Mice on a cysteine-free diet lost a third of their body weight by rapidly burning fat—exposing how one small amino acid plays a massive role in energy production and cellular stress.
Scientists genetically altered mice so they couldn’t make the amino acid cysteine and fed them a diet completely lacking it. In just one week, the mice lost a staggering 30% of their body weight.
This dramatic weight loss was due to a breakdown in energy metabolism caused by the depletion of coenzyme A, a molecule critical to turning food into energy.
Cysteine Deprivation Sparks Rapid Weight Loss
In a striking new study, mice that were genetically engineered to stop producing the amino acid cysteine, and then fed a cysteine-free diet, lost 30 percent of their body weight in just one week.
Published on May 21 in Nature, the research shows that cysteine depletion throws the body’s metabolism into chaos. Without this essential amino acid, the mice’s cells could no longer convert food into energy effectively. As a result, their bodies began burning through fat stores at a rapid pace in a desperate attempt to meet energy demands.
Led by researchers at NYU Grossman School of Medicine, the study sheds light on how cells process fuel sources like carbohydrates and fats. It also highlights the central role of a small molecule called coenzyme A (CoA). When cysteine levels dropped, CoA levels plummeted as well, crippling the cellular machinery needed to turn food into energy.
CoA is involved in over 100 metabolic reactions and works with about 4% of all enzymes in the body. Until now, it’s been difficult to study directly because mice with defective CoA production usually don’t survive past infancy. But this research offers the first detailed look at how CoA operates in adult mice—and what happens when it fails.
A Fundamental Shift in How We View Metabolism
“Our surprising findings reveal that low cysteine levels triggered rapid fat loss in our study mice by activating a network of interconnected biological pathways,” said co-senior study author Evgeny Nudler, PhD, the Julie Wilson Anderson Professor in the Department of Biochemistry and Molecular Pharmacology at NYU Grossman School of Medicine, and an investigator with the Howard Hughes Medical Institute. “While driving weight loss in the clinic remains a key future mission, we are most excited for the moment about the profound, fundamental aspects of metabolism revealed in this study,” added Dr. Nudler.
The current finding does not immediately suggest a new approach to weight loss, the authors caution, as cysteine is found in nearly all foods. Achieving a truly cysteine-free diet would require patients to consume a specially formulated solution that would be challenging for most. Moreover, because cysteine is involved in numerous cellular pathways, eliminating it, such as through a drug that inhibits cysteine production, could make organs more vulnerable to everyday toxins, including medications.
Plant-Based Diets and Sulfur Amino Acid Intake
That said, the study authors say it is worth considering that fruits, vegetables, and legumes contain much lower levels of cysteine and its precursor, the sulfur-containing amino acid methionine, than red meat. While earlier studies have linked low sulfur amino acid intake to health benefits, this study clarifies that these benefits are due to cysteine depletion specifically, and not methionine restriction.
“Given that achieving maximum cysteine deprivation weight loss in the mice was dependent on both diet and deletion of the gene, moving forward we can now restore cysteine production genetically in specific cells or tissues and determine the role of each in the dramatic weight loss we observed,” said co-senior author Dan L. Littman, MD, PhD, the Helen L. and Martin S. Kimmel Professor of Molecular Immunology in the Department of Pathology, and a professor in the Department of Cell Biology, at NYU Grossman School of Medicine. “We hope in the future to hijack parts of this process to induce a similar weight loss in humans but without completely removing cysteine,” added Dr. Littman, who is also an investigator with the Howard Hughes Medical Institute.
A Unique Look at Essential Amino Acids
The study is the first to examine the effects of removing cysteine, or any of the nine essential amino acids, which must be obtained through diet and are required for building proteins that make up most of the body’s enzymes, tissues, and signaling molecules. The findings revealed that eliminating cysteine from the mammalian body led to far greater weight loss than the removal of any other essential amino acid.
Specifically, cysteine deprivation disrupted oxidative phosphorylation, the main process for producing adenosine triphosphate (ATP), the molecule that serves as cells’ energy currency. Oxidative phosphorylation is known to be tightly dependent on CoA. As a result, sugar-derived intermediate molecules (carbon skeletons) such as pyruvate, orotate, citrate, and α-ketoglutarate were no longer used efficiently, and were instead lost in the urine. In response, the body turned to stored lipids (fats) to make energy.
Cellular Stress Responses Amplify Fat Loss
Further, the team found that cysteine restriction activates both the integrated stress response (ISR), a signaling network that restores cellular balance after stress, and the oxidative stress response (OSR), which is triggered by higher levels of reactive oxygen species (ROS) following depletion of glutathione, the body’s primary antioxidant. ROS can oxidize (take away electrons from) and damage sensitive cell parts like DNA.
Remarkably, this simultaneous activation of ISR and OSR—previously observed only in cancer cells—was shown to occur in normal tissues in mice in the cysteine-restriction group, with the two stress responses reinforcing each other. The study also shows that ISR and OSR, acting independently of CoA depletion, increase production of the stress hormone GDF15, which contributes to food aversion and degradation of acetyl-CoA-carboxylase, a key enzyme in lipid synthesis. This increased weight loss further in the study mice by preventing the replenishment of their fat stores.
Reference: “Unravelling cysteine-deficiency-associated rapid weight loss” by Alan Varghese, Ivan Gusarov, Begoña Gamallo-Lana, Daria Dolgonos, Yatin Mankan, Ilya Shamovsky, Mydia Phan, Rebecca Jones, Maria Gomez-Jenkins, Eileen White, Rui Wang, Drew R. Jones, Thales Papagiannakopoulos, Michael E. Pacold, Adam C. Mar, Dan R. Littman and Evgeny Nudler, 21 May 2025, Nature.
DOI: 10.1038/s41586-025-08996-y
Along with Drs. Evgeny Nudler and Dan Littman, the study’s co-senior authors, co-first authors were Alan Varghese, a joint student in labs of Drs Littman and Nudler in the Department of Cell Biology, and Ivan Gusarov in the Department of Biochemistry and Molecular Pharmacology at NYU Grossman School of Medicine. Additional NYU Langone contributors included Daria Dolgonos, Yatin Mankan, and Mydia Phan from the Department of Cell Biology; Ilya Shamovsky and Drew Jones from the Department of Biochemistry and Molecular Pharmacology; Begoña Gamallo-Lana and Adam Mar from the Department of Neuroscience; Rebecca Jones from the Division of Advanced Research Technologies; Thales Papagiannakopoulos from the Department of Pathology, and Michael Pacold from the Department of Radiation Oncology and Perlmutter Cancer Center. Other study authors were Maria Gomez-Jenkins and Eileen White of Rutgers Cancer Institute of New Jersey, and Rui Wang of the Department of Biology at York University in Toronto.
The study was supported by the long-term funding from the Howard Hughes Medical Institute (HHMI) and the Blavatnik Family Foundation. Additional support was provided by the National Institutes of Health grants S10OD010584-01A1, S10OD018338-01, 1OT2CA278609-01, R35GM147119, and R01AI158687. The research was also funded by the American Cancer Society (grant RSG-21-115-01-MM), the Natural Sciences and Engineering Research Council of Canada (grant RGPIN-2023-05099), and Cancer Research UK (grant CGCATF-2021/100022).
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