Epigenetics are the changes in the gene expression which are not caused by changes in the DNA sequences, meaning it a change in the phenotype but not the genotype. It is the study of the genes that are possibly inheritable. The environment you live in plays a key role in epigenetics and how your genes are expressed.
How does epigenetics have anything to do with digestion?
A chemical tag is something that can alter a gene expression. It attaches onto the DNA and blocks transcription. They could also attach to histones and activate or deactivate the genes by tightening or loosening the nucleosome structure. Chemical tags can be altered because of diet. When you have a poor diet, your body gets negatively affected in many aspects.