Nuts

What it is

Tree nuts include almonds, Brazil nuts, cashews, hazelnuts, macadamias, pecans, pistachios and walnuts [1]. Nuts are energy-dense, and the energy the body absorbs from them appears lower than standard calorie values predict [2].

What the research says

Trials show a small drop in LDL cholesterol. A 2025 meta-analysis of 113 trials found LDL fell by about 0.12 mmol/L and total cholesterol by about 0.14 mmol/L, with small falls in triglycerides; HDL did not change significantly [3]. A 2015 meta-analysis of 61 trials found LDL fell by 4.8 mg/dL per daily one-ounce serving [4]. A 2023 review rated the LDL evidence very low certainty because of inconsistency and possible publication bias [5].

Heart events have not been measured in trials of nuts alone. The 2015 Cochrane review found no trial reporting heart attacks or other clinical events [6]. Cohort studies of about 467,000 people link higher nut intake to a lower risk of dying from coronary heart disease (risk ratio 0.70), but these are observational [7]. In the PREDIMED trial, a whole Mediterranean diet that supplied free mixed nuts cut major heart events (heart attacks, strokes or heart deaths) by about 28% over a median of 4.8 years compared with advice to eat a low-fat diet; the trial did not test nuts alone [8].

Doses used in studies

The 2025 review's trials used a median of 45.5 grams of nuts a day [3]. The 2015 review found stronger LDL effects at 60 grams or more a day, and its trials ran from 3 to 26 weeks [4]. Weight trials ran for more than three weeks [9].

Safety and interactions

Tree nut allergy usually starts in childhood, rarely fades and is one of the main causes of serious allergic reactions [1]. One trial in the Cochrane review reported an allergic reaction to nuts [6]. Three trials in the same review reported no significant weight gain [6].

In chronic kidney disease, the evidence rests on four studies, all with moderate-to-high risk of bias; walnuts lowered LDL and posed no electrolyte risk in them [10].

No upper intake limit was found in the studies cited here [3][6]. Pregnancy and breastfeeding were not reported in the reviews cited here [6]. Those reviews do not report interactions with medicines, so people taking cholesterol-lowering or blood-thinning medicines should ask a doctor [6].

Caveats and open questions

Heart attack and stroke outcomes for nuts alone come from observational studies and small, short trials [6][7]; the large PREDIMED trial tested a whole Mediterranean diet containing nuts, not nuts alone [8]. Most cholesterol results are blood markers, not heart outcomes. Several reviews are funded by, or include authors linked to, nut industry groups [3][11]. Long-term weight effects are not measured in these trials [9].