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Dietary supplements · Walnuts
Whole and opened walnuts with a kernel

Whole and opened walnuts with a kernel

Ivar Leidus · CC BY-SA 4.0

Strong evidence22 studies
How we rate

“Strong” = several concordant meta-analyses or systematic reviews. “Moderate” = one synthesis, or several controlled trials. “Limited” = early trials only. The rating is about the quality of the studies, not about how useful the supplement is.

Walnuts

A handful of walnuts a day slightly lowers total cholesterol, LDL and triglycerides, and improves arterial flexibility; it neither makes you gain nor lose weight, and changes neither blood sugar nor the memory of seniors.

Heart

Benefits

  • Cholesterol: −8.58 mg/dL of total cholesterol, −5.68 mg/dL of LDL and −10.94 mg/dL of triglycerides on average in a meta-analysis of 13 trials; the largest one, 49 trials and 4,611 participants, confirms the drop in all three.
  • Without changing anything else: added to the usual diet of 87 adults, without dietary advice, walnuts lowered total cholesterol and triglycerides, especially in those who started out the highest.
  • Arteries: dilation of the arm artery, a sign of a healthy wall, increases by 0.93 to 0.94 points in two meta-analyses; in 24 type 2 diabetics, 56 g per day for 8 weeks improved it.
  • Blood pressure of seniors: in a two-year trial in 305 elderly people, walnuts lowered systolic blood pressure, especially in cases of mild hypertension, and fewer treatments had to be adjusted.
  • No extra kilos: in seniors who ate 28 to 56 g per day for two years, weight did not move any more than without walnuts (−0.4 kg vs −0.6 kg).
  • Sperm: 75 g per day added to the diet of 117 young men improved sperm vitality, motility and shape.

Precautions

Blood sugar: in 24 type 2 diabetics, fasting blood sugar rose slightly during the 8 weeks of eating walnuts, while cholesterol dropped. Digestion: 42 g per day for 3 weeks in 60 students did not cause digestive issues, and rather promoted normal bowel movements. Limitations: weight: the meta-analysis of 27 trials finds no effect of walnuts on weight, waist circumference or fat mass; they do not help with weight loss. Blood sugar: no decrease in fasting blood sugar or other blood sugar markers in a meta-analysis of 16 studies. Blood pressure: no overall effect in meta-analyses of 18 and 36 trials; the small drops seen in certain subgroups are considered clinically insignificant. Memory: two years of walnuts changed nothing in the cognition of 708 healthy seniors, and a meta-analysis cannot draw a conclusion; in 64 students, only verbal reasoning improved (+11.2%), not memory or mood.

Recommended dosage

28 to 56 g per day (one to two handfuls) in long trials, 42 to 43 g per day in several trials lasting 3 to 8 weeks.

How to take it

  • Dose: 30 to 60 g per day in the largest trial, two years in 708 seniors; 42 to 56 g per day in most short trials.
  • Instead of something else: in the trials, walnuts replace part of the diet, around 12 to 15% of the day's calories.
  • Duration: the drop in cholesterol becomes more pronounced when the trial lasts longer; diastolic pressure only drops in trials lasting at least 12 weeks.
  • Calories: a 28 g portion provides 146 kcal to the body, 39 kcal less than what nutritional tables announce.
  • During a diet: on a hypocaloric diet, 100 overweight adults lost just as much weight with or without walnuts, with slightly better LDL and systolic pressure in the walnut group.
  • Timing of intake: no study in this file compares walnuts eaten in the morning, at a meal or as a snack.

Did you know?

Three weeks of 42 g of walnuts per day increased the proportion of several intestinal bacteria that produce butyrate, such as Faecalibacterium and Roseburia, by 49 to 160% in 18 adults.

What the studies say

  • This systematic review and meta-analysis of 36 randomized clinical trials in adults evaluated the effects of walnut consumption on blood pressure and endothelial function. Walnuts showed no overall significant effect on systolic or diastolic blood pressure. In contrast, walnut intake significantly increased flow-mediated dilation (FMD), suggesting an improvement in vascular health through the reduction of endothelial dysfunction.

    Mashayekhi G, Ashtary-Larky D, Karimi M, Asbaghi O, Porkar Rezaeyeh A, Shouhani Z, Hosseini A, Naderian M. — Journal of human nutrition and dietetics : the official journal of the British Dietetic Association (2026) — View the source study

For information only: not a substitute for medical advice. Dietary supplements are not a replacement for a varied, balanced diet. Learn more