Does pre-workout break intermittent fasting?

Pre-workout supplements contain a variety of ingredients that help increase focus, energy, and strength during training. However, a common question among bodybuilders is whether pre-workout supplements break intermittent fasting.

Whether a pre-workout breaks an intermittent fast depends on the specific ingredients in the supplement. If the pre-workout provides fewer than 50 or even zero calories and contains ingredients that don't cause insulin spikes, it won't break an intermittent fast.

Breaking intermittent fasting means consuming calorie-rich foods or drinks to kick-start metabolic and hormonal processes in the body after a period of not eating.

Fasting is a state in which a person has not consumed calories for a certain period, and the body uses energy reserves, such as stored fat, to maintain its vital functions.

During fasting, certain metabolic changes begin to occur, such as reduced insulin levels, increased fat breakdown, and, in prolonged fasts, ketosis—a state where the body uses fat as its primary energy source.

Calorie intake, whether through solid or liquid foods, "breaks" this fasting state. This happens because nutrient intake, especially carbohydrates and proteins, triggers the release of insulin, a hormone responsible for regulating blood glucose levels.

Insulin promotes the absorption of glucose by cells, which signals to the body that it no longer needs to rely on energy reserves, such as body fat. Thus, breaking the fast marks the end of the period in which the body is in energy conservation mode and returns to a state of processing and storing nutrients from food.

Since each pre-workout can contain a wide variety of ingredients, it's impractical to give a single answer when someone asks, "Do pre-workouts break intermittent fasting?"

An appropriate answer depends on the ingredients in the pre-workout in question. Below, we'll provide an overview of the most common pre-workout ingredients and how they may (or may not) break a fast.

Proteins and proteinogenic amino acids

Many pre-workouts may contain protein and/or proteinogenic amino acids, such as BCAAs, which provide 4 calories per gram and can break a fast. BCAAs themselves can be insulinogenic, meaning they trigger insulin action.

However, the “atypical” and non-proteinogenic amino acids often found in pre-workout supplements, including creatine, taurine, L-citrulline, betaine, L-theanine, and beta-alanine, are considered “calorie-free” due to their distinct metabolic and physiological roles.

Given the insulinogenic nature of high glycemic carbohydrates like maltodextrin and dextrose, which are very common in pre-workouts, they are not ideal during an intermittent fasting window.

While pre-workouts may only contain 2-4 grams of these carbohydrate 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 consume and shouldn't have a significant impact on fat loss.

Artificial sweeteners have come under fire in recent years, with some evidence suggesting they negatively impact insulin sensitivity. However, most studies on the topic suggest that artificially sweetened zero-calorie beverages don't appear to impact intermittent fasting outcomes.

Stimulants, such as caffeine, don't break intermittent fasting because they're calorie-free. The same can be said for nootropics and micronutrients (vitamins and minerals), which don't trigger insulin action because they're calorie-free.

Benefits of pre-workout during fasting

The main benefit of taking a pre-workout supplement while fasting is that caffeine helps provide energy, alertness, and focus. This is even more important when you're fasting before a workout, as you won't have the body's preferred energy source (carbohydrates) available for training.

Additionally, you'll feel the effects of pre-workout more quickly in a fasted state, as there won't be food in your stomach to delay its absorption. Protein, fiber, and fat slow digestion, so if you take a pre-workout supplement after consuming these nutrients, it will take longer to feel the effects of your pre-workout.

Generally, taking pre-workout on an empty stomach is harmless. However, if you're sensitive to caffeine or have a sensitive stomach in general, taking pre-workout on an empty stomach may cause some undesirable symptoms, such as:

In general, these symptoms are harmless, but they should be taken into account if they interfere with your routine.