Scientists are increasingly concerned about excessive fat stored inside skeletal muscle, a condition linked to insulin resistance and age-related metabolic decline. This internal fat buildup is fueled by high-fat diets, sedentary lifestyles and aging, and it can impair the way muscles use glucose and fatty acids.
Unlike fat stored beneath the skin, tiny lipid droplets inside muscle cells can interfere directly with normal cellular function. Over time, this can reduce metabolic flexibility and increase the risk of type 2 diabetes and other lifestyle-related diseases. Researchers are therefore searching for strategies that specifically target muscle fat without damaging muscle tissue.
Blueberry compound under the spotlight
A Japanese research team led by Associate Professor Takakazu Mitani of Shinshu University has identified the berry-derived compound pterostilbene as a promising candidate. Pterostilbene is a polyphenol found in blueberries, grapes and several other fruits and is already known for its potential effects on the liver and adipose tissue.
The new study, published in Food Bioscience, investigated how pterostilbene affects skeletal muscle cells. Researchers were particularly interested in whether the compound could influence peroxisome proliferator-activated receptor δ, or PPARδ, a key regulator of fat burning and cellular energy use.
PPARδ plays a central role in fatty acid oxidation, helping cells convert fat into usable energy. When this pathway is active, it can limit lipid accumulation inside muscle fibers. However, there are currently no approved therapies that directly target excess muscle fat, leaving room for both medical and nutritional approaches.
How the lab experiments were done
To investigate potential natural compounds, the researchers screened a panel of food-derived phytochemicals using cultured C2C12 mouse skeletal muscle cells. They examined whether any of the compounds could reduce abnormal fat accumulation without interfering with the cells’ ability to grow and differentiate into muscle fibers.
Among the compounds tested, pterostilbene produced the most pronounced reduction in lipid accumulation. Importantly, treated cells continued to develop normally, suggesting that the compound did not interfere with basic muscle-cell development or maturation under laboratory conditions.
Further analysis showed that pterostilbene did not prevent fatty acids from entering muscle cells. Instead, researchers detected increased glycerol release into the surrounding medium, indicating that stored triglycerides were being broken down. Gene-expression analyses also showed increased activity in pathways involved in fatty acid oxidation.
Stabilizing a key metabolic regulator
The researchers then investigated the underlying molecular mechanism and found that pterostilbene increased PPARδ signaling in an unexpected way. Many experimental compounds activate PPARδ by binding directly to the receptor and influencing its activity.
Pterostilbene appeared to work differently. It increased the amount of PPARδ protein inside the cells by slowing its degradation through the ubiquitin-proteasome system, one of the major mechanisms cells use to dispose of proteins they no longer need.
With less PPARδ being degraded, more of the protein remained available to regulate genes involved in fat metabolism. This stabilization increased PPARδ transcriptional activity and strengthened the expression of genes that help convert stored lipids into energy.
The researchers suggest that identifying compounds capable of maintaining PPARδ stability could provide another direction for nutritional and pharmaceutical research into muscle fat metabolism.
From lab bench to real-world health?
Mitani and his colleagues argue that the findings provide a scientific foundation for exploring functional foods and supplements targeting muscle fat metabolism. Pterostilbene itself could potentially be investigated as a bioactive ingredient in products designed around metabolic health and healthy aging.
However, the findings are currently limited to experiments conducted in cultured cells. The study does not demonstrate that pterostilbene can prevent or treat obesity, type 2 diabetes or myosteatosis in animals or humans, nor does it establish appropriate doses or long-term safety for such uses.
Isolated compounds derived from foods can also behave differently in the body than the whole foods in which they naturally occur. Further research will therefore require controlled animal experiments followed by human trials to determine whether the observed effects on PPARδ and lipid breakdown also occur in living organisms.
Future studies are expected to examine how pterostilbene is absorbed, how effectively it reaches skeletal muscle and whether its effects on PPARδ occur without unwanted activity in other biological pathways. Such evidence would be needed before targeted nutritional or therapeutic applications could be considered.
For now, the findings add to research showing that certain plant-derived compounds can influence important metabolic regulators. While blueberries or supplements should not be considered substitutes for exercise and balanced nutrition, the study illustrates how food-derived molecules could eventually complement lifestyle measures aimed at supporting muscle and metabolic health.
