Common additives used in every day foods including bread, margarine and sweets may be behind the huge rise in bowel cancer, scientists claim.
Emulsifiers, which are added to most processed foods to aid texture and extend their shelf life, alter gut bacteria in the stomach.
Experts fear the additives may be creating higher amounts of bad bacteria, disrupting the healthy balance within the gut.
This alteration causes inflammation within the intestine which provides tumours with a habitable environment to grow in, new research suggests.
Previous research has found microorganisms living in the stomach are a key driving factor behind inflammatory bowel disease.
Crohn's disease and ulcerative colitis, two of the most popular forms of the disease, are known to aid tumour growth.
The inflammation caused by the disease has previously been found to alter levels of bad bacteria and is found in many cases of colorectal cancer.
But now US researchers believe emulsifiers may be partially responsible for this link, because they promote colon tumorigenesis - the production of tumours.
It is the second most common form of cancer death in the UK, behind lung cancer killing 16,200 each year.
The disease is the fourth most commonly diagnosed, after breast, prostate and lung, with 41,000 cases identified every year.
Researchers from Georgia State University fed mice with two very commonly used emulsifiers.
They were given either polysorbate 80 or carboxymethylcellulose at doses similar to those in the majority of processed foods.
Experts found consuming the additives drastically changed the bacterial make-up of the stomach.
They also discovered that it causes low-grade inflammation which allowed cancer cells to thrive and grow.
Lead researcher Dr Emilie Viennois said: 'The incidence of colorectal cancer has been markedly increasing since the mid-20th century.
'A key feature of this disease is the presence of an altered intestinal microbiota that creates a favourable niche for tumorigenesis.
'The dramatic increase in these diseases has occurred amidst constant human genetics, suggesting a pivotal role for an environmental factor.'
The US researchers are now testing to see what triggers the alteration and the exact way it can cause cancer.
The findings were published in the journal Cancer Research.