HICA, short for alpha-hydroxy-isocaproic acid, is a natural byproduct of leucine metabolism. Your body produces it in small amounts when muscle and connective tissue break down leucine, an essential amino acid involved in muscle repair. It’s sold as a sports supplement, typically marketed for building lean muscle and reducing soreness after hard training, though the scientific evidence behind those claims is mixed.
How Your Body Makes HICA
Leucine is one of the three branched-chain amino acids and plays a central role in triggering muscle protein synthesis. When your body metabolizes leucine, it produces several downstream compounds. One pathway leads to HMB (a more widely studied supplement), and another produces HICA. Both are natural substances your tissues generate in small quantities during normal metabolism.
HICA also shows up naturally in fermented foods. Certain strains of lactobacilli, the beneficial bacteria used in sourdough fermentation, produce HICA as a metabolic byproduct. Research on fermented whole-grain rye foods found notably higher levels of HICA compared to versions made without sourdough or bacterial fermentation. So if you eat fermented grain products, you’re already consuming trace amounts.
What HICA Is Supposed to Do
The supplement is marketed primarily for two purposes: increasing lean body mass and reducing delayed-onset muscle soreness (DOMS) after intense exercise. The proposed mechanism involves protecting muscle tissue from breakdown rather than directly building new muscle. Lab research on animal models found that HICA increased markers of muscle protein synthesis, and cell studies suggest it may help reduce muscle wasting triggered by inflammatory signals. Specifically, one lab study on muscle cells found HICA suppressed inflammation-driven protein degradation and reduced muscle cell shrinkage by dialing down certain inflammatory pathways.
That anti-catabolic angle is what separates HICA’s marketing pitch from standard protein supplements. The idea is that by slowing muscle breakdown during intense training periods, you retain more of what you build.
What the Human Studies Actually Show
The evidence in humans is thin and contradictory. The most cited study, led by Finnish researcher Antti Mero, gave soccer players 1.5 grams of HICA per day (split into three 500-milligram doses) during four weeks of intense training. The HICA group saw small increases in lean body mass compared to the placebo group, and the researchers reported reductions in muscle soreness.
That study was small, with only eight people in the HICA group, which makes it hard to draw strong conclusions. And when a later randomized controlled trial by Teixeira and colleagues tested HICA supplementation in healthy young men over a longer eight-week resistance training program, it found no benefits on fat-free mass, muscle thickness, or exercise performance compared to placebo. The same research group also tested HMB alongside HICA and found neither supplement improved training-induced changes in body composition.
So the current picture is one positive but very small study, contradicted by a larger and longer follow-up. That’s not enough to confidently say HICA works for muscle growth or soreness reduction in humans.
Typical Dosage in Supplements
Most HICA supplements and the clinical research that exists use a dose of 1.5 grams per day, usually split into three servings of 500 milligrams. In the Mero study, subjects took each dose mixed with liquid, spread throughout the day. Some products combine HICA with branched-chain amino acids or bundle it into pre-workout and post-workout formulas, but there’s no research specifically showing that timing HICA around workouts matters more than simply hitting the daily total.
How HICA Compares to HMB
Both HICA and HMB come from leucine metabolism, and both are marketed as anti-catabolic supplements. HMB has a much larger body of research behind it, with dozens of studies spanning decades. While HMB’s results are also debated, there’s at least a meaningful volume of data to evaluate. HICA has only a handful of human studies, making it far less established.
The key practical difference: HMB has enough research to appear in position statements from sports nutrition organizations, while HICA remains largely unproven. If you’re choosing between the two, HMB has a stronger (though still imperfect) evidence base.
Safety Profile
HICA is a substance your body produces naturally, and it occurs in fermented foods, which gives it a reasonable baseline safety profile. The clinical trials that have been conducted at 1.5 grams per day over four to eight weeks did not report significant adverse effects. However, the total number of people studied is small, and there are no long-term safety trials. Like most sports supplements, HICA is not evaluated by regulatory agencies for effectiveness before it reaches store shelves.