Black garlic, for your gut bacteria
Black garlic
Whole bulbs or peeled cloves
Garlic aged until it turns black, soft and sweet. Early research looks at what it does for gut bacteria; it's a small start, and we say so.
Evidence C
What it is
Ordinary garlic held warm and humid for weeks, until the cloves turn black, soft and sweet, with notes of molasses and tamarind. Ageing also changes its chemistry: it has more S-allyl cysteine (SAC) than fresh garlic, and loses most of raw garlic's bite.
What the gut research shows
- One 12-week trial in 64 adults: daily black garlic raised Latilactobacillus, a lactic-acid bacterium. Bifidobacterium and a few others trended up, but not by enough to be sure.
- Aged garlic extract, a related product, gave a wider variety of gut bacteria and more Lactobacillus in a 12-week trial of 49 people.
- In mice, black garlic's brown compounds (melanoidins) increased bacteria that make short-chain fatty acids, which feed the cells lining the gut.
- No study yet shows these shifts change digestion, weight or how you feel.
How to choose
- Ingredients: garlic, and nothing else.
- Whole bulbs keep longer; peeled cloves are easier to eat.
- The cloves should be soft and sticky, not hard or dry.
- Black garlic isn't the same as aged garlic extract (such as Kyolic), which is aged in liquid. Their research doesn't transfer one to one.
Watch out
- Garlic in large amounts may increase the risk of bleeding. Ask your doctor if you take a blood thinner, and tell your surgeon before an operation.
- Garlic can cause stomach upset, wind and garlic breath.
The evidence Grade C
Mostly mechanistic or observational. It's food, so that's fine; we just say so.
Ageing changes garlic's chemistry: black garlic has more S-allyl cysteine (SAC) and other water-soluble compounds than fresh garlic. On gut bacteria, the human evidence is one small trial. In 64 Thai adults carrying extra weight around the middle, 12 weeks of daily black garlic raised Latilactobacillus, a lactic-acid bacterium; rises in Bifidobacterium and a few others were only trends. That trial measured gut bacteria, not health. A 12-week trial of aged garlic extract, a related but different product, found a wider variety of gut bacteria and more Lactobacillus. In mice on a high-fat diet, black garlic's brown compounds shifted gut bacteria too. Whether any of this changes digestion or how you feel hasn't been tested.
- Trial: black garlic and gut bacteria in 64 adults (Krutkabgaew et al., 2023, Thai Journal of Toxicology)
- Trial: aged garlic extract and gut bacteria, GarGIC (Ried et al., 2018)
- Mouse study: black garlic melanoidins and gut bacteria (Wu et al., 2020)
- Review: black garlic's compounds and the research so far (Ahmed and Wang, 2021)
- NIH NCCIH: Garlic
Last reviewed 2026-10-23.