1. THE TWO MAIN PERSPECTIVES
Dr. Sabine Hazan — Gastroenterologist, ProgenaBiome
Dr. Hazan focuses on Bifidobacteria, often called “Bif”. She has found that low or absent Bifidobacteria is common in many chronic conditions. Her research shows certain nutrients, especially vitamin C, can raise Bif levels. She emphasises testing and being careful with commercial probiotics.
Dr. William Davis — Cardiologist, author of Wheat Belly and Super Gut
Dr. Davis focuses on SIBO, or Small Intestinal Bacterial Overgrowth. He argues that fecal-type bacteria have moved up into the small intestine in a large percentage of people. This can contribute to endotoxemia, where bacterial toxins leak into the blood, and may drive many modern health problems. His main tool is a homemade high-count fermented product he calls “SIBO Yogurt”.
These two views are complementary: Hazan looks mainly at missing beneficial bacteria in the colon; Davis looks mainly at unwanted bacteria living in the wrong place, the small intestine.
2. SYMPTOMS AND CONDITIONS LINKED TO MICROBIOME PROBLEMS
Both doctors connect microbiome disruption to a wide range of issues. This list is organised by common patient complaints.
Digestive symptoms
- Bloating, gas, abdominal pain or discomfort
- Diarrhea, constipation, or alternating bowel habits
- Food intolerances, especially to onions, garlic, beans, wheat, dairy, nightshades, FODMAPs, histamine foods, fructose
- Feeling worse after fiber, prebiotics, or many commercial probiotics
- Fat malabsorption, including greasy or floating stools
Conditions often linked include IBS, IBD such as Crohn’s or ulcerative colitis, SIBO, recurrent C. difficile, and leaky gut symptoms.
Metabolic and weight issues
- Difficulty losing weight, especially abdominal fat
- Insulin resistance, prediabetes, type 2 diabetes
- Fatty liver
- High triglycerides or small dense LDL particles
Energy, mood and brain
- Fatigue and brain fog
- Anxiety, depression or mood swings
- Sleep problems
Skin
- Rosacea, psoriasis, eczema, seborrheic dermatitis and acne
Women’s health and hormonal symptoms
- Perimenopause or menopause symptoms such as hot flashes, mood changes, sleep disruption, joint or back pain
- PMS or irregular cycles, sometimes reported as improving when SIBO or low Bif is addressed
Musculoskeletal and pain
- Fibromyalgia
- Restless legs
- Back pain or joint pain that does not fully respond to usual treatments
Immune and inflammatory
- Autoimmune conditions
- Frequent infections or slow recovery
- Long COVID or post-viral symptoms
- Allergies or heightened food sensitivities
Other
- Obesity
- Neurodegenerative concerns, with Davis citing higher rates of SIBO in Parkinson’s and Alzheimer’s studies
- Skin aging and loss of muscle, which Davis links partly to microbial changes
Key idea from both doctors: many of these problems may share a common root — either missing protective bacteria, especially Bifidobacteria, or overgrowth of the wrong bacteria in the small intestine. Improving the microbiome may improve several symptoms at once.
3. WHAT TO AVOID — ACCORDING TO THESE DOCTORS
Shared recommendations
- Unnecessary antibiotics, and antibiotic residues in some meats
- Excess alcohol. One glass of wine may be neutral; several is harmful.
- Ultra-processed foods, refined sugars and industrial seed oils
- Long-term stomach acid blockers, PPIs, when not clearly needed
From Dr. Hazan
- Low-quality or “dead” probiotics. Many commercial products do not contain the live Bif they claim.
- Continuing whatever is still killing Bif, including antibiotics, certain additives or poor diet
- Assuming yogurt or kefir automatically contains live Bifidobacteria. Her lab found many labelled products did not.
From Dr. William Davis
- Wheat and most grains, the core of the Wheat Belly approach
- Sugars and high-fructose foods that feed unwanted microbes
- Long-term strict low-FODMAP diets without addressing underlying SIBO, as these can further reduce microbial diversity
- Relying only on commercial multi-strain probiotics that do not colonise the small intestine or produce bacteriocins
4. WHAT TO ADD / INTERVENTIONS
Dr. Sabine Hazan’s main tools
Her published study showed it significantly raises Bifidobacterium levels. Effects may be temporary and quality matters.
Supports the microbiome and Bif. Test levels and dose appropriately with a clinician.
Increases Bifidobacterium and reduces Proteobacteria in her data. Used in IBS/IBD patients.
Support the overall gut “factory”. Choose verified sources; many commercial yogurts fail her tests.
Know your baseline Bif levels. Her lab, ProgenaBiome, specialises in this.
Hazan stresses: stop what is destroying Bif first, then nourish what remains. True engraftment, or permanent colonisation, is difficult.
Dr. William Davis’s main tools
Contains L. reuteri, L. gasseri and B. subtilis at very high counts. These species can live in the small intestine and produce natural antibiotics, called bacteriocins, that push back SIBO microbes. Davis recommends a minimum of four weeks daily, then intermittent use to help prevent relapse.
Maps where microbes are fermenting: small intestine versus colon. Davis advises stopping L. reuteri for about two weeks before retesting.
Removes major drivers of dysbiosis and insulin resistance. This is the foundation of his earlier work.
Vitamin D, magnesium, omega-3s and iodine may support the gut lining and reduce insulin resistance.
Once SIBO is improved, carefully reintroduce non-grain fibres. These can worsen symptoms if SIBO is still active.
SIBO Yogurt overview
Davis chooses three microbes that colonise the small intestine and produce bacteriocins. He ferments them for a prolonged time, around 36 hours, with prebiotic fibre to reach hundreds of billions of bacteria per serving. People typically eat ¼–½ cup per day.
5. PRACTICAL PATIENT SCENARIOS
“I have IBS with bloating and food intolerances.”
- Both doctors would consider this classic for SIBO or low Bif.
- Davis: test with breath hydrogen, then use SIBO Yogurt.
- Hazan: check Bif levels; consider vitamin C, bovine IgG and careful fermented foods.
“I’m in perimenopause with back pain, mood swings, and weight gain around the middle.”
- Davis links abdominal fat, insulin resistance and systemic inflammation partly to SIBO and endotoxemia.
- Addressing SIBO, removing grains and sugars, and supporting vitamin D and magnesium is his typical path.
- Hazan would look for low Bif as a contributor to immune and metabolic issues.
“I react badly to fibre, onions, garlic, or most probiotics.”
- Davis: this is often a sign of hydrogen-positive SIBO. Eradicating SIBO frequently restores tolerance.
- Hazan: this may indicate depleted Bif or other dysbiosis; testing helps guide next steps.
“I have fatigue, brain fog, or skin issues such as rosacea.”
Both view these as possible downstream effects of endotoxemia or missing protective bacteria.
6. KEY STUDIES & DIRECT LINKS
Dr. Sabine Hazan — peer-reviewed papers
- Vitamin C improves gut Bifidobacteria in humans, Future Microbiology, 2022. DOI: 10.2217/fmb-2022-0209. PubMed: https://pubmed.ncbi.nlm.nih.gov/36475828/.
- Lost microbes of COVID-19: Bifidobacterium, Faecalibacterium depletion…, BMJ Open Gastroenterology, 2022. DOI: 10.1136/bmjgast-2022-000871. PDF: BMJ Open Gastroenterology full PDF.
- Gut Microbiome Alterations Following Oral Serum-Derived Bovine Immunoglobulin…, Cureus, 2024. DOI: 10.7759/cureus.75884. PubMed: https://pubmed.ncbi.nlm.nih.gov/39822451/. PMC: https://pmc.ncbi.nlm.nih.gov/articles/PMC11737532/.
- Bifidobacterium Against COVID-19: A Mother and Her Newborn’s Gut Microbiome, case report, Cureus, 2024. DOI: 10.7759/cureus.60038.
Dr. William Davis
Davis’s SIBO Yogurt work is primarily described in his book Super Gut (2022) and on his website/blog rather than in traditional peer-reviewed trials of the yogurt itself. He draws on the broader SIBO literature, especially work by Dr. Mark Pimentel, and clinical observations with the AIRE device.
- Book: Super Gut: A Four-Week Plan to Reprogram Your Microbiome, Restore Health, and Lose Weight
- Website / blog: drdavisinfinitehealth.com
Supporting broader literature
- SIBO is well documented in IBS, fibromyalgia and other conditions in the gastroenterology literature.
- Bifidobacteria decline with age, antibiotics and various diseases is widely reported.
7. HOW TO USE THIS INFORMATION AS A PATIENT
- Recognise patterns. If you have several items from the symptom list, especially food intolerances, bloating, metabolic issues or mood issues, microbiome disruption may be worth investigating.
- Test rather than guess. Breath testing for SIBO, Davis’s focus, or stool sequencing for Bifidobacteria, Hazan’s focus, can give clearer direction.
- Start with foundations. Clean diet, removing wheat/grains/sugars where appropriate, optimising vitamin D, magnesium, sleep and stress.
- Layer targeted tools. Vitamin C / bovine IgG in Hazan’s style, or SIBO Yogurt in Davis’s style, depending on what testing shows.
- Be patient and monitor. Microbiome changes take weeks to months. Track symptoms and retest when possible.
- Work with a clinician. This is especially important if you have IBD, significant weight loss, blood in stool, severe pain, fever, persistent vomiting, pregnancy, immune compromise or other red-flag symptoms.
8. Quick Reference Table
Last updated: August 2026. Sources are the published papers of Dr. Sabine Hazan and the clinical teachings/books of Dr. William Davis. Always verify the latest versions of papers via PubMed or the journal sites.