A Spanish study (part of PREDIMED) took three identical groups of women and followed them for 5 years. The first group ate a low-fat diet; the second ate a colourful Mediterranean Diet with the addition of 30 gms of mixed nuts a day; and the third group ate a Rainbow Diet with an extra 4 tea-spoonsful of olive oil a day.
The group on the extra olive oil had a 68% lower breast cancer risk than the low-fat group. Each additional 5% of calories from olive oil further reduced risk by 28%. The women eating the nuts had a 41% lower risk than the low fat group. Overall, the two groups on the colourful Mediterranean Diet combined had a 51% lower risk than the control group.
(Ref: JAMA Intern Med. 2015 Sep 14:1-9. Epub 2015 Sep 14).