Vegan Diarrhea: What's Normal And What's Not?

Diarrhea is a common issue for people transitioning to a vegan diet. It can be caused by a sudden increase in fiber intake, which pulls water into the gastrointestinal tract and leads to loose stools. Other causes include zinc deficiency, food allergies or intolerances, and conditions like Small Intestine Bacterial Overgrowth (SIBO), Irritable Bowel Syndrome (IBS), and Inflammatory Bowel Disease (IBD). While it usually lasts only a few days, chronic diarrhea can be a sign of more serious problems and requires medical attention.

High-fibre foods

If you are experiencing loose stools, it is recommended to reduce your fibre intake and then gradually add it back in. You may also want to keep a food journal to track your fibre intake and identify any problem foods.

Some lower-fibre vegan foods that you can eat while adjusting your fibre intake include:

• Cooked potatoes or sweet potatoes without skins
• Juiced vegetables (most fibre is removed)
• Melons (cantaloupe, honeydew, watermelon)
• Acorn squash (no seeds)

It is important to note that cooking vegetables thoroughly can also help reduce digestive issues.

In addition to reducing fibre intake, you can also try a digestive enzyme supplement, such as Vegan Bean-Zyme, to help with the breakdown of high-fibre foods.

If reducing fibre intake and using digestive enzymes do not help with your diarrhoea, it is recommended to consult a physician to rule out any other potential causes, such as zinc deficiency, food allergy or intolerance, or irritable bowel syndrome (IBS).

Food allergies or intolerances

Food allergies and intolerances are two distinct medical conditions with overlapping symptoms, including diarrhea. However, it is important to understand the differences between them.

Food Allergy

Food allergy, also known as hypersensitivity, involves an abnormal immune reaction to a typically harmless substance. On the first exposure to the offending food, the body's immune system produces antibodies called immunoglobin E (IgE), specific to that allergen. During subsequent exposures, the allergen binds to these IgE antibodies, triggering a more rapid and aggressive immune response. This intense reaction can lead to oral inflammation, canker sores, cramps, nausea, diarrhea, gas, hives, and possibly respiratory distress.

Symptoms of a food allergy can appear immediately after consuming the offending food or may take several hours to manifest, ranging from mild to severe. The most severe reaction, anaphylactic shock, can be life-threatening and typically occurs within an hour of exposure. It is characterised by symptoms such as wheezing, difficulty breathing, swelling of the throat and tongue, vomiting, and fainting.

Food allergies affect approximately 5-6% of young children and 3-4% of adults in Western countries. Allergies tend to run in families and are more prevalent in children, with some outgrowing their food allergies over time. Common allergies in children include eggs, milk, wheat, soy, and peanuts. In adults, allergies to peanuts, tree nuts, fish, and shellfish are more common.

Food Intolerance

Food intolerance, on the other hand, does not involve the body's immune system. It is an adverse reaction to a food item, typically originating in the gastrointestinal system, due to a limited ability or inability to digest or absorb certain foods or their components. Symptoms of food intolerance usually begin about half an hour after consumption but may take up to 48 hours to appear. These symptoms include nausea, bloating, abdominal pain, and diarrhea.

Lactose intolerance and non-celiac gluten intolerance are two examples of food intolerances. Up to 70% of the world's population experiences lactose intolerance, where the body does not produce sufficient lactase, an enzyme necessary for digesting the sugar lactose found in milk and dairy products. In non-celiac gluten intolerance, also known as "wheat intolerance," consuming gluten can lead to gastrointestinal symptoms such as bloating, abdominal pain, and dissatisfaction with stool consistency, despite there being no evidence of small intestine damage.

Managing Food Allergies and Intolerances

Whether you are dealing with a food allergy or intolerance, it is crucial to identify and avoid trigger foods. Keeping a food journal can be immensely helpful in pinpointing specific problem foods. Working with a healthcare professional or a registered dietitian nutritionist is advisable to ensure your diet remains well-rounded and meets your nutritional needs.

While a vegan diet does not inherently cause diarrhea, a sudden shift to a plant-based diet can lead to digestive issues like diarrhea, gas, and bloating due to a significant increase in fiber intake. Temporarily reducing fiber intake and gradually reintroducing it can help ease these symptoms. Additionally, ensuring adequate zinc intake is important, as zinc deficiency is a potential cause of diarrhea, and vegans tend to have lower zinc levels than meat-eaters.

Zinc deficiency

Diarrhea is a common issue for people switching to a vegan diet, and there are many potential causes. It is often caused by a sudden increase in fiber intake, but zinc deficiency could also be a factor.

Vegans tend to meet the RDA for zinc, but due to zinc being harder to absorb from plant foods, some may need more than the RDA. Zinc is important for fighting infections, speeding up chemical reactions, and supporting the immune system. A zinc deficiency can lead to impaired immune function, loss of appetite, growth retardation, hair loss, eye and skin lesions, weight loss, taste abnormalities, and lethargy.

Vegan sources of zinc include legumes, nuts, seeds, oatmeal, beans, wholemeal bread, and lentils. Fermented soy foods such as tempeh and miso also enhance zinc absorption.

Other Potential Causes of Diarrhea

In addition to zinc deficiency, other possible causes of diarrhea in vegans include food allergies or intolerances, Small Intestine Bacterial Overgrowth (SIBO), Irritable Bowel Syndrome (IBS), and Inflammatory Bowel Disease (IBD). Diarrhea can also be caused by infections, such as a parasite, or food poisoning.

To identify the cause of diarrhea, it is recommended to keep a food journal and consult a physician if the issue persists.

Small Intestine Bacterial Overgrowth (SIBO)

Small Intestinal Bacterial Overgrowth (SIBO) is an abnormal increase in the overall bacterial population in the small intestine, particularly types of bacteria not commonly found in that part of the digestive tract. This condition is sometimes called blind loop syndrome. SIBO is often a complication of abdominal surgery but can also result from structural problems and some diseases.

SIBO occurs when circumstances such as surgery or disease slow the passage of food and waste products in the digestive tract, creating a breeding ground for bacteria. The excess bacteria often cause diarrhea and may cause weight loss and malnutrition.

The small intestine is the longest section of the digestive tract, measuring about 20 feet (6.1 meters). Food mixes with digestive juices here, and nutrients are absorbed into the bloodstream. Unlike the large intestine (colon), the small intestine normally has relatively few bacteria due to the rapid flow of contents and the presence of bile. However, in SIBO, stagnant food in the bypassed small intestine becomes an ideal breeding ground for bacteria. The bacteria may produce toxins and interfere with the absorption of nutrients. The breakdown products following bacterial digestion of food can also trigger diarrhea.

Factors that increase the risk of SIBO include:

• Gastric surgery for obesity or ulcers
• A structural defect in the small intestine
• An injury to the small intestine
• An abnormal passageway (fistula) between two segments of the bowel
• Crohn's disease, intestinal lymphoma, or scleroderma involving the small intestine
• A history of radiation therapy to the abdomen
• Diverticulosis of the small intestine
• Adhesions caused by previous abdominal surgery

SIBO can lead to escalating problems, including:

• Poor absorption of fats, carbohydrates, and proteins
• Vitamin deficiency, particularly fat-soluble vitamins A, D, E, and K, as well as vitamin B-12
• Weakened bones (osteoporosis)
• Kidney stones

The diagnosis of SIBO is controversial, and there is no consensus on the gold standard for diagnosing the condition. Two tests are commonly employed: bacterial culture and breath tests. The bacterial culture method involves performing anaerobic and aerobic colony counts of small bowel luminal contents, but this method is cumbersome and time-consuming. Breath testing is now the predominant method to evaluate patients as it is simple, safe, and non-invasive.

The treatment goals for SIBO are threefold:

• Correct the underlying cause, which may include dietary, surgical, or medical therapies
• Provide nutritional support, if necessary, especially for those with weight loss or vitamin and mineral deficiencies
• Treat the overgrowth with antibiotic therapy to reduce or eliminate the bacterial overload and reverse mucosal inflammation

Irritable Bowel Syndrome (IBS)

There is no clear solution for those with IBS, and a vegan diet may not be the answer. Many plant-based foods can irritate the gastrointestinal (GI) system and cause or worsen IBS symptoms. However, a vegan diet may be worth trying if you suffer from IBS.

IBS is often linked to the foods eaten, with two-thirds of people with IBS attributing their symptoms to the intake of certain foods. Adopting a diet that eliminates foods considered difficult to digest, such as the low FODMAP diet, may be a better way to control IBS symptoms than following a strictly vegan diet.

The low FODMAP diet does not exclude meat and dairy products, but it can be adapted to align with the principles of veganism. The low FODMAP diet measures foods by their ability to break down in the small intestine. Foods low in FODMAPs cause fewer GI reactions because the body breaks them down before they reach the colon.

Food that remains intact by the time it is in the colon requires extra water and causes more gas. These factors can produce uncomfortable IBS symptoms that can last for hours or days after eating a triggering food.

Veganism may encourage you to be more mindful of your diet and prompt you to plan well-rounded meals. It also promotes the consumption of plant-based foods, which contain a wide variety of nutritional benefits. However, many plant-based foods can worsen IBS symptoms, causing bloating, constipation, or diarrhea.

A vegan diet that avoids triggering foods could also leave out essential vitamins and minerals, such as protein, iron, and calcium. It is best to work with a doctor or registered dietitian nutritionist to be sure your diet supports your overall health.

• Eat breakfast, lunch, and dinner, as well as snacks as needed, according to a regular schedule.
• Make meal plans that pack a nutritional punch, and adhere to your diet.
• Watch your food portions and avoid huge meals and long gaps between mealtimes.
• Eat slowly and chew your food carefully before swallowing.
• Exercise at least 150 minutes per week if engaging in moderate activity.
• Drink 6 to 12 cups of water per day.
• Avoid processed foods.
• Consume sugary or spicy foods in moderation, as they could potentially trigger your IBS.
• Keep a journal of your symptoms and note if you suspect any foods or beverages triggered your IBS.

If you have IBS and experience uncomfortable symptoms, consider working with a registered dietitian nutritionist or a doctor. A professional can help you plan a well-rounded diet that takes into account your nutritional needs.

Adopting a low FODMAP diet may require a period of time where you eliminate certain foods and slowly add potentially triggering items back over time. A healthcare professional can ensure you do this safely.

Changing your diet may help reduce IBS symptoms. However, a vegan diet could worsen your IBS symptoms if you consume foods that stress your GI system. The low FODMAP diet may reduce IBS symptoms by eliminating hard-to-digest foods from your meals. You can try the low FODMAP diet whether you are a vegan or not.

Talk to a medical or nutrition professional for the healthiest guidance on managing IBS through your diet.

Frequently asked questions