A natural compound present in blueberries and grapes may help muscle cells break down stored fat, according to new laboratory research from Japan. However, the findings are limited to cultured mouse muscle cells and do not demonstrate fat loss in people.

The compound, pterostilbene, is a naturally occurring antioxidant found in blueberries, grapes and other berries. Previous research has connected it to metabolic benefits, but researchers knew little about its potential effects on skeletal muscle.

During laboratory experiments, the Japanese research team examined how pterostilbene affected cultured mouse skeletal tissue. The compound increased fatty acid oxidation and reduced lipid accumulation in the cells.

The findings were published Sept. 1 in the journal Food Bioscience. According to a news release, abnormal fat buildup can result from diets high in fat, inactivity and aging.

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Excess fat within muscle cells can interfere with how the body uses glucose and fatty acids. It may also contribute to insulin resistance, according to the article.

Researchers screened several compounds derived from food to compare their effects in the cultured cells. Pterostilbene produced the strongest reduction in fat accumulation without interfering with muscle growth.

The compound appeared to preserve a protein that helps regulate how cells process fat, according to the study. Researchers said this process encouraged cells to break down fat already stored within them.

"Our findings establish a scientific framework for developing functional foods and nutritional supplements that target muscle fat metabolism," lead researcher Takakazu Mitani, an associate professor at Shinshu University, said in a statement.

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Mitani also said the research offers an "experimental framework" that could help scientists identify other natural compounds capable of protecting the same protein. The work therefore provides researchers with a method for investigating additional compounds derived from food.

At the same time, the results represent an early step rather than evidence that blueberries, grapes or supplements can produce fat loss in humans. The experiments were performed in cultured mouse cells, not in animals or people.

The findings could provide a starting point for studying dietary approaches that might one day help address obesity, type 2 diabetes and metabolic decline associated with aging. However, studies involving both humans and animals are still needed to determine whether the laboratory effect translates beyond cultured cells.

Johannah Katz, a registered dietitian from Florida, warned that experiments using cells cannot reflect the full complexity of metabolism in people. Using a cell model "strips away the complexity of human metabolism," she told Fox News Digital.

"In people, pterostilbene has to be digested, absorbed, metabolized, circulated and actually reach muscle tissue at an effective dose," Katz said. The sequence creates questions that the laboratory experiments did not answer.

"We also can't assume mouse muscle cells will respond exactly like human muscle," she added. Therefore, the cellular response observed by the researchers cannot be treated as proof of the same response in people.

Katz said the study identified a potential mechanism that may help explain why fat accumulation was reduced in the cells. That result is different from demonstrating that eating blueberries or taking pterostilbene supplements directly causes fat loss.

"Blueberries and grapes are nutritious foods for many reasons, but this study alone doesn't show that eating more of them will reduce fat buildup in human muscle," Katz said.

The research ultimately points to a possible role for pterostilbene in muscle fat metabolism while leaving major questions unresolved.