Alpha-Hydroxyisocaproic Acid.
Alpha-Hydroxyisocaproic Acid supplementation for targeted health support. May reduce muscle protein breakdown. Proposed anti-catabolic effects. Some evidence for reduced DOMS. Weak leucine-like signaling.
Reviewed March 2026
- Category
- Amino acid
What Alpha-Hydroxyisocaproic Acid is, and what it does.
- Does it work
- Interesting metabolite with some research, but limited evidence compared to leucine/HMB. Not a priority supplement.
- How much to take
- 500-1500mg daily, often divided. Studies used around 500mg 3x daily.
- Time to feel it
- Trials ran about four weeks before measuring soreness and lean mass. What people report is slightly less day-after soreness across a training block, not a same-session change.
- The first dose
- Day one passes without a sensation. It joins a pool your body already makes from leucine, and what trials measured, soreness and lean mass, needed about four weeks to show up.
- With regular use
- Possible reduced soreness and modest lean mass support. Effects are subtle if present.
- How well tolerated
- Appears well tolerated in available studies. No serious adverse events reported.
- How it feels
- Subtle at best. Some notice less soreness after training. No acute effects.
- The overlooked benefit
- Your body already makes it from leucine and clears it in urine, so a dose adds to an existing pool. It branches off the same node as HMB rather than sitting downstream of it.
250 to 500mg a day is where Alpha-Hydroxyisocaproic Acid works.
Source: Based on leucine metabolite research; limited sports supplement data
The proof, claim by claim.
These words describe the research, not the molecule's worth. Research strength is how much work stands behind one claim, and it is never a product score.
Alpha-Hydroxyisocaproic Acid has emerging evidence. Based on 59+ studies.
- Reduces muscle sorenessSome positive studies
- Anti-catabolic effectsTheoretical and some supportive data
- Increases lean massSmall studies with mixed results
- Better than HMB or leucineInsufficient comparison data
Questions people ask about Alpha-Hydroxyisocaproic Acid.
- Is HICA better than HMB?
- HMB has more research. HICA is less studied. Both are leucine metabolites with anti-catabolic claims.
- How does it compare to leucine?
- Leucine is better studied for muscle protein synthesis. HICA may have complementary anti-catabolic effects.
- Does it build muscle?
- Some studies show slight lean mass increases. Effects are modest. Not a powerful muscle builder.
- Is it natural?
- Yes, your body makes HICA from leucine metabolism. Also found in some fermented foods.
- Why isn't it more popular?
- Limited research, modest effects, and competition from better-studied supplements like leucine and HMB.
- Who might benefit?
- Athletes in caloric deficit or doing very high volume training where anti-catabolic support matters most.
Why these belong in the same formula. Each row says what the basis is, from settled biochemistry through to a trial that measured the pair.
Alpha-hydroxyisocaproic acid is the hydroxy metabolite of alpha-ketoisocaproate, the keto acid formed when leucine is transaminated. The two occupy consecutive positions on one pathway, so they are the same signal delivered at different points.
Leucine is transaminated to alpha-ketoisocaproate, which is reduced to HICA. Supplying either loads the same short branch of leucine metabolism.
HMB and HICA are both downstream products of alpha-ketoisocaproate, formed by different enzymes from the same intermediate. They share an origin, so their effects overlap rather than stack cleanly.
Branched-chain aminotransferase needs pyridoxal 5-phosphate to convert leucine to the keto acid that HICA comes from. B6 status sets the flux into this branch.
The branched-chain ketoacid dehydrogenase complex that clears alpha-ketoisocaproate runs on thiamine pyrophosphate. Thiamine supply decides how much of the keto acid is oxidised rather than diverted to HICA.
The same branched-chain ketoacid dehydrogenase complex requires FAD, which riboflavin supplies. Riboflavin adequacy is part of what keeps leucine catabolism moving normally.
Further down the leucine route, 3-methylcrotonyl-CoA carboxylase is a biotin-dependent enzyme. Biotin status governs the disposal end of the pathway HICA sits on.
Leucine catabolism proceeds through several coenzyme A thioesters, and pantothenic acid is the precursor of coenzyme A. Low pantothenate constrains the same downstream steps.
Valine uses the same branched-chain aminotransferase and dehydrogenase complex as leucine, so the three branched-chain amino acids compete for one enzyme set. A large load of one shifts the handling of the others.
Branched-chain transamination donates its amino group to glutamate and onward to glutamine, which carries the nitrogen out of muscle. Glutamine supply intersects the same nitrogen route this branch uses.
HICA sits downstream of leucine, and whey isolate is one of the densest ordinary sources of leucine in a supplement stack. Taking both means the leucine pool that feeds transamination is already loaded, so the added HICA is not the only input to that branch. This is a substrate relationship, not a demonstrated performance effect.
Casein releases amino acids slowly, including leucine, isoleucine and valine. HICA is a leucine end metabolite, so the two occupy the same metabolic branch from opposite ends. No trial has measured the pair together.
Isoleucine, valine and leucine are transaminated by the same aminotransferase and their keto acids are handled by the same branched-chain keto acid dehydrogenase complex. Loading one branched-chain amino acid heavily can shift flux through that shared machinery. Formulators normally keep the three in a fixed ratio for this reason.
Creatine works on phosphocreatine resynthesis and cell hydration, which has nothing to do with the leucine catabolic branch HICA belongs to. Because the mechanisms do not overlap, the two are routinely put in the same product without interfering. There is no combination trial for this pair.
Beta-alanine feeds carnosine synthesis and intramuscular buffering; HICA is a leucine metabolite with no buffering role. The pairing is a formulation choice rather than a measured interaction.
Most HICA raw material on the market is supplied as a calcium salt, so every gram of the ingredient also carries a small amount of elemental calcium. Anyone already taking a separate calcium product should count that contribution when adding up daily intake. This is a label arithmetic point, not a biological effect.
Magnesium is required for ATP to function as a substrate in essentially every kinase reaction in muscle, including the ones that run during resistance work. That supports normal muscle contraction generally and is independent of the leucine branch. Nothing here has been measured with HICA specifically.
The conversion of alpha-ketoisocaproate to HICA is an NAD-linked reduction, and niacin is the dietary precursor of NAD. Adequate niacin status therefore supports the normal running of that step in either direction. This is settled cofactor biochemistry rather than a tested supplement pairing.
The branched-chain keto acid dehydrogenase complex that oxidises leucine's keto acid uses lipoic acid as one of its bound cofactors, alongside thiamine and riboflavin derivatives. That complex sits at the fork that decides whether the keto acid is oxidised or reduced to HICA. The relationship is textbook; no one has supplemented the two together and measured an outcome.
Bicarbonate raises extracellular buffering capacity for high-intensity work, a mechanism unrelated to leucine metabolism. Any combined use is stacking separate approaches to the same session rather than an interaction. Early, and the gastrointestinal load of bicarbonate is the practical limit.
Nothing specific on file for Alpha-Hydroxyisocaproic Acid. Match the label to the daily amount above, and tell your doctor what you take.
Not medical advice. Show the label to your pharmacist.What Alpha-Hydroxyisocaproic Acid actually does.
One enzyme decides whether leucine's intermediate is burned or turned into HICA, and it needs several B vitamins to work normally.
The body already makes and excretes small amounts of this compound.
On its own it is a sticky acid, so it is sold as a salt.
Alpha-hydroxyisocaproic acid, also called leucic acid or HICA, is a downstream metabolite of leucine: branched-chain aminotransferase converts leucine to alpha-ketoisocaproate, and that keto acid can either be oxidatively decarboxylated or reduced to the alpha-hydroxy acid.
Where Alpha-Hydroxyisocaproic Acid comes from.
It is made in a factory from the amino acid leucine, then turned into a salt so it can be put in a capsule.
Chemically synthesised. The molecule is identical to the one a plant or an animal makes, and building it deliberately means a known purity, a fixed dose and no crop contaminants. For several nutrients this is the only route that reaches a usable amount.
Commercial routes start from L-leucine or from alpha-ketoisocaproate, both available as bulk amino acid industry intermediates.
The keto group at position two is reduced, or a corresponding nitrile or ester intermediate is hydrolysed, to give 2-hydroxy-4-methylpentanoic acid. Chemical and enzymatic reductions are both used industrially.
The crude acid is crystallised and washed to remove unreacted starting material and reaction by-products.
The acid is neutralised with calcium or sodium hydroxide to a defined stoichiometry, then dried; assay is run against the salt, so the label percentage reflects the salt and not the free acid.
Milled and sieved to a capsule or drink-mix particle size, then blended with flow aids as needed.
Suppliers generally do not disclose whether the reduction step is chemical or enzymatic, nor the fermentation origin of the starting leucine.
Getting Alpha-Hydroxyisocaproic Acid from food.
The whole-food sources on file. A supplement closes the gap, it does not replace dinner.
A gram-for-gram figure (how much of each you would eat to match a dose) will appear here once it is sourced and reviewed. This page will not print a number it cannot cite.
The forms it comes in.
The essence, in one line each.
- The authors reported no effect of HMB or alpha-HICA on training-induced changes in body composition, which is a failure to detect a difference rather than evidence that none exists.Randomised trial. Teixeira et al., 2019 (European Journal of Sport Science). PMID 30588860 ↗
- Leucine metabolites, alpha-HICA among them, did not enhance training-induced performance or muscle thickness in this trial; the result is a null, not a demonstration of equivalence.Randomised trial. Teixeira et al., 2019 (Medicine and Science in Sports and Exercise). PMID 30102677 ↗
- Leucine metabolites including alpha-HICA did not produce detectable changes in phase angle, bioimpedance vector patterns or strength; phase angle and bioimpedance are body-composition markers, not performance outcomes.Randomised trial. Campa et al., 2021 (Applied Physiology, Nutrition, and Metabolism). PMID 33337947 ↗
These are the studies our verdict leans on, chosen from the 3 we read for Alpha-Hydroxyisocaproic Acid. The full linked list is below.
FDA Disclaimer: These statements have not been evaluated by the Food and Drug Administration. This information is for educational purposes only and is not intended to diagnose, treat, cure, or prevent any disease. Consult your healthcare provider before starting any supplement regimen.