Pre-Workout Supplements and Fasting

What Breaks a Fast in Pre-Workout

• Sugar or other carbohydrates: provide calories and break a fast
• BCAAs or EAAs (amino acids): provide energy and stimulate insulin, so they break a fast in the usual sense
• Whey or other protein: breaks a fast
• MCT oil or other fats: provide calories
• Caffeine, creatine, beta-alanine, citrulline, and plain electrolytes on their own: provide little or no energy at typical doses and are generally considered fasting-compatible

Many commercial pre-workouts include amino acids, sugar, or other added ingredients. Always read the label.

Caffeine

Caffeine is one of the most studied performance supplements. Research suggests it can, for many people:

• Modestly improve endurance performance
• Improve some measures of strength and power
• Make exercise feel easier

Studies have typically used doses of around 3–6 mg per kg of body weight about 30–60 minutes before exercise, but many people get a benefit from lower doses, and higher doses increase side effects. Start low. Most health agencies consider up to about 400 mg of caffeine per day, from all sources, generally safe for healthy adults; single doses of around 200 mg are commonly considered safe for healthy adults.

Common sources:

• Black coffee (roughly 70–140 mg per 8 oz cup)
• Caffeine tablets (often 100–200 mg each)
• Pre-workout powders (often 150–300 mg or more per scoop)

On an empty stomach, caffeine is more likely to cause jitters, nausea, a racing heart, or light-headedness. Drink enough fluids, count all your caffeine sources for the day, avoid late-day doses that affect sleep, and never combine several high-caffeine products. See coffee and fasting.

Beta-Alanine

Beta-alanine increases muscle carnosine, which helps buffer acid build-up during hard exercise. Research suggests effects are modest and most relevant to:

• High-intensity efforts lasting roughly 1–4 minutes
• Repeated hard intervals

It has little effect on maximal strength or very short efforts. Studies have typically used a few grams a day, split into smaller doses, for several weeks, because it works by building up muscle carnosine over time rather than acutely. It commonly causes a harmless tingling sensation (paresthesia), especially with larger single doses.

It provides negligible calories at typical doses.

L-Citrulline

Citrulline is converted in the body to arginine, which is used to make nitric oxide, a molecule involved in blood flow. Research results are mixed:

• Some studies suggest a small improvement in repetitions during resistance training
• Evidence for reduced muscle soreness or improved endurance is inconsistent

Studies have commonly used several grams of L-citrulline or citrulline malate taken about an hour before exercise. It provides very little energy at these doses.

Creatine

Creatine monohydrate is among the most researched sports supplements. It increases the creatine stored in muscle, which supports short, high-intensity efforts. Research suggests it can:

• Improve strength and power when combined with resistance training
• Increase the amount of high-intensity work you can do
• Support gains in lean mass over time (part of the early weight increase is water in muscle)

Effects on the brain and cognition are being studied, but the evidence is still limited. A daily dose of around 3–5 g is commonly used in research, and timing does not appear to matter much. It provides no meaningful calories. People who eat little or no meat or fish have lower dietary creatine and may see a larger increase in muscle stores. If you have kidney disease or take medication that affects the kidneys, check with your healthcare provider first.

Ingredients With Weak Evidence

• BCAAs/EAAs: break a fast, and offer little benefit if you already eat enough protein
• L-arginine: much of an oral dose is broken down before it reaches the bloodstream; citrulline is often preferred for this reason
• Glutamine: limited evidence for performance benefits in healthy people
• Taurine: evidence for performance is limited and mixed
• Yohimbine: can raise heart rate and blood pressure and cause anxiety; it has safety concerns and is best avoided
• “Pump” ingredients: mostly marketed for appearance during training, with little evidence of performance benefit
• “Testosterone boosters”: weak evidence, and some products have been found to contain undeclared substances
• Proprietary blends: the label does not show the dose of each ingredient, so you cannot tell how much you are getting

A Simple Approach

You do not need a pre-workout product to train well while fasting. If you want to use something, a simple, transparent approach is easier to control than a multi-ingredient product:

• A cup of black coffee before training, if caffeine agrees with you
• Water, plus a pinch of salt or a sugar-free electrolyte drink for longer or sweaty sessions (see electrolytes and fasting)
• Optionally, creatine taken daily at any time

Single-ingredient products let you see exactly what you are taking. Start with one thing at a time so you can tell how it affects you.

Choosing a Commercial Pre-Workout

If you buy a pre-workout product:

• Choose products with full labels showing the dose of each ingredient
• Check the total caffeine per scoop and count it toward your daily total
• Look for independent third-party testing
• Avoid products with amino acids, sugar, or significant calories if you want to stay fasted
• Avoid products marketed on novel or unusual stimulants
• Try half a scoop first, particularly on an empty stomach

Frequently Asked Questions