Digestion breaks food into absorbable pieces and keeps the gut barrier working. It needs energy, good blood flow, thyroid-supported acid and enzyme work, and a calm stress chemistry. A cold, hypothyroid, seed-oil gut leaks and ferments.

Barrier and fuel

[edit]

Intestinal cells turn over fast and burn fuel continuously. Low thyroid, low sugar, and high PUFA raise permeability and endotoxin entry. Cooked simple food is easier than raw bulk and industrial fiber stacks.[1]

See Endotoxin, Leaky gut, Thyroid, Carrot.

Practice

[edit]

Warm meals, adequate salt, carbohydrate with protein, and lower seed oils. Raw carrot salad is a mechanical tool for some; it is not a universal rule. See Roadmap/04 - Gut health for the full practical guide.

See Milk, Sugar, Roadmap, Harm reduction.

Attention and the cephalic phase

[edit]

Thinking about food starts digestion before the first bite. In healthy adults, 30 minutes of talking about appetizing food raised gastric acid output from 4 to 13 mmol/h, about 66% of the response to sham feeding, while talking about current events or sports did not raise it significantly.[2] Screen distraction can also cut saliva during a meal: in 26 adults chewing mashed potato while watching a video clip, salivary flow and mucin fell and chewing lasted longer.[3] For intake and fullness data on screen meals, see Body composition#Distracted eating.

The food should be appetizing so that it stimulates the whole system. Pavlov was one of the pioneers in studying digestion scientifically. He showed that the knowledge of the food and the sensory quality of the food completely dominates the digestive process.

— Ray Peat[4]

Relaxing and moving around reduces nervous tension, which increases secretions. You can see it even in saliva. When you're very anxious, your mouth tends to go dry because the shift in the nervous system shuts off secretions starting in the mouth and affecting all the way down.

— Ray Peat[5]

Thyroid and motility

[edit]

Thyroid hormone acts on gut smooth muscle. In 30 women with primary hypothyroidism versus 10 healthy controls, mean esophageal transit was longer (52.6 vs 24.3 s) and gastric emptying was slower (49.1 vs 30.4 min).[6] A 2024 review of thyroid disorders and gastrointestinal motility groups constipation with hypothyroidism and diarrhea with hyperthyroidism across gut segments.[7] Slowed small-bowel clearance is one reason SIBO is common after overt hypothyroidism; see SIBO and Hypothyroidism.

Excess thyroid can push the other way. Hyperthyroidism often presents with more frequent stools or diarrhea, though gastric emptying itself can be delayed, rapid, or normal in individual patients.[7]

Common conditions

[edit]

Stomach acid (HCl) activates pepsin and partly sterilizes food; low acid can impair protein digestion and mineral absorption, though chronic antacid use has its own tradeoffs, and ulcers/GERD need proper diagnosis before acid-boosting experiments. GERD (reflux of stomach contents into the esophagus) is driven by low stomach acid from chronic acid blockers, low thyroid, and large late meals; acid suppression is a short-term tool with long-term costs; meal timing, thyroid support, and less liquid fat at night are the practical levers.

Among people aged 60–99, fundic atrophic gastritis (serum pepsinogen I/II ratio <2.9) was found in 31.5% in one elderly cohort, and prevalence rose with age, a histology pattern that lowers acid output.[8] In 206 healthy adults aged 18–98, pentagastrin-stimulated acid was about 30% lower at ages 65–98 than in younger groups; after adjusting for oxyntic histology and H. pylori, age itself had no independent effect on acid output.[9] In 248 independently living adults aged ≥65, basal gastric content was still acidic (pH <3.5) in 84%.[10] Population surveys do not consistently show GERD symptom prevalence rising with age; clinical series more often find worse reflux oesophagitis severity among older GERD patients.[11]

It's usually associated with disturbed muscle action of the whole stomach and intestine and gall bladder. High estrogen, serotonin, prostaglandins, low thyroid, inflammation, and bacterial overgrowth in the small intestine are often involved. Stimulating the intestine with a daily raw carrot often helps.

— Ray Peat[12]

H. pylori is a common stomach bacterium linked to ulcers and gastritis; a meta-analysis of 184 studies across 62 countries estimated roughly 4.4 billion people were infected worldwide in 2015, ranging from 18.9% prevalence in Switzerland to 87.7% in Nigeria. Diagnosis and treatment are medical, and chronic antacid-only strategies miss the organism entirely.[13]

See also

[edit]

References

[edit]
  1. ↑ Ray Peat, "Fats, functions and malfunctions," raypeat.com.
  2. ↑ Feldman M, Richardson CT. "Role of thought, sight, smell, and taste of food in the cephalic phase of gastric acid secretion in humans," Gastroenterology. 1986;90(2):428-433. PMID 3940915.
  3. ↑ Khramova DS, Vityazev FV, Zueva NV, et al. "Video clip observation during chewing influences intraoral manipulations, bolus properties, and sensory perception of texture," J Texture Stud. 2026;57(1):e70063. PMID 41562341.
  4. ↑ Ray Peat, "Digestion", Politics and Science (recorded 26 Apr 2010)
  5. ↑ Ray Peat, "How to Fix Your Digestion & Poop", Get Fit with Jodelle (10 Sep 2019)
  6. ↑ Yaylali O, Kirac S, Yilmaz M, Akin F, Yuksel D. "Does hypothyroidism affect gastrointestinal motility?," Gastroenterol Res Pract. 2009;2009:529802. doi:10.1155/2009/529802. PMID 20224642. Cross-sectional scintigraphy.
  7. ↑ 7.0 7.1 Xu GM, Hu MX, Li SY, Ran X, Zhang H, Ding XF. "Thyroid disorders and gastrointestinal dysmotility: an old association," Front Physiol. 2024;15:1389113. doi:10.3389/fphys.2024.1389113. PMID 38803365. Review.
  8. ↑ Krasinski SD, Russell RM, Samloff IM, et al. "Fundic atrophic gastritis in an elderly population. Effect on hemoglobin and several serum nutritional indicators," J Am Geriatr Soc. 1986;34(11):800-806. PMID 3771980.
  9. ↑ Feldman M, Cryer B, McArthur KE, et al. "Effects of aging and gastritis on gastric acid and pepsin secretion in humans: a prospective study," Gastroenterology. 1996;110(4):1043-1052. PMID 8612992.
  10. ↑ Hurwitz A, Brady DA, Schaal SE, et al. "Gastric acidity in older adults," JAMA. 1997;278(8):659-662. PMID 9272898.
  11. ↑ Becher A, Dent J. "Systematic review: ageing and gastro-oesophageal reflux disease symptoms, oesophageal function and reflux oesophagitis," Aliment Pharmacol Ther. 2011;33(4):442-454. PMID 21138458.
  12. ↑ Ephemera: Emails & Exchanges from the Archives (2012–2024), "Digestive System: GERD Causes," on the causes of GERD
  13. ↑ Hooi JKY, Lai WY, Ng WK, et al. "Global Prevalence of Helicobacter pylori Infection: Systematic Review and Meta-Analysis," Gastroenterology. 2017;153(2):420-429.