Over the past decade, whole food plant-based diets (WFPBDs) have gained popularity as evidence has emerged regarding their association with improved morbidity and mortality for many patient populations, including those with gastrointestinal diseases. Multiple factors contribute to the benefits of a WFPBD, including the impact of fiber on the gut microbiome, reduction of the additives found in processed foods such as emulsifiers and stabilizers, and the anti-inflammatory properties of plant-based foods compared to animal-based foods. This review discusses general components and benefits related to WFPBDs, with an evidence-based focus on their role in managing and preventing gastrointestinal disorders. In addition, we offer practical guidance and tools for healthcare providers to help their patients adopt and sustain a WFPBD.  

Introduction

Whole food plant-based diets (WFPBDs) emphasize maximizing the intake of plant-based foods while minimizing highly processed and animal-based foods. Over the last decade, WFPBDs have been emerging with strong evidence regarding their impact on morbidity and mortality in various diseases.¹ Current evidence has highlighted the positive effect of WFPBDs on not only gastrointestinal (GI) diseases but also metabolic syndrome, cardiovascular diseases, cognitive function, and overall mortality risk.^1-3 WFPBDs encourage a high-fiber intake to influence the diversity and composition of the gut microbiome, a key connection between diet and metabolic health.⁴ Ultra-processed foods may play a role as a significant contributor to the development of GI disorders such as inflammatory bowel disease (IBD), colorectal cancer, and metabolic dysfunction-associated steatotic liver disease (MASLD).^2,5,6 WFPBDs aim to address and mitigate the underlying factors that may contribute to these disorders.^1-3,5,6

Despite the increasing popularity of WFPBDs, there are still inconsistencies in its definition, leading to confusion about its composition among patients and healthcare providers. This review explores the core principle of WFPBDs and their multifaceted connections to various GI disorders. We will also outline a patient-centric approach for providers to help patients adopt new dietary habits while addressing the potential challenges of WFPBDs.

What is a Whole Food Plant-based Diet?

The WFPBD focuses on the consumption of vegetables, fruits, whole grains, and legumes in their most natural form while reducing or eliminating animal products.⁷ This emphasis on whole foods inherently decreases the intake of emulsifiers and stabilizers, which are standard components of ultra-processed foods. Emulsifiers, often used to improve texture and shelf life, have been associated with increased inflammation and detrimental changes to the microbiome composition.⁸ Similarly, stabilizers, such as maltodextrins, have been linked to intestinal protective mucus layer damage and the subtle development of intestinal inflammation.⁸

WFPBD can be tailored to fit individual preferences, offering flexibility in food choice while maintaining its core principle of whole, minimally processed plant-based diet. Patients may adopt various forms of WFPBD, such as vegan, lacto-ovo-vegetarian, pescatarian, or Mediterranean diets (MD).⁷ (See Table 1) With guidance from registered dietitians and healthcare providers with expertise in WFPBD, patients can choose a dietary pattern that best matches their health goals and cultural preferences, all while supporting long-term health benefits and managing their GI diagnosis.

Fiber and the Gut Microbiome

Fiber is traditionally defined as the non-digestible components that make up the plant cell wall.⁹ It remains a critical part of the diet today, with plants serving as the primary source. Dietary fiber has various properties – solubility, fermentability, and viscosity – that influences its health benefits within the GI tract.¹⁰ Solubility refers to the ability of the fiber to dissolve in water. Fermentability indicates the ability of the gut bacteria to digest fiber. Viscosity refers to fiber’s capacity to hold water and form a thick, gel-like substance.⁴ As such, fiber can be categorized into many types: soluble/fermentable/viscous (e.g., pectin, galactomannans, beta-glucans), soluble/fermentable/non-viscous (e.g., inulin, oligofructose, fructo-oligosaccharides), and insoluble/non-fermentable/non-viscous (e.g., lignin, cellulose).^10,11 (See Table 2)

Gut microbiota is a community of microorganisms, including bacteria, archaea, fungi, and viruses, that reside within the GI tract, shaping our gut immune system by regulating the expression of colonic regulatory T cells.¹² Soluble, non-viscous, and fermentable fibers, once fermented by colonic bacteria, help generate short-chain fatty acids (SCFAs) such as butyrate and acetate, which are the preferred energy sources for colonic mucosa cells.¹³ SCFAs also promote the growth of beneficial gut bacteria, such as Bifidobacteria and Lactobacilli. Subsequently, they increase the immune reactive myenteric neurons and inhibit the signaling pathway for colonic inflammation.⁴ In contrast, a low-fiber diet can disrupt this process, resulting in dysbiosis, a harmful imbalance in the gut microbiota characterized by reduced bacterial diversity and an overgrowth of harmful microorganisms.^14,15

Meanwhile, insoluble/poorly fermentable fiber irritates gut mucosa, stimulates mucous, and water secretion. An osmotic load is then formed to improve absorption and decrease gastrointestinal transit time, alleviating chronic constipation.¹¹ 

Polyphenols and the Gut Microbiome

Polyphenols are natural metabolites synthesized exclusively by plants. Most polyphenols come from fruits, vegetables, grains, spices, herbs, and teas. Extensive studies on these compounds have highlighted their beneficial roles in promoting antioxidant, anti-inflammatory properties and healthy gut microbiome.¹⁶ Upon consumption, only a small fraction of polyphenols is absorbed in the small intestine.¹⁷ The remaining polyphenols are metabolized by the colon and undergo a transformative process facilitated by gut microbes. This process promotes a shift in the composition of the gut microbiota from harmful species, such as Clostridium spp. and Bacteroides spp., to beneficial bacteria, including Lactobacillus spp. and Bifidobacterium spp.^18,19 These beneficial species produce butyrate and promote anti-inflammation through a reduction in C-reactive protein.¹⁸

Other studies have noted the ability of polyphenols to interact and cause apoptosis of harmful cell membranes via hydrogen bonding with lipid bilayers.²⁰ This antimicrobial property allows polyphenols to inhibit the growth of pathogenic bacteria such as Escherichia coli and Klebsiella pneumoniae while providing protective effects against tumor cells.^17,20 Moreover, the antioxidant and anti-inflammatory effects of polyphenols are likely related to their ability to inhibit pro-inflammatory cytokines such as TNF-alpha and IL-6 and suppress free radical generation by activated neutrophils in the GI lumen.²¹ One of the most well-known polyphenols is curcumin, a natural compound found in turmeric. It has shown potential benefit for IBD patients. One study has demonstrated that daily intake of 2 grams of curcumin, combined with sulfasalazine or mesalamine, was more effective in preventing clinical relapse in patients with ulcerative colitis compared to treatment with sulfasalazine or mesalamine and placebo compound.²²

WFPBDs and Gastrointestinal Disorders 

Inflammatory Bowel Disease 

The Western diet is recognized as a predominant environmental risk factor in IBD.^23,24 A prospective study of long-term dietary fiber intake (median of 24.3g/day, mainly from fruits) demonstrated a reduced risk of Crohn’s disease in individuals who consumed higher quantities of fiber, particularly from fruit sources.²⁴ Likewise, a trial of 92 patients with ulcerative colitis (UC) showed lower clinical relapse rates with the regimen of a WFPBD and induction therapy compared to induction therapy alone.²⁵ 

Another small two-year clinical study examined remission rates in Crohn’s disease (CD) patients, who had initially achieved remission through medical or surgical intervention. They were advised to maintain a semi-vegetarian diet and avoid processed foods. Among the sixteen patients who adhered to the diet, 100% remained in remission after 1 year, and 92% maintained remission after two years. In contrast, remission rates were only 67% at one year and 25% at two years among the six patients who did not follow the diet.²⁶ Finally, the Diet to Induce Remission in Crohn’s Disease (DINE-CD) trial compared MD to the Specific Carbohydrate Diet and found no significant difference in symptomatic remission or inflammation reduction at six weeks between the two diets.²⁷ Thus, data suggest that recommending less restrictive diets, like the MD, would be reasonable for symptom control in IBD. (See Table 3)

Patients with symptomatic or significant fibro-stricturing IBD often have concerns about fiber consumption. For these individuals, the quantity, type, and particle size of fiber are critical to ensure optimal tolerance.²⁸ There is limited evidence on complete fiber restriction in individuals with strictures or active flares. Soluble fibers such as bananas, avocados, and most berries tend to be better tolerated.²⁹ In contrast, insoluble fiber, such as raw kale or apple skin, may need modification to small particle size into blended, mashed, and minced forms.³⁰ As an example, patients can replace apples with applesauce and garbanzo beans with hummus, and blend fruits and vegetables into a smoothie.³¹

Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a common GI disorder involving the gut-brain interaction. The 2021 American College of Gastroenterology (ACG) Clinical Guidelines recommend whole food soluble fiber such as oat bran and barley to treat global symptoms of IBS.³²

As a highlight, controlled trials have demonstrated a low-FODMAP (fermentable oligosaccharides, disaccharides, monosaccharides, and polyols) diet is effective in improving disease-specific quality of life, anxiety, and activity impairment in IBS patients with diarrhea predominance.³³ However, more studies are still needed to evaluate its efficacy in patients with IBS-constipation.³² The low-FODMAP approach involves 3 phases. The first is the elimination phase, during which all high-FODMAP foods are replaced with low-FODMAPs for 4-6 weeks. In the reintroduction phase, patients gradually reintroduce a high-FODMAP food one at a time to learn foods that exacerbate their symptoms. The last phase, personalization, is for patients to customize their diet based on what was learned from the trials of reintroduction. Patients can then retain the well-tolerated high-FODMAP items and limit the portions of those that were not.³³

A WFPBD can be tailored to fit the low-FODMAP with a few strategic adjustments. Low-FODMAP whole grains (e.g., oatmeal, quinoa), fruits (e.g., blueberries, kiwi), and vegetables (e.g., spinach, zucchini) can be included in WFPBD meals throughout the day. Research also shows that certain food processing methods can significantly reduce FODMAP content.³⁴ For example, pickling artichokes, onion, or garlic lowered their FODMAP content by 80-90%, while canning and simmering beans or lentils reduces their oligosaccharide content, increasing options for patients personalizing their WFPBD to a low-FODMAP diet.³⁴ 

Gastroparesis

Gastroparesis (GP) is defined by symptoms suggestive of gastric food retention and objective evidence of delayed gastric emptying without mechanical obstruction.³⁵ Traditionally, the dietary treatment for GP is low-fat and low-fiber meals 4-5 times daily, which came with its limitations such as malnutrition and digestive issues.^35,36 In the recent years, the recommendation has shifted to modifying food consistency to small particle size by blending, mincing, mashing, or chopping.^35,37 A 2018 experimental study explored how the particle size of food influenced gastric emptying. The study compared two solid meals with identical components but different gastric sizes, demonstrating that the smaller particle size diet significantly increased gastric emptying rates.³⁸ Further supporting this, a 2014 randomized controlled trial showed a significant reduction of GP symptoms with use of a small particle size diet.³⁷

For GP patients following a WFPBD, small and frequent meals in small particle size are often recommended to optimize tolerance. Plant foods with large particle sizes, such as food with husks or peels (e.g., pineapple, corn, and cabbage), foods with membranes (e.g., oranges and apples), raw vegetables, seeds, and grains should be cooked, ground, or blended.³⁵

Metabolic Dysfunction-Associated Steatotic Liver Disease

MASLD is a spectrum of diseases, including steatosis, metabolic dysfunction-associated steatohepatitis (MASH), fibrosis, cirrhosis, and MASH-related hepatocellular carcinoma.³⁹  The MASLD term replaced what was formerly known as non-alcoholic fatty liver disease (NAFLD).³⁹ MASLD is thought to be the result of excess triglyceride storage in the liver in addition to at least one cardiometabolic risk factor.⁵ Obesity and diabetes mellitus strongly correlate with the development and progression of MASLD. MASLD/MASH and alcohol-associated liver disease are the two most common indications for liver transplantation among patients without hepatocellular carcinoma in the United States.³⁹ Diet modification has been recommended to prevent and treat MASLD.^5,40

A longitudinal analysis involving 1521 participants conducted from 1998-2011 demonstrated that adherence to a MD or a WFPBD over a six-year period led to reductions in liver fat accumulation and risk of MASLD.⁴¹ Like WFPBD, MD emphasizes minimally processed foods, with key elements including legumes, whole grain, healthy fats (from extra virgin olive oil and fats), vegetables and fruits, while limiting red meat and sweets. MD also encourages the intake of omega-3 fatty acid (EPA and DHA) from fish.²⁷ These healthy components collectively improve insulin resistance, decrease central obesity, and reduce MASLD risk regardless of genetic susceptibility.⁴² 

Celiac Disease

Treatment of celiac disease consists of a lifelong gluten-free diet (GFD). Strict adherence is necessary for improving the health of duodenal mucosa, alleviating symptoms, and normalizing celiac-specific antibodies. Microscopic mucosa recovery occurs six months to three years after initiating the GFD.⁴³ For those following a WFPBD, providers can recommend gluten-free whole grains such as quinoa, millet, sorghum, amaranth, buckwheat, teff, and wild rice.⁴⁴ These grains offer higher protein and fiber contents compared to wheat and are also rich in antioxidants like carotenoids, and essential vitamins and minerals such as iron, calcium, and thiamine.^44-46 Furthermore, gluten-free grains and plant-based protein sources like soy milk, yogurt, tofu and flour from nuts, seeds, or legumes can enhance the nutritional value of WFPBD for individuals with celiac.^44,46 

Gastroesophageal Reflux Disease

Gastroesophageal reflux disease (GERD) is highly prevalent, with a global burden that has increased by 77.53% from 1990 to 2019, making it critical for clinicians and healthcare systems to prioritize preventative and management strategies.⁴⁷ Acid suppression therapy and dietary changes are considered first-line medical therapies.⁴⁸ 

The 2022 ACG Clinical Guidelines suggests that alcohol, smoking, chocolate, peppermint, and high-fat foods reduce lower esophageal sphincter pressure, thereby worsening GERD symptoms. Additionally, coffee, citrus, and spicy food can irritate the esophageal lining, evoking symptoms.⁴⁸ In 2023, Rizzo et al. conducted an online survey of the dietary habits of 4352 Italian individuals and found that those adhering to strict WFPBDs such as a vegan diet, had a reduced incidence of GERD compared to those following animal-based dietary patterns.⁴⁹ WFPBDs provide a higher concentration of fiber and other nutrients such as vitamin C, β-carotene, folate, and vegetable protein, which have preventative and protective effects for GERD as well as esophageal and gastric cancers.⁵⁰ 

Making the Transition to a WFPBD

Patients often express concerns that plant-based meals will be less enjoyable, difficult to prepare, or ingredients may not be as readily available.⁵¹ Tools such as motivational interviewing with open-ended questions and collaborative discussions, can help healthcare providers assess patients’ current attitudes towards food and their motivations to explore the transition to a WFPBD.⁵² Dietitians, upon referral, play a key role in providing primary education and counseling on the benefits of a plant-based diet. They can also offer patient-specific ongoing guidance for WFPBD implementation that respects cultural and financial factors while aiming to treat and manage GI disorders.⁵³

A practical technique to initiate patients on a new diet involves having them practice sectioning a plate into various plant-based food groups for at least one meal a day. For example, using the MD pattern, providers can recommend that half of the plate be filled with vegetables, while the other half is divided between plant-based protein (such as tofu or legumes) and whole grains, with a portion for dessert.⁵⁴ This structure supports managing GI or liver disorders while ensuring a balanced meal. Animal-based protein such as poultry and fish are meant to be consumed in moderation, ideally 2-3 times per week.⁵⁵ Online resources, food pyramids, smartphone apps, and social media can provide patients with culinary support and education.⁵⁶ (See Table 4) Community and patient group cooking classes can also be a valuable tool for recipe demonstration, easing the transition to a WFPBD. (See Table 5)

Nutrient Challenges for WFPBDs

Protein

Protein consumption while on a WFPBD is often of concern, especially in the geriatric population, as they must consume adequate high-quality dietary protein to prevent age-related muscle loss. A meta-analysis using sixty-four studies across Europe, Asia, and North America showed a lower average protein intake in vegetarians and vegans; however, it was well within the recommended intake level.⁵⁷  Older vegetarians should include high-protein foods such as soy products, legumes, nuts, and seeds two to three times daily. In patients with GI disorders such as IBS, plant-based protein sources such as quinoa and certain soy products like tempeh and soy cheese are low-FODMAP and may be better tolerated.⁵⁸

Vitamin and Mineral Deficiencies

Individuals on WFPBD tend to have the same, if not higher, levels of key vitamins and minerals, including vitamin A, vitamin B1, vitamin B12, folate, vitamin C, vitamin E, calcium, magnesium, and phosphorus.⁵⁹ However, strict versions of WFPBD, such as a vegan diet, which exclude animal-based, fish, and dairy products, can put patients at risk for vitamin D and calcium deficiencies. To counter this, patients on vegan WFPBD should ensure they consume calcium fortified plant-based dairy alternatives like fortified almond or soy milk or consider calcium supplements if necessary.⁵⁹ Leafy greens, especially the low-oxalate ones like bok choy or kale have higher calcium bioavailability than cow’s milk, although they contain less total calcium.⁶⁰ Therefore, compared to dairy products, though patients need a larger quantity to match the daily required calcium, leafy green can be a more efficient source for absorption.⁶⁰ Amaranth, adzuki beans, navy beans, quinoa, and firm tofu are plant-based sources that also provide good sources of calcium and zinc.^44,46 

Another major concern is vitamin B12, which is primarily found in animal products. Hence, WFPBD patients should incorporate plant-based B12 sources such as fortified grains like breakfast cereals, or plant-based dairy. Supplementation of B12 is an important consideration for patients with a strict vegan WFPBD.⁶¹ 

Iron consumption is another concern regarding the adoption of a WFPBD. There are two primary forms of iron in food: heme iron (in animal products, well-absorbed 13-35%) and non-heme iron (in plant and animal products, lower absorption rate 2-20%). In addition, legumes and nuts contain phytate, one of the most potent iron absorption inhibitors.⁶² Vegetarian men are generally iron-sufficient in studies. Iron insufficiency is detected more frequently in premenopausal women. Iron study monitoring should, therefore, be considered in this population.⁶²

Conclusion

WFPBDs have seen a surge in popularity over the past decade, primarily driven by increasing health awareness among patients and a growing body of scientific evidence that supports the role of WFPBDs in disease prevention and management. For patients with GI disorders, adopting the WFPBD can offer numerous health benefits, including GI symptom reduction, promoting diversity and composition of the gut microbiome, and modulating inflammation. Dietary recommendations must be patient-centered and tailored to meet individual needs to ensure sustainability and improve long-term outcomes. Achieving these outcomes is most effective when approached by a multidisciplinary team, including primary care providers, gastroenterologists, and dietitians. 

References

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