Intermittent Fasting & Bodybuilding

Intermittent fasting is a technique where you fast for an extended period of time, then follow that fast with a period of eating, and cycle back and forth between these fasting and feeding periods. The type of intermittent fasting that I've found to work best for losing body fat and maintaining muscle is 16/8 intermittent fasting. That means every day you fast for 16 hours and have an 8-hour feeding window.

Intermittent fasting has become increasingly popular in the last few years. However, I've been interested in its application for fat loss for a couple decades. Yale University School of Medicine, along with colleagues at The University of Copenhagen did a bit of work on fasting and fat loss in the early 2000s. They published several papers that show one of the key mechanisms in fasting-induced fat loss has to do with an increase in the activity of genes that increase the number of calories the body burns and the amount of fat it burns.

More specifically, when you fast, it turns on genes that encode for certain uncoupling proteins and for enzymes that increase fat burning. The uncoupling proteins basically poke holes in the mitochondria inside muscle cells. The mitochondria are where most of your energy is derived from, especially at rest. By poking "holes" in the mitochondria, they produce less energy, so they have to burn far more calories to produce the same amount of energy in the form of ATP. In other words, when you fast you burn more calories and fat. What's interesting is that it was found that when you finally eat after fasting, the activity of many of these genes are increased even further!

Research shows that fasting may also work through a number of other different mechanisms that lead to increased calorie and fat burning. Studies also suggest that fasting provides numerous health benefits, such as lower cholesterol and triglyceride levels, higher HDL (good) cholesterol levels, and even greater longevity. One study also found that intermittent fasting in men increased red blood cell and hemoglobin levels in the blood. Hemoglobin is the protein in red blood cells that carries oxygen in the bloodstream to the muscles. Increasing red blood cells and hemoglobin levels is what endurance athletes like cyclists are trying to increase when they illegally "dope" with EPO (erythropoietin). And yet IF may do this naturally.

Muscle Matters

Some proponents claim that IF even benefits muscle building. While yes, you can build muscle with IF, there's really no research showing that IF benefits muscle growth over a traditional diet.

One study in men during Ramadan found that subjects lost no muscle mass during their form of IF (fasting during the day and eating only between sunset and dawn) yet lost a significant amount of body fat. However, some heavily muscled guys have reported that IF doesn't allow them to maintain their muscle mass and they tend to end up losing some.

The bottom line on IF and building muscle is this: Yes, you can build muscle while doing IF, but it's probably not the best approach for someone who's goal is to truly maximize muscle growth. For that individual, a more standard bodybuilding diet where you're eating every 2-3 hours and fasting only when you sleep would be recommended.

Carb Considerations

There's no debating the fact that intermittent fasting works well to enhance fat loss. However, it's not a method of dieting that needs to be used from the get-go. Instead, use it once you've hit a plateau and you can no longer lower carbs and calories. Since you want to keep protein and fat as high as possible, IF allows you one more step before you need to start whittling away at those two critical macros to lower calories and continue losing body fat. So you should first slowly lower your carbs over time.

Once you get down to consuming about 0.25 grams of carbs per pound of body weight per day, it will be virtually impossible to lower carbs any more. That's because most of the carb sources making up the 0.25 grams per pound are coming from the carbs in protein powders and vegetables. These carbs are fairly unavoidable and are also a good source of fiber, so it wouldn't make sense to try and nix these from your diet.

Another reason to wait to use IF until after you've eliminated most of your carbs is that IF works very well with a low-carb diet. Yale found that when you fast and then re-feed with a low-carb meal, the activity of the genes that increase calorie and fat burning are further increased with the meal. However, when you re-feed with a higher-carb meal, the activity of many of these genes are decreased. So following IF with a low-carb diet helps you to maximize calorie and fat burning.

Calorie Counting

Total calorie intake is another reason you should wait until a later stage in your diet to introduce IF. When you only have an 8-hour window to eat, you often can't consume as much food as when you can eat all day. This is one of the fringe benefits of IF – it automatically limits calorie intake. If you start using IF early on in your diet, you may not be able to consume enough food during your feeding window, which will make it hard to drop calories in later stages as your fat loss plateaus.

Since you're cramming so many meals into an 8-hour time frame, meals will come more frequently than you were previously eating. Meals will be spaced an hour or two apart, and even as frequently as 30 minutes in some cases. If you find you can't consume this many meals, you can also combine some of them. For example, in the sample meals below, the snack that comes before dinner is a protein shake and peanut butter. You can have this shake with dinner and enjoy the peanut butter as a dessert.

Meal Timing

For the average Joe or Jane, the time of day you fast and the time of day you eat makes little difference. However, those who work out (like ALL members of should manipulate their fasting and feeding windows based on when they train.

If you train in the morning, start your 8-hour feeding window with your post-workout meal. That means you'd train completely fasted and your first meal would be your post-workout shake. But since you skipped your pre-workout shake, your post-workout shake should include both your pre- and post-workout shakes and supplements. For example, if you train from 7:00 am – 8:30 am, then your feeding window starts at 8:30 am with your post-workout shake and ends at 4:30 pm with a snack of slow-digesting protein. If you train in the morning but ending your feeding window in the late afternoon is too early for you, you could postpone your postworkout shake by 2-3 hours. It's not ideal for maintaining muscle mass, but it certainly won't hamper fat loss.

Supplementing BCAAs

Some recommend sipping on branched-chain amino acids (BCAAs) during their fasting period to better preserve muscle. While this technique would definitely help with preserving and building muscle, it is technically putting you in a fed state. In other words, you're not truly fasting. As you know, amino acids combine to form protein. There are 20 aminos that are used as the building blocks of protein. These include the nine essential amino acids leucine, isoleucine, valine, tryptophan, threonine, phenylalanine, methionine, lysine and histidine, as well as the 11 nonessential amino acids arginine, serine, cysteine, glycine, proline, alanine, tyrosine, aspartic acid, asparagine, glutamic acid and glutamine.

If you consume just one of these amino acids, you're essentially consuming protein and therefore are technically not fasting. The BCAA leucine poses a special problem with IF. Here's why: The brain uses blood leucine levels as an indicator of how fed the body is. So if you're sipping on BCAAs, the leucine is signaling the brain that you're currently well fed. Although no work has been done on this issue during fasting, it's easy to project that if the brain senses you're fed, the benefits that come from fasting may be compromised. A suggestion is to avoid BCAAs and any of the 20 proteinogenic amino acids (those used in the building of proteins) until you're in your feeding period.

Amino acids that aren't proteinogenic can be consumed during fasting. I'm talking about amino acids like beta-alanine, betaine, D-aspartic acid and, even though they're not amino acids (but some people classify them as such), carnitine and creatine. These are fine to sip on during the day, especially if you're training in a fasted state.

Intermittent Fasting Meal Plan

The sample meal plans below show you how to apply intermittent fasting for the four main training time points throughout the day. And while you schedule your fasting and eating around the time you train, you can also adjust the time you train to better match when you want to fast and eat. For example, let's say that you normally train in the morning but find that it's almost impossible for you to fast at night because your cravings are so strong later in the day. In that case, training later in the day so that you fast in the morning and eat at night when your cravings are high.

Although the meals in the sample diets below still list breakfast, lunch and dinner, these meals may not necessarily be consumed at the "normal" time for that meal. For example, in the morning workout example below, if you finish your workout at 8:00 am and consume your postworkout meal at this time, your feeding window ends at 4:00 pm. That means lunch will be consumed some time before noon and dinner would be consumed probably before 3:00 pm. These sample diets provide about 11 calories, 1.5 g protein, 0.25 g carbs, and 0.5 g fat per pound of body weight daily for a 200-pound person. That means that they provide about 2,100 calories, almost 300 g protein, about 50 g carbs and about 100 g fat.