Ray Peat on Fiber

Short answer: Ray Peat separated fiber into two kinds. Fermentable fiber feeds bacteria and raises endotoxin and serotonin. Fiber that resists fermentation and carries antibacterial compounds, like raw carrot and bamboo shoots, protects the bowel.

What Ray Peat wrote about fiber

He wrote that fermentable fibers, including pectins and fructooligosaccharides, support the formation of bacterial toxins. In animals they can cause anxiety and aggression, and in horses some fibers raise the serotonin in the blood. Source: Serotonin: Effects in disease, aging and inflammation

Grains, beans and other seeds contain fermentable fibers that can irritate the intestine. He advised avoiding those, along with starches that resist quick digestion. Source: Serotonin: Effects in disease, aging and inflammation

The fibers he liked are raw carrots and bamboo shoots, because they contain antibacterial chemicals and lower endotoxin and serotonin. Source: Serotonin: Effects in disease, aging and inflammation, Rosacea, inflammation, and aging: The inefficiency of stress

He linked fiber to estrogen. The liver sends estrogen out with the bile, and the right fiber helps it leave the body. That is where the carrot came in. Source: Natural Estrogens

He defended cascara, a traditional laxative. He thought the idea of laxative abuse was misleading and pointed to research on emodin, its active compound, showing anticancer and antiviral activity. Source: Cascara, energy, cancer and the FDA's laxative abuse

He warned about carrageenan, a seaweed gum used as a thickener. He wrote that it has caused colitis in humans, enters even a healthy gut, and is common in milk products, so people blame the milk. Source: Food-junk and some mystery ailments: Fatigue, Alzheimer's, Colitis, Immunodeficiency

On constipation he was skeptical of the advice to drink more water, because water is absorbed high in the intestine and mainly dilutes the blood. Source: Water: swelling, tension, pain, fatigue, aging

What he suggested in practice

• Avoid fermentable fiber and starch that resists digestion.
• Use a raw carrot or bamboo shoots as the daily fiber.
• Activated charcoal can bind endotoxin, but only now and then, because it also binds vitamins.

Where he wrote about it

This topic comes up in 35 of the articles on his site. These are the most relevant ones:

• Food-junk and some mystery ailments: Fatigue, Alzheimer's, Colitis, Immunodeficiency · original on raypeat.com ↗
• Cascara, energy, cancer and the FDA's laxative abuse · original on raypeat.com ↗
• Natural Estrogens · original on raypeat.com ↗
• Autonomic systems · original on raypeat.com ↗
• Stem cells, cell culture, and culture: Issues in regeneration · original on raypeat.com ↗
• Cataracts: water, energy, light, and aging · original on raypeat.com ↗
• Serotonin: Effects in disease, aging and inflammation · original on raypeat.com ↗
• Multiple Sclerosis and other hormone related brain syndromes · original on raypeat.com ↗

My take

This matches what I see. Soluble fiber and resistant starch slow digestion and feed Gram-negative bacteria. I get my fiber from carrots and mushrooms.

Quick answers

Did Ray Peat say fiber is bad?

Not all fiber. He warned against fermentable fibers such as pectin and those in grains and beans, and recommended fibers that resist fermentation and have antibacterial effects, such as raw carrot and bamboo shoots.

What fiber did Ray Peat recommend?

Raw carrots and bamboo shoots. He also mentions activated charcoal for occasional use.