Gut

The gut (intestinal tract) digests food, absorbs nutrients, and, in mainstream medicine, hosts a large microbiome. In Ray Peat's writing, the gut is also the main entry route for bacterial Endotoxin (LPS) when barrier function or motility fails, making intestinal health central to systemic Inflammation, hormone balance, and mitochondrial function. Germ-free animals, raised with no gut bacteria at all, show what's at stake: they eat more calories than conventionally colonized animals yet stay leaner and don't develop the same anxiety, which Peat took as evidence that the bacteria themselves, not the food, are the source of the damage (see Endotoxin).

Endotoxin and the liver

The liver is the major source of the acute phase proteins, and it is constantly burdened by toxins absorbed from the bowel; disinfection of the bowel is known to accelerate recovery from stress.

— Ray Peat

When endotoxin enters blood, it impairs cytochrome oxidase and synergizes with stored PUFA, Peat's explanation for why gut irritation can produce thyroid suppression, estrogen elevation, and stress-hormone cascades.

Animal data: rats on high-PUFA diets show greater endotoxin-induced vascular leak than EFA-deficient rats. Pigs fed linoleic or fish oil had worse lung injury with LPS than pigs on palmitic acid.

Serotonin and the gut

~90% of body serotonin is produced in the gut (see Serotonin). Peat ties fermentable fibers, bacterial toxins, and slow transit to increased serotonin and endotoxin absorption, overlapping with Histamine and mast-cell activation in allergy and stress.

Intestinal sensation and consciousness

The intestine is powerfully related to consciousness, affecting not only our moods but even the way we feel ourselves in relation to our surrounding space. For example, motion sickness demonstrates the way our sense of movement in space is attached to our stomach and intestine - if we are on a ship, looking at things inside the ship that aren't moving in relation to our body, the real motion sensed by our body conflicts with what our eyes are seeing, and we interpret the inner movement as nausea, but if we just glance at the horizon, the inner sensation of motion suddenly is interpreted accurately as our body moving through space, and the nausea disappears. When there are actual forces being applied to our intestine from the inside, created by bacterial growth, gas, and toxins, our consciousness tries to make sense of it, and the result can be dizziness, a sense of disorientation or falling, so that our sense of location can seem ambiguous or confused.

— Ray Peat

Intestinal gas, bacterial growth, and toxins can contribute to dizziness and spatial disorientation. Looking at the horizon can resolve the visual-motion conflict of motion sickness; reducing intestinal disturbance addresses internally generated signals.

Gut microbiome and psychiatric disease

Bacterial products from the gut reach the brain through the pathways above, and mendelian-randomization and case-control studies extend Peat's endotoxin/stress framework to depression, bipolar disorder, and schizophrenia.

A systematic review of 44 observational studies (2,510 psychiatric cases, 2,407 controls) found no consistent difference in the number of gut bacteria between psychiatric patients and controls, but consistent shifts in which bacteria were present: depleted short-chain-fatty-acid producers, excess lactic-acid-producing bacteria, and altered taxa tied to glutamate and GABA metabolism, across major depressive disorder, bipolar disorder, and schizophrenia. A parallel review of the human bipolar disorder and depression literature reported the same pattern, reduced beneficial bacteria and increased pathogenic taxa correlating with mood-episode severity.

Mendelian-randomization studies, which use genetic variants to test causal direction rather than mere correlation, show gut microbiome composition and schizophrenia risk are bidirectionally causal: nine bacterial taxa raise risk and six lower it, acting through immune, tryptophan-metabolism, vagal, and short-chain-fatty-acid pathways. Genetic susceptibility to major depression raises irritable bowel syndrome risk in a one-directional analysis. A five-disorder mediation analysis found depression's effect on irritable bowel syndrome was partly mediated by reduced acetate and by insomnia, and schizophrenia's effect was over half mediated by elevated β-hydroxybutyrate, a ketone body.

A case-control study of 132 schizophrenia patients found altered bacterial tyrosine biosynthesis correlating with cognitive dysfunction; tyrosine is the amino-acid precursor for both thyroid hormone and dopamine, tying a gut-bacterial finding directly to Peat's thyroid/dopamine framework. Reviews of the field caution that psychotropic medication itself substantially alters gut microbial composition, confounding cause and effect in cross-sectional psychiatric-microbiome studies.

See Schizophrenia, Depression.

Substances for gut healing

Mastic gum

Mastic gum, a resin from Pistacia lentiscus, has demonstrated ulcer-healing effects. A double-blind placebo-controlled trial (n=38, endoscopically proven duodenal ulcer) found that 1 g/day of mastic for 14 days achieved endoscopic healing in 70% of patients vs 22% with placebo (p<0.01). Symptomatic relief occurred in 80% of the mastic group vs 50% in controls. Mastic is also used traditionally for SIBO and upper gut disinfection; its antibacterial properties against H. pylori are documented.

NSAIDs and gut permeability

NSAIDs (ibuprofen, naproxen, aspirin at high doses) increase intestinal permeability within hours of a single dose, not just after prolonged use. A review of the human data found that all conventional NSAIDs increase intestinal permeability within 24 hours of ingestion, equally evident with short-term and long-term use. This drug-induced leakiness can allow endotoxin and other luminal contents to enter the bloodstream, compounding the metabolic burden on the liver and amplifying the endotoxin/inflammation cycle that Peat described as central to chronic disease.

Intestinal barrier

The intestinal barrier is the mucosa and tight junctions that keep gut contents out of blood; mainstream gastroenterology calls increased permeability "leaky gut."

Cellular energy metabolism is the basis for maintaining the barrier functions. Energy depletion causes the endothelial cells lining blood vessels to become excessively permeable.

— Ray Peat

When this barrier fails, endotoxin enters portal and systemic blood, triggering cytokines and stress hormones. See Leaky gut, Harm reduction.

Tissue memory (extracellular matrix)

The gut lining renews itself completely every three to five days, the fastest turnover rate in the body, but the scaffold those cells sit on does not reset the same way. In mouse colitis models, an acute injury reshapes the intestinal extracellular matrix (ECM) through accumulation of collagen XVIII, and this altered "modECM" persists for over a year after the original inflammation resolves, trapping signaling molecules and steering intestinal stem cells toward a wound-associated, pro-inflammatory state instead of normal regeneration. Silencing collagen XVIII prevented the ECM damage from becoming irreversible and blocked the chronic disease state entirely, identifying it as a specific, targetable driver of persistent gut dysfunction rather than a passive scar. This gives a structural, non-bacterial mechanism for why gut symptoms can outlast the endotoxin/serotonin trigger that started them, complementing rather than replacing the mechanisms above. See IBS.

Peat on reducing gut inflammation

Asked how to reduce deep gut inflammation, Peat said: "The main thing is to reduce the fermentable grains, nuts, vegetables, starches, and use the foods that are easily, quickly digested and absorbed. Milk, meat, eggs, and sweet fruit such as oranges are quickly digested and so they don't support so much bacterial growth. And there are some fibrous foods that are also antiseptic." He listed raw carrot, bamboo shoots, and cooked mushrooms as fibrous foods with antiseptic properties that can be kept in the diet.

Peat diagnostic orientation to gut health

Peat organized GI health around four interacting factors:

1. Gut transit time - Slow transit allows bacterial overgrowth, endotoxin absorption, and estrogen recirculation; fast transit indicates adequate thyroid and digestive function.
2. Stomach acid - Low acid (common in hypothyroidism) impairs protein digestion and mineral absorption, allowing bacterial survival into the small intestine.
3. Bile - Adequate bile flow is needed for fat digestion and endotoxin clearance; bile stagnation increases LPS absorption.
4. Diet - Avoid foods and irritants that cannot be digested; add insoluble fibers (raw carrot, bamboo shoots, cooked mushrooms), antimicrobial foods (coconut oil), and bile stimulants.

When these four are in balance, the small intestine remains relatively sterile and endotoxin load stays low. When any one fails, the others tend to follow, producing the characteristic endotoxin/serotonin/estrogen cascade.

Practical approaches discussed

Peat and FunctionalPS discuss:

• Raw carrot salad (fiber + vinegar/oil) to reduce endotoxin reabsorption and estrogen recirculation
• Easily digested foods; caution with fermentable Starch and resistant fibers in sensitive people
• Coffee, Gelatin/broth, Aspirin, and (context-specific) antibiotics
• Supporting Thyroid and Liver clearance

See Roadmap/04 - Gut health for the full practical protocol.

Oatmeal and potatoes do provide fiber, but they are good food for bacteria, and bacterial endotoxin is usually the basic problem causing hormone imbalance, by being a chronic burden for the liver, keeping it from storing enough sugar to process thyroid and the other hormones effectively.

— Ray Peat

See Intestinal barrier, Leaky gut, Harm reduction.

See also

• Endotoxin
• Serotonin
• Starch
• Liver
• Inflammation
• Schizophrenia
• Depression