Role of the food matrix and digestion on calculation of the actual energy content of food

Abstract

The energy content of food is calculated on the basis of general factors for fat, protein, and carbohydrates. These general factors were derived by W.O. Atwater in the late 19th century, while additional factors for dietary fiber, polyols, and organic acids were introduced more recently. These factors are applied indiscriminately to all types of foods, yet the same nutrient may be digested to different extents to generate energy, depending on the characteristics of the food matrix, the processing methods applied to foods, and the meal composition. As a consequence, the actual energy content of food may differ from what is theoretically calculated with the Atwater factors. In this review, the relationship of macronutrient digestibility with food structure, macronutrient structure, and food composition is examined, and the implications for the amount of energy achievable through diet are highlighted. Estimates of the discrepancy between calculated energy content and actual energy content are provided for different diets. The findings may have implications for consumer purchasing decisions as well as for the design of dietary interventions.

A Critical Review on the Role of Food and Nutrition in the Energy Balance

“…The actual energy content of some foods may differ from the energy, which is theoretically calculated, due to differences in macronutrient digestibility and food structure [23,24]. One of the best examples of this discrepancy is represented by nuts.…”

“…Several mechanisms have been proposed to explain this discrepancy, including appetite control, increased DIT (as discussed below), and discrepancies in available metabolizable energy (ME, i.e., the amount of the food available energy to the human organism) [24]. To calculate the food ME, each energy-contributing food component is multiplied by its Atwater factor [23]. However, recent evidence has demonstrated that the Atwater factors do not provide accurate ME values for several nuts in healthy volunteers [26][27][28][29].…”

“…The reason for this discrepancy is partly due to the structure of nuts, which limits the accessibility of digestive enzymes. In oilseeds, such as nuts, lipids are stored in oil bodies which are covered by a thin layer of phospholipids and proteins and encapsulated in cell walls [30], whose components (e.g., cellulose, hemicellulose, peptic substances and lignin) are mainly indigestible by human digestive enzymes [23]. After nut mastication, large particles representing clusters of intact cells remain, which provide protection against disintegration and a physical barrier for enzyme hydrolysis and microbiota metabolism [31].…”

Nuts in the diet and bodyweight: What's the relationship?

“…The metabolisable energy can vary with nut type due to differences in structure ( e.g. hardness) and composition, which can affect chewing duration and/or bite strength, and thus particle size and bioaccessibility of energy (Capuano et al ; McArthur et al ). The actual metabolisable energy values of different nuts have been shown to be lower than the values calculated using Atwater factors that can be found within food composition tables.…”

“…For example, whole natural almonds were found to have a slightly lower metabolisable energy than dry roasted almonds (4.42 ± 0.24 kcal/g vs. 4.86 ± 0.24 kcal/g: P < 0.05) (Gebauer et al ). This has been suggested as being due to the dehydrating effects of the roasting process reducing the hardness of the almonds, resulting in a higher proportion of smaller particles of nut produced during chewing, and thus a greater bioaccessibility of macronutrients and a greater amount of energy available to be absorbed (Grundy et al ; Capuano et al ).…”