Few fruits have garnered as much attention in the health research literature as grapes. Part of the reason may be their widespread presence in diets worldwide. With the exception of Antarctica, grapes are cultivated on all of the earth's continents, and researchers from many different countries have been especially interested in this food. But an even greater part of the reason involves the amazing nutrient composition of grapes themselves. Every year, it seems like the list of health-supportive grape nutrients grows longer, and it can be challenging just to keep up with the many phytonutrients provided by this popular food.
Organized according to science-based categories, the list below will give you a general idea of the phytonutrient richness of grapes. While a single grape variety is unlikely to contain all of the phytonutrients listed below, grapes as a group have been shown to provide us with the following health-supportive nutrients:
- Stilbenes
- resveratrol
- piceatannol
- pterostilbene
- Flavanols
- catechins
- epicatechins
- procyanidins
- proanthocyanidins
- viniferones
- Flavonols
- quercetin
- kaempferol
- myricetin
- isorhamnetin
- Phenolic Acids
- caffeic acid
- coumaric acid
- ferulic acid
- gallic acid
- Carotenoids
- beta-carotene
- lutein
- zeaxanthin
In addition to the above-listed nutrients, grapes have also been shown to contain the hormone and antioxidant melatonin as well as unique oligopeptides (small protein-like molecules) that have anti-bacterial and other properties.
With their overwhelming number of health-supportive phytonutrients, it is not surprising that grapes have been shown to provide many of our body systems with predictable benefits. Areas of benefit in grape research include the cardiovascular system, respiratory system, immune system, inflammatory system, blood sugar regulating system, and nervous system. Another area of special benefit is cancer prevention, with risk of breast, prostate, and colon cancer emerging as the most likely areas of grape anti-cancer benefits. The following paragraphs will give you a closer look at some key areas of health research on grapes.
Antioxidant Benefits
The wealth of antioxidant nutrients in grapes is somewhat startling! In addition to providing us with conventional antioxidant nutrient like vitamin C and manganese, grapes are filled with antioxidant phytonutrients that range from common carotenoids like beta-carotene to unusual stilbenes like resveratrol, and the total number of different antioxidant nutrients in grapes runs well into the hundreds. (Even the hormone melatonin has been identified in grapes and is known to act as an antioxidant provided by this food.) It's important to note that the seed and the skin contain the richest concentration of antioxidants. It's very rare to find a higher concentration of an antioxidant in the fleshy part of the grape than is present in the seed or skin. For this reason, most of the health research on grape antioxidants has not been conducted on whole grapes. Instead, this research has been conducted on grape skin, grape skin extract, grape seed, grape seed extract, or on grape extracts that contain skin and seed and flesh. As a general rule, the flesh of the grape contains approximately 1/20th-1/100th of the total antioxidant capacity of the seed or the skin.
The greater concentration of antioxidants in the skin and seed of grapes does not mean that we don't benefit from eating the whole grape, including the flesh! But it does mean that we need to treat grape studies as a whole as most likely reflecting stronger short-term antioxidant benefits than would be associated with short-term intake of whole grapes.
Research on antioxidant benefits provided by grapes or grape components includes the following findings. Grapes and grape components can:
- help prevent certain oxygen-related enzymes from becoming overactive. These enzymes include xanthine oxidase and catalase.
- increase our blood levels of glutathione (a critical antioxidant nutrient) and also increase the ratio of reduced-to-oxidized glutathione (one important measure of antioxidant capacity).
- help protect cell membranes from free radical damage.
- lower levels of oxygen reactive molecules in our blood.
- reduce oxidation of fat (lipid peroxidation).
- lower biomarkers of oxidative stress.
Anti-Inflammatory Benefits
Along with their strong antioxidant support, grapes provide us with equally strong anti-inflammatory benefits. Once again, research studies in this area have seldom involved dietary intake of whole grapes, but rather supplemental intake of grape components or grape extracts. Still, we have every reason to believe that these same anti-inflammatory benefits are offered by whole, fresh grapes, perhaps just not to the same extent in a short-term situation (like the few weeks or months that characterize most research studies). It's important to remember that we can enjoy grapes over a lifetime!
Grapes have been determined to lower our risk of excessive and unwanted inflammation in a variety of ways. Many pro-inflammatory messaging molecules can have their activity level reduced by grape intake. These molecules include interleukin 6 (IL-6), interleukin 1-beta (IL-1B), and tumor necrosis factor alpha (TNF-alpha). Overproduction of the pro-inflammatory enzymes cyclo-oxygenase 1 and 2 (COX-1 and COX-2) is also less likely following intake of grape components.
Cardiovascular Benefits
No body system is better situated to reap the benefit of antioxidants and anti-inflammatory molecules in grapes than the cardiovascular system. All cells in our blood need protection from potential oxygen damage (especially in our arteries where oxygen concentration in our blood is especially high). Our blood vessel linings also need strong antioxidant support. Chronic inflammation in our cardiovascular system is also a primary concern for many types of cardiovascular disease, and optimal regulation of inflammatory system activity is especially important in lowering our risk of atherosclerosis and other conditions.
The list of cardio benefits provided by grapes and grape components is perhaps the most impressive of all grape benefits. It's also one of the reasons that consumption of grapes in the form of red wine has been regarded by some researchers as a key for understanding "the French Paradox." The French Paradox refers to research observations about heart health in the French population in relationship to their saturated fat intake. Despite eating fairly large amounts of saturated fat in their overall diet, the French population as a whole has been observed to have much lower levels of heart disease than would be expected with high saturated fat intake. One of the reasons might be the anti-inflammatory (and antioxidant) support provided to their cardiovascular system on a regular basis by red wine. The idea that red wine (from red grapes) could help explain the French Paradox is just one more reason for us to consider grapes as a great addition to a heart healthy diet.
All of the following cardio benefits have been demonstrated in research studies on grapes and grape components:
- better blood pressure regulation, including blood pressure reduction if high
- better total cholesterol regulation, including total cholesterol reduction if high
- reduced LDL cholesterol levels
- reduced LDL oxidation
- reduced levels of reactive oxygen molecules in the blood
- reduced likelihood of cell adhesion to the blood vessel walls
- less clumping together of platelet cells, when inappropriate
- enhanced release of nitric oxide from endothelial cells lining the blood vessel walls in situations where vasodilation is needed
- better inflammatory regulation in the blood
- increase levels of glutathione in the blood
Blood Sugar Benefits
In terms of blood sugar regulation, not all fruits are created equal. Watermelon, for example, has a relatively high glycemic index (GI) value in the range of 70-75, and is not considered to be a food that can be freely eaten by persons having difficulty with blood sugar balance. Grapes, on the other hand, have long been classified as a low glycemic index (GI) food, with GI values ranging between 43-53. In the case of grapes, recent studies have also shown that the low GI value of grapes is a good indicator of this fruit's blood sugar benefits. Studies have now connected grape intake to better blood sugar balance, better insulin regulation, and increased insulin sensitivity. We suspect that the strong phytonutrient content of grapes plays a key role in providing these blood sugar-related benefits.
Anti-Aging and Longevity Benefits
Several grape phytonutrients may play a role in longevity and may provide us with anti-aging benefits. Best-studied in this area of health benefits is resveratrol (a stilbene phytonutrient presently mostly in grape skins, but also in grape seeds and grape flesh). Resveratrol has recently been shown to increase expression of three genes all related to longevity. (These three genes are SirT1s, Fox0s, and PBEFs.) Interestingly, some researchers have shown a parallel between activation of these longevity genes by resveratrol and activation by calorie-restricted diets. (In aging and longevity research, our ability to get optimal nutrition for the fewest possible amount of calories is related to our longevity, and the more we can decrease our calories while staying optimally nourished, the better our chances of healthy aging and longevity.)
Cognitive Benefits
Several recent studies on grape extract intake by animals, as well as grape juice intake by humans, suggest that grapes may provide us with some important cognitive benefits. For example, daily consumption of Concord grape juice in a 1-2 cup amount over a period of several months has been shown to improve the scores of study participants on the California Verbal Learning Test. Other studies on animals have shown that excessive accumulation of reactive oxygen species (ROS) in the brain can be prevented with intake of grape extracts, as can excessive accumulation of beta-amyloid protein in the hippocampus region of the brain. Synthesis of pro-inflammatory messaging molecules in the brain (including IL-6, IL-1B, and TNF-alpha) has also been shown to be reduced by intake of grape extracts. While large-scale human studies are needed to confirm these potential benefits, we expect that grape benefits for our cognitive health will be confirmed in future research.
Anti-Microbial Benefits
Numerous grape phytonutrients have been shown to have anti-microbial properties. These phytonutrients range from common flavonoids like quercetin to less common stilbenes like piceatannol and resveratrol. Recent studies have determined that grapes may also contain unique sets of oligopeptides (short protein-like molecules) that have anti-microbial properties. Exactly how we benefit from these anti-microbial substances in grapes is not yet known. But researchers have begun to speculate about their possible role in helping us prevent microbe-related problems like food-borne illness. While research in this area is clearly in its early stages, it will be interesting to see whether diets that are rich in grapes (or grape products like red wine) turn out to be associated with reduced risk of microbe-related problems like food-borne illness.
Anti-Cancer Benefits
The antioxidant and anti-inflammatory properties of grapes make them a natural for protection against cancer because chronic oxidative stress and chronic inflammation can be key factors in the development of cancer. If our cells get overwhelmed by oxidative stress (damage to cell structure and cell function by overly reactive oxygen-containing molecules) and chronic excessive inflammation, our risk of cell cancer is increased. By providing us with rich supplies of antioxidant and anti-inflammatory nutrients, grapes can help us avoid this dangerous combination of chronic oxidative stress and chronic inflammation.
Research on grapes, grape components and cancer has focused on three cancer types: breast cancer, colon cancer, and prostate cancer. In the case of breast cancer, the grape phytonutrients receiving the most research attention have been the catechins, proanthocyanidins, and stilbenes (especially resveratrol). For colon cancer, more research attention has been focused on grape flavonoids and grape anthocyanins. (This research tendency may mean that dark purple, red, and black grapes could end up being better choices for colon cancer prevention than green grapes, even though the jury is still out in this area.) One interesting development in the research on grapes and colon cancer prevention has involved studies on GADF, or grape antioxidant dietary fiber. While GADF is a proprietary product that may eventually be sold in the marketplace as a dietary supplement, the idea that grape fiber and grape antioxidants combine to provide our colon with special support makes perfect sense. Fiber is greatly needed for a healthy colon, and grapes provide us with approximately 1 gram of fiber in every 60 calories. Antioxidants are also needed, and grapes come through strong in the antioxidant category. This antioxidant-plus-fiber combination may be one of the reasons that colon cancer prevention has jumped out in health research on grapes. In the area of prostate cancer, it is the stilbenes (including resveratrol) have been the major focus in research on the anti-cancer properties of grapes.
