If you spend much time throwing weights around, you’ve probably heard of “intermittent fasting” as a tool that some people are using to lose weight and bulk muscle. Naturally, we’re all about bulking muscle be we’re also skeptical of fads, and you should be too.
Here, we’ll explore the science of intermittent fasting, determine whether it’s right for you, and talk about how to proceed.
What Is Intermittent Fasting?
Fasting, in case you haven’t been wandering in the desert recently, means not eating. Generally. It might mean “not eating as much as you probably want to.”
However, for nutritional purposes, fasting refers to a period between 18 and 48 hours (Dunford & Doyle, pg. 83). Anything between three and 18 hours is the “post-absorptive state” and anything longer than 48 hours is “starving.”
“Intermittent fasting” is a sort of quasi-diet trend that involves, essentially, eating and not eating on a schedule. Different people and different programs work differently. Some call for eating normally or eating more than normal on some days and not eating at all on other days. Some call for complete fasting but only during certain hours of the day.
As you might have guessed, intermittent fasting is best used for reducing and controlling body weight. However, it’s a little more complex than just “not eating causes weight loss.”
Intermittent Fasting and Nutrient Management
When you eat food, those nutrients don’t go directly from your stomach to your fat stores or your muscles or your bones. Those nutrients float around for a while first. So, while waiting an hour after you eat to exercise is enough to avoid cramps, waiting longer makes it more likely that your body will use stored fat to fuel your workout (ibid, pg. 178).
You may be wondering, ‘If I workout while those nutrients are still floating around instead of fasting, won’t that just prevent those fat and carbs from being stored in the first place?’ The short answer is “Yes.” However, if you’re working out not just to lose fat but to gain muscle, fasting may have additional appeal to you.
Fat and carbs aren’t the only energy yielding nutrient. Your body can also break down protein for energy. This is how low and no carb diets work. You’re eating primarily protein and breaking down primarily protein for fuel. You’re avoiding a lot of fat and carb storage but you’re also wasting a lot of protein.
Through intermittent fasting, you’re allowing your body to store protein that doesn’t get burned later on. You’re also allowing your body to store fat and carbs but those fat and carbs do get burned when you work out.
Working Out While Fasting
If you’re asking about fat storage etc., you’re probably also wondering ‘If I’m going to build muscle, don’t I need lots of protein? How do I get lots of protein if I don’t eat?’ It’s a fair question. The answer is that intermittent fasting is better for muscle toning than for muscle building.
You do need a lot of protein to build muscle and most people that do intermittent fasting work out during days that they also fast. If you push your body too hard without enough readily available protein, your body will break down your own muscles to get the protein that they need to do the work (Bagchi et al., pg. 118).
However, this only kicks in if you really go all out. You can safely and productively maintain “submaximal/moderate intensity” exercise without compromising performance, though you may see decreased performance and even run into problems “near maximal/higher intensity” workouts (ibid, pg. 339).
In other words, you can workout during intermittent fasting – even on fasting days – as long as you think “low weight, high rep” instead of “high weight, low rep.”
Intermittent Fasting as a Dietary Tool
Balancing intermittent fasting and exercise can be tricky. However, if looked at as a thing within its own benefits and values rather than as a dietary accessory to your workout regimen, it becomes even more appealing.
If nothing else, intermittent fasting presents hard and fast rules for when to eat and when not to eat, but these rules operate on a very short scale. There are clear cut rules on a switch that you flip on and off either every day or every few days compared to most diets that tell you to follow often specific and lengthy rules indefinitely.
Let’s look at one popular intermittent fasting model: 16:8. In this model, all of your eating happens within an eight-hour period. It’s not technically “fasting” by the definition given above, but it’s pretty close and not at all unreasonable. It’s biggest benefit is that it removes late-night snacking which is bad for everyone and particularly difficult for some.
The short time windows of intermittent fasting don’t just make it easier to stick to, they also help your body stay in tune. As we discussed in our article on skip days, if your body becomes accustomed to too spartan a lifestyle for too long, it can switch into panic mode and actually try to store more calories.
By only fasting for a few hours or even a day or two at a time and then returning to your normal diet, you keep resetting your metabolism, preventing the plateaus that can be associated with other diets.
Is Intermittent Fasting Right for You?
Most people should be able to manage fasting as a way to manage weight by toning muscle and reducing body fat. However, if you’re on either end of the spectrum, you should think twice about it. Intermittent fasting can be hard and hard on your body.
If you have a weight problem and think that intermittent fasting could be the solution, talk to your primary care provider before you start. Similarly, if you think it’s the secret to building more muscle, talk it over with your trainer, coach, or physician before you begin.
Bagchi, Debasis; Nair, Sreejayan; & Sen, Chandan K (editors). “Nutrition & Enhanced Sports Performance: Muscle Building, Endurance, & Strength.” Elsiever. Boston, MA. 2013.
Dunford, Marie & Doyle, Andrew J. “Nutrition for Sport and Exercise.” Thompson Wadsworth. Belmont, CA. 2008.