Background – Nuts are often referred to as high oxalate containing foods but reliable data on the oxalate content of many commonly eaten nuts are hard to find.
Objectives - This study was conducted to determine the oxalate contents in common nuts either grown or imported into New Zealand. Samples of imported nuts were purchased from supermarkets in Christchurch while home-grown nuts were obtained directly from the growers. Gastric soluble and intestinal soluble oxalates were extracted from the nuts using an in vitro assay. The extracted oxalates were then determined by HPLC chromatography.
Outcomes – The gastric soluble oxalate contents of the nuts represent the total oxalate in the samples, however, the more interesting fraction is the intestinal soluble oxalate. This is the fraction that will be absorbed in the small intestine. Peanuts, Spanish peanuts, peanut butter, ginkgo and pecan nuts all contained relatively low levels of intestinal soluble oxalate ranging from 129 to 173 mg intestinal soluble oxalate/100 g fresh weight (FW). Almonds, Brazil, cashew and candle nuts contained higher levels of intestinal soluble oxalate ranging from 216 to 305 mg/100 g FW. Pine nuts contained the highest levels of intestinal soluble oxalate (581 mg/100 g FW) while in contrast, chestnuts and pistachio nuts were low (72 and 77 mg /100 g FW). Over all the nuts studied the mean soluble oxalate contents was 78% of the total oxalate content (range 41 to 100%).
Conclusion – The results obtained in this study confirm that the soluble oxalate contents of nuts range widely and people who have a tendency to form kidney stones would be wise to moderate their consumption of certain nuts.