The Cancer Research
For cancer risk, walnuts are the most studied among the nuts.
There are a few dozen studies investigating cancer and whole walnuts, with many more on the compounds they contain. Walnut’s alpha-linolenic acid, ellagic acid and flavonoids are well studied in the laboratory.
Current Evidence: AICR/WCRF expert report and its updates (CUP)
AICR’s report and its continuous updates find evidence currently too limited to draw any conclusions about walnuts – or any nuts – and cancer risk.
"Several animal studies show that including walnuts in the diet slows or prevents the growth of breast and prostate cancers. The addition of walnuts to your plate is a good cancer preventive measure.”
- Lauri Byerley, PhD, LSU Health New Orleans
Open Areas of Investigation: Laboratory Research
In mice, several studies found that consuming walnuts resulted in decreased breast and colon tumor growth compared to the animals eating a standard diet. Limited studies in mice also show reduced growth of prostate cancer. One study indicated that consuming a walnut diet altered the expression of genes that regulate cell growth. Walnuts’ omega-3 fat, alpha-linolenic acid, seemed to account for some, but not all, of the protection seen.
Walnuts also contain ellagic acid, a phytochemical also found in raspberries, strawberries and pecans. Bacteria in our digestive tract convert ellagic acid into compounds called urolithins. In cell and animal studies, urolithins show antioxidant, anti-inflammatory and direct cancer-inhibiting effects.
Cell and animal studies studies have also investigated gamma-tocopherol, one of the eight forms of vitamin E. Most studies on the fat-soluble types of vitamin E have focused on alpha-tocopherol, the form listed on nutrition labels and recognized as most important for our health. Yet several studies suggest that walnuts’ gamma-tocopherol has stronger anti-inflammatory and cancer-protective effects than alpha-tocopherol.
Open Areas of Investigation: Human Studies
A couple of short-term studies suggest that eating walnuts can raise antioxidant levels in the body. One study also suggested it decreased signs of DNA damage. Yet one of the longer human studies involving 21 people found that their blood level of antioxidants were the same both before and after eating walnuts every day for six weeks.
Intervention trials including walnuts as part of a Mediterranean diet show potential benefits, such as helping people lose abdominal fat, lower blood pressure and lower their triglycerides. Yet overall, more human studies are needed to clarify walnuts’ effects on inflammation, antioxidants, and cancer risk.