Western diet impacts the gut, may heighten IBD, colon cancer risk

• Past research has linked the Western diet to an increased risk for several diseases.
• Researchers from the Teagasc Food Research Centre have found an association between the Western diet and an increased risk for both IBD and colorectal cancer by negatively impacting the gut microbiome.
• Scientists also reported the Mediterranean diet is effective in managing diseases like IBD, type 2 diabetes, and cardiovascular disease.

Over the years, studies have shown that the Western diet — typically high in saturated fats , sugars, and additives — can potentially harm a person’s health and increase their risk for conditions such as type 2 diabetes , obesity , Alzheimer’s disease , and cardiovascular disease .

Now, researchers from the Teagasc Food Research Centre in Ireland add to this body of knowledge with a new review — which appears in Nature Reviews Microbiology — highlighting an association between the Western diet and an increased risk for both inflammatory bowel disease (IBD) and colorectal cancer.

This, the researchers suggests, is likely due to this diet’s negative impact on the gut microbiome .

Conversely, scientists report that the Mediterranean diet is effective in managing conditions like IBD, type 2 diabetes, and cardiovascular disease.

How 6 global diets compare when it comes to health

For this study, researchers compared six diets followed worldwide to examine their potential health benefits and risks, as well as their impact on the gut microbiome. These were:

• the Mediterranean diet
• high-fiber diet
• plant-based diet
• high-protein diet
• ketogenic (keto) diet
• Western diet.

“We chose to focus on these six diets because they are among commonly consumed diets worldwide, that represent a spectrum from healthy to not healthy diets,” Catherine Stanton, PhD , senior principal research officer in the Food Biosciences Department of Teagasc Food Research Centre in Ireland and lead author of this study, explained to Medical News Today .

“It is important to understand how diet positively and negatively affects the gut microbiome to enable people to make informed decisions that can improve health and potentially reduce the risk or progression of certain diseases, such as cardiovascular disease and IBD,” she told us.

“IBD and cancer, particularly colon cancer, and cardiovascular disease are serious and potentially life-threatening diseases,” Stanton continued. “Emphasizing the link between diet and these diseases can help raise awareness, encourage early intervention, and guide dietary recommendations, ultimately improving health outcomes and enhancing quality of life.”

Western diet reduces gut microbiome diversity

With regard to the Western diet, Stanton and her team suggest it is linked to a “marked reduction” in the diversity of the gut microbiome compared to the other diets.

Because of this and the lower fiber content normally found in the Western diet, the microbiome produces fewer short-chain fatty acids (SCFAs). Previous research shows SCFAs may help reduce inflammation , protect the heart from disease, and fight off obesity.

Additionally, when a person consumes red meat, certain compounds from the meat can be changed by the gut microbiome into trimethylamine, which is then converted to trimethylamine N-oxide (TMAO) in the liver.

Higher TMAO levels are often associated with an increased risk for cardiovascular disease , chronic kidney disease , and certain cancers, including colorectal cancer .

Stanton explained:

“The Western diet, characterized by high consumption of ultra-processed foods , saturated fats, and red meat, and low intake of fruits, vegetables, and whole grains, can disrupt the balance of the gut microbiome. This imbalance is due to high saturated fat, low fiber, and limited nutrient diversity, which can lead to inflammation and promote the growth of harmful bacteria.”

Mediterranean diet has positive effect on gut microbiome

When evaluating the Mediterranean diet compared to the other five diets, researchers found it promoted certain bacteria and reduced harmful ones, improving gut microbiome composition and thereby increasing SCFA production.

The researchers also reported the Mediterranean diet’s impact on the gut microbiome made it helpful in managing diseases such as IBD, type 2 diabetes, and heart disease.

“The Mediterranean diet features abundant fruits, vegetables, whole grains, olive oil, fish, dairy, and reduced red meat consumption,” Stanton said.

“This diverse diet, rich in healthy fats, prebiotic foods , and fiber, supports a balanced and diverse gut microbiome. Additionally, it has anti-inflammatory effects, boosts the immune system, and fosters the growth of beneficial gut bacteria, making it effective in disease prevention,” she further noted.

Confirming detrimental effects of the Western diet

Stanton advised doctors to use these findings to emphasize to their patients that diet can be a valuable, low-cost tool for improving quality of life, preventing or slowing disease progression, and promoting longevity.

“When discussed thoroughly with your doctor, diet can also serve as a potent adjuvant therapy for conditions such as cardiovascular disease, IBD, and even psychiatric disorders like depression and Alzheimer’s disease,” she added. “Further studies are needed on the impact of diet in early life on long-term gut microbiota and health outcomes.”

MNT also spoke with Wael Harb, MD , a board-certified hematologist and medical oncologist at MemorialCare Cancer Institute at Orange Coast and Saddleback Medical Centers in Orange County, CA, about this review.

Harb, who was not involved in the research, commented that this review effectively highlights the detrimental effects of the Western diet on gut health, providing further evidence of the increased risk of colorectal cancer and inflammatory bowel disease related to the high content of fat and sugar in Western diets.

“The father of medicine, Hippocrates, said ‘Let food be thy medicine’ and this ancient wisdom is more true today than ever before in that understanding the impact of diet on the gut microbiome is crucial because it directly influences our overall health,” he told us.

Like Stanton, Harb advised that: “The Western diet [upsets] the balance of beneficial bacteria for most chronic [inflammatory diseases]. Educating people about the connection empowers them to make informed diet choices and promote gut health and lower disease risk.”

What diet is best for your health?

After reviewing this research, Monique Richard, MS, RDN, LDN , a registered dietitian nutritionist and owner of Nutrition-In-Sight, told MNT the correlations between diet quality and composition and acute and chronic diseases related to gut health are not surprising in the least.

“As a registered dietitian nutritionist (RDN), I educate people on what it means and the importance of being a ‘qualitarian’ because of the impact each choice has [on] our body, the planet, and our future self,” Richard explained. “The microbiome’s health affects our immune system, our mental health, and so much more.”

To help people determine which diet might be best for their overall health, Richard first advised consulting a registered dietitian nutritionist (RDN) to see what specific diet may work for their individual needs based on taste preferences, access to food, culinary skills, genetic predisposition, cultural heritage, and current health.

“Ideally, we are looking to meld the benefits of all the [healthy dietary] patterns together in a sustainable way [to] enhance longevity but also quality of life. An emphasis on high-fiber foods, foods rich in poly and monounsaturated fats , lean proteins, and a diet filled with colorful fruits, vegetables, and a variety of whole grains , nuts, seeds and pulses (beans), herbs, spices, and water is the optimal goal in a balanced and appropriate portion distribution.”

— Monique Richard, MS, RDN, LDN

Richard also suggested readers ask themselves the following questions:

• After which types of meals do I feel my best?
• What works best for my lifestyle and budget?
• Do I often experience cramps, bloating, diarrhea, reflux, or pain after eating certain foods?

“Think of the microbiome as your body’s armor — only working from the inside out,” Richard said. “The more we make it robust and strong, the easier it can fight off the ‘bad guys’ and help our bodies defend themselves against germs, disease, and assault.”