Anthocyanin antioxidants in tart cherries improve cardiovascular and diabetes lab values, and activate PPAR genes to burn fat.

UMHS – Phytonutrients in tart cherries have even more potential health benefits than previously expected, according to new data from an animal study conducted by University of Michigan Health System researchers that might earn tart cherries the label of “superfood.”

In a study involving rats, the animals that received powdered tart cherries in their diet had lower total cholesterol, lower blood sugar, less fat storage in the liver, lower oxidative stress and increased production of a molecule that helps the body handle fat and sugar, compared with rats that didn’t receive cherries as part of an otherwise similar diet. All of the rats had a predisposition toward high cholesterol and pre-diabetes, but not obesity.

All the measures on which the two groups of animals differed are linked to metabolic syndrome, a collection of risk factors linked to high rates of heart disease and Type 2 diabetes. Tens of millions of Americans have metabolic syndrome; most don’t know it.

The researchers say the correlation between cherry intake and significant changes in metabolic measurements suggest a positive effect from the high concentrations of antioxidant compounds called anthocyanins that are found in tart cherries. The new results were announced in an oral presentation at the Experimental Biology 2007 meeting in Washington, D.C.

It’s not yet known if cherry-rich diets might have a similar impact in humans, but a
U-M team will soon launch a small clinical trial to start to find out. The amount of cherries used in the study is estimated to be the human intake equivalent of about 1 ¼ to 1 ½ cups of whole frozen cherries or a little more than ½ cup of dried cherries per day. Previous studies have shown that the compounds in cherries may offer protection against heart disease due to enhancements in blood vessel health. Other studies suggest that cherries have anti-inflammatory benefits that may help ease the pain of arthritis and gout.

The study’s lead author is E. Mitchell Seymour, M.S., a U-M research associate and supervisor of the U-M Cardioprotection Research Laboratory, which studies the potential preventive benefits of antioxidant-rich foods. Support for the new study comes from an unrestricted grant from the Cherry Marketing Institute, a trade association for the cherry industry. CMI has no influence on the design, conduct or analysis of any U-M research it funds. (Cherry-enriched diets reduce metabolic syndrome and oxidative stress in lean Dahl-SS rats. Experimental Biology 2007 225.8)

“Rats fed tart cherries as 1 percent of their total diet had reduced markers of metabolic syndrome,” says Seymour. “Previous research by other groups studied pure anthocyanin compounds rather than anthocyanin-containing whole foods, and they used concentrations of anthocyanins that would be very difficult if not impossible to obtain in the diet.” “We are interested in a whole-foods approach, using amounts of fruit that are relevant to human diets. We are enthusiastic about the findings that tart cherries conferred these beneficial effects at such a modest daily intake.”

“These data from whole tart cherries join other findings that suggest a correlation between anthocyanin intake and reductions in cardiovascular and metabolic risk factors,” he says.

The rats were fed either a carbohydrate-enriched diet or a diet that, by weight, included 1 percent cherries or 10 percent cherries. The higher cherry dose was used to look for any toxic effects; none were seen.

The cherries were Montmorency tart cherries grown in northern Michigan, frozen, and powdered. Michigan is the nation’s largest producer of tart cherries, which are used in pies and jams as well as juice. They are different from the sweet Bing cherries that are often eaten raw, and have higher concentrations of antioxidant anthocyanins than sweet cherries.

By the end of the study, the rats that received the 1-percent cherry diet had total cholesterol, triglyceride, glucose and insulin levels that were significantly lower than those of the rats that did not receive cherries. The same was true for those on the 10-percent cherry diet, compared with rats that received a diet with an equivalently high level of carbohydrates not from cherries.

The researchers also measured plasma TEAC, a measure of antioxidant capacity in the blood on which a higher reading means better ability to neutralize damaging free radical molecules produced in the body during metabolism. The rats that received cherries had higher antioxidant capacity, indicating lower oxidative stress in their bodies, than those that did not.

In addition to blood measures, the researchers measured the level of fat in the livers of the rats, and the genetic expression of PPAR (peroxisome proliferator-activating receptor) in the liver.

The “fatty liver” measure is important because the storage of excess energy as fat in the liver is a common effect in metabolic syndrome – and because it feeds the vicious cycle of increased cholesterol and decreased response to insulin that can lead to cardiovascular disease and Type 2 diabetes.

Meanwhile, the measure of PPAR messenger RNA in the liver reflects the readiness of the liver tissue to express functional PPAR. PPAR is important to the process by which the body burns fat instead of storing it, and it is important in the formation of blood lipids like LDL, typically known as the “bad cholesterol”. Drugs in the classes known as thiazolidinediones and glitazars activate PPAR and are often used to manage high cholesterol and risk for Type 2 diabetes.

In the current study, the rats that received cherries had both a lower level of fat in their livers, and a higher expression of the PPAR genes for PPAR-alpha and PPAR-gamma than those that did not. The correlation between the two was dose-dependent, but the results of the 1 percent group were almost as good as the 10% group.

Now, the Cardioprotection Laboratory team has embarked on a new study in rats that have Type 2 diabetes, both with and without obesity and in the presence of low-fat and high-fat diets. They will look at whether tart cherries have an impact on the storage of fat in fat tissue and in muscle, and on the production of specific blood lipids like LDL and HDL. In addition, they will characterize tart cherries chemically, to assess the levels of phytochemicals in whole cherries, cherry juice and dry cherries, so that we can one day have even better data on the benefits of tart cherries for cardiovascular health, blood sugar, and fat metabolism.