SOURCES

Macadamia integrifolia and Macadamia tetraphylla trees are members of the family Proteaceae that originated in Australia. The trees have been cultivated in the United States, primarily in Hawaii and California, since the late 1800s.¹ The majority of commercial macadamia nuts in the United States originate from Hawaii. Macadamia nuts contain 75% fat by weight, of which 80% is monounsaturated. Ingestion of a high-monounsaturated fat diet based on macadamia nuts in humans has been shown to lower serum cholesterol and low-density lipoprotein levels.^2,3 Proteins (27% to 30%) and sugars (6% to 8%) comprise the majority of the oil-free components of macadamia nuts.¹ One novel protein found in macadamia nuts is being investigated for its potential antimicrobial activity.^4,5

Macadamia nuts are popular snack foods, both as plain nuts and when incorporated into candies, cakes, and cookies. Ingredients other than macadamia nuts, such as chocolate, may also need to be considered as potential toxicants in cases where candies or baked goods containing the nuts have been ingested. Macadamia nut toxicosis has to date only been reported in dogs, who will readily ingest the nuts or products made from them.⁶

TOXIC DOSE

In dogs, ingestion of 2.2 grams of raw or roasted nuts per kilogram of body weight has been associated with the development of clinical signs.⁷ Another source out of Australia cited a toxic dose, from field cases, as being between 0.7 and 4.9 g/kg body weight (5 to 40 nuts for a 20-kg dog).⁸ In experimental trials, weakness was associated with doses ranging from 2.4 to 62.4 g/kg, while vomiting occurred with doses ranging from 7 to 62.4 g/kg. Based on these numbers, and assuming that a roasted macadamia nut weighs between 2.1 and 3 g (Gwaltney-Brant, personal observation), the minimum toxic dose of macadamia nuts for dogs is approximately 1 nut/kg. In four dogs experimentally dosed with a slurry of commercially available macadamia nuts at 20 g/kg, all dogs developed significant clinical signs of toxicosis.⁶

TOXICOKINETICS

No toxicokinetic studies have been reported in dogs. In dogs experimentally dosed with macadamia nuts, serum triglyceride levels peaked in 3 to 8 hours and returned to normal within 12 hours following dosing,⁶ which suggests relatively rapid absorption of the lipid component of the nuts. The peak triglyceride levels mirrored most of the peak clinical effects seen in the experimental dogs.