day. I'm doing 20 hours fasting and 4 hours eating window in which I only eat one meal - that's all. This is what I do 6 days a week. I take one rest day off on Sunday.

What is your advice regarding this?

Answer:

Thanks for reaching out. Great questions. There’s a lot there.

Focus on the Process

A big piece of advice is this: there are lots of nutrition and fitness plans. It's easy to get caught up in the hype and think you should change something. If you feel good and are making progress, think twice before changing. There are no quick fixes.

Of course we all hear stories of people who are fast-responders and see amazing results with a certain diet or workout. The chances are that those people would see very fast results with any program. It's not fair, but a small percentage of the population are lucky and experience rates of progress that are well above average. Most of us don't.

So the headline is this: don’t get over-excited and expect too much from diets or routines that seem too good to be true.

Instead, be patient and focus on the process. If you're seeing modest but consistent results that's perfect.

You mentioned the Keto Diet. While this is one method for weight loss, maintaining a true ketogenic diet vs. a low carb diet is quite challenging. You can read about that a little here.

The bottom line is that if what you’re doing is already working for your goals, don’t change it. Even though it’s tempting to try to improve your diet plan to speed up your results, it’s smarter to just stick to the thing that’s already a proven path to success.

Exercise

Basically your workout routine sounds fine for a young guy like yourself. It’s a lot of activity, but as long as you’re feeling good the cardio sessions are moderate intensity (i.e. you’re not pushing yourself to the max 6-12x/week) it should be fine. Make sure to maintain a weight training regime so you’re building muscle. This helps with long-term fat loss because it boots your resting metabolism.

[Note: this was a young individual with low stress and good resilience. Many people’s lifestyles don’t support training twice a day based on sleep, stress, nutrition, etc.]

Thinking About Fasting

Fasting is one method that can work, although it’s definitely not the only one.

If you like the fasting and feel that it works well for you, that’s fine. The good thing about some intermittent fasting protocols is that they’ve been shown to be a good way to reduce calories and improve insulin sensitivity (basically this means better ability to burn fat and regular blood sugar) without as many drawbacks. Those drawbacks that other low calorie diets can include are a drop in your metabolic rate (how many calories you burn at rest - more on this later) and a reduction in muscle mass (muscle tissue helps maintain a high metabolism). If you’re curious about it, I recommend reading “The Complete Guide to Fasting” by Dr. Jason Fung. You can start by watching this video:

All that being said, fasting can still have problems.

Because of your high level of activity, I would recommend expanding the eating window to 6 hours and taking 2 meals. This would enable you to take more energy in, as well as more nutrients. You'll be able to get more protein, minerals and vitamins.

Especially in the long-term, you’ll need to be careful about only eating once a day. It might work well for now, but it isn’t going to be sustainable beyond a certain point. No one can say when that day will arrive, but it will come eventually; it could be in a week or in many months from now, especially as you begin to lose more fat/get leaner.

Let's say you're only eating 700 cals per day right now in your one meal. This is very low and not enough to sustain your long-term energy needs. At the moment, stored energy in body fat is used to make up the difference and you are losing weight. But after a while this becomes a stress on the body, and it can go into starvation mode. If that happens, not only will fat loss stop, but you’ll start to feel burnt out and low energy. I see this type of thing often. Even though it seems counter-intuitive, you need to eat MORE food in this scenario.

The body’s response to fasting is a little different than with normal low calorie diets, and you can read about the long-term problems with major calorie restriction here. The article shows what happened to people on the reality TV diet show The Biggest Loser. It shows that even though the contestants weren't fasting or arguably even eating a high quality diet (for instance, highly processed cereals were regularly consumed and also advertised on the show), I'd guess that the same adaptations would happen to anyone who practices fasting/calorie restriction for extended periods of time.

So here's the take away lesson: if/when progress slows or stops, or you notice that you feel less energetic, you should actually start eating more. As long as you're eating quality food, you should start losing fat again and feel much better overall.

Finally, make sure to eat mainly unprocessed foods and consider taking a multi-vitamin with your meal. It will be very difficult to get enough nutrition into one meal no matter how hard you try.