It is a good quality study because they explain very well how the studies included in the meta-analysis have been selected and how some results have been recalculated in order to homogenise and summarise them. They use modern techniques and describe them well.  

It is an interesting study because it focuses on summarising information on the effect of substitutions of animal foods with plant foods as sources of protein. 

This type of analysis is relatively recent and complements traditional analyses that focus on examining the effect of a food on the development of disease. In other words, it is not only the amount of food consumed that is important, but also what is not consumed if too much is consumed, or what is consumed instead if too little is consumed.  

Furthermore, this work is in line with what is currently considered a healthy diet, with a higher content of vegetable protein sources and a lower content of animal protein sources, especially red and processed meat. The new Spanish dietary guidelines, published by AESAN a few months ago, go in this direction. 

An important limitation of the work is that these types of substitutions are based on theoretical calculations, not on actual changes in the diet of study participants. This type of analysis is considered a methodological advance, but it is still a simulation. More studies are needed to examine how real changes over time have an impact on health. In addition, some types of food considered as a group (dairy, fish) are composed of foods with different properties, and most of the studies reviewed have not gone as far as examining substitutions at this level of detail.