Garlic and Black Garlic Explained Simply

1. What Is Garlic and Black Garlic?

Garlic is the bulb of a plant called Allium sativum. It has long been used as a spice and is a daily ingredient in many kitchens. Black garlic is made from whole garlic bulbs that are stored warm and moist for weeks. In the process, the bulb becomes dark, and the taste becomes mild and sweetish. Garlic and black garlic therefore come from the same plant, but are prepared differently and are assessed separately in studies.

2. Where Is It Found, and What Is It Made From?

Garlic is found in fresh cloves, dried garlic powder, oil extracts and aged extracts. Black garlic and preparations that are adjusted to specific ingredients also belong to this. It is made from the bulbs of the plant, which grows in temperate climates and is cultivated worldwide. Black garlic is produced from fresh bulbs by storage for weeks at controlled warmth and moisture. Other allium plants such as onion, leek, chives and wild garlic do not belong to this.

3. What Does Garlic and Black Garlic Do? What Research Shows

Blood Lipids

There are several large reviews on the effect on blood lipids. According to them, total and LDL cholesterol as well as triglycerides decreased more with garlic than with a sham preparation 2315. In people with type 2 diabetes, mainly total cholesterol decreased 10. With aged garlic extract, mainly LDL cholesterol decreased 11. In a controlled study (with a comparison group), garlic powder tablets lowered total and LDL cholesterol. HDL cholesterol also rose 32. In moderately elevated cholesterol, however, blood lipids remained without difference with raw garlic, powder and aged extract 31. Also in a large, long-term study in China, garlic did not change blood lipids 28. For black garlic, there are only a few small studies so far. In a small controlled study, HDL cholesterol rose more than with placebo (sham). The other blood lipid values remained unchanged 61. A low-dose extract from black garlic did not change the usual blood lipid values 43.

Blood Pressure

Most and largest studies are available on blood pressure. Several large reviews found lower upper and lower values in adults with high blood pressure with garlic preparations than with placebo 712132225. In one review, dried garlic powder lowered both values 23. For aged garlic extract, the upper value was confirmed to be lowered, while the lower value was only borderline 6. Mean arterial pressure decreased more with garlic powder and freeze-dried extract than with placebo in two controlled studies 3757. Pulse pressure decreased with aged garlic extract 51. In people who already took blood pressure medication, an extract from black garlic slightly lowered blood pressure. The blood pressure-raising enzyme ACE was also less active than with placebo 58. In moderately elevated cholesterol, the lower blood pressure value decreased with such an extract 45. Aged garlic extract lowered the upper, but not the lower value in a review 11. In treated but uncontrolled hypertension (high blood pressure), it had an effect only at higher baseline values 49. In women with polycystic ovary syndrome, a garlic preparation showed only a trend for the upper value and no difference for the lower value 42. The evidence is strong. It is based mainly on reviews of powder, aged extract, and other preparations 62325. Black garlic has so far been tested for blood pressure only in two small studies 4558.

Vascular Function

There are many studies on vascular function with mostly favorable results. In controlled studies with aged garlic extract, arterial stiffness was lower than with a sham preparation 4451. The strength of evidence is estimated as high.

Immune Function

For immune function, there are predominantly favorable results. Two large reviews found lower values of the inflammatory marker CRP with garlic, but no difference in the inflammatory messenger IL-6. TNF-α decreased overall 2 or with aged garlic extract 19. In controlled studies with aged garlic extract, IL-6 was lower than with placebo 364654. Certain defense cells were also more active 33. For colds, one review found only one suitable study: in it, people with a preparation containing the garlic substance allicin had fewer colds than with placebo. The authors see this as an initial indication that must be confirmed 8. Other results showed no difference. With aged garlic extract, the number of colds was the same, but they were milder 33. In another study, the proportion of natural killer cells remained the same 46. The overall picture applies predominantly to aged garlic extract. With an extract from black garlic, the inflammatory values did not change 58.

Cancer Risk

The picture is mixed for cancer risk. In intestinal polyps, high-dose aged garlic extract slowed the number and size of benign growths more than a very low dose in a small controlled study 4748. Two reviews rely on this study 1726. In a large study in a region with high stomach cancer risk, garlic did not lower the number of stomach cancer cases. Garlic also brought no confirmed advantage in the precursors of stomach cancer and in the long-term evaluation 2930. One review on nutrition considers garlic consumption a protective factor against colorectal cancer 24. Another describes cancer-inhibiting effects of sulfur compounds from laboratory, animal and clinical studies 18. The forms studied range from aged garlic extract to extracts and oil to fresh cloves. It remains open whether the results can be transferred to other population groups and to black garlic, which was not tested in these studies.

Stomach and Gut

For the stomach and intestines, there is mainly a large review on allicin from garlic. In addition to standard treatment, it increased the rate at which the stomach germ H. pylori was eliminated and improved the healing of stomach ulcers 5. In addition, the diversity of the gut flora increased in a controlled study with aged garlic extract. More Lactobacillus and Clostridia were found 51. A review summarizes this finding 7. The strength of evidence is moderate. However, it is based mainly on allicin as an addition to standard treatment and a small study on the gut flora.

Other Investigations

In non-alcoholic fatty liver, garlic powder improved liver fat more often than placebo and lowered body weight more 3435. Garlic preparations lowered fasting blood glucose or insulin resistance more than placebo in controlled studies 343840. In heart failure due to coronary heart disease, heart function, ejection fraction, and quality of life improved more with black garlic than with placebo 60. Antioxidative capacity in the blood increased more with extract from black garlic 58 and black garlic 60 than with placebo. With garlic tablets, markers for oxidative stress improved only compared with baseline 52. Compared with placebo, the body's own protective substances against cell damage such as catalase and glutathione increased with garlic 41. With aged extract, malondialdehyde, a sign of cell damage from oxygen, decreased more than with placebo 53. In two small crossover studies with aged extract, such markers remained unchanged 5556.

4. How Was Garlic and Black Garlic Taken in the Studies?

Most frequently studied were dried garlic powder in tablet form 323537 and aged garlic extract in capsules 4449. Fresh cloves, oil extracts and black garlic were tested less often as their own preparation 3161.

5. Is Garlic and Black Garlic Safe? Side Effects in the Studies

The studies report mostly good tolerability; several controlled studies observed no serious side effects 34353650. Most frequently mentioned were gastrointestinal complaints, bad breath and occasionally skin rash. They did not occur with statistically confirmed frequency more often than with placebo 8912. According to a review, garlic together with the diabetes drug chlorpropamide can lower blood sugar too much and reduce the level of the blood thinner warfarin 27. In a study with aged garlic extract, the bleeding risk in people taking blood thinners did not increase 39.

All details with tables and sources: full expert page on Garlic and Black Garlic