Dr. Will Bulsiewicz's Guide to Identifying and Managing Food Intolerances

Food intolerances can significantly impact your quality of life, causing uncomfortable symptoms that range from bloating and gas to headaches and fatigue. Unlike food allergies, which trigger immediate immune responses, intolerances can be trickier to identify and often go undiagnosed for years. Dr. Will Bulsiewicz, a renowned gastroenterologist and bestselling author of "Fiber Fueled," has developed comprehensive approaches to help identify and manage these challenging dietary issues.

With his science-backed methods and patient-centered philosophy, Dr. B (as his patients affectionately call him) offers practical strategies that can help you navigate the complex world of food intolerances without unnecessary dietary restrictions. This guide explores his methodology and provides actionable steps to help you identify problematic foods and develop a personalized plan for optimal gut health.

Understanding Food Intolerances: The Basics

Food intolerances differ fundamentally from food allergies. While allergies involve the immune system and can cause potentially life-threatening reactions, intolerances typically affect the digestive system and result in uncomfortable but not dangerous symptoms. According to Dr. Bulsiewicz, many people mistakenly self-diagnose food allergies when they're actually experiencing intolerances.

"The confusion between allergies and intolerances leads many people to unnecessarily restrict their diets," Dr. Bulsiewicz explains. "This can actually harm gut health in the long run by reducing dietary diversity and potentially limiting intake of beneficial plant foods."

Common Types of Food Intolerances

Several types of food intolerances are particularly common. Lactose intolerance affects approximately 65% of the global population, making it difficult to digest dairy products due to insufficient lactase enzyme. Gluten sensitivity (distinct from celiac disease) can cause digestive distress when consuming wheat, barley, and rye. FODMAP intolerances involve difficulty digesting certain fermentable carbohydrates found in many fruits, vegetables, grains, and dairy products.

Dr. Bulsiewicz also highlights histamine intolerance, which occurs when the body cannot properly break down histamine in foods like aged cheese, fermented foods, and certain vegetables. Sulfite sensitivity can cause reactions to preservatives in wine, dried fruits, and processed foods. Understanding these distinctions helps target the appropriate testing and management strategies.

The Gut-Symptom Connection

One of Dr. Bulsiewicz's key insights is the connection between gut health and seemingly unrelated symptoms. "Many people don't realize that skin issues, brain fog, joint pain, and even mood changes can stem from food intolerances affecting gut function," he notes. This gut-symptom connection explains why food intolerances can manifest in such diverse ways, making them particularly challenging to identify without systematic approaches.

The gut microbiome—the ecosystem of bacteria living in our digestive tract—plays a crucial role in how we process foods. Imbalances in this ecosystem can contribute to or exacerbate food intolerances. Dr. Bulsiewicz emphasizes that addressing the microbiome is often key to resolving food sensitivities in the long term.

Identifying Your Food Intolerances

Dr. Bulsiewicz recommends a methodical approach to identifying food intolerances, beginning with careful observation and documentation. Random elimination of foods based on internet searches or fad diets can lead to nutritional deficiencies and unnecessary restrictions. Instead, he advocates for a structured process that preserves dietary diversity while pinpointing problematic foods.

The Food-Symptom Journal Method

The foundation of Dr. Bulsiewicz's approach is the food-symptom journal—a detailed record of everything you eat and any symptoms you experience. "Most people think they know what they're eating, but our memories are notoriously unreliable," he explains. "A detailed food journal reveals patterns we might otherwise miss."

For optimal results, record not just what you eat but when, how much, and under what circumstances. Note symptoms with timing, intensity, and duration. After 2-3 weeks of consistent journaling, review your records looking for correlations between specific foods and symptom flare-ups. This method often reveals surprising connections and helps narrow down potential trigger foods for further investigation.

Elimination and Reintroduction Protocol

Once you've identified potential trigger foods through journaling, Dr. Bulsiewicz recommends a structured elimination and reintroduction protocol. This involves completely removing suspected trigger foods for 2-4 weeks—long enough for symptoms to resolve if the food was indeed causing problems. The elimination phase should be followed by careful, systematic reintroduction of one food at a time, with 2-3 days between each reintroduction to observe any returning symptoms.

"The reintroduction phase is where the real learning happens," says Dr. Bulsiewicz. "It's not just about identifying problematic foods but also understanding your threshold—how much of a food you can tolerate before symptoms appear." This nuanced approach prevents unnecessary long-term restrictions and provides valuable information about your unique digestive capacity.

Professional Testing Options

While food journals and elimination diets form the cornerstone of identification, Dr. Bulsiewicz acknowledges the value of certain professional tests in specific situations. Hydrogen breath tests can help diagnose lactose intolerance, fructose malabsorption, and small intestinal bacterial overgrowth (SIBO). Blood tests can identify celiac disease and true food allergies. Stool tests may reveal digestive enzyme deficiencies or microbiome imbalances that contribute to food sensitivities.

However, Dr. Bulsiewicz cautions against unvalidated food sensitivity tests that claim to identify dozens of intolerances from a single blood sample. "Many of these tests haven't been scientifically validated and can lead to unnecessary food restrictions," he warns. "Always discuss testing options with a healthcare provider knowledgeable about digestive health."

Managing Food Intolerances Effectively

Once you've identified your food intolerances, the next step is developing a management strategy that minimizes symptoms while maintaining nutritional adequacy and quality of life. Dr. Bulsiewicz emphasizes that management doesn't always mean complete elimination—many people can enjoy small amounts of trigger foods or find ways to make them more digestible.

Threshold Management Strategies

For many food intolerances, the issue isn't binary but dose-dependent. "Most people with lactose intolerance can handle small amounts of dairy, especially fermented options like yogurt or aged cheese," Dr. Bulsiewicz explains. Understanding your personal threshold allows for more flexibility in your diet while keeping symptoms under control.

Practical threshold management might include spacing out consumption of trigger foods rather than consuming them all at once, combining trigger foods with other foods that slow digestion, or using specific preparation methods that reduce problematic compounds. For example, soaking beans before cooking can reduce their FODMAP content, making them more tolerable for sensitive individuals.

Enzyme Supplements and Other Aids

Digestive enzyme supplements can be valuable tools for managing certain food intolerances. Lactase supplements help break down lactose in dairy products, while alpha-galactosidase aids in digesting complex carbohydrates in beans and certain vegetables. Histamine intolerance may be managed with diamine oxidase (DAO) supplements that help break down histamine in foods.

Dr. Bulsiewicz recommends using these supplements strategically rather than relying on them for every meal. "Enzymes can be helpful for occasional restaurant meals or special occasions when you want to enjoy a trigger food," he advises. "But they shouldn't replace the work of identifying your optimal diet and improving your gut health."

Rebuilding Tolerance Through Gut Health

Perhaps the most revolutionary aspect of Dr. Bulsiewicz's approach is his focus on rebuilding tolerance rather than accepting permanent restrictions. "Many food intolerances aren't fixed conditions but reflections of current gut health," he explains. "By systematically improving gut function and microbiome diversity, many people can expand their dietary tolerance over time."

The Microbiome Approach

The gut microbiome plays a crucial role in how we digest and respond to foods. Dr. Bulsiewicz recommends gradually increasing dietary diversity to cultivate a more robust microbiome. "Each different plant food you eat feeds different beneficial bacteria," he notes. "Aim for 30 different plant foods weekly—including vegetables, fruits, whole grains, legumes, nuts, and seeds—to support microbiome diversity."

Fermented foods like yogurt, kimchi, sauerkraut, and kefir introduce beneficial bacteria directly into the gut ecosystem. Regular consumption of these foods has been shown to reduce inflammatory markers and improve digestive function, potentially helping to overcome food sensitivities over time.

Gradual Reintroduction and Desensitization

For many food intolerances, especially those involving FODMAPs or histamine, gradual reintroduction can help build tolerance. Dr. Bulsiewicz recommends starting with tiny amounts of previously problematic foods—well below your symptom threshold—and very slowly increasing over weeks or months. This approach, similar to immunotherapy for allergies, helps train your digestive system and microbiome to handle these foods more effectively.

"Patience is essential in this process," Dr. Bulsiewicz cautions. "Rebuilding tolerance takes time and consistency. But many of my patients who thought certain foods were permanently off-limits have successfully reintroduced them through this methodical approach."

When to Seek Professional Help

While self-management works for many food intolerances, Dr. Bulsiewicz emphasizes that certain situations warrant professional guidance. Persistent or severe symptoms, significant weight loss, blood in stool, or symptoms that disrupt daily life should prompt medical evaluation. These could indicate conditions beyond food intolerance, such as inflammatory bowel disease, celiac disease, or other digestive disorders requiring specific treatment.

Working with a registered dietitian who specializes in digestive health can provide personalized guidance through elimination diets and reintroduction protocols. Gastroenterologists can offer specialized testing and rule out more serious conditions. Functional medicine practitioners often take a holistic approach to identifying underlying factors contributing to food intolerances.

"The right professional support can make the journey much smoother," says Dr. Bulsiewicz. "Look for providers who understand the complexity of food intolerances and focus on expanding your diet rather than just restricting it."

Conclusion

Dr. Will Bulsiewicz's approach to food intolerances offers hope and practical guidance for the millions struggling with digestive symptoms. By combining careful observation, systematic elimination and reintroduction, and strategies to improve overall gut health, most people can identify their trigger foods and develop personalized management strategies that maintain quality of life.

The journey to understanding your food intolerances requires patience and persistence, but the rewards—reduced symptoms, improved nutrition, and greater dietary freedom—make the effort worthwhile. With Dr. Bulsiewicz's science-backed methods, you can move beyond random restrictions toward a truly personalized approach to food and digestive health.