In fact, whole unroasted almonds provide 25% fewer calories than the amount listed on nutrition labels, while whole roasted almonds provide 19% less calories and chopped roasted almonds 17% fewer calories.
The calories in almond butter, however, did not differ from calories estimated using Atwater factors, said the scientists from USDA’s Agricultural Research Service (ARS).
Traditionally, calories are determined using what are known as the Atwater factors, which was developed over 100 years ago, and assigns an estimated number of calories per gram of fat, protein and carbohydrate in a food.
The study, jointly funded by USDA ARS and Almond Board of California, used a new method to measure the number of calories in almonds actually digested and absorbed by human subjects, taking bioavailability into account.
Teasing out the discrepancy
According to Dr Janet Novotny, the team expanded upon the Atwater method to “tease out the caloric value of a single target food. Then, using the study participants’ energy intake and energy output, we were able to measure the number of calories actually digested and absorbed from a single food – in this case, almonds.”
This was not the first time that a study has shown that almonds provide fewer calories than thought. In 2012, the same researchers found a discrepancy between the calories predicted by Atwater and the actual energy value of almonds in the human diet.
However, it was the first study to determine how food processing impacts the metabolizable energy of the nuts.
The impact of processing
The researchers concluded the Atwater method of calculating calories may exaggerate the calories from almonds because it has not taken into account actions like chewing, for instance.
Chewing – and other mechanical processes such as chopping and grinding – does not completely break down almond cell walls. The larger the particle size after ‘processing’, the less it’s able to be broken down by digestive enzymes and more is excreted, so fewer calories are absorbed.
The reverse is also true: the smaller the particle size, the more almond cells are exposed to digestive enzymes and the more calories are absorbed. This is particularly true after roasting the nuts, which have more fragile cells walls that are easily broken down.
According to Dr David Baer, “Calories are created equal but their availability from foods is not equal. These new findings confirm that we actually get fewer calories than we thought from almonds, whether they are whole or chopped, roasted or unroasted, and the amount of calories absorbed is mostly dependent on the form of almonds consumed.”
Food & Function. 2016;7(10):4231-4238
‘Food processing and structure impact the metabolizable energy of almonds.’
Authors: Gebauer SK, Novotny JA, Bornhorst GM and Baer DJ.