Phytoene in tomatoes may help protect against fatty liver disease

New study suggests a lesser-known compound in tomatoes may help protect against fatty liver disease, which affects more than 1 in 3 American adults.

For decades, the red pigment lycopene has been considered the tomato’s star nutrient. But new research from Tufts University suggests that phytoene, a colorless precursor of lycopene, may also contribute to tomatoes’ protective effects against a form of chronic fatty liver disease affecting up to 38% of U.S. adults.  

The study, published in Molecular Nutrition & Food Science, found that mice given phytoene developed substantially less fatty liver disease than mice fed the same unhealthy diet without the compound. Although it is not visible in ripe red tomatoes, phytoene is a natural building block that plants convert into lycopene and other carotenoids—the red, yellow, and orange pigments that give many fruits and vegetables their vibrant colors.  

As many as 100 million adults in the United States—and up to 75% of Americans with obesity or diabetes—are estimated to have metabolic dysfunction-associated steatotic liver disease. In this condition, too much fat builds up in liver cells. Over time, this excessive fat accumulation can cause liver inflammation and damage that, in more advanced cases, leads to scarring of the liver called cirrhosis.  

Scientists have known for years that tomatoes may help protect the liver. Yet tomato powder has outperformed purified lycopene in protecting the liver in animal studies, suggesting that other compounds in tomatoes may also contribute to these beneficial effects.

Both lycopene and phytoene are found in substantial amounts in tomatoes and tomato products. But we know from previous research that phytoene is actually more readily absorbed by the body.”

Na Youn Lee, study’s lead author and Ph.D. candidate at the Gerald J. and Dorothy R. Friedman School of Nutrition Science and Policy, Tufts University

For the new study, the researchers fed two groups of mice a high-refined-carbohydrate diet for six months to mimic dietary patterns associated with fatty liver disease in humans, including high consumption of sugary foods and beverages. Half of the mice also received phytoene supplementation at a dose equivalent to a person eating about three to four medium-sized raw tomatoes or 100 grams of tomato paste—or a little more than a third of a cup—per day.

The team then compared liver health, metabolism, and gut bacteria in the mice that received phytoene with those that did not. The scientists also examined differences between male and female mice, as well as between normal mice and mice lacking two enzymes involved in converting carotenoids into biologically active metabolites.

The mice given phytoene developed much less severe fatty liver disease than those that did not receive the supplement. Rather than working by altering the gut microbiome, phytoene appeared to activate several key proteins involved in regulating liver metabolism, helping the liver burn excess fat for energy rather than allowing it to accumulate.

Mice that lacked the enzymes needed to metabolize phytoene accumulated much higher levels of the compound in their bodies but did not receive the same protection against fatty liver disease. This finding suggests that the liver-protective effects may come from smaller compounds produced when the body breaks down phytoene. Because people can have genetic differences in the enzymes that metabolize phytoene, more research is needed to identify these metabolites and determine whether some individuals may benefit more from phytoene than others.

The study also found that females accumulated more phytoene in the liver than males, suggesting that sex may influence how the body absorbs or metabolizes the compound. The authors noted that future studies could explore whether these differences affect phytoene’s ability to protect against fatty liver disease.

“Our findings have broad implications, as phytoene is not only abundant in yellow, orange, and red tomatoes, but also exists in many common fruits and vegetables, including carrots, red peppers, pink grapefruit, watermelon, and apricots,” said Xiang-Dong Wang, the study’s senior author and a senior scientist at the Jean Mayer USDA Human Nutrition Research Center on Aging at Tufts University. “Should further research validate our findings, encouraging people to eat more phytoene-rich fruits and vegetables could be a useful strategy to help prevent metabolic liver disease or slow its progression in high-risk individuals.”