Food labels compute energy with the , a system that assigns fixed values per gram of protein, fat and carbohydrate. Earlier work showed that for some nuts the energy actually available to the body is less than those factors predict. Nobody had measured walnuts.
Not quite. A 28 gram serving of walnuts delivered 146 kilocalories against a calculated 185, which is 39 fewer per serving and 21 percent less than the Atwater factors predict. The authors note this could help explain why people who eat nuts do not gain excessive weight.
Previous studies had shown that the metabolizable energy content of certain nuts, meaning the energy available to the body, is less than the Atwater factors predict. Very few nuts had been investigated, and no information existed for walnuts.
So the study fed them. Eighteen healthy adults, mean age 53, took part in a randomized design with two three-week treatment periods. Each used the same fully controlled base diet, unsupplemented in one period and supplemented with 42 grams of walnuts a day in the other.
One 28 gram serving of walnuts contained 146 kilocalories, or 5.22 per gram, against a calculated value of 185 kilocalories, 6.61 per gram. That is 39 kilocalories less per serving, and 21 percent less metabolizable energy than predicted.
The conclusion is consistent with other tree nuts: the Atwater factors overestimate walnut energy. The authors suggest the result could help explain why consumers of nuts do not gain excessive weight, and could improve the accuracy of .
wat. A serving of walnuts gave up 146 of its 185 labeled calories.
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A number printed on every package turns out to be a model, and for this food the model is off by a fifth.
How do we know?
Baer, Gebauer and Novotny ran a randomized crossover feeding study in 18 healthy adults. Two three-week periods used the same fully controlled base diet, one unsupplemented and one with 42 grams of walnuts a day.
What is still unknown
Eighteen adults and one food, and the correction applies to walnuts rather than to labels in general.
Learn something?
Where to next
Does it matter when you eat, if the calories are the same either way?calories