Macadamia nuts: a fat swap with a small lipid effect

The strongest evidence that includes this nut is a meta-analysis of 21 randomised trials in adults, and in it macadamia shows nothing of its own. Nuts as a group lowered systolic blood pressure by 1.29 mm Hg (95% CI -2.35 to -0.22, p = 0.02) in people without type 2 diabetes, and by nothing in the total population. The effect traced to pistachios, which lowered it by 1.82 mm Hg (95% CI -2.97 to -0.67), while the other nuts did not. Each subgroup by nut type rests on few trials. What macadamia has of its own is a five-week controlled feeding trial in 25 mildly hypercholesterolaemic adults. There 42.5 g a day per 2100 kcal lowered LDL cholesterol from 3.44 to 3.14 mmol/L and total cholesterol from 5.45 to 4.94 mmol/L, against an average American diet matched at 33 percent total fat. That same swap cut saturated fat from 13 to 7 percent of energy, which is part of what moved. Added instead to what people already ate, at about 15 percent of daily calories for eight weeks in 35 adults with abdominal obesity, LDL cholesterol fell 4 percent with an interval from -14.3 to 4.8 mg/dl, so it did not reach significance.

The numbers, per 100 g

What your body absorbs

• Measured by collecting everything that came out, a 28 g serving of walnuts delivered 146 kcal instead of the 185 kcal on the label, 21 percent less than the Atwater factors predict. The nut measured here was the walnut, not macadamia. — 18 healthy adults, mean age 53 years, randomised crossover with two 3-week fully controlled feeding periods, 42 g of walnuts a day against the same base diet without them, with bomb calorimetry of all urine and faeces (n = 18) Evidence B source
  146 kcal per 28 g serving against the calculated 185 kcal, a shortfall of 39 kcal per serving and 21 percent below the Atwater prediction (p below 0.0001)

What it does to your health

• Swapping 42.5 g of macadamia nuts a day into an average American diet for five weeks lowered LDL cholesterol from 3.44 to 3.14 mmol/L in mildly hypercholesterolaemic adults. — 25 mildly hypercholesterolaemic adults, 15 women and 10 men, randomised crossover controlled feeding, 42.5 g of macadamia nuts per 2100 kcal for 5 weeks against an average American diet matched at 33 percent total fat (n = 25) Evidence B source
  Total cholesterol 4.94 against 5.45 mmol/L and LDL cholesterol 3.14 against 3.44 mmol/L (p below 0.05), with no change in triglycerides
• Adding macadamia nuts at 15 percent of daily calories for eight weeks added no weight and no body fat in adults with abdominal obesity, and the cholesterol fall of 4 percent did not reach significance. — 35 free-living adults aged 40 to 75 with abdominal obesity and at least one further cardiometabolic risk factor, randomised crossover, usual diet plus macadamia nuts at about 15 percent of daily calories for 8 weeks against usual diet without nuts (n = 35) Evidence B source
  No significant change in weight, BMI, waist circumference, percent body fat or glycaemic measures; total cholesterol down 2.1 percent (-4.3 mg/dl, 95% CI -14.8 to 6.1) and LDL cholesterol down 4 percent (-4.7 mg/dl, 95% CI -14.3 to 4.8), neither significant
• Across 21 randomised trials, nuts lowered systolic blood pressure by 1.29 mm Hg in people without type 2 diabetes, and the effect traced to pistachios rather than to macadamia or the other nuts. — Adults aged 18 and over in 21 randomised controlled trials of single or mixed nuts, including macadamia, lasting at least 2 weeks, published between 1958 and October 2013 (n = 21 trials) Evidence A source
  Systolic blood pressure lower by 1.29 mm Hg (95% CI -2.35 to -0.22, p = 0.02) in people without type 2 diabetes and unchanged in the total population; pistachios lower systolic pressure by 1.82 mm Hg (95% CI -2.97 to -0.67) while other nuts do not

Safety, limits and interactions

• Among six raw tree nuts sampled at United States retail, macadamia had the highest Salmonella prevalence at 4.2 percent of samples, and none was detected in pecans or in-shell hazelnuts. — 3656 retail samples of six raw tree nuts collected across the United States between October 2014 and October 2015 and tested by the FDA culture method (n = 3656) Evidence C source
  Macadamia 4.20 percent (95% CI 2.40 to 6.90) against walnuts 1.20 percent, cashews 0.55 percent, pine nuts 0.48 percent and shelled hazelnuts 0.35 percent; contamination levels were low, with the highest at 0.092 MPN per gram

What people believe that the data does not support

• The United States lets macadamia nuts carry a heart claim, and the wording FDA cleared says the research is supportive but not conclusive at 1.5 ounces a day. — Not applicable: a regulatory decision on label wording, issued by FDA in 2017 after reviewing a qualified health claim petition Evidence E source
  FDA does not intend to object to the claim at an intake of 1.5 ounces of macadamia nuts a day within a diet low in saturated fat and cholesterol
• Europe went the other way: the nut heart-health claim it refused had already excluded macadamia from the nuts it covered. — Not applicable: a regulatory decision recorded in the EU register of nutrition and health claims Evidence E source
  Claim POL-HC-7666 recorded as non-authorised, and its substance field names peanuts and tree nuts while excluding brazil, macadamia and cashew nuts

Who this works differently for

• Macadamia is a real tree nut allergen: in 66 supervised food challenges, 27 percent reacted to a 1 g dose, and half of those reactions were anaphylaxis. — 66 patients undergoing macadamia nut oral food challenges at one Japanese department between January 2013 and June 2024, 33 at a 1 g loading dose and 33 at 10 g (n = 66) Evidence C source
  Challenge positive in 27 percent at 1 g and 12 percent at 10 g; among positives, anaphylaxis in 52 percent of the 1 g group and 3 percent of the 10 g group; the skin prick test did not predict anaphylaxis

What is still unknown

• The calories on a nut label overstate what the body gets, and macadamia is one of the nuts where nobody has measured how much. — 21 human and in vitro studies of tree nuts and peanuts in adults aged 18 and over, searched to June 2021; the nuts actually measured were almonds, cashews, hazelnuts, pistachios, walnuts and peanuts (n = 21 studies) Evidence C source
  Metabolizable energy consistently below the Atwater prediction, 22.6 kJ/g for pistachios and 18.5 kJ/g for raw almonds, and rising with processing in the order whole nuts, chopped, flour and raw, roasted, butter

The bottom line

The steadiest finding is about weight. In those 35 free-living adults aged 40 to 75, eight weeks of macadamia at roughly 15 percent of calories left weight, BMI, waist circumference, percent body fat and glycaemic measures unchanged. A neighbouring question has no answer for this nut. Measured by burning everything that came out, a 28 g serving of walnuts delivered 146 kcal against the 185 kcal the Atwater factors predict, 21 percent less, in 18 adults on fully controlled diets for three weeks. A review of 21 studies searched to June 2021 found the same shortfall for almonds, cashews, hazelnuts, pistachios, walnuts and peanuts. Macadamia was not among the nuts measured, so what carries over to macadamia is at most the mechanism, and not the numbers. Two cautions are specific to macadamia. Raw nuts at retail carried Salmonella in 4.20 percent of samples (95% CI 2.40 to 6.90), the highest of six tree nuts in a survey of 3656 United States retail samples collected in 2014 and 2015. The amounts found were very low, the highest at 0.092 MPN per gram, and only raw nuts were sampled, so roasting is not covered. The second is allergy. Among 66 patients sent for a supervised macadamia food challenge at one Japanese department between 2013 and 2024, 27 percent reacted at a 1 g loading dose and 12 percent at 10 g. Among those who reacted, anaphylaxis occurred in 52 percent of the 1 g group and 3 percent of the 10 g group. People referred for a challenge are already suspected of allergy, so these rates do not describe the general population, and the two dose groups were not assigned at random, which is why the lower dose looks worse. The skin prick test did not predict anaphylaxis. Regulators read the same literature and split. The United States allows a qualified health claim, the weakest tier the FDA grants. Its cleared wording says supportive but not conclusive research shows that eating 1.5 ounces a day of macadamia nuts may reduce the risk of coronary heart disease, within a diet low in saturated fat and cholesterol and without increasing saturated fat or calories. That last condition is part of the claim and is the easiest part to drop when quoting it. In the European register, the nut heart-health claim POL-HC-7666 stands as non-authorised, and its own wording had already excluded macadamia from the nuts it covered.

Sources

1. macn-r5-05 · randomised crossover trial
   The ME of the walnuts was 21% less than that predicted by the Atwater factors (P < 0.0001).
   J Nutr, 2016 · checked 2026-09-24
2. macn-r5-01 · randomised crossover trial
   Thus, macadamia nuts can be included in a heart-healthy dietary pattern that reduces lipid/lipoprotein CVD risk factors.
   J Nutr, 2008 · checked 2026-09-24
3. macn-r5-02 · randomised crossover trial
   Daily consumption of macadamia nuts does not lead to gains in weight or body fat under free-living conditions in overweight or obese adults
   J Nutr Sci, 2023 · checked 2026-09-24
4. macn-r5-03 · meta-analysis of RCTs
   Total nut consumption lowered SBP in participants without type 2 diabetes...Pistachios seemed to have the strongest effect on reducing SBP and DBP.
   Am J Clin Nutr, 2015 · checked 2026-09-24
5. macn-r5-06 · prevalence survey
   Salmonella was not detected in pecans and in-shell hazelnuts.
   J Food Prot, 2017 · checked 2026-09-24
6. macn-r5-08 · qualified health claim
   Supportive but not conclusive research shows that eating 1.5 ounces per day of macadamia nuts, as part of a diet low in saturated fat and cholesterol and not resulting in increased intake of saturated fat or calories may reduce the risk of coronary heart disease.
   FDA, review of the qualified health claim petition for macadamia nuts and coronary heart disease · checked 2026-09-24
7. macn-r5-09 · regulatory decision
   POL-HC-7666 Nuts - peanuts and tree nuts (almonds, hazelnuts, pecans, pistachios and walnuts), excluding brazil, macadamia and cashew nuts Eating 30g of nuts per day as part of a balanced diet helps maintain heart health. Non-authorised
   EU Register on nutrition and health claims, claim POL-HC-7666, snapshot 2026-09-21 · checked 2026-09-24
8. macn-r5-07 · retrospective cohort
   Macadamia nut OFC has the potential to induce severe allergic reactions, including anaphylaxis.
   Arerugi, 2025 · checked 2026-09-24
9. macn-r5-04 · systematic review, 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 2026-09-24