Pistachio nuts, walnuts and almonds: energy release during digestion
What it found
In lab tests using nuts chewed by seven healthy adults, pistachios, walnuts and almonds each released about 77 to 78 percent of their fat after simulated intestinal digestion, with no significant difference between the three nuts.
What they found
Studies in people
Chewing effort
People needed more chews to swallow almonds than walnuts or pistachios. The average was 35 chews for almonds, 30 for walnuts and 30 for pistachios.
Animal and lab studies
Particle size after digestion
After intestinal digestion, walnut particles were larger (396 µm) than pistachio (347 µm) and almond (301 µm) particles. Almonds gave the smallest particles.
Fat release
About 77 percent of the fat in walnuts, 76 percent in almonds and 78 percent in pistachios was released after the intestinal phase. There was no significant difference between the nuts.
Cell wall rupture
More walnut cells were ruptured after intestinal digestion compared with pistachio cells. But the amount of fat released did not match the number of ruptured cells.
Internal structure
In lab images, walnut and almond fat was stored as one dense clump, while pistachio fat was in smaller scattered droplets. Pistachio cells were also more loosely packed.
What the authors conclude
“These findings indicate walnuts, almonds and pistachios yield similar, but limited amounts of energy (~80 %) during digestion, likely through varied mechanisms.”
Also in their conclusions
- They conclude that walnuts, almonds and pistachios yield similar, but limited amounts of energy (about 80 percent) during digestion, likely through varied mechanisms.
- They say that for nuts including walnuts, the limited fat release may stem in part from the ready breakdown of their proteins at low pH, allowing fat droplets to clump together and resist digestion.
- They suggest that the structural integrity of cells may not be the main factor affecting fat release in walnuts and other nuts, and that the internal structure of the nut content matters greatly.
How it was done
The authors wanted to understand why energy extraction from nuts is lower than expected from their physical hardness, and whether chewing and digestion break down walnuts, almonds and pistachios differently.
Seven healthy adults chewed 5 g portions of walnuts, almonds and pistachios. The chewed samples were then put through a lab model of stomach and intestinal digestion, and particle size, cell wall damage and fat release were measured.
What it can’t tell you
- This was a lab study using chewed nut samples, not a study of what happens inside the human body.
- The number of people who chewed the nuts was small (seven), so chewing results may vary between individuals.
- The study cannot show how gut bacteria affect fat that reaches the colon, or whether these findings apply to other nut types or processing methods.
Who paid
- Authors work at
- Purdue University, USA
The paper
- Title
- Energy extraction from nuts: walnuts, almonds and pistachios
- Type
- Study
- Evidence
- Studies in people · animals · lab
- Summarised from
- Full text
- Licence
- CC BY. Words in quotation marks are the authors’; the rest is our summary.
- Cite
- McArthur BM, Mattes RD (2020). Energy extraction from nuts: walnuts, almonds and pistachios. The British journal of nutrition. doi:10.1017/S0007114519002630Free full textPubMed 31619299DOI
Summary written 30 Sep 2026. Check it against the paper before it changes what you eat. How we summarise papers · Report an error