Garlic intake and colorectal cancer risk in people
What it found
In people, eating more garlic was linked to a lower risk of colorectal cancer, but the link was seen mainly in case-control studies and not in cohort studies.
What they found
Studies in people
Overall risk link
People who ate the most garlic had a lower risk of colorectal cancer compared with those who ate the least. The authors combined the results from 11 studies.
Case-control vs cohort
The lower risk was seen in case-control studies but not in cohort studies. In cohort studies, the risk was about the same for high and low garlic eaters.
Rectal vs colon cancer
The link was stronger for rectal cancer than for colon cancer.
By region
Studies from Europe showed a stronger link than those from Asia and America. The one Australian study also showed a notable link.
By sex
When the studies were split by sex, no significant link was found in either men or women.
Animal and lab studies
Possible mechanisms
In lab tests, garlic compounds have shown effects on cancer cells, such as slowing their growth. The authors say the exact way garlic might protect against cancer is still unclear.
What the authors conclude
“In summary, garlic intake can lower CRC risk.”
Also in their conclusions
- They conclude that garlic intake can lower colorectal cancer risk.
- They note that this conclusion was mainly based on case-control studies, while no definite result was obtained from cohort studies.
- They advise that more large-scale prospective cohort studies are needed to clarify and quantify the protective effect of garlic against colorectal cancer.
How it was done
Colorectal cancer is common worldwide, and diet may play a role. The authors wanted to clarify the relationship between garlic intake and colorectal cancer risk because previous studies had given conflicting results.
They combined 11 studies published from 1991 to 2018, involving 12,558 people with colorectal cancer. The studies were from America, Asia, Europe and Australia, and included 8 case-control and 4 cohort studies.
What it can’t tell you
- The studies were observational, so they can show a link but cannot prove that garlic itself causes the lower risk.
- The amount and type of garlic eaten were not measured the same way across all studies.
- The results were based mainly on case-control studies, which can be affected by people remembering their past diet differently.
Who paid
- Conflicts
- The authors have no conflicts of interest to disclose.
- Authors work at
- Affiliated Hospital of Nanjing University of Chinese Medicine, China
The paper
- Title
- Garlic intake and the risk of colorectal cancer: A meta-analysis
- Type
- Systematic review and meta-analysisThe authors follow a set, published method to find every relevant study, then combine the numbers from them into one result.
- Evidence
- Studies in people · animals · lab
- Summarised from
- Full text
- Cite
- Zhou X, Qian H, Zhang D, Zeng L (2020). Garlic intake and the risk of colorectal cancer: A meta-analysis. Medicine. doi:10.1097/MD.0000000000018575Free full textPubMed 31895803DOI
Summary written 26 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error