Atwater factors overestimate the calorie content of walnuts (371.1)

Abstract

Walnuts are a good source of magnesium, a shortfall nutrient, and contain a significant source of alpha‐linolenic acid. Their unique fatty acid profile likely contributes to their beneficial effect on cardiovascular health, with walnuts being the first whole food for which the US FDA permitted a qualified health claim. These health benefits make walnuts an important part of a healthful dietary pattern; however, their perceived high energy density may be a barrier to consumption. Recent research has shown that Atwater calculations overestimate the energy content of other tree nuts by 5‐20%; however accuracy of the Atwater estimated energy content of walnuts has not been investigated. A RCT was conducted in which 18 subjects were fed 2 diets, a base diet (0 g/d walnuts) and the base diet with all foods reduced and 42 g/d of walnut pieces added. After adaptation to both diets, subjects collected all urine and feces voided for 7 to 10 d at the end of each 3‐wk diet period. These samples and diets were freeze dried and gross energy was measured by bomb calorimetry. The metabolizable energy (ME) content of walnuts was found to be 5.22 kcal/g (146 kcal/serv) as compared to the Atwater‐calculated amount of 6.61 kcal/g (185 kcal/serv). Thus, Atwater factors overestimate by 21% the ME content of walnuts. These data will better inform consumers about the energy content of their foods.Grant Funding Source: USDA and California Walnut Commission