A handful of grapes, a few weeks, and a small study has landed on a big claim.
Researchers say eating about three daily servings of grapes for two weeks changed gene expression in skin cells from four human volunteers and helped their skin better resist damage from ultraviolet radiation in sunlight.
The study found the grape-related genetic activity was “ubiquitous and variable” but, in all four volunteers, supported the skin’s ability to withstand UV damage.
Biochemist John Pezzuto and his coauthors reported that skin cells from the volunteers showed enhanced keratinization, a process in which skin cells flatten and build up keratin proteins that form a protective layer. The sampled cells also showed signs of cornification, which the researchers described as another protective response involving programmed cell death, along with other genetic changes identified through Gene Ontology enrichment analysis.
The researchers said those changes were matched by lower levels of malondialdehyde across the 30-day study period. They described malondialdehyde as a chemical marker of oxidative stress from UV damage, and said levels were sometimes reduced by two-fold or three-fold compared to control skin samples.
Why that happened is still unclear. “The mechanism responsible for this grape-induced diminution of malondialdehyde generation remains to be characterized,” the team wrote.
Pezzuto, dean of the College of Pharmacy and Health Sciences at Western New England University, said in a statement he was “now certain” that grapes “mediate a nutrigenomic response in humans.”
The new paper builds on earlier work by Pezzuto and colleagues. In a prior study of 29 participants who ate 2.25 cups of grapes per day for a similar two-week period, 31 percent developed greater resistance to UV exposure.
For the new study, the researchers randomly selected four volunteers from that group of 29 to undergo the gene expression analysis. The paper was published in May in ACS Nutrition Science.
Pezzuto has also studied resveratrol, a bioactive compound found in grapes and grape products including red wine. He has said that work helped support his view of grapes as a “superfood” alongside produce such as açai berries, blueberries and broccoli.
“Much of the attention received by grapes stem from our research,” as Pezzuto told NPR’s The Academic Minute in August. “But importantly, grapes contain more than 1600 natural compounds and they all function together in complex ways.”
Pezzuto said the findings may extend beyond skin. “Beyond skin, it is nearly certain that grape consumption affects gene expression in other somatic tissues of the body, such as liver, muscle, kidney, and even brain,” he said. “This helps us to understand how consumption of a whole food, in this case grapes, affects our overall health.”
The study was financially supported by the California Table Grape Commission, a public group set up by the California state legislature in 1967 to “protect and enhance the reputation of California fresh grapes.”
Pezzuto and coauthor Richard B. van Breemen, a pharmacologist at Oregon State, also serve on the commission’s scientific advisory committee.
“It’s very exciting to be working in the post-genomics era where we can finally start to employ functional genomics and actually visualize complex matrices indicative of nutrigenomic responses,” Pezzuto said.
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