4.5. Strengths and Limitations
obesity
OBESITY
One of the main strengths of this pilot research is that it was carried out within the framework of a randomized clinical study in which more than 200 people were characterized. A methylation array was used to analyze around 850,000 methylation sites in each individual at baseline. Multiple methylation sites were identified as associated with the reduction in BMI percentage after the intervention with the two types of diets, thus demonstrating the impact that epigenetics has on the response and regulation of anthropometric measures and suggesting that epigenetic markers can be very useful in the precision dietary treatment of obesity. Furthermore, although a pilot study, it was a robust study, since the association of CpG sites with the dietary intervention response was not affected by potential confounding factors, as the model was adjusted for age, sex, and cell composition.The designed epigenetic model successfully predicted the percentage of BMI loss with each of the two diets (MHP and LF). For this model, blood was used as the study tissue, which is an accessible, easy, minimally invasive tissue. Therefore, the designed methylation score can be used as biomarkers in the future using blood samples. On the other hand, with the results obtained, future research can be developed, and the model can also allow the integration of new variables for improvement.It is important to mention that the information obtained from the methylation data of these subjects refers to the methylation situation at that moment and of the tissue that was studied, but this information may vary with time and the tissue analyzed.Another limitation of this pioneer study was the expression of the genes in which the methylation sites identified in this research were located, as it was not analyzed.It would be interesting to know if the changes in methylation have any real influence on the expression levels. It should be taken into account that this research was carried out in a Spanish population, mostly of Caucasian origin, so the data obtained cannot be extrapolated to a demographically different population. It is important to point out that several studies suggest that epigenetic marks are dependent on race, origin, and many lifestyle factors, including perinatal factors, and there are many factors that influence the degree of individual methylation, so that small differences in methylation can be found between individuals. As DNA methylation somewhat shows a maternal inheritance, another limitation is that we did not have twins in the study.On the other hand, there are technological limitations that can influence methylation values, as they are dependent on the equipment used; reagents; and sample handling (blood preservation, cell isolation, DNA extraction, bisulfite treatment, etc.). For this reason, it is difficult to compare between different studies.