August 19, 2026

How Fat and Muscle Signal Each Other Into a Vicious Cycle in Sarcopenic Obesity

By Dr. Zakira Naureen, Associate Professor, University of Nizwa
Metabolic Health Body Composition Young Adults

In Simple Terms

  • Why losing muscle and gaining fat are not just two things that happen at once, but can actively make each other worse
  • Why chemical signals from your fat tissue can quietly work against your muscles, and signals from muscle can work against fat control
  • Why this pattern has already been found in some young adults with a completely normal BMI
  • What kind of exercise the research shows can help interrupt this cycle

Fat tissue and muscle tissue are often treated as opposites on a bathroom scale, one going up while hopefully the other stays put. But at a cellular level, both tissues are constantly exchanging chemical messages through the bloodstream, and neither works in isolation. When that exchange functions normally, it helps the body balance how much energy it stores and how much it burns. In sarcopenic obesity, something in that exchange goes wrong, and the result is not simply two separate problems sitting side by side. Excess fat and declining muscle appear to actively reinforce one another through a loop of signaling molecules that researchers now call adipomyokines.

Two Endocrine Organs Talking to Each Other

Adipose tissue, particularly the visceral fat that surrounds abdominal organs, is not just a storage depot. It functions as an endocrine organ, releasing proteins called adipokines into circulation. Two of the best studied are leptin, which signals fullness to the brain, and adiponectin, which has anti-inflammatory and insulin sensitizing effects and tends to fall as visceral fat expands. As visceral fat grows, it also ramps up secretion of pro-inflammatory cytokines, most notably interleukin-6 (IL-6) and tumor necrosis factor alpha (TNF-alpha), according to a 2022 review in the journal Cells describing the crosstalk between adipose cells and myocytes in sarcopenic obesity.

Muscle tissue does something similar in reverse. It secretes its own family of signaling proteins called myokines, including myostatin, a well known negative regulator of muscle growth, and irisin, which is released during muscle contraction and helps convert white fat into a more metabolically active, calorie burning form. The same review notes that IL-6 is unusual in that both fat and muscle secrete it, and its effect depends heavily on context: released by contracting muscle in short bursts, it supports fat oxidation and glucose uptake, but chronically elevated IL-6 from expanding visceral fat instead contributes to systemic low-grade inflammation.

How the Signals Turn Into a Vicious Cycle

The concerning part is how these pathways interact once fat mass rises and muscle mass falls together. Elevated myostatin, which increases in animal models and human subjects with obesity, does more than suppress muscle growth. The Cells review describes evidence that myostatin also promotes adipogenesis (the formation of new fat cells) and appears to inhibit the synthesis of irisin. Since irisin normally promotes fat browning and supports insulin sensitivity, less irisin means less of that protective effect, which in turn allows more fat accumulation and more inflammatory adipokine output. Rising TNF-alpha and IL-6 from visceral fat, meanwhile, interfere with insulin signaling inside muscle cells and are linked to impaired muscle protein synthesis, compounding the muscle loss side of the equation. A related process, the buildup of fat directly inside muscle fibers rather than just around them, has been covered in more depth in our earlier piece on myosteatosis, and it appears to be closely tied to this same inflammatory environment.

It is worth being honest about the uncertainty here. The Cells review itself notes that the relationship between circulating myostatin and skeletal muscle mass in humans remains controversial, with some studies finding an inverse relationship in frail older adults and others finding the opposite. The broad direction of the crosstalk (more visceral fat associated with more inflammatory signaling and less favorable myokine activity) is fairly consistent across studies, but the precise molecular sequence and how much any single messenger contributes is still being worked out.

Evidence From Young Adults, Not Just Older Patients

Sarcopenic obesity research has historically focused on older adults, but the 2022 consensus statement on definition and diagnostic criteria for sarcopenic obesity from the European Society for Clinical Nutrition and Metabolism (ESPEN) and the European Association for the Study of Obesity (EASO) makes a point of noting that the condition is not exclusively geriatric. Of 75 studies reviewed for that consensus process, 28 involved populations with a mean age under 65, and the panel explicitly states that obesity itself, independent of age, can drive muscle loss through oxidative stress, inflammation and insulin resistance.

More directly relevant to younger populations, a 2026 cross-sectional study in the journal Healthcare examined body composition data from 4,793 adults aged 18 to 35. Within the subset who had a normal BMI, 40.6 percent were classified as having normal-weight obesity, meaning a healthy BMI but a body fat percentage above 30 percent in women or 20 percent in men. That group showed significantly higher visceral fat area than their normal-weight, normal-fat peers, along with significantly lower skeletal muscle mass percentage and a lower phase angle, a bioelectrical impedance measure of cell membrane integrity that the study authors interpreted as compatible with a state of relative sarcopenia, even in people in their 20s and 30s with an unremarkable BMI. The authors were careful to note this is a cross-sectional, single-site convenience sample from Mexico and cannot establish causation, but it is a useful, recent illustration that the fat-muscle imbalance underlying sarcopenic obesity can already be measurable well before old age. Readers who want the fuller picture of how this shows up specifically in younger adults can see our complete guide to sarcopenic obesity in young adults.

What the Exercise Trials Show

If inflammatory crosstalk between fat and muscle helps drive the condition, the logical question is whether exercise can interrupt it, and here the trial evidence is more direct. A 2025 systematic review and network meta-analysis in Frontiers in Nutrition pooled 14 randomized controlled trials totaling 955 participants with sarcopenic obesity, comparing aerobic training, resistance training, combined resistance and aerobic training, and multicomponent training (which adds balance or flexibility work). Multicomponent training produced the largest reduction in body fat percentage and was the only modality that significantly increased fat-free mass, while resistance training alone was the most effective at improving handgrip strength. The review's authors also point to a mechanistic link: several of the pooled and cited trials found that multicomponent and combined training reduced circulating IL-6, TNF-alpha and high-sensitivity C-reactive protein, and that these reductions correlated with the improvements in body fat and lean mass, which is consistent with exercise working partly by calming the same inflammatory signaling described above rather than through calorie burning alone.

Where the Evidence Is Still Thin

A few caveats are worth keeping in mind. Almost all of the randomized exercise trials in this specific evidence base enrolled older adults who already met formal sarcopenic obesity criteria, not younger adults at earlier or subclinical stages, so the exact magnitude of benefit for a 25-year-old with normal-weight obesity is extrapolated rather than directly tested. The molecular crosstalk studies are also largely observational or based on cell and animal models, meaning they can show association and plausible mechanism but not always prove that a given signaling change is a cause of muscle loss rather than a downstream marker of it. And the adipomyokine story is only one contributor among several that overlap with it, alongside factors already covered on this site such as anabolic resistance from inactivity, insulin and testosterone shifts, and the muscle costs of very rapid weight loss.

What This Means for You

None of this requires waiting for a specialty blood panel before acting. The same intervention that shows up repeatedly in the trial evidence, structured exercise that combines resistance training with other modalities, is also the most accessible one. The consensus statement from ESPEN and EASO also recommends looking beyond BMI, using waist circumference and, where available, body composition or functional strength measures to catch this pattern earlier, since BMI alone cannot detect the visceral fat and reduced muscle mass at the center of this signaling loop.

This post is for general education and isn't medical advice. Speak with a healthcare provider about your individual risk.

References

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