It was only comparatively recently that researchers developed a potential measure of biological age using patterns of DNA methylation, a collection of epigenetic alterations that are in some cases similar between different individuals of the same age. It makes sense that there should be age-related patterns to find in our biochemistry, as we all age due to the same root causes: degenerative aging is the consequence of a few forms of cellular and molecular damage, and since the damage is the same, some of the reactions to that damage should also be the same.
Researchers have now had enough time to apply the new DNA methylation measure in larger studies and process the data. I imagine we'll be seeing more results like this one over the next few years. In this case the data adds to the voluminous support for the negative impact of excess fat tissue on long-term health:
Scientists have found, for the first time, that obesity significantly quickens the aging process of the liver and have revealed that carrying excessive weight can negatively impact certain human tissues. The researchers used an 'epigenetic clock' [based on] a naturally occurring process called methylation, which is a chemical modification of the DNA molecule. To reach their findings in this study and examine the connection between increased body weight and epigenetic acceleration, the [scientists] worked with and used [the] aging clock method on almost 1,200 human tissue samples, 140 of which were liver samples.
The researchers found that the aging clock was quite accurate and was able to match the biological age with the chronological age of liver tissue samples taken from subjects with little body fat. On the other hand, the scientists found that liver tissues taken from subjects who were obese had a tendency of having a higher biological age than their chronological age. While they found that obesity has no affect the epigenetic age of human tissues such as fat, muscle or blood, [the] epigenetic age of the liver, on average, increased by 3.3 years for every 10 units of Body Mass Index (BMI). "This does not sound like a lot, but it is actually a very strong effect. For some people, the age acceleration due to obesity will be much more severe, even up to 10 years older."