Eating yogurt for breakfast may heal bacteria in the gut and slash the risk of colon cancer, according to a new study.
Colon cancer has surged in young Americans, with diagnoses expected to nearly double from 2010 to 2030.
Experts are racing to find a cause, with one theory centred on lifelong exposure to harmful bacteria lining the gut and stimulating the growth of cancer cells.
Now, doctors from Harvard University have found that people who eat at least two servings of yogurt a week could lower their risk of colon cancers caused by bacteria by 20 per cent.
The researchers looked at colon cancer tumours caused by Bifidobacterium, a type of bacteria that normally helps digest fibre and ward off infections.
However, excess levels can lead to inflammation in the colon, which damages cells and causes them to grow out of control, resulting in cancer.
The researchers believe healthy bacteria, including Bifidobacterium, found in fermented foods like yogurt can reduce the amount of harmful bacteria living in the gut, reducing the risk of bacteria-fueled colon cancers.
However, they found no link between yogurt and reduced risk of colon cancers caused by other factors such as genes, obesity and chemical exposure.
Dr Andrew T Chan, chief of the Clinical and Translational Epidemiology Unit at Massachusetts General Hospital, said: 'This paper adds to the growing evidence that illustrates the connection between diet, the gut microbiome and the risk of colorectal cancer.
'It provides an additional avenue for us to investigate the specific role of these factors in the risk of colorectal cancer among young people.'
The American Cancer Society estimates more than 154,000 Americans will be struck with colon cancer this year, and just under 53,000 will die.
In the UK, 44,000 Brits are diagnosed each year, and there are roughly 16,800 deaths.
Recent evidence from Johns Hopkins University suggests bacteria may play a role in at least half of colon cancer patients without a family history of the disease.
The new study, published in the journal Gut Microbes, analysed health data from 132,056 healthcare workers from the Nurses' Health Study (NHS) and Health Professionals Follow-Up Study (HPFS) databases.
Patients on average were between 60 and 65 years old. Two-thirds of patients were women.
NHS participants were followed from 1976 through to 2016, and those from HPFS were followed from 1986 through to 2016.
Participants filled out regular questionnaires about diet and lifestyle factors, including how many servings of plain and flavoured yogurt they consumed every week.
The team found 3,079 patients were diagnosed with colorectal cancer and took tissue samples from their tumours to look for bacteria. They were able to find information on bacteria in 1,121 cases.
Of those 1,121 cases, 31 per cent of tumours (346) were positive for Bifidobacterium.
Eating yogurt made no difference in the risk of non-bacteria colon cancers, though getting at least two servings per week lowered the risk of Bifidobacterium-positive colon cancers by 20 per cent.
Dr Tomotaka Ugai, co-senior study author and pathologist at Brigham and Women's Hospital, said: 'It has long been believed that yogurt and other fermented milk products are beneficial for gastrointestinal health.
'Our new findings suggest that this protective effect may be specific for Bifidobacterium-positive tumours.'
The experts said further research is needed to determine how exactly yogurt lowers the risk of certain colon cancers, but they speculated that the healthy bacteria in yogurt could change bacteria in the gut microbiome, including Bifidobacterium.
Yogurt contains probiotics, which are made of several forms of live bacteria that have been shown to promote healthy digestion.
Along with balancing healthy bacteria in the gut, probiotics have been shown to reduce intestinal inflammation, lowering the risk of cancer cells forming.
Probiotics in yogurt may also help reduce constipation by making stools smoother. This reduces the amount of time stools spend in the colon and potentially spread harmful bacteria.
One of the study's caveats is focusing on patients who are mostly between ages 50 and 60, which limits data on early-onset colorectal cancer.
Dr Shuji Ogino, chief of the Program in Molecular Pathological Epidemiology at Brigham and Women's Hospital, said: 'Our study provides unique evidence about the potential benefit of yogurt.
'My lab’s approach is to try to link long-term diets and other exposures to a possible key difference in tissue, such as the presence or absence of a particular species of bacteria.
'This kind of detective work can increase the strength of evidence connecting diet to health outcomes.'
