In 30 seconds
- If you train fasted, the amino acid shortfall from beforehand can carry on after the session, because muscle breaks down more during exercise.
- In a trial with 24 men who trained fasted, 7.3 g of BCAAs 30 minutes beforehand reduced muscle soreness at 48 and 72 hours.
- In a meta-analysis of 18 trials, BCAAs reduced muscle soreness between 24 and 96 hours after exercise.
- After your session, have a meal with at least 25 g of protein: BCAAs are 3 of the 9 essential amino acids.
Yes, it does, especially if you train hard in the morning without breakfast. A serving of BCAAs before or during your session gives you leucine, isoleucine and valine without having to eat, and that is exactly how they were tested in one of the trials on muscle soreness. What they do not do is replace the meal afterwards.
What happens in your muscles when you train fasted
After a night without food, you arrive at your session with no recent amino acids. According to the review by Aragon and Schoenfeld, that shortfall can continue after the session, because muscle protein breakdown increases during fasted exercise 1.
That is why their recommendation is clear: if you start training more than 3-4 hours after your last meal, have at least 25 g of protein as soon as you finish 1.
What about fat? If you are interested in training fasted to lose fat, we go through all the studies in fasted cardio.
Branched-chain amino acids
Leucine, isoleucine and valine, in three figures
What BCAAs provide
BCAAs are leucine, isoleucine and valine: 3 of the 9 essential amino acids, the ones your body cannot make. They account for around 25% of the amino acids in foods with complete protein 2.
They have two particular features 2:
- Muscle can use them for energy during exercise, unlike the other essential amino acids.
- Leucine, above all, can stimulate protein synthesis in the muscle you have trained.
In a trial with 10 trained men, taking 5.6 g of BCAAs after strength training increased muscle protein synthesis by 22% compared with placebo 5.
The fasted trial
Muscle soreness at 48 and 72 hours: BCAAs versus placebo
The trial that tested them fasted
This is the study that comes closest to training without breakfast. In Jackman's trial, 24 men with no strength-training experience arrived at the laboratory first thing in the morning, after an overnight fast 3.
- Before: half took 7.3 g of BCAAs 30 minutes before training, with 3.5 g of leucine. The other half took a placebo.
- The effort: 12 sets of 10 eccentric quadriceps extensions at 120% of their maximum. A session designed to cause muscle soreness.
- Afterwards: they kept taking BCAAs, up to 29.2 g a day in 4 servings, over the following days.
The result? Soreness with the knee bent was lower with BCAAs at 48 hours (21 versus 32 mm on the pain scale) and at 72 hours (17 versus 27 mm). Overall, pain over those 72 hours was 64% lower 3.
Loss of strength and creatine kinase did not change. The authors conclude that BCAAs may be an effective aid for reducing muscle soreness after intense eccentric exercise 3.
What the meta-analyses say
The most recent meta-analysis pooled 18 trials, 13 with strength exercise and 5 with endurance exercise 4:
- Muscle soreness: less pain at 24, 48, 72 and 96 hours, with the largest effect at 48-72 hours.
- Creatine kinase: lower immediately after exercise and at 72 hours.
- Doses: from 3.15 to 29.3 g a day, for 1 to 28 days.
Its authors conclude that BCAAs can be used as an effective strategy to speed up recovery after intense exercise 4. You will find all the details in muscle soreness and muscle damage.
How much to take
Grams of BCAAs a day in the studies
How to take them if you train fasted
| When | What to take |
|---|---|
| When you get up | Water. |
| 15-30 minutes before training | One serving of BCAAs dissolved in water. |
| During, if the session is long | Water, or the rest of your BCAAs in sips. |
| When you finish | A meal with at least 25 g of protein. |
Our own summary based on Jackman et al., 2010, and Aragon and Schoenfeld, 2013.
One serving a day is enough to start with. According to the US National Institutes of Health, up to 20 g a day of BCAAs, split into several servings, has raised no safety concerns in studies lasting up to 6 weeks 2.
Do BCAAs break a fast?
It depends on why you are fasting. BCAAs are amino acids, the same ones that make up the protein in food 2.
- If your fast is strict, for religious reasons or on medical advice, have only water.
- If what you do is train before breakfast, they fit in well: that is exactly the situation in Jackman's trial 3.
What they do not replace
BCAAs are 3 of the 9 essential amino acids. To build muscle, you need all of them. The International Society of Sports Nutrition estimates that about 10 g of essential amino acids, on their own or within a serving of 20-40 g of protein, maximally stimulate muscle protein synthesis 6.
That is why the meal afterwards matters so much. If you are not sure what to put on your plate, we give you ideas with their grams in what to eat after training. And if you are torn between the two supplements, you will find the answer in BCAAs or protein.
Frequently asked questions
Can you take BCAAs on an empty stomach?
Yes. In one trial, men who trained after an overnight fast took 7.3 g of BCAAs 30 minutes beforehand and had less muscle soreness at 48 and 72 hours than with placebo.
When should I take BCAAs if I train fasted?
Between 15 and 30 minutes before you start, or in sips during the session. And when you finish, a meal with at least 25 g of protein.
Do BCAAs break a fast?
They are amino acids, the same ones that make up the protein in food. If your fast is strict, for religious or medical reasons, have only water. If what you do is train before breakfast, they fit in well.
How many BCAAs should you take?
The muscle soreness trials used 3.15 to 29.3 g a day. According to the US National Institutes of Health, up to 20 g a day split into several servings has raised no safety concerns in studies lasting up to 6 weeks.
Sources
- Aragon AA, Schoenfeld BJ. Nutrient timing revisited: is there a post-exercise anabolic window? J Int Soc Sports Nutr. 2013;10:5. View publication
- Office of Dietary Supplements, National Institutes of Health. Dietary supplements for exercise and athletic performance: fact sheet for health professionals. View publication
- Jackman SR, Witard OC, Jeukendrup AE, Tipton KD. Branched-chain amino acid ingestion can ameliorate soreness from eccentric exercise. Med Sci Sports Exerc. 2010;42(5):962-970. View publication
- Salem A, Ben Maaoui K, Jahrami H, et al. Attenuating muscle damage biomarkers and muscle soreness after an exercise-induced muscle damage with branched-chain amino acid (BCAA) supplementation: a systematic review and meta-analysis with meta-regression. Sports Med Open. 2024;10:42. View publication
- Jackman SR, Witard OC, Philp A, Wallis GA, Baar K, Tipton KD. Branched-chain amino acid ingestion stimulates muscle myofibrillar protein synthesis following resistance exercise in humans. Front Physiol. 2017;8:390. View publication
- Kerksick CM, Arent S, Schoenfeld BJ, et al. International Society of Sports Nutrition position stand: nutrient timing. J Int Soc Sports Nutr. 2017;14:33. View publication
Information based on published studies. It does not replace the advice of a doctor or registered dietitian. The results describe what was measured in each study, not the properties of any specific product. A varied and balanced diet and a healthy lifestyle are important.
