A woman exercises at a gym in Havana on May 17, 2016. (Xinhua/ AFP PHOTO)

WASHINGTON, Jan. 17 (Xinhua) -- An American study shows that the human body undergoes dramatic changes during even short periods of weight gain and loss.

The study, published online on Cell Systems Wednesday, shows that even with modest weight gain -- about 6 pounds or over 2.7 kilograms -- the human body will change in dramatic fashion at the molecular level.

Bacterial populations have morphed, immune responses and inflammation flared, and molecular pathways associated with heart disease activated, it shows.

The study, led by Michael Synder, genetics professor from the Stanford University School of Medicine, included 23 participants, among which thirteen were insulin-resistant, which is a precursor for Type 2 diabetes, and 10 were insulin-sensitive, the healthy group who are able to process insulin normally.

At the outset of the study, Snyder and his team found molecular markers for inflammation were only found in the bloodstreams of insulin-resistant participants.

Then, the participants received a high-calorie diet, and after 30 days they had, on average, tacked on 6 pounds. It shows that inflammation markers go up in both the insulin-resistant and healthy groups, and in the latter group, a microbial population known to protect against insulin resistance shoot up.

But the most striking change is a shift in gene expression associated with increased risk for a type of heart failure called dilated cardiomyopathy, in which the heart cannot pump blood efficiently to the rest of the body, Snyder said.

"That was quite surprising. I didn't expect 30 days of overeating to change the whole heart pathway," he said.

The good news is that when study participants lose the weight, most of the rest of the body's systems recalibrate back to their original states.

However, a small subset of weight-gain-associated shifts in protein and molecule production does persist, even after participants have shed the extra pounds, the study finds.