Nuts to you—Walnuts, that is

Abstract

Mention walnuts to an equine veterinarian and the first thoughts are likely to be about laminitis caused by the use of black walnut shavings as bedding. Recent studies, however, suggest that walnuts may indirectly increase the health of horses by decreasing the risk of coronary heart disease (CHD) in equine veterinarians. Of course, no studies were conducted in which equine veterinarians were fed walnuts, nor am I aware of any studies that show that a decrease in the incidence of CHD in veterinarians would improve the health of horses. But it seems logical to me that a healthy veterinarian would be of more help to a sick horse than a deceased veterinarian would. Such convoluted reasoning provides justification to present a column on the benefits of veterinarians eating walnuts in a journal devoted to improving the health of a horse. The impetus for this column was reading several articles in the popular press and on the Internet. It was claimed that walnuts could decrease the incidence of CHD in a lengthy review (38 pages) in the May issue of the Journal of Nutrition about the potential health benefits of walnuts.1 There are several types of walnuts. The 2 most common in the United States are Black and English. Black walnut trees (Juglans nigra), the source of toxic shavings, provide valuable wood and nuts that are used for baking.2 The English walnut (Juglans regia) is used for snacks and for flavoring foods. Thus, it is the walnut consumed in greatest amounts and the one that has been used in studies on the potential health benefits of walnuts. English walnuts perhaps should be called Persian walnuts because that name more nearly indicates the area from which the species came.3 The English walnut tree does not thrive in England because the summers are too cool. The name may have resulted from the fact that the walnuts were transported by English ships.4 Walnuts have long been used in folk medicines.2 The Romans thought walnuts had medicinal value in addition to being a delicious food.3 The renewed interest in potential health benefits of walnuts may be related to their rich content of n-6 (linoleate) and n-3 (linolinate) polyunsaturated fatty acids. Other nuts are rich in monounsaturated fatty acids that are similar to vegetable oils and margarine. A team of 5 experts evaluated in detail the scientific evidence of potential health benefits from walnuts.1 Their conclusions included the following: (1) walnuts, as part of a heart-healthy diet, lowers blood cholesterol concentrations in humans and animals; (2) walnuts are unique compared with other nuts because they are predominant in n-6 (linoleate) and n-3 (linolinate) polyunsaturated fatty acids; and (3) walnuts contain multiple health-beneficial components that have a low lysine:arginine ratio and high levels of vitamin E, arginine, folate, fiber, tannins, and polyphenols. It was reported that the clinical dietary intervention studies show that consuming walnuts does not cause a net gain in body weight when they are eaten as a replacement food. The conclusions about the value of walnuts for prevention of CHD were not as definite. Although it was acknowledged clinical studies suggest a reduced risk of CHD, it was suggested that the results must be considered inconclusive because there have only been 5 controlled, peer-reviewed studies and the total number of subjects was not great. But it was also pointed out that a large number of human prospective observational studies showed an inverse association of the relative risk of CHD and coronary vascular disease with the frequent daily consumption of small amounts of nuts, including walnuts. In any case, walnuts appear to reduce cholesterol. The optimal intake of walnuts has not been established. Consumption of 5 oz (140 g) per week has been reported to be useful. Almario et al found a significant decrease in cholesterol but no increase in weight gain with daily intakes of 1.7 oz (48 g) of walnuts per 2,020 calories. The lack of increase in weight is unusual because 1.7 oz are about 15 to 20 walnut halves or over 1 cup.