The number of people under the age of 50 diagnosed with bowel cancer has increased at an alarming rate in recent decades. Two new studies from Flinders University suggest this rapid surge may be due to changes in eating habits.

"We've identified many direct links between poor diet choices and digestive cancers," explains nutrition epidemiologist Yohannes Melaku.

"Unhealthy dietary patterns, marked by high consumption of red and processed meats, fast foods, refined grains, alcohol and sugary beverages, present a worrying relationship with an increased risk of gastrointestinal cancers."

Responsible for 1 in 3 cancer deaths worldwide, gastrointestinal (GI) cancers can occur virtually anywhere in the digestive system, from the throat to the stomach, pancreas, intestines, rectum, and anus.

Epidemiologist Zegeye Abebe and colleagues reviewed research on dietary patterns and GI cancers, identifying 28 eligible studies for further analysis. While there were some contradictions between individual investigations, collectively the studies suggested healthy dietary patterns generally decreased cancer risk.

Some of the same team also analysed data from 97,561 people and found those who had a diet containing high fiber and unsaturated fats were less likely to develop colorectal cancer. This cancer is predicted to kill 1.6 million people in 2040.

"With the growing number of digestive cancers, such as bowel cancer, being diagnosed worldwide, and increasingly in people under 50 years old, it's time for action to protect people's digestive health," explains Melaku.

"Our studies demonstrate that nutrition education and promoting healthy eating patterns could be pivotal in reducing GI cancer risks and improving patient outcomes."

As a systematic review of observational studies, the analysis can't distinguish cause from effect, but based on past research, the team suspects the mechanisms behind the diet and cancer links involve inflammation processes as well as interactions through our microbiome.

Foods rich in antioxidants such as berries, leafy greens, fruits, vegetables, almonds, walnuts, flax seeds, turmeric, ginger, garlic, citrus, fatty fish and colorful vegetables are all anti-inflammatory. Whereas, red meat, sugary drinks, and refined carbohydrates, like those in white bread, are inflammatory. They can also increase insulin resistance.

"Insulin resistance increases the risk of cancer through activation of insulin like growth factor 1," Abebe and team write.

Their findings support global guidelines for healthy eating, echoing other research that shows diets full of junk food and red meat are bad for our health. Time and time again, diets that focus on fresh fruits and vegetables are associated with better health outcomes.

"Whilst our results are promising, more work needs to be done with a greater focus on nutrition in clinical settings using nutritional biomarkers to better understand the relationship between diet and GI cancer," says epidemiologist Amy Reynolds.

"We need to understand how different dietary patterns may influence the risk of developing digestive cancers. We also want to see an increase in education around healthy eating which could lead to better health outcomes for those at risk for GI cancers."

This research was published in the European Journal of Nutrition and Nutrition Reviews.