Abstract

Plant foods contain a surprising number of different toxins. A few well-known plants, including some grown in Thailand are known to contain high levels of oxalates however, some plants have not yet been fully investigated. A few plants have become fashionable to promote health because they contain antioxidants but some of these plants will contain oxalates as well. In many cases there is little published data to confirm the oxalates levels of these plants. If plant leaves are boiled before they are consumed this allows soluble oxalate to be leached out and discarded in the cooking water. This means that the cooked food contains considerably lower levels of soluble oxalates than the original raw plants. Cooking in a wok generally concentrates the oxalate contents as much of the cooking water is removed as steam. However, during cooking some of the soluble oxalates can combine with free calcium in the food and be converted to insoluble oxalates; these are not absorbed in the digestive tract. The preparation of juices using fruit or vegetables are being promoted as healthy alternatives, this poses further problems, as they may be prepared from raw vegetable leaves, such as spinach, which contain high levels of oxalates. These juices are not cooked so the oxalate concentration is not reduced during their preparation. Recent research has shown that the addition of calcium salts to these juices can considerably reduce the soluble oxalate content of the drink prepared without changing the taste.

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