Despite decades of research focusing on obesity, what happens in the body when you lose weight and why losing weight can improve your health is still not well understood.
The new study, currently published naturally on Wednesday (July 9th), provides clues as to what is actually happening. Weight loss suggests that it does more than shave pounds – it can change fat at the cellular level, rewire the way tissue metabolism, and perhaps even “rejuvenate” it.
This study also provides insight into why weight loss does not necessarily eliminate all health problems associated with obesity. This study found that poor health markers in obesity, such as cells that promote inflammation, are not resolved after weight loss.
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“What we’re excited about is that we really understand the ‘Yins and Yangs’ of weight loss,” William Scott, an obesity researcher at Imperial College London, told Live Science.
Thanks to this type of research, “in the future we can develop drugs that target the good parts, but we can also block harmful bits that stick to obesity,” he added.
Zoom in to fat cells
To understand what’s going on with fat cells when people lose weight, Scott and his colleagues collected samples of subcutaneous abdominal fat that grows under the skin around the abdomen from 25 obese volunteers before and after weight loss surgery. Samples were collected between 5 and 18 months postoperatively, when participants lost an average of 55 pounds (25 kilograms) and were still in the “active” weight loss phase, Scott said.
Related: Fat cells have a “memory” of obesity, research discovers
Samples were compared to organizations collected from 24 lean volunteers with body weight indexes in the “normal” range. We also compared the data to previously published “Atlas” of all white fats in the body. This also catalogs the chemical processes that occur in that adipose tissue.
Scientists studied how weight loss affected cellular activity. They measured which genes were active in each cell by examining RNA molecules. RNAs copy information from genes and are cousins of DNA that act as protein blueprints, so they look at which RNAs are present and can be used as measures of gene activity. This method, called single nuclear RNA sequencing, reveals what the cells were trying to do at the time of sampling and how they were interacting at that time.
It is important to gain that level of insight into adipose tissue. Because, contrary to popular belief, it is not a monolithic, passive mass. Instead, it consists of many cell types, including adipocytes (also known as fat cells), immune cells, vascular cells, and neurons. These diverse cells send signals to the body and brain, helping to regulate metabolism, appetite and overall health.
Overall, this study analyzed RNA expression in more than 170,000 cells within adipose tissue.
Reversing and recycle fat molecules
This study showed that adipose tissue in the larger body tends to “age.” This means that some cells are senesced and more damaged than younger cells. Scientists suspect that these senescent cells can fuel obesity-related diseases because they promote inflammation, fibrosis, or scarring.
However, weight loss seems to reverse that aging and the tissue appears healthier.
“The body cleans up damaged, harmful cells and effectively rejuvenates our tissues,” Scott said. “We weren’t really surprised by it,” as other studies suggested, “but we were surprised to see how it seemed to be happening.”
Furthermore, weight loss appears to change the way fat molecules, called lipids, interact with fat molecules. High lipid levels in the blood can be harmful to the body. When the storage capacity within adipose tissue is exceeded, lipids accumulate in other tissues such as the liver and pancreas, possibly contributing to insulin resistance, liver disease and diabetes.
New research suggests that adipocytes not only break down lipids, but also use ingredients to create new fat molecules. This process can burn energy and help you lose weight, and can prevent harmful fats from building up in other organs and causing problems.
However, some cellular changes associated with obesity were not reversed. Researchers have noticed that immune cells that penetrate obese fatty tissue and promote the disease are still present after weight loss.
“We found that obesity hardwired some of the processes within the cell,” Scott said. “Adipose tissue has a memory,” meaning losing weight means that you “never get better” as much as maintaining a healthy weight in the first place.
Andrew Huy, a lipid metabolism researcher at the University of Sydney, was not involved in the study, but told Live Science via email that all the methods the team used wouldn’t capture all the complex cell interactions they could be playing with. So you can’t be sure that fat cells are “rejuvenated” or that immune cells remain after weight loss, he said.
Furthermore, although this study only looked at subcutaneous fat, visceral fat surrounding the organs is known to be more closely associated with disease. So studying visceral fat may help determine what promotes obesity disease, Hui argued.
Scott added that the study cannot explain what promotes the observed changes in adipose tissue during weight gain or loss. He hopes that further research will help show what is happening at different stages of weight loss and profit.
Weight loss surgery may have helped to guide cellular changes and weight loss rather than promote change in itself, said Dr. Francesco Rubino, a metabolic surgery researcher at King’s College London in the UK, suggesting he was not involved in the study.
He told Live Science in an email that he believes the film supports the idea that dramatic weight loss in itself is not the sole goal of obesity treatment. He and others have suggested that metabolic health benefits occur even with slight weight loss, and that improving metabolism is important.
“We assume there is a percentage between weight loss and outcomes. I think that’s a fundamental mistake,” Rubino told Live Science. “You shouldn’t judge a successful treatment based solely on weight loss, because you may lose weight and still get great benefits,” he added.
This article is for informational purposes only and is not intended to provide medical advice.
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