Low Fermentation Eating vs. Fast Tract Diet

A Comprehensive Clinical Guide for Practitioners and Patients

Yoon Hang Kim, MD, MPH

Introduction

Small Intestinal Bacterial Overgrowth (SIBO) affects an estimated 70 million Americans and is increasingly recognized as a significant contributor to irritable bowel syndrome (IBS) symptoms.¹ Up to 80% of individuals diagnosed with IBS may have underlying SIBO contributing to their symptoms.² Dietary intervention has emerged as a cornerstone of SIBO management, working alongside antimicrobial therapy to reduce symptoms and prevent relapse.

This article examines two prominent dietary approaches: the Low Fermentation Eating (LFE) protocol developed by Drs. Mark Pimentel and Ali Rezaie at Cedars-Sinai Medical Center, and the Fast Tract Diet created by Dr. Norm Robillard, founder of the Digestive Health Institute. Understanding the principles, food allowances, and practical applications of each diet enables clinicians to better guide patients toward sustainable symptom management.

Understanding the Pathophysiology

SIBO is characterized by excessive bacterial populations in the small intestine. In healthy individuals, the small bowel maintains relatively low bacterial counts through several protective mechanisms, most notably the migrating motor complex (MMC)—a cyclical pattern of electrical activity that produces "housekeeper waves" approximately every 90 minutes during fasting states.³

Research at Cedars-Sinai has demonstrated that food poisoning from pathogens such as Salmonella, Campylobacter, E. coli, and Shigella can cause nerve damage to the small intestine through the release of cytolethal distending toxin B (CdtB). This damage reduces MMC frequency, leading to bacterial accumulation and overgrowth.⁴

Both dietary approaches discussed here aim to limit fermentable substrates that feed bacterial populations while supporting the gut's natural cleansing mechanisms.

Low Fermentation Eating (Cedars-Sinai Diet)

Overview and Principles

The Low Fermentation Eating (LFE) protocol was developed by Dr. Mark Pimentel and Dr. Ali Rezaie based on decades of microbiome and motility research at Cedars-Sinai Medical Center.⁵ Unlike more restrictive elimination diets, LFE is designed for long-term sustainability while effectively managing SIBO symptoms.

Core Principles:

1. Meal Spacing: Space meals 4-5 hours apart with no snacking between meals. This allows the MMC to activate and clear debris from the small intestine.
2. Evening Fasting: Avoid eating close to bedtime to maximize overnight cleansing waves.
3. Carbohydrate Selection: Choose easily digestible carbohydrates that humans absorb efficiently, leaving minimal residue for bacterial fermentation.
4. Portion Control: Limit carbohydrates to one serving per meal.

Foods Allowed on Low Fermentation Eating

Proteins (Unrestricted)

All meats, poultry, fish, seafood, eggs, and organ meats are permitted. Avoid breaded, processed, or marinated meats containing high-fructose corn syrup (HFCS).

Carbohydrates (One Serving Per Meal)

• White rice (jasmine, sushi, paella varieties)
• White or wheat bread, sourdough, rye bread (NOT whole wheat or multigrain)
• Pasta (white flour or gluten-free from white rice, corn, or almond flour)
• Potatoes and sweet potatoes
• Polenta, quinoa, couscous
• Refined cereals (Rice Krispies, cornflakes, Original Special K)
• Corn or flour tortillas

Vegetables

• Root vegetables: potatoes, carrots, beets, turnips, parsnips, yams
• Fruiting vegetables: tomatoes, peppers, cucumbers, zucchini, squash, eggplant
• Alliums: onion, garlic, shallots, leeks (cooked, in small amounts)
• Greens: arugula, kale, spinach (best tolerated); butter lettuce and romaine may be less tolerated initially
• Others: green beans, mushrooms, pumpkin, corn, olives, fennel root

Fruits (One Serving at a Time)

Berries (strawberries, blueberries, raspberries, blackberries), citrus fruits, grapes, melons (limit to one cup), stone fruits (peaches, nectarines, plums, cherries), kiwi, pineapple, mango, papaya, pomegranate.

Dairy

• Lactose-free milk and products, Lactaid milk
• Hard aged cheeses (Parmesan, cheddar, Manchego, Gruyère, Asiago)
• Ghee, butter (small amounts)
• Non-dairy alternatives (almond, rice, coconut, oat, hemp milks)

Nuts, Seeds, and Fats

All nuts (almonds, cashews, walnuts, pecans, pistachios, macadamia, pine nuts) and most seeds (pumpkin, sesame, sunflower, hemp) are permitted. Avoid chia seeds and flax seeds. All cooking oils are allowed.

Sweeteners

Table sugar (cane, turbinado, caster), maple syrup, honey (small amounts), dark chocolate. Note: Table sugar is absorbed in the upper GI tract before bacteria can ferment it.

Foods to Avoid on Low Fermentation Eating

Artificial Sweeteners and Sugar Alcohols

Sucralose (Splenda), stevia, sorbitol, xylitol, mannitol, lactitol, erythritol, saccharin, agave, monk fruit. These non-digestible sugars provide 100% of their calories to bacteria.

High-Fiber Carbohydrates

• Whole wheat and multigrain breads
• Brown rice, oatmeal, bran, barley, bulgur, farro, millet
• Whole wheat pasta, soba noodles

Cruciferous and Gas-Producing Vegetables

Broccoli, cauliflower, cabbage, Brussels sprouts, asparagus, artichokes, bok choy, bean sprouts, radish.

Legumes

ALL beans (black, kidney, pinto, navy, lima, cannellini, fava, chickpeas), lentils, hummus, and soy products (tofu, tempeh, edamame).

Fruits

Apples, pears, bananas, dried fruits (all), dates, figs, prunes, raisins, fruit juice concentrates.

Dairy

Regular milk, yogurt (including lactose-free yogurt due to live cultures), soft unaged cheeses, cream cheese, soy milk.

Fast Tract Diet

Overview and Principles

The Fast Tract Diet was developed by Norman Robillard, PhD, a microbiologist and founder of the Digestive Health Institute. This approach was presented at Digestive Disease Week in 2013 as a drug- and antibiotic-free strategy for managing SIBO and related conditions.⁶

Core Principle: The Fast Tract Diet uses a quantitative "Fermentation Potential" (FP) point system rather than simple food lists. Each food is assigned an FP value based on a formula that considers net carbohydrates, glycemic index, fiber content, and sugar alcohol content.

The FP Formula:

FP = Net Carbs × (100 - GI)/100 + Fiber + Sugar Alcohols

The lower the FP value, the lower the symptom potential. Daily FP goals typically range from 20-45 grams depending on symptom severity.

Five Categories of Fermentable Carbohydrates

The Fast Tract Diet is unique in that it restricts ALL five types of fermentable carbohydrates:

5. Lactose – milk sugar found in dairy products
6. Fructose – fruit sugar, especially in excess of glucose
7. Resistant Starch – starch that resists digestion (undercooked pasta, cooled/reheated starches, legumes)
8. Fiber – both soluble and insoluble fiber
9. Sugar Alcohols – sorbitol, xylitol, mannitol, erythritol, etc.

Low FP Foods (Allowed)

Proteins and Fats (Zero FP)

All meats, fish, poultry, eggs, seafood, and fats/oils have zero FP and are unrestricted.

Carbohydrates (Low FP Options)

• Jasmine rice, sushi rice, sticky rice (high glycemic index = low FP)
• White bread, French bread
• Potatoes (well-cooked, served hot)
• Rice pasta (lower FP than wheat pasta)

Vegetables (Low FP)

Leafy greens (spinach, arugula, kale), zucchini, summer squash, green beans (small portions), tomatoes, peppers, cucumbers.

Fruits (Low FP, Small Portions)

Strawberries, blueberries, raspberries, cantaloupe, citrus fruits (lemon, lime).

Dairy

Hard aged cheeses, cream, butter, lactose-free products. Lactase enzyme supplementation may be used.

Sweeteners

Dextrose (pure glucose), rice syrup, regular sugar (small amounts).

High FP Foods (Avoid)

High Resistant Starch

• Brown rice
• Al dente pasta (undercooked starches have higher resistant starch)
• Cooled and reheated potatoes or rice (retrogradation increases resistant starch)
• Beans and legumes

High Fiber

Whole grains, bran, beans, lentils, raw vegetables in large quantities.

High Fructose

Honey (large amounts), apples, pears, watermelon, agave, high-fructose corn syrup.

Lactose and Sugar Alcohols

Regular milk, ice cream, soft cheeses, sorbitol, xylitol, mannitol, erythritol, and "sugar-free" products.

Comparison of Dietary Approaches

Clinical Considerations

Patient Selection

Low Fermentation Eating may be more appropriate for patients who prefer straightforward food lists without calculations, those with mild to moderate SIBO, vegetarians or patients with other dietary restrictions requiring flexibility, and those seeking a long-term sustainable approach.

Fast Tract Diet may benefit patients who prefer quantitative tracking and data-driven approaches, those with severe or treatment-resistant SIBO, patients with concurrent acid reflux or LPR (laryngopharyngeal reflux), and individuals comfortable using mobile applications for food tracking.

Integration with Treatment

Neither diet alone is curative for SIBO. Dietary modification is most effective when combined with antimicrobial therapy (rifaximin, herbal antimicrobials) and prokinetic support to restore MMC function.⁷ Dr. Pimentel notes that these diets are not meant as permanent eating patterns but rather as 3-month trials to assess symptom response, after which gradual reintroduction may be attempted.⁸

Nutritional Monitoring

Prolonged restrictive diets can lead to nutritional deficiencies. Studies on similar low-fermentation approaches show potential decreases in retinol, thiamin, riboflavin, and calcium with extended use.⁹ Periodic nutritional assessment is recommended for patients on long-term dietary restriction.

Conclusion

Both Low Fermentation Eating and the Fast Tract Diet offer evidence-informed approaches to managing SIBO symptoms through carbohydrate modification. Low Fermentation Eating provides simplicity and sustainability with its qualitative food lists and strong emphasis on meal spacing, making it accessible to a broad patient population. The Fast Tract Diet offers precision through its quantitative FP system, appealing to patients who prefer data-driven dietary management.

The optimal choice depends on individual patient preferences, symptom severity, and lifestyle factors. Both approaches share core principles: limiting fermentable carbohydrates, avoiding sugar alcohols and artificial sweeteners, and allowing the gut's natural cleansing mechanisms to function. When integrated with appropriate antimicrobial therapy and prokinetic support, these dietary strategies can significantly improve quality of life for patients with SIBO and related functional gastrointestinal disorders.

About the Author

Dr. Yoon Hang Kim MD is a board-certified preventive medicine physician with over 20 years of clinical experience. He completed his integrative medicine fellowship at the University of Arizona under Dr. Andrew Weil and holds certifications in preventive medicine, medical acupuncture, and integrative/holistic medicine.

Through his telemedicine practice, Dr. Kim specializes in using LDN (Low Dose Naltrexone) to treat autoimmune conditions, chronic pain, integrative oncology, and complex conditions, including fibromyalgia, chronic fatigue, MCAS, and mold toxicity. He is the author of three books and more than 20 articles, and has helped establish integrative medicine programs at institutions nationwide.

Consulting, Professional Education, Speaking/Writing Engagement: www.yoonhangkim.com

99-Person Membership-Based Telemedicine: www.directintegrativecare.com

LDN Advocacy and Education: www.LDNSupportgroup.com

References

1. Good LFE LLC. Low Fermentation Eating Guide. goodlfe.com. Accessed January 2026.

2. Rupa Health. The Cedars-Sinai Diet: A Comprehensive Guide for IBS and SIBO Patients. January 2025.

3. Pimentel M, Rezaie A. The Microbiome Connection. Agate Publishing; 2022.

4. Pimentel M, et al. Cedars-Sinai Medical Center SIBO research. siboinfo.com.

5. Houser K, Berlin R. The Good LFE Cookbook. Good LFE LLC; 2022.

6. Robillard N. Fast Tract Digestion IBS. Digestive Health Institute; 2013. Presented at Digestive Disease Week 2013.

7. Rezaie A, et al. Nutritional Approach to Small Intestinal Bacterial Overgrowth: A Narrative Review. PMC. 2024.

8. Cedars-Sinai Newsroom. Irritable Bowel Syndrome: Mark Pimentel, MD. November 2025.

9. The IBS Dietitian. The Low Fermentation Diet for SIBO. theibsdietitian.com. September 2024.

10. Digestive Health Institute. Fast Tract Diet. digestivehealthinstitute.org. Accessed January 2026.

Disclaimer: This article is for educational purposes only and does not constitute medical advice. Patients should consult with qualified healthcare providers before initiating any dietary intervention for SIBO or other medical conditions.