One in three people has a common gene variant that significantly raises the chances developing bowel cancer from eating meat, a study has shown.
Another mutation is thought to enhance the ability of fruits and vegetables to protect against bowel cancer.
Scientists believe the digestion of processed and red meat could promote an immune response that can trigger tumour development.
They suspect the newly discovered variant, known as rs4143094, could sabotage the body's ability to suppress this harmful response.
In about 36% of the population, it is thought to affect the activity of a gene that acts as an immune system regulator.
Researchers in the US made the discovery after systematically searching more than 2.7 million genetic sequences for interactions with the consumption of red and processed meat.
The study compared DNA from 9,287 patients with colorectal, or bowel, cancer and 9,117 cancer-free individuals.
Lead scientist Jane Figueiredo, from the Keck School of Medicine at the University of Southern California, said: "Diet is a modifiable risk factor for colorectal cancer. Our study is the first to understand whether some individuals are at higher or lower risk based on their genomic profile. This information can help us better understand the biology and maybe in the future lead to targeted prevention strategies.
"We are not saying that if you don't have the genetic variant that you should eat all the red meat you'd like. People with the genetic variant ... have an even higher increased risk of colorectal cancer if they consume high levels of processed meat, but the baseline risk associated with meat is already pretty bad."
Another variant, rs1269486 on chromosome 8, was found to have a beneficial interaction with the right kind of diet. For people with this variant, eating healthy quantities of fruits and vegetables may be more than normally protective against bowel cancer.
The findings were presented at the annual meeting of the American Society of Human Genetics in Boston.
More than 30 susceptibility "alleles" - gene alterations - linked to bowel cancer have been identified by scientists. They include rare variants with a strong impact on risk, and common variants with a low impact.
"Colorectal cancer is a disease that is strongly influenced by certain types of diets," Dr Figueiredo added. "We're showing the biological underpinnings of these correlations, and understand whether genetic variation may make some people more or less susceptible to certain carcinogens in food, which may have future important implications for prevention and population health."
The study forms part of a continuing international collaboration of scientists called the Genetics and Epidemiology Colorectal Cancer Consortium (Gecco).
"Gecco aims to continue to discover additional colorectal cancer-related variants by investigating how genetic variants are modified by other environmental and lifestyle risk factors, including biomarkers as well as how they influence patient treatment response and survival," said co-author Ulrike Peters, from the Fred Hutchinson Cancer Research Centre in Seattle.