Most pre-workout supplements are marketed at people who train fed. Fasted training has different considerations: the most useful ingredients (caffeine, beta-alanine, citrulline) work fasted; others (BCAAs, sugar-based ergogenics, BCAA blends) break the fast or do nothing useful. This guide covers which ingredients are actually worth taking before fasted training and which to skip.
Table of Contents
What Breaks a Fast in Pre-Workout
- Sugar / carbs: obviously breaks fast
- BCAAs / EAAs: raise insulin, activate mTOR - break fast
- Whey or other protein: breaks fast
- MCT oil: calories, breaks fast
- Caffeine, beta-alanine, citrulline, creatine, electrolytes alone: don’t break fast
Many commercial pre-workouts contain BCAAs, even small amounts. Read labels.
Caffeine
The most evidence-supported ergogenic. Effects:
- Improved power output
- Better endurance performance
- Reduced perceived effort
- Mild fat oxidation increase
Dose: 3-6 mg per kg body weight, 30-45 minutes pre-workout. For 80 kg adult: 240-480 mg.
Sources:
- Black coffee (95-150 mg per 8oz)
- Caffeine pills (100-200 mg)
- Pre-workout powders (typically 150-300 mg per scoop)
Warning: combine with adequate fasting electrolytes. Caffeine in a fasted dehydrated state amplifies dizziness and tachycardia.
Beta-Alanine
Increases muscle carnosine, which buffers acid build-up during high-intensity exercise. Effects modest but real:
- Improved performance in efforts lasting 1-4 minutes
- Better repeated sprint capability
- Doesn’t affect 1RM or short efforts much
Dose: 3-6 g daily total, often split. Loading takes 4+ weeks before benefits accumulate. Causes harmless “tingles” (paresthesia) at higher single doses.
Doesn’t break a fast. Useful for fasted high-intensity work.
L-Citrulline
Increases nitric oxide and improves blood flow to muscles. Effects:
- Improved endurance in resistance training (more reps per set)
- Reduced post-workout soreness
- Modest endurance performance benefit
Dose: 6-8 g L-citrulline (or 8-10 g citrulline malate) 30-60 minutes pre-workout.
Doesn’t break a fast. Useful for fasted resistance training.
Creatine
The most studied performance supplement. Increases muscle creatine stores, improving high-intensity performance. Effects:
- Improved strength and power
- Increased work capacity
- Slight muscle gain (water content + actual hypertrophy support)
- Possible cognitive benefits
Dose: 5 g daily, any time. Doesn’t need to be pre-workout. Doesn’t break a fast. Vegans particularly benefit (dietary creatine is essentially zero).
Ingredients to Skip
- BCAAs/EAAs: break fast, modest evidence anyway
- L-arginine: poorly absorbed - citrulline does it better
- Glutamine: limited performance evidence
- Taurine: minimal evidence at supplementation doses
- Yohimbine: useful only fasted but raises anxiety in many; limited utility
- “Pump” ingredients (glycerol, etc.): mostly cosmetic effects
- “Test boosters”: very weak evidence base
- Pre-workouts with proprietary blends: can’t see actual doses; usually under-dosed on the active ingredients
A Sensible DIY Stack
For most fasted training:
- Black coffee or 200 mg caffeine pill
- 5 g creatine (any time of day)
- 3 g beta-alanine (split across day)
- 6-8 g L-citrulline 30-60 min pre-workout
- Pinch of salt in water
Cost: roughly $30-50/month for all of the above as separate supplements. Effects: real, evidence-based, fast-compatible.
Commercial Pre-Workouts
If buying a pre-workout:
- Look for transparent labelling (actual doses, not “proprietary blend”)
- Adequate caffeine (200+ mg)
- Adequate citrulline (6+ g)
- Beta-alanine present (3+ g)
- Avoid those with BCAAs if maintaining strict fast
- Avoid those with sugar or significant calories
- Avoid those marketed primarily on novelty stimulants
Frequently Asked Questions
Will black coffee work as a pre-workout?
For caffeine, yes. Doesn’t provide the other ingredients but caffeine alone is the most-evidenced pre-workout ergogenic.
Should I take creatine pre-workout or post?
Doesn’t matter for performance. Consistency of daily intake matters more than timing. Take whenever convenient.
How long before BCAA-free pre-workout takes effect?
Caffeine peaks 30-45 min. Citrulline peaks 30-60 min. Beta-alanine works through accumulated muscle carnosine, not acute dose - takes weeks to load.
Will the “tingle” from beta-alanine cause problems?
Harmless paresthesia from histamine effect. Splitting the dose into smaller portions reduces it. Many find it pleasant.
What about nootropics in pre-workout?
L-tyrosine, L-theanine reasonable; many novelty nootropics in pre-workouts have weak evidence. Most don’t break a fast meaningfully but don’t add much either.
Should I cycle off caffeine?
Tolerance develops over weeks. Periodic 1-2 week breaks restore sensitivity. Or maintain consistent moderate intake without cycling.
The Bottom Line
Caffeine, beta-alanine, citrulline, and creatine are the evidence-based pre-workout ingredients that don’t break a fast. BCAAs/EAAs break the fast and aren’t worth it. Build a DIY stack with these four ingredients for $30-50/month, or buy a transparent-label pre-workout that includes them in adequate doses. Skip the proprietary blend pre-workouts marketed on novelty stimulants - they’re usually under-dosed on what actually works.