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What are stem cells and how does obesity change them

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Stem cells and obesity

The human body contains cells capable of becoming almost anything, muscle, nerve, blood, bone. These are stem cells, and they sit at the center of one of the most exciting and rapidly advancing areas in modern medicine. But stem cell biology is not only relevant to future therapies. It intersects directly with something far more immediate: how obesity alters cells at a level that persists long after the weight is gone. Understanding both, what stem cells are and what chronic obesity does to fat cells, offers genuinely useful insight into how the body works, why weight loss is so difficult to sustain, and where medicine is heading.

» GROUNDBREAKING: Japan approves first iPSC stem cell therapies

Stem cells: What they are and why they matter

Most cells in the human body have a fixed identity. A liver cell does liver work. A neuron fires electrical signals. A red blood cell carries oxygen. Stem cells are different. They possess two defining properties that set them apart from virtually every other cell type: the ability to divide and produce more of themselves, and the ability to differentiate, to transform into specialized cell types with entirely different functions. This combination of self-renewal and differentiation is what makes them so biologically significant and so therapeutically promising.

Stem cells’ regenerative potential spans embryonic, adult, and induced pluripotent stages, offering unprecedented therapeutic opportunities across conditions including cancer, neurodegenerative disorders, cardiovascular disease, spinal cord injuries, and diabetes. That breadth of potential explains why stem cell research attracts such intense scientific and commercial attention, and why it also attracts an equally intense need for rigorous regulation.

The three main types of stem cells

Not all stem cells are alike. They differ meaningfully in where they come from, how versatile they are, and what ethical considerations they carry.

Embryonic stem cells (ESCs) are derived from early-stage human embryos, typically those left over from in vitro fertilization procedures, and are pluripotent, meaning they can differentiate into virtually any cell type in the body. Their versatility is extraordinary. Their use, however, involves the destruction of an embryo, which raises ethical objections that continue to generate genuine debate in both scientific and policy communities. Despite ethical and scientific concerns, iPSCs have transformed stem cell research as a flexible and ethical substitute for embryonic stem cells, demonstrating enormous promise in drug discovery, disease modeling, and possible clinical use.

Adult stem cells are found throughout the body in tissues including bone marrow, skin, fat, and muscle. They are multipotent, capable of becoming several related cell types, but not any cell type. Hematopoietic stem cells, found in bone marrow, give rise to all blood and immune cells. Mesenchymal stem cells can differentiate into bone, cartilage, and fat, and are of increasing interest for their immunomodulatory properties. Adult stem cells carry no ethical baggage and can often be sourced from the patient’s own body, reducing immune rejection risk.

Induced pluripotent stem cells (iPSCs) represent arguably the most transformative development in modern stem cell science. In 2012, the discovery of a way to reprogram mature mouse and human cells into a primitive state, from which they could develop into any cell type in the body, won Shinya Yamanaka a share of the Nobel Prize in Physiology or Medicine. iPSCs are adult cells reprogrammed back to a pluripotent state using a defined set of transcription factors. They have the versatility of embryonic stem cells without the ethical concerns, and they can be generated from a patient’s own tissue, making personalized, rejection-free therapies theoretically possible.

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From laboratory to clinic: What stem cell therapies can actually do today

The distance between scientific promise and clinical reality in stem cell medicine has historically been considerable. But that gap is narrowing, and several treatments have crossed from experimental to approved.

The most established application is the hematopoietic stem cell transplant, better known as the bone marrow transplant — which has been used for decades to treat leukemia, lymphoma, and other blood disorders by replacing a diseased blood-forming system with healthy donor cells. This remains a life-saving procedure for thousands of patients each year and represents the gold standard of what stem cell medicine can accomplish when the biology is well understood.

More recent milestones signal the pace of progress elsewhere. Ryoncil received FDA approval in December 2024 as the first mesenchymal stem cell therapy approved for pediatric steroid-refractory acute graft-versus-host disease, a life-threatening complication of bone marrow transplantation, in patients aged two months and older. For conditions where no effective treatment previously existed, this is a meaningful development, not merely a regulatory footnote.

iPSC-derived therapies are now entering clinical trials at an accelerating rate. As of December 2024, 115 global clinical trials involving 83 distinct pluripotent stem cell-derived products had received regulatory approval, targeting indications across ophthalmology, neurology, and oncology. Two trials published in Nature in early 2025 reported encouraging results in Parkinson’s disease: one Japanese group and one North American group both injected neural cells derived from stem cells into patients with Parkinson’s and reported meaningful reductions in symptom severity at 18 to 24 months, results that have prompted plans for larger phase II trials.

To date, more than 1,200 patients have been treated with pluripotent stem cell-derived products in clinical trials, accumulating to over 100 billion clinically administered cells, with no generalizable safety concerns identified so far. That accumulating safety record is significant, it does not mean these therapies are without risk, but it does mean that the foundational concern of uncontrolled tumor formation, which dominated early discussions, is not materializing as the primary barrier it was once feared to be.

A critical perspective: Promise does not mean certainty

The optimism surrounding stem cell medicine deserves a counterweight. Potential treatments need to be subject to the highest standards of safety and efficacy, and regulators around the world must not put stem cell therapy’s promise at risk by rushing the final stage of the process. That concern is not abstract, unregulated stem cell clinics operating outside clinical trial frameworks have caused documented patient harm, and the gap between genuine research and commercial exploitation remains a live problem. Around 90% of pharmaceutical Phase III trials fail to produce an approved treatment, and stem cell therapies face the same brutal attrition. Statistical data on the low success rates of Phase III clinical trials in the pharmaceutical sector directly apply to stem cell therapies, which encounter similar challenges around clinical efficacy, safety, and regulatory approval.

The global stem cell therapy market was valued at approximately $14.8 billion in 2023 and is projected to reach $31.4 billion by 2030, which means commercial incentives are substantial, and patient education about what is genuinely approved versus what is still experimental is more important than ever.

Obesity and cellular memory: Why your fat cells don’t forget

One of the most consequential recent discoveries in metabolic science has nothing to do with willpower or caloric deficits, it concerns what obesity does to the cells themselves, and crucially, what remains after the weight is gone.

A landmark study published in Nature in November 2024 by researchers at ETH Zürich used advanced single-nucleus RNA sequencing to examine fat tissue from humans and mice before and after significant weight loss. The study found that both human and mouse adipose tissues retain cellular transcriptional changes after appreciable weight loss, and that persistent obesity-induced alterations in the epigenome of mouse adipocytes negatively affect their function and response to metabolic stimuli. In plain language: fat cells change their gene activity during obesity, and those changes do not fully reverse when weight is lost.

Mice carrying this obesogenic memory showed accelerated rebound weight gain, and the epigenetic memory could explain future transcriptional dysregulation in adipocytes in response to further high-fat diet feeding. Previously obese mice, when re-exposed to a high-fat diet, gained nearly three times as much weight as mice that had never been obese, despite being at the same weight at the point of re-exposure. The fat cells, beyond simply remembering their prior state of obesity, appeared to aim to return to this state, according to study co-author Ferdinand von Meyenn, an epigeneticist at ETH Zürich.

What epigenetics has to do with the yo-yo effect

Epigenetics refers to changes in gene activity that occur without altering the underlying DNA sequence. Think of it as a layer of biological annotation on top of your genes, marks that tell cells which genes to read loudly, which to quiet, and which to switch off entirely. These marks are responsive to environment: diet, stress, toxin exposure, and metabolic state all leave epigenetic signatures.

Research found that obesity-induced genes remained deregulated after weight loss, with downregulated metabolic genes and upregulated fibrosis and apoptosis-related genes, implying that obesity causes molecular changes in adipose tissue that weight loss alone does not reverse. Genes responsible for normal fat cell metabolism remained suppressed. Genes driving inflammation and tissue stiffening remained elevated. The biological function of the fat cell was altered, and it stayed altered.

This finding carries an important implication for how society understands obesity. Clinically, these findings challenge stigmatizing narratives around obesity by providing a biological basis for weight regain, independent of behavioral factors. The persistent difficulty of maintaining weight loss is not primarily a failure of discipline, it is, at least in part, a cellular phenomenon with measurable biological mechanisms.

It also raises questions about current weight loss medications. Research on semaglutide and tirzepatide has shown that substantial weight regain occurs after their withdrawal, indicating that at least these treatments do not induce stable, persistent changes in the epigenetic state of fat cells. Disrupting the obesogenic epigenetic memory itself, rather than simply reducing calorie intake or absorption, may be a necessary goal for genuinely durable weight management, and it is now an active area of research.

Frequently Asked Questions (FAQ)

What is the simplest way to explain what a stem cell is?

A stem cell is a cell that has not yet committed to a specific identity. It can divide to make copies of itself, and it can transform into more specialized cells, like muscle, nerve, or blood cells, depending on signals from its environment. Most cells in the body are fixed in their role; stem cells are not.

Are stem cell therapies available now, or are they still experimental?

Both. Several stem cell-based therapies are fully approved and in routine clinical use, bone marrow transplants, certain cord blood products, and most recently Ryoncil for pediatric graft-versus-host disease. Many others are in clinical trials at various stages. A large number of clinics worldwide offer stem cell treatments that have not been through clinical trials and are not approved, patients should be cautious about distinguishing between the two.

Does the epigenetic memory of obesity ever go away?

Current evidence suggests it persists for an extended period, but whether it is permanent is not yet established. Fat cells have an average lifespan of approximately ten years before being replaced, and they may retain epigenetic marks for extended periods, and currently, there are no pharmaceutical interventions available to erase the relevant epigenetic markers. Nutritional and lifestyle interventions may eventually modify these marks, but more research is needed.

What does this mean for people trying to lose weight?

It means that weight regain after loss has a genuine biological explanation that goes beyond motivation. It does not mean weight management is futile, quite the opposite. But it does mean that sustained interventions, whether dietary, pharmaceutical, or surgical, are likely needed for long-term success, rather than a single episode of weight loss. It also reinforces why preventing obesity in the first place, especially in children, carries such long-term significance.

Can iPSCs be used to treat any disease?

Not yet, but the range of diseases being explored in clinical trials is expanding rapidly, including Parkinson’s disease, age-related macular degeneration, type 1 diabetes, heart failure, and certain cancers. The technology is still being refined in terms of safety, manufacturing consistency, and long-term durability of effect.

Conclusion: Two frontiers, one body

Stem cell science and obesity research may seem like separate topics, but they share a common thread. Both are fundamentally about what happens at the level of the individual cell: how cells acquire their identity, how they remember past states, and how that memory shapes biology in ways that have profound consequences for health and disease.

Stem cells represent a future of medicine in which damaged or missing cells can be replaced, genetic errors corrected, and tissues regenerated, possibilities that are no longer theoretical, but increasingly clinical. The epigenetic memory of obesity represents a different kind of cellular reality: one that explains why the body resists change, why weight loss is genuinely hard to maintain, and why understanding biology at the cellular level matters for every person trying to improve their health.

In both cases, the science undercuts oversimplification. Stem cells are not miracle cures, they are powerful tools being carefully validated. Obesity is not a failure of character, it is a condition that reshapes cellular biology in ways that persist. The more clearly we understand both, the better equipped we are to make informed decisions about our own health and to interpret the medical advances that are transforming what is possible.

Last updated

April 1, 2026

Medically reviewed by:

Sources | Medically and scientifically proven evidence on stem cells

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