The thought of only eating during a few hours of the day, or even every other day, may sound a little crazy, but intermittent fasting (IF) has been suggested as an effective weight-loss tool, with research supporting its ability to increase fat oxidation, reduce body weight, and accelerate fat loss.[1,2]

Let's look at the science behind why this approach works, how to do it, and how supplements could help you get results.

What Is Intermittent Fasting?

The central idea behind the implementation of intermittent fasting is to reduce overall calorie consumption, ideally resulting in weight loss. Typically, IF protocols will involve eating nothing or very little (up to 25 percent of your normal daily caloric intake) for a period of 16-24 hours. Following the restrictive phase, you'll return to relatively normal energy intake for 4-24 hours, depending on which version of IF you're following.

Which Intermittent Fasting Method Is Best?

There are several different intermittent fasting plans, and at first glance it may be a little overwhelming trying to figure out which plan is optimal for you. While I can't tell you which one will work best, I can give you details about the more popular diets.

This list is by no means comprehensive. Just make sure to select an IF protocol that works well with your schedule so it will be easier to maintain.

Three Popular Intermittent Fasting Plans

Lean Gains

Originally created by Martin Berkhan, the central ideas behind the Lean Gains dieting program involve restricting calorie consumption for a period of 16 hours, followed by 8 hours of eating. Although it may be tempting to gorge yourself on whatever you want during the calorie-consumption phase, Berkhan suggests aiming for a higher protein intake on workout days and prioritizing carbohydrates over fat. Rest days should be lower calorie than training days, continuing the high protein intake but flipping fat and carbohydrate intake.

The Alternate-Day Diet

Created by James Johnson, M.D., the Alternate-Day Diet, also known as the UpDayDownDay Diet, follows a 24-hour rotation of low-calorie intake and normal-calorie intake. You're advised to use moderation on the regular-calorie-consumption days, though, so you don't end up looking like the Michelin Man on Thanksgiving.

The Warrior Diet

The Warrior Diet, written by Ori Hofmekler, is another IF protocol. As described by the author, the diet pairs a 20-hour fast with a 4-hour feeding window. The goal of the fast is to increase the actions of the Sympathetic Nervous System—commonly known as fight-or-flight—which may help to stimulate lipolysis and increase metabolic rate.[3]

The feeding window is used to increase the activity of the Parasympathetic Nervous System (or the Rest-and-Digest system), which will help increase the absorption of glucose and assist with recovery.[4]

IF and Weight Loss

In a fed state, the human body uses insulin to bring glucose into cells to manufacture energy. During periods of fasting, when food is absent, the body's level of blood glucose significantly decreases. This lowers insulin release and increases insulin sensitivity, resulting in increased fatty acid oxidation. Since IF may decrease both glucose and insulin levels, the body could potentially use stored fat as fuel.[5,6]

As Jim Stoppani explains in the article "Intermittent Fasting: Everything You Need To Know," it may help you burn more fat even while eating the same amount of calories, which is a huge deal. Essentially, temporarily going without food turns on certain fat-burning genes.[7]

Among the overweight and obese, IF is as effective as continuous energy restriction for weight loss.[8] Also, since insulin sensitivity appears to regulate appetite, periodically fasting may help you feel less hungry.[9] The potential to simultaneously enjoy increased fat burn and less hunger is why people like this diet approach so much.

It makes sense that calorie restriction via if might be as effective as continuous restriction—the most common dieting format—so long as a similar energy deficit is achieved.

So it sounds perfect, right? Not so fast. One short-term fasting study, covering 15-30 hours, demonstrated an increased rate of protein breakdown.[10] The last thing that most bodybuilders and serious gym rats want is to lose any of the hard-earned muscle they've lost blood, sweat, and tears over!

Plus, purposeful fasting of 20 hours or more, lasting only two weeks, may invoke a starvation-related decrease in resting metabolic rate.[11] A decreased metabolic rate may slow down the weight-loss train and quickly derail your cut.

Don't ditch the diet yet, though. Stay tuned for specific supplements to help combat these effects and increase protein synthesis for maximum muscle growth.

Effects of Intermittent Fasting on Athletic Performance

Previous research has demonstrated that IF may have slightly negative effects on aerobic and anaerobic measures, such as running and jump power.[12] Additionally, fasted athletes may experience higher levels of fatigue during training, but this does not necessarily mean a decrease in performance or strength.[13,14] Supplements can help with this.

Stop Cheating on Your Diet: IF and Appetite

Think that restricting calories will ultimately lead you to a destructive binge-eating episode? Think again. Participants in a study on alternate-day fasting were shown to decrease emotional eating and increase their restrictive eating.[15] They were less hungry, more satisfied, and significantly less likely to cheat on their diet than if they were not following IF!

One reason IF makes it easier not to cheat is you can have bigger, more satisfying meals. Pro bodybuilder and powerlifter Layne Norton explains this perk in his article "The Facts About Intermittent Fasting, Fat Loss, and Muscle Growth."

"Spread, say, 2,500 calories over 6-8 meals, and you'll end up with some pretty paltry portions," Norton says, "but those same calories over 1-2 meals can make for a fantastic food celebration…When I dropped from eight meals per day to four, I was much more satisfied, and my hunger levels dropped."

Supplements for Intermittent Fasting

So now that you've got the science down, let's look at the best way to not only achieve your fat-loss goals, but to also optimize your gym performance and thrive while on the IF diet!

In order to maximize your exercise performance, it may be best to train immediately prior to breaking your daily fast. This will allow the following strategies to optimize recovery and protein synthesis, and replenish energy stores.

During The Day

Branched-Chain Amino Acids (BCAAs): Few human trials have been done, but we can safely estimate that when following an IF diet, sipping on BCAAs throughout the day may help increase protein synthesis. This will help balance out some of the protein breakdown that may occur from fasting as discussed earlier.[16]


Caffeine: Not only does a little bit of caffeine before your lift help get you get fired up, but a dose of 1-3 milligrams per pound of body weight has been demonstrated to significantly increase upper-body strength![17]

Epigallocatechin-3-Gallate (EGCG): Because one of the primary goals of intermittent fasting is increased fat loss, one of your goals with supplementation should be to increase lipolysis (breakdown of stored fat) and fatty acid oxidation (use of fatty acids for energy).

EGCG, when combined with caffeine, has been demonstrated to lead to significant increases in fatty acid oxidation and increased metabolic rate.[18]

This combination may work synergistically to promote fat loss while minimizing any decreases in metabolic rate observed during periods of prolonged fasting. Dosing of EGCG should be approximately 150 milligrams per day to increase lipolysis.[19]

However, it may just be easier to ingest approximately 500-1000 milligrams of green tea extract containing at least 30 percent EGCG.

Beta-Alanine: Beta-alanine supplementation has been found to increase work capacity by decreasing fatigue associated with buildup of metabolites (e.g., hydrogen ions). This supplement works by increasing the amount of carnosine, an intracellular buffer, stored in the body.[20]

This buffer reduces the level of acidity in the blood, allowing for improved high-intensity exercise performance. The effective dose for beta-alanine is between 3.2 grams to 6.4 grams per day.

In order to avoid flushing or tingling of the skin, try splitting the dosage into 2-3 smaller servings per day.

Essential Amino Acids and Carbohydrates: Research has demonstrated that consuming 6 grams of essential amino acids (EAA), in addition to 35 grams of sucrose, immediately prior to resistance exercise significantly increases protein synthesis due to an increased influx of EAAs to the active muscle.[21]

In other words, slam about 100 grams of dried dates and some EAA right before hitting the iron to maximize your muscle gains.

During Your Workout

BCAAs: While there is limited research evaluating the use of BCAAs during resistance training, they seem to work in two ways: helping to avoid decreases in protein breakdown, resulting in an enhanced recovery, and decreasing central fatigue by decreasing the ratio of free tryptophan to BCAA present in the blood.[22]

For dosing, it is best to have at least 7 grams of BCAAs with 3.5 grams leucine, 1.75 grams isoleucine and 1.75 grams valine in a 2:1:1 ratio.[23,24]

For dosing, it is best to have at least 7 grams of BCAAs with 3.5 grams leucine, 1.75 grams isoleucine and 1.75 grams valine in a 2:1:1 ratio.[23,24]


Protein: Protein consumption following a bout of resistance training may lead to increased protein synthesis rates.[25] When 6 grams of EAA is combined with 35 grams of carbohydrate, increases in protein synthesis up to 400 percent have been observed.[26]

Additionally, 15 grams of whey protein consumed immediately prior to, then immediately following, weight training has demonstrated significant increases in protein synthesis.[27]

I recommend consuming 20-25 grams of a fast-digesting protein, like whey, immediately post-workout to jump-start the anabolic process.

Carbohydrates: After resistance-training exercise, carbohydrate ingestion (0.5 grams per pound of body weight), independent of protein, has been demonstrated to lead to decreases in muscle-protein catabolism, with small increases in protein synthesis.[28] Consuming carbs after a fasted workout will also help restore glycogen levels.

If you opt for a post-workout shake, try to find one that contains dextrose, as it has been shown to restore glycogen at a faster rate than maltodextrin. If you prefer to snack on actual foods, stick with moderate- to high-glycemic-index foods, such as pretzels, white rice, bananas, and potatoes.

Creatine: Creatine supplementation of 3-5 grams per day leads to significant increases in lean body mass, power output, strength, and muscle-fiber size. A recent study found that adding creatine into your post-workout routine may be superior to pre-workout ingestion for body composition and strength gains.[29]

IF Isn't for Everyone

If you prefer to snack on food throughout the day, or you feel better after eating three square meals, then do what works best for you. The best diet is the one that you'll stick to, the one that fits with your lifestyle, and the one that you enjoy the most!


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About the Author

Parker Hyde, CSCS, CISSN

Parker Hyde, CSCS, CISSN

Parker Hyde is certified as a CSCS and CISSN with a focus on exercise science. He has written a great deal regarding performance, nutrition, and much

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