A Beginner's Guide to Intermittent Fasting

A personal trainer with more than 20 years of experience on the diet explains the pros and cons.

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Oct 13 2018, 10:14pm

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Intermittent fasting is very popular these days, but I started using it years ago almost by accident. In fact, I’d been using a form of IF—a modified version of the 16:8 Diet—for the best part of a decade before I realized there was a name for what I was doing.

The 16:8 Diet is probably the most popular form of IF. It involves a 16-hour fast each day, usually from 8 pm to noon the following day. All your food for the day is eaten during an eight-hour feeding window.

In short, the 16:8 method involves skipping breakfast, making lunch your first meal of the day, and eating dinner no later than 8-9pm.

Does this type of intermittent fasting get results? Or is it just another gimmick that’ll soon be forgotten when the next fad diet comes along?

My intermittent fasting results

My experience with intermittent fasting started in the late 1990s, when I got into the habit of going to the gym first thing in the morning before eating anything. I’d been reading Body-for-LIFE by Bill Phillips, and “fasted cardio” was one of the things he recommended.

The idea was to skip breakfast, train in a fasted state, then leave an hour after your workout before eating anything. So I’d go to the gym on the way to work, train, and then eat something when I got to the office.

But then I quit my job and started my own business working from home. I’d fire up the computer as soon as I got out of bed, work for an hour or two, and then go to the gym.

The main reason I did this was to avoid the rush hour traffic. But there was another benefit I wasn’t expecting. The morning hours were highly productive for me. I found it so much easier to get into that “flow state” where you’re lost in what you’re doing and time seems to pass a lot faster than normal. As a result, I was able to get a lot more work done.

This seems to be one of the more common intermittent fasting results. Plenty of people report feeling more focused and getting more work done during the first few hours of the morning, when they’re deep into a fast. It seemed like a waste to spend my most productive hours of the day in the gym, or even to sit down and eat breakfast.

Gradually, the amount of time I spent working got longer and longer. I ended up going to the gym at around 11am, which would push my “breakfast” back to between 12 and 1pm. This is an eating pattern very similar to the one Martin Berkhan talks about on leangains.com.

Having used intermittent fasting for the best part of 20 years, here’s what I think about it.

Intermittent fasting is a very simple way to create the energy deficit you need to lose fat

You just don’t eat breakfast, and then go about the rest of your day. That simplicity gives it a big advantage over most other diets.

The calories that you normally have in the morning are eliminated from the diet. This means that your calorie budget is distributed across fewer meals. As a result, those meals can be larger and more “normal” than your typical diet fare.

Because your feeding window is smaller than it otherwise would be, you also end up eating less often.

Back in the day when I worked at a gym, the early shift used to start at 6.30 am. If I’d done the late shift the night before, this often meant getting by on just four or five hours of sleep, which isn’t enough for me.


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But I still used to sacrifice 30-45 minutes of precious sleep time and get up earlier than I needed to. That was so I had time to make food to eat during the day. At the time, I believed (wrongly as it turns out) that I wouldn’t be able to build muscle if I went more than a few hours without eating anything.

The fact that IF lends itself to a lower meal frequency has a big advantage in the “time spent preparing and eating food” department. And I certainly don’t miss the smell of tinned tuna at five in the morning.

Intermittent fasting sits well with the current body of evidence on diet and weight loss

We’ve known for a while that eating six versus three meals a day has no benefits as far as fat loss is concerned. We also know that IF performs just as well as continuous calorie restriction when it comes to preserving muscle while dropping fat. And that breakfast doesn’t affect your ability to lose weight whether you eat it or skip it.

You’d think that 16 hour fasts would give you less energy. For me, the opposite is true.

As I mentioned earlier, my most productive time of day is the first few hours in the morning, especially with some caffeine inside me. Skipping breakfast doesn’t hinder my ability to get stuff done. In fact, I usually get a lot more done in the morning than I do in the afternoon after I’ve had something to eat.

When I started training first thing in the morning on an empty stomach, I was worried that my performance in the gym would take a hit. Which it did at first. But after a few weeks of getting used to it, things got back to normal.

I’m not saying that intermittent fasting improved my strength. But it certainly didn’t make it worse.

Intermittent fasting isn't perfect

IF started out as an effective way to free yourself from the various “rules” associated with dieting—eating six small meals a day, avoiding large meals at night, not skipping breakfast—most of which were largely pointless as far as weight loss is concerned.

The same thing, however, is now happening in reverse, with some IF proponents preaching an equally pointless set of rules about what and when you’re supposed to eat.

Google around for information about intermittent fasting results, and you’ll also see a lot of nonsense from “biohackers” getting excited about how fasting raises growth hormone levels by 2000%, as if this is somehow of critical importance when it comes to improving your body composition (it isn’t).

Like any diet, intermittent fasting has the potential to go wrong. Some people eat so much during the “feeding window” that they end up in a calorie surplus rather than the deficit required to lose weight.

I’ve also heard of guys cramming the vast majority of their food intake for the day—sometimes in excess of 6000 calories—into a single evening meal.

IF normally goes hand in hand with a more “flexible” approach to dieting. But that doesn’t change the fact that a calorie deficit is still required if you want to lose fat.

Nor does it mean that you can ignore the macronutrient composition of your diet and expect your results to be all that they could be. For best intermittent fasting results, you still need to pay attention to the quality of your diet.

One downside to the 16:8 method is the low protein frequency

There’s a growing body of research to suggest that distributing protein intake evenly throughout the day does a better job at increasing muscle protein synthesis—a key driving force behind muscle growth – compared to the same amount of protein squeezed into a smaller number of larger meals.

In other words, meal frequency might not have much of an impact on your rate of weight loss. But protein frequency may very well affect your ability to gain (or retain) muscle while you drop fat (a subject I cover in some depth in this ebook).

That’s why I use a slightly “tweaked” version of the 16:8 diet, which involves additional protein-only feedings in the fasted window.

That said, the optimal protein feeding frequency for you will depend on your daily protein requirements, which in turn is affected by how much muscle you have, how much training you’re doing, how long you’ve been training with weights, and how close you are to your maximum muscular potential.

There is no “one size fits all” prescription that will apply to all people, all the time, and the optimal protein frequency for a male bodybuilder training four to five days a week will differ from that of an inactive female half his size.

There may be some health benefits associated with intermittent fasting, which Bojan Kostevski has summarized here. But any superior metabolic effects compared to conventional meal patterns are based more on speculation than any hard evidence.

TL;DR

Overall, my results with intermittent fasting have been extremely positive. That said, I don’t think there’s any magic about it. It’s just a simple way to stay within your calorie budget for the day.

The research out there shows that intermittent fasting doesn’t perform any better (or any worse) than continuous calorie restriction when it comes to weight loss.

The main benefit is convenience and simplicity, rather than any massive difference in terms of results.

Christian Finn is a UK-based personal trainer who holds a masters degree in exercise science. He writes frequently about fitness and nutrition on his personal site, MuscleEvo.

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