Dr. Axe Wire · Food, herbs & supplements · gut

Whole Nut Cells May Reach The Colon Intact In Small Crossover Study

A small crossover study found undigested nut fat shows up in stool, hinting that whole nut cells travel further into the gut than expected.

By Dr. Axe Editorial Team · October 25, 2026 · 1 source · Watch

Photo: Pexels

A small study published October 19, 2026 in Food & Function found that eating 30 grams of mixed nuts a day for three weeks left more undigested fat in stool than three weeks without nuts, with microscopic nut particles visible only during the nut period.

15adults, crossover design

30gmixed nuts daily

3weeks on, 3 weeks off

Researchers tracked 15 healthy adults through a crossover design: three weeks eating 30 grams a day of mixed almonds, macadamias and pistachios, and three weeks eating no nuts, with everyone completing both periods. Stool samples collected after the nut period showed a statistically significant increase in total fecal lipid content compared with the no-nut period, along with visible lipid-containing nut particles under the microscope that were absent during nut abstinence. Stool pH, dry matter, ash content, short-chain fatty acid levels and ammonium levels did not change in a consistent way between the two periods. Genetic sequencing of the gut microbes, the community of microorganisms living in the gut, showed large differences from person to person, with only modest shifts tied to the nut period itself. Computer-predicted functional analysis pointed to differences in fat-processing pathways between the two periods.

Nut fat sits inside a plant cell wall, a tough outer layer that digestive enzymes in the small intestine cannot easily break down. When that wall survives digestion, the fat inside it can travel further down the gut, where it may become available to bacteria living in the colon instead of being absorbed earlier. This reframes some nut fat as a potential fuel source for gut microbes rather than something the body absorbs entirely upstream.

Microscopic examination of faecal samples revealed lipid-containing nut particles following nut consumption, which were not observed during the nut abstinence

Study authorsFood & Function, 2026

This was a small, short pilot in 15 people over six weeks total, with no comparison group eating a different fat source. The gut microbiota changes were modest and highly variable between individuals, so no specific bacterial species can be credited with a consistent response.

Dr. Axe’s Take

Undigested fat reaching the colon here is not a digestion failure. Nut cell walls are built sturdy, and that structure appears to protect some of the fat until it reaches bacteria further down the gut. I recommend whole raw or lightly roasted nuts over nut butters or flours, since grinding destroys the cell-wall structure this effect seems to depend on. Almonds, macadamias and pistachios together bring fiber and healthy fats that can feed different microbes. Keep it to a small handful, about the 30 grams used here, since nuts are calorie-dense. Choose whole nuts as your go-to form rather than processed nut products.

— Dr. Axe

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Story summary

Who: 15 healthy adults, unrestricted diets, crossover design
Design: Crossover intervention: 3 weeks of 30g daily mixed nuts vs 3 weeks of nut abstinence
Dose: 30g per day of mixed almonds, macadamias and pistachios
Primary result: Significantly higher total fecal lipid content after nuts than after abstinence; visible nut-cell lipid particles seen only after nuts
Secondary: No significant change in fecal pH, dry matter, ash, short-chain fatty acids or ammonium; modest, highly individual gut microbiota shifts; predicted lipid-metabolism pathway differences
Funding / conflicts: Funder listed in the journal record: University of Queensland. Conflicts not reported in the abstract.
Date: Oct 19, 2026