Nuts and seeds

People who eat a small handful of nuts most days die less often of heart disease and of anything at all, and the one large trial that supplied a daily 30 g of mixed nuts, as part of a Mediterranean diet, saw fewer heart attacks, strokes and cardiovascular deaths combined. Most of the benefit arrives by a modest handful, nuts don't cause the weight gain their calories predict, and the claims for diabetes and the brain are much weaker than the heart ones.

Eat a small handful of plain or dry-roasted nuts most days, about 20–30 g of any kind, peanuts included, in place of red meat, crisps or sweets rather than on top of them. Seeds, especially flax, are a fine addition. Keep Brazil nuts to the occasional one or two, and avoid nuts entirely if you are allergic.

What counts as a nut

Walnuts, almonds, hazelnuts, cashews, pistachios and pecans are tree nuts. Brazil nuts are botanically seeds and peanuts are legumes, but because their nutrition and culinary use are so similar, the research lumps all of them together as "nuts".^[1] Seeds such as flax, chia, pumpkin, sunflower and sesame are usually grouped with nuts in nutrition research. All of them are rich in unsaturated fats, protein and fibre.^[2]

A standard serving in the studies below is 28 g, about one ounce or a small handful.

Nut eaters die less often, and most of the gain comes early

The largest dose-response analysis pooled 20 prospective studies. Each extra 28 g of nuts a day went with about 22% lower death rates from any cause (relative risk 0.78, 95% confidence interval 0.72–0.84), 21% less cardiovascular disease, 29% less coronary heart disease and 15% less cancer. The confidence interval is the range where the true effect most plausibly lies; when it crosses 1.0 the result is compatible with no effect, which is what happened for stroke (0.93, 0.83–1.05). Results were similar for tree nuts and peanuts.^[3]

The curve is not a straight line. Most of the reduction in risk appeared by about 15–20 g a day, or five to six servings a week, with no further fall in all-cause mortality above that.^[4] A later update of 63 cohort studies from 33 publications found the same picture: the highest nut eaters had about 23% lower all-cause mortality and 26% lower cardiovascular mortality than the lowest.^[5] An umbrella review that graded all these analyses rated the cardiovascular evidence as moderate quality.^[6]

All of this is observational, and nut eaters are different people. In two large US cohorts of nurses and other health professionals, those who ate nuts most often were leaner, less likely to smoke, more likely to exercise and ate more fruit and vegetables. After adjusting for those differences, people who ate nuts seven or more times a week still had about 20% lower death rates than those who ate none. That study was funded partly by a tree-nut industry foundation, as much of this field is.^[7]

The trial: nuts as part of a Mediterranean diet

In a Spanish trial called PREDIMED (Prevención con Dieta Mediterránea), 7,447 adults at high cardiovascular risk were assigned to a Mediterranean diet with extra-virgin olive oil, the same diet with 30 g of mixed nuts a day (15 g walnuts, 7.5 g hazelnuts, 7.5 g almonds) supplied free, or a low-fat control diet. Over a median of 4.8 years, 3.4% of the nut group had a heart attack, stroke or cardiovascular death against 4.4% of the control group, about 28% fewer events (hazard ratio 0.72, 95% confidence interval 0.54–0.95).^[8]

Those are the corrected figures. The original 2013 paper was retracted and republished in 2018 after protocol deviations were found for 1,588 participants; results were similar when they were left out. The trial tested a whole diet against a low-fat diet, so it cannot say how much of the benefit came from the nuts themselves. Funding was public; the walnuts, almonds and hazelnuts were donated by producers, who the paper says had no role in the study. The full story is on PREDIMED.

Nuts lower LDL cholesterol a little

Controlled trials show a modest, real effect. Across 61 trials in 2,582 adults, each daily 28 g serving of tree nuts lowered low-density lipoprotein (LDL, "bad") cholesterol by about 4.8 mg/dL (roughly 0.12 mmol/L), apolipoprotein B (ApoB) by 3.7 mg/dL (about 0.04 g/L) and triglycerides by 2.2 mg/dL (about 0.025 mmol/L). The dose mattered more than the type of nut, and the effect was stronger at 60 g a day or more.^[9] A review done for the Nordic nutrition guidelines found a similar drop in LDL, 0.13 mmol/L at a median of about 50 g a day, but no effect on blood pressure.^[10]

The longest trial is consistent. In a trial of 708 healthy adults aged 63–79 in Barcelona and California (628 with full lipid data), eating 30–60 g of walnuts a day for two years lowered LDL by 4.3 mg/dL (about 0.11 mmol/L, 3.6%) more than avoiding walnuts. That trial was funded by the California Walnut Commission.^[11]

Nut fat is mostly unsaturated, and Dietary fats explains why replacing saturated fat with unsaturated fat is what lowers LDL. For context, these drops are small next to what medication does; how to lower LDL properly is on Lipid management.

Why nuts don't fatten as much as their calories suggest

Nuts are energy-dense, but the body doesn't absorb all of it. In a controlled feeding study of 18 adults, a 28 g serving of almonds delivered about 129 kilocalories (540 kJ), against the 168–170 (about 700 kJ) that the standard calculation predicts; that calculation overestimated their energy by 32%.^[12] Part of the explanation is physical: the nut's tough cell structure keeps some of its fat from being absorbed, and nuts are filling.^[13]

The weight data agree. A meta-analysis of 86 randomised trials in 5,873 people found no weight gain from eating nuts, mostly in place of other foods, with a pooled difference of 0.09 kg that was well within chance (95% confidence interval −0.09 to 0.27 kg), rated high certainty. Most trials were designed to keep total calories about the same, and salted or unsalted, raw or roasted made no difference. In cohorts covering almost 570,000 people, nut eaters had about 7% lower risk of becoming overweight or obese. About 40% of the trials were funded by industry alone and another 29% partly.^[14]

In three US cohorts followed for two decades, each extra half-serving (14 g) a day tracked with 0.19 kg less weight gain per four years, and eating that half-serving in place of red meat, processed meat, French fries, desserts or crisps went with less gain.^[15] In PREDIMED, the nut group's weight over five years was no different from the low-fat group's, and its waist grew about 0.9 cm less.^[16] None of this means nuts are free calories; it means a handful in place of other snacks does not show up on the scale.

Diabetes and the brain: weaker than the heart

Type 2 diabetes. Despite the heart data, nuts do not clearly prevent diabetes. A meta-analysis of the observational studies found no association between total nuts, peanuts or tree nuts and new diabetes, and rated the certainty very low; peanut butter, oddly, was linked to slightly lower risk, at the same very low certainty.^[17] The Nordic review reached the same place: a 5% lower risk with a range running from 25% lower to 21% higher, too uncertain for any conclusion.^[18] In people who already have diabetes, 12 short and mostly poor-quality trials found that about 56 g of tree nuts a day lowered the long-term blood sugar marker HbA1c by just 0.07 percentage points.^[19] The ApoB-lowering effect, though, was larger in people with diabetes than in healthy ones.^[20]

The brain. Nuts are one of the MIND diet's targets, but the one long trial was null. The two-year walnut trial above found no difference in overall cognition, and only a post-hoc analysis of one site hinted at a benefit.^[21]

Peanuts count; peanut butter is less certain

In the cohort studies, cheap peanuts look as good as expensive tree nuts. In three cohorts of about 206,000 people, low-income Black and white Americans in the southeastern US and adults in Shanghai, where only peanuts were measured, the highest nut eaters had 21% (US) and 17% (Shanghai) lower death rates than the lowest.^[22] In large US cohorts, eating peanuts or tree nuts twice a week or more, or walnuts once a week or more, went with 13–19% less cardiovascular disease.^[23]

Peanut butter is the exception. In a cohort of 120,852 Dutch adults, peanuts and tree nuts were linked to lower mortality and peanut butter was not.^[24] If you eat it, choose one made from just peanuts and perhaps salt.

Walnuts stand out for one thing: like flax, they carry the plant omega-3 alpha-linolenic acid, whose own modest record is covered on Dietary fats. It is not a substitute for fish oil; see Omega-3.

Seeds: less studied, flax has the most

Seeds have far less evidence than nuts, and in the big analyses they mostly ride along in combined nuts-and-seeds categories. Of the seeds, flax has the best trials. Across 28 trials, whole flaxseed lowered LDL by about 0.16 mmol/L, while flaxseed oil did not; the effect was clearer in postmenopausal women and people with high cholesterol.^[25] Across 15 trials in 1,302 people, flaxseed products lowered blood pressure by about 3 mmHg systolic and 2 mmHg diastolic.^[26]

Chia is weaker. In 10 trials in people with overweight, it did not change LDL cholesterol or blood sugar; systolic blood pressure fell about 3 mmHg and waist size about 3 cm.^[27] Pumpkin, sunflower and sesame seeds have little evidence of their own; treat them as nutritious toppings, not remedies. Their fibre is covered on Fiber, along with the evidence that people with diverticular disease do not need to avoid nuts and seeds.

Salted, roasted and coated

Plain and dry-roasted nuts behave much the same; in the weight trials, roasting and salting made no difference.^[28] Salted nuts count as a processed food, not an ultra-processed one, but the salt adds to your daily total; see Salt and Ultra-processed food. Honey-roasted, chocolate-coated and flavoured nuts are closer to sweets than to the plain nuts the studies measured.

Brazil nuts: a selenium dose you can't read

Brazil nuts are the richest food source of selenium, and their content swings with the soil. In nuts from across the Brazilian Amazon, median selenium ranged from 2.07 to 68.15 mg per kg by region, so one nut could supply anywhere from about a tenth to nearly three times an adult man's daily requirement.^[29] In a trial where two nuts a day were meant to supply about 100 µg, they actually delivered 20–84 µg, 53 µg on average.^[30]

Europe's upper limit for adults is 255 µg a day from all sources.^[31] A handful of high-selenium nuts eaten daily could pass it, which is why Selenium advises the occasional Brazil nut and no supplement on top of regular ones.

Who should be careful: allergy and mould

Allergy. Nut allergies affect about 1–2% of adults, and peanut appears to be the leading food cause of anaphylaxis, the severe whole-body reaction.^[32] For parents, the advice has reversed: in a trial of infants at high risk, giving peanut early cut peanut allergy at age five from 13.7% to 1.9% among those who were not yet sensitised, and from 35.3% to 10.6% among those who already were.^[33] Babies with severe eczema or egg allergy should be assessed by a doctor before peanut is introduced.

Aflatoxins. These are toxins from moulds that grow on badly dried or stored crops. They damage DNA and cause liver cancer in people, and hepatitis B infection multiplies the risk. Europe's food-safety agency found the highest concentrations in nuts and oilseeds, especially pistachios and peanuts, though grains contribute most of the average person's intake.^[34] Brazil nuts are also prone when poorly dried.^[35] In grains, sorting out contaminated kernels reduces aflatoxin, and roasting nuts lowers it only partly.^[36] At home, throw away nuts that look mouldy, shrivelled or discoloured.

What to actually do

Aim for 20–30 g most days, a small handful; the cohort benefit mostly arrives by 15–20 g.
Swap, don't add. Use nuts as the snack instead of crisps, biscuits or sweets, and as the protein instead of some red meat.
Any nut will do. Peanuts look as good as almonds or walnuts; mixing types is fine. Mostly unsalted.
Add a spoon of flaxseed if you want a small extra nudge to LDL cholesterol and blood pressure; use ground seed, since the oil does not lower LDL.
Treat Brazil nuts as an occasional extra, not a daily habit, and don't add a selenium supplement if you eat them regularly.