Garlic intake and bowel cancer risk across 11 studies in people
What it found
People who ate the most garlic had a lower chance of developing bowel cancer compared with those who ate the least.
This link was seen in case-control studies but not in cohort studies that followed people over time.
What they found
Studies in people
Overall bowel cancer risk
People who ate the most garlic had about a 20 percent lower chance of bowel cancer than those who ate the least. This result came from combining all 11 studies together.
Case-control versus cohort studies
In case-control studies, where people recalled past diets after diagnosis, higher garlic intake was linked to lower cancer risk. In cohort studies, which followed people forward in time, no clear link was found.
Rectal versus colon cancer
Eating more garlic had a stronger link to lower rectal cancer risk than to lower colon cancer risk.
Differences by region
European studies showed a stronger link between garlic and lower cancer risk than studies from Asia or America. The single Australian study also stood out.
Animal and lab studies
How garlic might work
In lab tests on cancer cells and in animals, garlic compounds slowed cell growth and triggered cell death. Garlic may also help the body process cancer-causing substances differently.
What the authors conclude
- They conclude that eating garlic could lower the risk of bowel cancer.
- They note that this conclusion relies mostly on case-control studies, while cohort studies did not show a definite effect.
- They advise that their findings should be interpreted carefully and call for more large studies that follow people over time.
How it was done
Bowel cancer is the third most common cancer worldwide, and diet may play a role in its development. Earlier reviews gave mixed results on whether eating garlic lowers this risk, so the authors gathered newer data to check again.
The authors combined 11 observational studies published between 1991 and 2018, covering 12,558 bowel cancer cases in people. They compared those who ate the most garlic with those who ate the least. The studies were conducted in America, Asia, Europe, and Australia.
What it can’t tell you
- These are observational studies, so they can only show a link between garlic and cancer risk, not prove that garlic prevents cancer.
- People in case-control studies recalled their diets after being diagnosed, which may have affected how much garlic they reported eating.
- The amount of garlic counted as a serving varied across the studies, making it hard to know exactly how much to eat.
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 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error