Walnuts: two years of daily walnuts did nothing for memory

The Walnuts and Healthy Aging trial gave 708 healthy older people 30 to 60 grams of walnuts a day for two years and measured their thinking with a full neuropsychological battery. The global cognition score did not differ from the control group. That is the strongest test anyone has run of the claim walnuts are best known for, and it is negative. A difference did appear in one of the two study sites in an analysis done after the fact, which is the weakest kind of result and is how the trial usually gets reported. Compliance was good and the nuts were well tolerated, so this is not a failed experiment. It is an answer.

The numbers, per 100 g

What a real portion looks like

• People eat less at later meals after nuts, and their resting metabolism does not measurably change. — 28 articles from 27 studies with 1121 adults, across almonds, Brazil nuts, cashews, chestnuts, hazelnuts, peanuts, pistachios, walnuts and mixed nuts (n = 1121) Evidence A source
  Energy compensation after nut loads ranged from -280.5% to +176.4% and varied by form (whole or chopped) and by whether nuts were eaten alone or within a meal; resting energy expenditure rose by a non-significant 28.6 kcal a day (95% CI -10.7 to 67.8)

What your body absorbs

• Nuts deliver fewer calories than their label says, because some of the fat never leaves the cell walls. — 21 studies, both in vitro and in adults over 18 (n = 21 studies) Evidence C source
  Metabolizable energy was consistently lower than Atwater factors predict for almonds, cashews, hazelnuts, pistachios, walnuts and peanuts; measured values included 22.6 kJ/g for pistachios and 18.5 kJ/g for raw almonds; energy released rose with processing (butter above roasted above raw) and with grinding (flour above chopped above whole)

What it does to your health

• Walnuts lowered apolipoprotein B and left blood pressure alone. — 25 randomised controlled trials with 26 intervention arms and 2155 patients (n = 2155) Evidence A source
  Apolipoprotein B fell by 0.06 g/L (95% CI -0.10 to -0.01, p = 0.002); no effect on apolipoprotein A1 (-0.50, -1.34 to 0.33), systolic pressure (-1.20, -4.02 to 1.61) or diastolic pressure (-0.44, -2.55 to 1.67)

Safety, limits and interactions

• In chronic kidney disease the few studies there are found walnuts lowered LDL without upsetting electrolytes. — 4 studies (three trials and one cohort) with 1270 patients with chronic kidney disease, out of 2521 records screened (n = 1270) Evidence C source
  Walnuts lowered LDL cholesterol and blood pressure with no risk to electrolyte balance; Brazil nuts and baru almond oil affected oxidative stress and inflammation markers; total nut consumption was associated with lower all-cause mortality

What people believe that the data does not support

• Walnuts hold one of the few food claims Europe has ever authorised, and the snapshot does not say how many you need. — — Evidence E source
  Five register entries name walnuts, of which one is Authorised and four Non-authorised; the authorised wording is that walnuts contribute to the improvement of the elasticity of blood vessels

What is still unknown

• Two years of eating walnuts every day did nothing for the thinking of healthy older people. — 708 free-living adults aged 63 to 79, 68% women, cognitively healthy at entry; 636 completed (n = 708 randomised, 636 completed) Evidence B source
  No between-group difference in the global cognition composite (change -0.072 with walnuts against -0.086 in controls, p = 0.491); a post hoc analysis limited to the Barcelona cohort showed a difference (p = 0.040) and MRI showed greater network recruitment during a working memory task in controls

The bottom line

What walnuts do measurably is small and real: across 25 trials in 2155 people they lowered apolipoprotein B, a count of the particles that drive artery disease, and left blood pressure alone. The more interesting finding is about calories. Nuts consistently deliver less energy than their labels claim, because some of the fat stays locked inside cell walls, and how much escapes depends on the form: flour gives up more than chopped, chopped more than whole, nut butter more than roasted, roasted more than raw. Whole raw nuts are the stingiest version of themselves. Walnuts also hold one of the few food claims Europe has ever authorised, about the elasticity of blood vessels, and the snapshot we hold does not say how many you need to eat for it.

Sources

1. wal-dr-02 · systematic review and meta-analysis
   The meta-analyses identified a nonsignificant increase in REE associated with nut consumption (weighted mean difference: 28.6 kcal/d; 95% CI: -10.7, 67.8 kcal/d).
   Adv Nutr, 2023 · checked 2026-09-22
2. wal-dr-01 · systematic review with narrative synthesis
   The ME of nuts was consistently lower than that predicted by Atwater factors for investigated nut types (almonds, cashews, hazelnuts, pistachios, walnuts, and peanuts).
   Adv Nutr, 2023 · checked 2026-09-22
3. wal-dr-03 · systematic review and meta-analysis of randomised controlled trials
   Walnut significantly decreased ApoB (WMD = -0.06; 95% CI: -0.10, -0.01, p = 0.002), but did not affect ApoA1 (WMD = -0.50; 95% CI: -1.34, 0.33, p = 0.249), systolic blood pressure (SBP) (WMD = -1.20; 95% CI: -4.02, 1.61, p = 0.401) and diastolic blood pressure (DBP) (WMD = -0.44; 95% CI: -2.55, 1.67, p = 0.682).
   Endocrinol Diabetes Metab, 2026 · checked 2026-09-22
4. wal-dr-05 · systematic review
   Overall the findings indicate positive effects of Brazil nuts and baru almond oil on oxidative stress and inflammation markers, while walnuts reduced LDL cholesterol and blood pressure while posing no risk regarding electrolytes balance.
   Front Nutr, 2025 · checked 2026-09-22
5. wal-dr-06 · regulatory register entry
   POL-HC-6525 Walnuts Walnuts contribute to the improvement of the elasticity of blood vessels Authorised
   EU Register on nutrition and health claims, заява POL-HC-6525, знімок 2026-09-21 · checked 2026-09-22
6. wal-dr-04 · randomised controlled trial
   Walnut supplementation for 2 y had no effect on cognition in healthy elders.
   Am J Clin Nutr, 2020 · checked 2026-09-22