Does Pre-Workout Break a Fast?" It Depends—Here's What to Know

Does Pre-Workout Break a Fast?

Intermittent fasting has garnered a large following over the last few decades, particularly among fitness enthusiasts. Naturally, people who fast throughout the day often wonder, "Does pre-workout break a fast?"

Well, yes and no. The question "Will pre-workout break my fast?" requires a more involved answer than one might think, largely due to discrepancies in dosages and ingredients found across the myriad of pre-workout supplements available these days.

So, let's get into the nitty-gritty and provide some clarity on whether pre-workouts break a fast and if it really matters in the grand scheme of reaching your fitness goals.

Article Highlights:

  • Even though some pre-workouts contain a few calories per serving, most of those calories come from protein-sparing amino acids that may prove beneficial during a fasted workout (and without significantly impacting the so-called "metabolic switching" that occurs during a fast).

    • Assuming you hit the gym shortly after finishing your pre-workout supplement, your body will be burning conisderably more energy, thus returning to a fasted state.

  • Pre-workout powders that are formulated with fillers, notably maltodextrin, and artificial sweeteners may trigger an acute insulin response; however, it's unclear if ingesting small amounts of these ingredients before exercise negates the benefits of fasting (the evidence currently suggests it's not an issue).

  • A pre-workout supplement that's sweetened only with stevia or monk fruit and has no insulinogenic amino acids (e.g. BCAAs), such as Transparent Labs LEAN Pre-Workout, should not stimulate an insulin response nor break your fast.

What Is a Pre-Workout Supplement?

Pre-workout supplements are dietary supplements formulated with ingredients that help improve athletic performance through multiple mechanisms, especially by bolstering muscle strength, endurance, blood flow, mental focus, cognitive function, and perceived energy levels. Many pre-workout supplements contain the same foundation of ingredients, particularly caffeine, L-arginine (or L-citrulline), beta-alanine, branched-chain amino acids (BCAAs), and taurine.

What Are the Benefits of Fasting

Intermittent fasting is a popular regimen that prescribes a daily fasting period, or "window," followed by a shorter feeding window. A fasting period, also known as a "fast," is a physiological state in which the body is deprived of exogenous energy sources (e.g. food and calorie-containing liquids) for an extended period of time, usually no less than 12 hours and up to 24 hours. When the body is in a fasted state, various physiologic and metabolic transitions occur that are suggested to promote longevity, fat-burning, insulin response, cardiovascular function, and other health benefits [1].

While there's still plenty of controversy surrounding the putative health benefits of fasting, it's clear that some people simply appreciate the intermittent fasting lifestyle more than they do eating throughout the day. As such, we're not going to dive any deeper into the alleged benefits of intermittent fasting herein. We have covered this topic in-depth in another article if you're interested.

Does Pre-Workout Break Your Fast?

do pre-workouts break a fast

Since pre-workout supplements are so diverse, it's impractical to give a cookie-cutter answer when someone asks, "Do pre-workouts break a fast?". A proper answer depends on the specific pre-workout supplement in question, the active ingredients it contains, and any inactive ingredients (e.g. artificial sweeteners and maltodextrin) that might perturb fasting physiology/break your fast.

Thus, the following sections will provide an umbrella overview of common pre-workout ingredients (active and inactive) and detail their impact, if any, on fasting.

Amino Acids (e.g. BCAAs, Beta-Alanine, L-Theanine, L-Citrulline, and Taurine)

The majority of amino acids in nature are proteinogenic nutrients, meaning organisms use them to create proteins. For example, our bodies extract amino acids from the proteins in foods to synthesize new muscle proteins and peptide hormones, like human growth hormone and insulin.

In general, proteinogenic amino acids such as BCAAs and L-arginine contain ~4 calories per gram; therefore, a pre-workout supplement that contains evidence-based doses of these amino acids will "break your fast" (in a literal sense), but you'll also burn through that energy pretty quick if you're about the hit the gym.

BCAAs are also considered insulinogenic, meaning they increase insulin levels, but this isn't inherently "bad" for fasting since insulin is a potent anabolic and anti-catabolic hormone [2]. It's also worth note that the increase in insulin after ingesting BCAAs—which is monophasicis distinct from the biphasic insulin response after consuming a bolus of sugar/carbohydrates.

The "atypical" and non-proteinogenic amino acids frequently found in pre-workout supplements, including taurine, L-citrulline, betaine, L-theanine, and beta-alanine are considered "calorie-free" due to their distinct metabolic and physiological roles. In fact, L-citrulline may promote the benefits of intermittent fasting/calorie restriction [3].

Sugar, Artificial Sweeteners, and Other Carbohydrates

Given the insulinogenic nature of high-glycemic carbohydrates, such as maltodextrin and dextrose, they are not ideal during a fasting window. While pre-workouts may contain only contain 2-4 grams of these carb sources per serving, they will create a transient insulin spike that disrupts fasting physiology. But, in the grand scheme of things, this is a small amount of sugar to ingest and it shouldn't have a significant impact on fat loss.

Artificial sweeteners have been under fire in recent years, with some evidence suggesting they have a negative effect on insulin sensitivity [4]. However, a handful of clinical trials on intermittent fasting gave subjects the liberty to consume diet sodas and artificially sweetened beverages ad libitum during the fasting window, and it hasn't seemed to impact the outcomes one way or the other [5, 6, 7].

What About Stimulants, Nootropics, Vitamins, and Minerals?

Vitamins and minerals do not contain calories, nor do polyphenols (e.g. curcumin) or stimulants (e.g. caffeine and theobromine). Nootropics such as alpha-glycerylphosphorylcholine (GPC), citicoline, L-theanine, huperzine-A, and various herbal extracts are also devoid of energy. Even though these ingredients are in most pre-workout supplements, they won't break your fast.

How Many Calories Are in Pre-Workout Supplements?

Pre-workouts are not subject to the same labeling standards as foods and beverages. As a consequence, supplement companies can label their pre-workout supplement(s) as "zero calories" despite containing amino acids and filler carbohydrates (like maltodextrin) that provide calories.

In some cases, these supplements have upwards of 20 grams of amino acids and carbohydrates per serving, which is not an inconsequential amount of calories (~80) for someone trying to lose weight. Be mindful of this when you're looking for a "fasting-friendly" pre-workout supplement.

So, Do Pre-Workouts Break a Fast?

In short: Taking pre-workouts may break your fast (albeit briefly, in most cases).

Why (Some) Pre-Workouts Might Actually Be Good When Fasting

The advantages of taking a pre-workout supplement before exercising (on an empty stomach, nonetheless) seem to greatly outweigh the presumed "drawbacks" of potentially breaking a fast. For many gym-goers on the intermittent fasting bandwagon, having a cup of coffee with some skim milk or taking a scoop of pre-workout powder is like a "pre-gym ritual" that makes the fasting window more tolerable. Even though these might break your fast in the technical sense, it's doubtful they will significantly hinder your results.

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