This 2021 rodent study measured sequential liver changes caused by a high-fat diet:

“Using a longitudinal mouse study of diet-induced obesity in male mice, we investigated kinetics of hepatic DNA methylation and gene expression compared to those of obesity-induction to assess if they could be causal for development of insulin resistance. We aimed to find out if these changes were reversed by massive weight loss induced by vertical sleeve gastrectomy or metformin treatment.

We identified two CpG sites within exon 1 of Fgf21 that became gradually hypomethylated upon HFD feeding. DNA demethylation started between week two and four, to become significant at week five, and significantly correlated with hepatic Fgf21 gene expression.

These DNA methylation changes preceded development of insulin resistance, and were potentially causally involved in increased Fgf21 expression and plasma levels associated with insulin resistance. This points to a key regulatory function of gene body DNA methylation, which was eventually a compensatory response to counteract the developing insulin resistance.

HFD-induced decrease in Fgf21 DNA methylation could not be reversed by vertical sleeve gastrectomy or metformin treatment. As soon as weight loss slowed down or mice started to re-gain weight, differences in DNA methylation were no longer detected compared to sham-operated mice.

As the altered DNA methylation pattern was acquired during adulthood in differentiated cells, our data emphasize that metabolic programming via DNA methylation is dynamic and not restricted to fetal development. This supports the concept that individuals can actively influence their DNA methylation patterns by lifestyle choices.

Our data indicate that DNA methylation alterations in key metabolic tissues can be acquired by an obesogenic diet, and not easily be reversed by interventions common in obese and diabetic subjects.”

https://www.sciencedirect.com/science/article/pii/S0955286321003272 “Dietary induction and reversal of obesity and insulin resistance is associated with changes in Fgf21 DNA methylation in liver of mice”

This study attempted two interventions that didn’t have desired effects. All about the betaine mentioned others that may reverse liver epigenetic changes.