The Exam Room by the Physicians Committee Gut Health: The Truth About Low-Carb Diets | Dr. Will Bulsiewicz
Oct 9, 2025
Dr. Will Bulsiewicz, a leading gastroenterologist and author of "Fiber Fueled," dives into the complexities of gut health and low-carb diets. He reveals how low-carb eating can disrupt microbiome diversity and impact digestion, stressing the importance of fiber for producing short-chain fatty acids essential for colon health. Will offers practical tips to protect the microbiome while reducing carbs and compares low-carb diets to Mediterranean and plant-based approaches. He also addresses common issues like bloating and incomplete evacuation with insightful solutions.
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Food Shapes Your Microbiome
- Diet composition selects microbes: fiber feeds butyrate producers, fat selects bile‑tolerant microbes.
- High saturated fat and low fiber favor bile‑loving microbes linked to inflammation and colorectal risk.
Fiber, Not Just Water, Moves Stool
- To prevent constipation, prioritize fiber because it accelerates gut motility via microbial fermentation.
- Drinking extra water without fiber won't move stool through the colon effectively.
Choose Low‑Starch Plants Intentionally
- You can meet fiber needs on a low‑carb plan by prioritizing nonstarchy plant foods and being selective.
- But restricting fruits, legumes, and starchy plants reduces plant diversity and harms microbiome diversity.