Does brown fat decline with obesity and age?
Does brown fat decline with obesity and aging? What PET/CT evidence shows
Around 2007, doctors using PET/CT scans to look for cancer began noticing that some “hot spots” seen with this type of imaging were not tumors at all. Researchers later identified much of this activity as brown adipose tissue (BAT), or brown fat. Brown fat is unusually active metabolically, so it takes up a lot of glucose and shows up clearly on PET/CT scans.
Beginning in 2009, studies using PET/CT in humans showed that the amount of brown fat varies widely from person to person. One of the most consistent findings was that people with obesity tend to have less brown fat than lean people.
Key Health Benefits of Brown Fat
Higher amounts of brown fat have been linked to:
- Leanness [1-17]
- Better blood sugar control and insulin sensitivity [17-19]
- Increased fat oxidation (using fat for energy)
- Lower triglyceride levels
- Higher HDL (“good”) cholesterol [17]
These human findings match decades of animal research, especially in mice and rats. In animals, reducing brown fat tends to promote obesity and type 2 diabetes, while increasing it helps protect against those conditions. [1, 20-23]
Can We Increase Brown Fat in Humans?
Yes, brown fat can also be increased in humans. For example, repeated cold exposure for 10 days or more can raise brown fat volume and activity, increase resting energy use, and improve insulin sensitivity while reducing body fat. [17,24]
The Role of Aging
Brown fat activity naturally declines as we age [27,28]. Studies suggest this happens for two main reasons:
Reduced Stem Cell Renewal: The precursor cells responsible for generating new brown fat cells become less efficient over time [17].
Decreased Activity: The brown fat cells that do form in older adults are less active than those in younger adults [25,26].
This age-related decline in brown fat activity may help explain why maintaining a healthy weight becomes increasingly challenging as we get older.
Sources
1. Yoneshiro T, Aita S, Matsushita M, Okamatsu-Ogura Y, Kameya T, Kawai Y, Miyagawa M, Tsujisaki M, Saito M. Age-related decrease in cold-activated brown adipose tissue and accumulation of body fat in healthy humans. Obesity (Silver Spring). 2011 Sep;19(9):1755-60.
2. Becher T, Palanisamy S, Kramer DJ, Eljalby M, Marx SJ, Wibmer AG, Butler SD, Jiang CS, Vaughan R, Schöder H, Mark A, Cohen P. Brown adipose tissue is associated with cardiometabolic health. Nat Med. 2021 Jan;27(1):58-65. doi: 10.1038/s41591-020-1126-7.
3. van Marken Lichtenbelt WD, Vanhommerig JW, Smulders NM, Drossaerts JM, Kemerink GJ, Bouvy ND, Schrauwen P, Teule GJ. Cold-activated brown adipose tissue in healthy men. N Engl J Med. 2009 Apr 9;360(15):1500-8.
4. Cypess AM, Lehman S, Williams G, Tal I, Rodman D, Goldfine AB, Kuo FC, Palmer EL, Tseng YH, Doria A, Kolodny GM, Kahn CR. Identification and importance of brown adipose tissue in adult humans. N Engl J Med. 2009 Apr 9;360(15):1509-17. PubMed PMID: 19357406.
5. Virtanen KA, Lidell ME, Orava J, Heglind M, Westergren R, Niemi T, Taittonen M, Laine J, Savisto NJ, Enerbäck S, Nuutila P. Functional brown adipose tissue in healthy adults. N Engl J Med. 2009 Apr 9;360(15):1518-25. PubMed PMID: 19357407.
6. Crisan M, Casteilla L, Lehr L, Carmona M, Paoloni-Giacobino A, Yap S, Sun B, Leger B, Logar A, Penicaud L, Schrauwen P, Cameron-Smith D, Russell AP, Peault B, Giacobino JP. A reservoir of brown adipocyte progenitors in human skeletal muscle. Stem Cells. 2008 Sep;26(9):2425-33.
7. Vincent F, Nueda A, Lee J, Schenone M, Prunotto M, Mercola M. Phenotypic drug discovery: recent successes, lessons learned and new directions. Nat Rev Drug Discov. 2022 Dec;21(12):899-914. doi: 10.1038/s41573-022-00472-w.
8. Mocciaro G, Capodici A, De Amicis R. GLP-1 receptor agonists induce loss of lean mass: so does caloric restriction. BMJ Nutr Prev Health. 2025 Mar 3;8(1):e001206. doi: 10.1136/bmjnph-2025-001206.
9. Leibel RL, Rosenbaum M, Hirsch J. Changes in energy expenditure resulting from altered body weight. N Engl J Med. 1995 Mar 9;332(10):621-8. doi: 10.1056/NEJM199503093321001. Erratum in: N Engl J Med 1995 Aug 10;333(6):399. PMID: 7632212.
10. Dulloo AG. Physiology of weight regain: Lessons from the classic Minnesota Starvation Experiment on human body composition regulation. Obes Rev. 2021 Mar;22 Suppl 2:e13189. doi: 10.1111/obr.13189.
11. Dulloo AG, Jacquet J, Montani JP. Pathways from weight fluctuations to metabolic diseases: focus on maladaptive thermogenesis during catch-up fat. Int J Obes (Lond). 2002;26(Suppl 2):S46-S57.
12. Dulloo AG, Jacquet J, Seydoux J, Montani JP. The thrifty ‘catch-up fat’ phenotype: its impact on insulin sensitivity during growth trajectories to obesity and metabolic syndrome. Int J Obes (Lond). 2006;30 (Suppl 4):S23-S35. https://doi.org/10.1038/sj.ijo.0803516
13. Dulloo AG, Jacquet J, Girardier L. Poststarvation hyperphagia and body fat overshooting in humans: a role for feedback signals from lean and fat tissues. Am J Clin Nutr. 1997 Mar;65(3):717-23. doi: 10.1093/ajcn/65.3.717.
14. Dulloo AG, Jacquet J. Adaptive reduction in basal metabolic rate in response to food deprivation in humans: a role for feedback signals from fat stores. Am J Clin Nutr. 1998 Sep;68(3):599-606. doi: 10.1093/ajcn/68.3.599. PMID: 9734736.
15. Thivel D, Doucet É, Lazzer S, Montaurier C, Pereira B, Bosy-Westphal A, Muller MJ, Boirie Y, Isacco L. Adaptive thermogenesis in response to weight loss and weight regain: first evidence in adolescents with severe obesity. Br J Nutr. 2026 Jan 28;135(2):149-155. doi: 10.1017/S0007114525105837.
16. Yan M, Wang H, Sha W, Fu Y. UCP1-Dependent Thermogenic Adipose Tissue in Human Disease: Adipose-Centered Mechanisms, Biomarker Limitations, and Translational Perspectives. Int J Mol Sci. 2026 Jul 19;27(14):6416. doi: 10.3390/ijms27146416.
17. Saito M, Okamatsu-Ogura Y. Thermogenic Brown Fat in Humans: Implications in Energy Homeostasis, Obesity and Metabolic Disorders. World J Mens Health. 2023 Jul;41(3):489-507.
18. Matsushita M et al. Impact of brown adipose tissue on body fatness and glucose metabolism in healthy humans. Int J Obes 2014 38: 812-817.
19. Chondronikola M, Volpi E, Borsheim E, Porter C, Annamalai P, Enerback S, Lidell ME, Saraf MK, Labbe SM, Hurren NM, Yfanti C, Chao T, Andersen CR, Cesani F, Hawkins H, and Sidossis LS. Brown adipose tissue improves whole-body glucose homeostasis and insulin sensitivity in humans. Diabetes 63: 4089-4099, 2014.
20. Boss O, and Farmer SR. Recruitment of brown adipose tissue as a therapy for obesity-associated diseases. Front Endocrinol (Lausanne) 3: 14, 2012.
21. Himms-Hagen J. Brown adipose tissue thermogenesis, energy balance, and obesity. Can J Biochem Cell Biol. 1984 Jul;62(7):610-7. doi: 10.1139/o84-081. PMID: 6383575.
22. Rothwell NJ, Stock MJ. A role for brown adipose tissue in diet-induced thermogenesis. Nature. 1979 Sep 6;281(5726):31-5. doi: 10.1038/281031a0.
23. Trayhurn P. Origins and early development of the concept that brown adipose tissue thermogenesis is linked to energy balance and obesity. Biochimie. 2017 Mar;134:62-70. doi: 10.1016/j.biochi.2016.09.007.
24. Yoneshiro T, Aita S, Matsushita M, Kayahara T, Kameya T, Kawai Y, Iwanaga T, Saito M. Recruited brown adipose tissue as an antiobesity agent in humans. J Clin Invest. 2013 Aug;123(8):3404-8. doi: 10.1172/JCI67803.
25. Rogers NH, Landa A, Park S, Smith RG. Aging leads to a programmed loss of brown adipocytes in murine subcutaneous white adipose tissue. Aging Cell. 2012;11:1074–1083. doi: 10.1111/acel.12010. [DOI] [PMC free article] [PubMed] [Google Scholar]
26. Graja A, Schulz TJ. Mechanisms of aging-related impairment of brown adipocyte development and function. Gerontology. 2015;61:211–217. doi: 10.1159/000366557. [DOI] [PubMed] [Google Scholar]
27. Ouellet V, Routhier-Labadie A, Bellemare W, Lakhal-Chaieb L, Turcotte E, Carpentier AC, and Richard D. Outdoor temperature, age, sex, body mass index, and diabetic status determine the prevalence, mass, and glucose-uptake activity of 18F-FDG-detected BAT in humans. J Clin Endocrinol Metab 96: 192-199, 2011.
28. Pfannenberg C, Werner MK, Ripkens S, Stef I, Deckert A, Schmadl M, Reimold M, Haring HU, Claussen CD, and Stefan N. Impact of age on the relationships of brown adipose tissue with sex and adiposity in humans. Diabetes 59: 1789-1793, 2010.
Does brown fat decline with obesity and aging? What PET/CT evidence shows
Around 2007, doctors using PET/CT scans to look for cancer began noticing that some “hot spots” seen with this type of imaging were not tumors at all. Researchers later identified much of this activity as brown adipose tissue (BAT), or brown fat. Brown fat is unusually active metabolically, so it takes up a lot of glucose and shows up clearly on PET/CT scans.
Beginning in 2009, studies using PET/CT in humans showed that the amount of brown fat varies widely from person to person. One of the most consistent findings was that people with obesity tend to have less brown fat than lean people.
Key Health Benefits of Brown Fat
Higher amounts of brown fat have been linked to:
- Leanness [1-17]
- Better blood sugar control and insulin sensitivity [17-19]
- Increased fat oxidation (using fat for energy)
- Lower triglyceride levels
- Higher HDL (“good”) cholesterol [17]
These human findings match decades of animal research, especially in mice and rats. In animals, reducing brown fat tends to promote obesity and type 2 diabetes, while increasing it helps protect against those conditions. [1, 20-23]
Can We Increase Brown Fat in Humans?
Yes, brown fat can also be increased in humans. For example, repeated cold exposure for 10 days or more can raise brown fat volume and activity, increase resting energy use, and improve insulin sensitivity while reducing body fat. [17,24]
The Role of Aging
Brown fat activity naturally declines as we age [27,28]. Studies suggest this happens for two main reasons:
Reduced Stem Cell Renewal: The precursor cells responsible for generating new brown fat cells become less efficient over time [17].
Decreased Activity: The brown fat cells that do form in older adults are less active than those in younger adults [25,26].
This age-related decline in brown fat activity may help explain why maintaining a healthy weight becomes increasingly challenging as we get older.
Sources
1. Yoneshiro T, Aita S, Matsushita M, Okamatsu-Ogura Y, Kameya T, Kawai Y, Miyagawa M, Tsujisaki M, Saito M. Age-related decrease in cold-activated brown adipose tissue and accumulation of body fat in healthy humans. Obesity (Silver Spring). 2011 Sep;19(9):1755-60.
2. Becher T, Palanisamy S, Kramer DJ, Eljalby M, Marx SJ, Wibmer AG, Butler SD, Jiang CS, Vaughan R, Schöder H, Mark A, Cohen P. Brown adipose tissue is associated with cardiometabolic health. Nat Med. 2021 Jan;27(1):58-65. doi: 10.1038/s41591-020-1126-7.
3. van Marken Lichtenbelt WD, Vanhommerig JW, Smulders NM, Drossaerts JM, Kemerink GJ, Bouvy ND, Schrauwen P, Teule GJ. Cold-activated brown adipose tissue in healthy men. N Engl J Med. 2009 Apr 9;360(15):1500-8.
4. Cypess AM, Lehman S, Williams G, Tal I, Rodman D, Goldfine AB, Kuo FC, Palmer EL, Tseng YH, Doria A, Kolodny GM, Kahn CR. Identification and importance of brown adipose tissue in adult humans. N Engl J Med. 2009 Apr 9;360(15):1509-17. PubMed PMID: 19357406.
5. Virtanen KA, Lidell ME, Orava J, Heglind M, Westergren R, Niemi T, Taittonen M, Laine J, Savisto NJ, Enerbäck S, Nuutila P. Functional brown adipose tissue in healthy adults. N Engl J Med. 2009 Apr 9;360(15):1518-25. PubMed PMID: 19357407.
6. Crisan M, Casteilla L, Lehr L, Carmona M, Paoloni-Giacobino A, Yap S, Sun B, Leger B, Logar A, Penicaud L, Schrauwen P, Cameron-Smith D, Russell AP, Peault B, Giacobino JP. A reservoir of brown adipocyte progenitors in human skeletal muscle. Stem Cells. 2008 Sep;26(9):2425-33.
7. Vincent F, Nueda A, Lee J, Schenone M, Prunotto M, Mercola M. Phenotypic drug discovery: recent successes, lessons learned and new directions. Nat Rev Drug Discov. 2022 Dec;21(12):899-914. doi: 10.1038/s41573-022-00472-w.
8. Mocciaro G, Capodici A, De Amicis R. GLP-1 receptor agonists induce loss of lean mass: so does caloric restriction. BMJ Nutr Prev Health. 2025 Mar 3;8(1):e001206. doi: 10.1136/bmjnph-2025-001206.
9. Leibel RL, Rosenbaum M, Hirsch J. Changes in energy expenditure resulting from altered body weight. N Engl J Med. 1995 Mar 9;332(10):621-8. doi: 10.1056/NEJM199503093321001. Erratum in: N Engl J Med 1995 Aug 10;333(6):399. PMID: 7632212.
10. Dulloo AG. Physiology of weight regain: Lessons from the classic Minnesota Starvation Experiment on human body composition regulation. Obes Rev. 2021 Mar;22 Suppl 2:e13189. doi: 10.1111/obr.13189.
11. Dulloo AG, Jacquet J, Montani JP. Pathways from weight fluctuations to metabolic diseases: focus on maladaptive thermogenesis during catch-up fat. Int J Obes (Lond). 2002;26(Suppl 2):S46-S57.
12. Dulloo AG, Jacquet J, Seydoux J, Montani JP. The thrifty ‘catch-up fat’ phenotype: its impact on insulin sensitivity during growth trajectories to obesity and metabolic syndrome. Int J Obes (Lond). 2006;30 (Suppl 4):S23-S35. https://doi.org/10.1038/sj.ijo.0803516
13. Dulloo AG, Jacquet J, Girardier L. Poststarvation hyperphagia and body fat overshooting in humans: a role for feedback signals from lean and fat tissues. Am J Clin Nutr. 1997 Mar;65(3):717-23. doi: 10.1093/ajcn/65.3.717.
14. Dulloo AG, Jacquet J. Adaptive reduction in basal metabolic rate in response to food deprivation in humans: a role for feedback signals from fat stores. Am J Clin Nutr. 1998 Sep;68(3):599-606. doi: 10.1093/ajcn/68.3.599. PMID: 9734736.
15. Thivel D, Doucet É, Lazzer S, Montaurier C, Pereira B, Bosy-Westphal A, Muller MJ, Boirie Y, Isacco L. Adaptive thermogenesis in response to weight loss and weight regain: first evidence in adolescents with severe obesity. Br J Nutr. 2026 Jan 28;135(2):149-155. doi: 10.1017/S0007114525105837.
16. Yan M, Wang H, Sha W, Fu Y. UCP1-Dependent Thermogenic Adipose Tissue in Human Disease: Adipose-Centered Mechanisms, Biomarker Limitations, and Translational Perspectives. Int J Mol Sci. 2026 Jul 19;27(14):6416. doi: 10.3390/ijms27146416.
17. Saito M, Okamatsu-Ogura Y. Thermogenic Brown Fat in Humans: Implications in Energy Homeostasis, Obesity and Metabolic Disorders. World J Mens Health. 2023 Jul;41(3):489-507.
18. Matsushita M et al. Impact of brown adipose tissue on body fatness and glucose metabolism in healthy humans. Int J Obes 2014 38: 812-817.
19. Chondronikola M, Volpi E, Borsheim E, Porter C, Annamalai P, Enerback S, Lidell ME, Saraf MK, Labbe SM, Hurren NM, Yfanti C, Chao T, Andersen CR, Cesani F, Hawkins H, and Sidossis LS. Brown adipose tissue improves whole-body glucose homeostasis and insulin sensitivity in humans. Diabetes 63: 4089-4099, 2014.
20. Boss O, and Farmer SR. Recruitment of brown adipose tissue as a therapy for obesity-associated diseases. Front Endocrinol (Lausanne) 3: 14, 2012.
21. Himms-Hagen J. Brown adipose tissue thermogenesis, energy balance, and obesity. Can J Biochem Cell Biol. 1984 Jul;62(7):610-7. doi: 10.1139/o84-081. PMID: 6383575.
22. Rothwell NJ, Stock MJ. A role for brown adipose tissue in diet-induced thermogenesis. Nature. 1979 Sep 6;281(5726):31-5. doi: 10.1038/281031a0.
23. Trayhurn P. Origins and early development of the concept that brown adipose tissue thermogenesis is linked to energy balance and obesity. Biochimie. 2017 Mar;134:62-70. doi: 10.1016/j.biochi.2016.09.007.
24. Yoneshiro T, Aita S, Matsushita M, Kayahara T, Kameya T, Kawai Y, Iwanaga T, Saito M. Recruited brown adipose tissue as an antiobesity agent in humans. J Clin Invest. 2013 Aug;123(8):3404-8. doi: 10.1172/JCI67803.
25. Rogers NH, Landa A, Park S, Smith RG. Aging leads to a programmed loss of brown adipocytes in murine subcutaneous white adipose tissue. Aging Cell. 2012;11:1074–1083. doi: 10.1111/acel.12010. [DOI] [PMC free article] [PubMed] [Google Scholar]
26. Graja A, Schulz TJ. Mechanisms of aging-related impairment of brown adipocyte development and function. Gerontology. 2015;61:211–217. doi: 10.1159/000366557. [DOI] [PubMed] [Google Scholar]
27. Ouellet V, Routhier-Labadie A, Bellemare W, Lakhal-Chaieb L, Turcotte E, Carpentier AC, and Richard D. Outdoor temperature, age, sex, body mass index, and diabetic status determine the prevalence, mass, and glucose-uptake activity of 18F-FDG-detected BAT in humans. J Clin Endocrinol Metab 96: 192-199, 2011.
28. Pfannenberg C, Werner MK, Ripkens S, Stef I, Deckert A, Schmadl M, Reimold M, Haring HU, Claussen CD, and Stefan N. Impact of age on the relationships of brown adipose tissue with sex and adiposity in humans. Diabetes 59: 1789-1793, 2010.
