For this assignment I was asked to review the data of studies looking at net metabolized energy of ground nuts after human consumption. See table below for my summarized findings.
The Atwater general factor system is a system most commonly used to make an estimate of 'available' energy in a food product. What we see on the back of a label is usually the total available energy from that product determined via the Atwater general factor system. However, 'available' energy does not not take into account the complex human physiology and (in)efficiency of the system itself. For all we now, gross energy does not even closely resemble net metabolized energy. For this reason alone, reconsidering the total amount of net utilized energy from (especially) nutrient dense food products is warranted.
Taken together, there is a limited amount of research evaluating different kinds of ground nuts. While the studies found in the table measured energy lost via feces (stool) analysis and had a control group where fat was kept constant, most research only measured total stool fat and lacks a control group. Thus, it makes it hard to convert those numbers to actual net metabolized energy of ground nuts since there is no way to reliably assess if the fat found in the stool represent the fat of a particular food. Studies that didn't assess net metabolized energy directly and had no control group were therefore excluded from this table review.
As you can see in the table, average % energy loss (e.g. the percentage of kcal that is off from the Atwater prediction) is 19.62%. Ground nuts are known for reducing cardiovascular risk, while also inducing a strong satiating response. These results could, if constant, explain why diets with nuts result in more weight loss, because gross metabolized energy does not represent actual net metabolized energy. Future research should look at a more larger variety of ground nuts.
Some authors hypothesized that this net energy loss of ground nuts is because of the complex molecular bonds that can be found in ground nuts and are hard to break down. They don't however mention the absence of enzymes necessary to break down those complex molecular bonds After performing this review, I hypothesize that there exists significant individual variability in enzyme production (as seen with lactase production), and largely explains why a large amount is lost in net digestion and absorption.