Fruits and vegetables are deemed to be “healthy". A vast number of studies have indeed demonstrated lower rates of diabetes, heart disease and cancer in populations consuming more fruits and vegetables. Is this because these plant products contain chemicals that inhibit body processes that cause disease, or is it because people who eat more fruits and vegetables eat less meat which causes disease? Most likely both factors are at play. Meat is high in saturated fats that are implicated in heart disease and when cooked at high temperatures, meat forms a number of carcinogens. Fruits and vegetables are low in fat and contain a number of compounds that neutralize free radicals, the highly reactive species that form during metabolism and are capable of damaging tissues. Extensive research has attempted to nail down exactly what those beneficial compounds are and whether specific fruits or vegetables contain amounts that would merit a recommendation to specifically include them in the diet. It should be pointed out that many studies that explore the benefits of fruits are funded by vested interests. Their hope is to find data that can be used, often with some imaginative interpretation, to confer the mantle of “superfood” on their product.
“Two Cups of Grapes Per Day Could Help You Live Longer, Study Shows,” was the headline that came to my attention. Living longer is not an unattractive proposition, and eating two cups of grapes a day is within the realm of possibility, so I figured I would read further. Indeed, the study showed a reduction in non-alcoholic liver disease and increased longevity when grapes are added to a “high-fat western-pattern” diet. But there is a little issue here. I am not a female mouse! The fact that this study by researchers from Western New England University was carried out on female mice was not in the headline. Furthermore, the mice were not exactly eating grapes. They were eating freeze-dried grape powder. Now, I am perfectly willing to accept that the grape powder provided benefits for the mice. The researchers were even able to show that supplementation with it resulted in a change in gene expression. Some of these changes that are associated with reduction of free radicals were enhanced, while those associated with cholesterol synthesis were down regulated. All very interesting, but as the saying goes, humans are not large mice.
So, what about humans eating grapes? The same researchers enlisted twenty-nine volunteers who for two weeks added three servings of grapes to their diet. Again, not exactly grapes, but 36 grams of freeze-dried powder that was made from a mixture of different grapes. A two-week long study is too short to determine any effect on health, so the goal was to investigate any changes in the subjects’ microbiome, the population of gut bacteria that can affect health in various ways. If grapes were to cause some significant change in the composition of the microbiome, then possible health outcomes could be contemplated. The researchers were very thorough. Fecal, urine and blood samples were taken and a great deal of effort was expended to determine the composition of the microbiome before and after grape consumption. There was no change in the diversity or total numbers of the gut bacteria with grape consumption but the numbers of some individual bacteria were altered. Whether this is of any significance remains unknown, so this study, which was funded by the California Table Grape Commission, does not provide any support that eating grapes has a positive effect on human health. What it shows is that eating grapes can influence the microbiome, but that is likely to be the case for any food that is consistently consumed.
The reason that I mention these studies is that grapes have a history of being portrayed as a cure for disease. Grape therapy even has a specific name, “ampelotherapy,” from Ampelos, the Greek mythological figure who represented the grapevine. In the middle of the nineteenth century German Dr. Veit Kaufmann introduced the idea that grapes should be consumed in large amounts for good health but it was South African author Johanna Brandt who went further and claimed in her book “The Grape Cure” that she had cured herself of stomach cancer by fasting for a couple of days and then consuming only grapes and water for two weeks followed by a diet of fresh fruits and raw vegetables. Needless to say, grapes cannot cure cancer. Still, Brandt’s book is still enthusiastically promoted today by alternative practitioners such as naturopath Christopher Vasey in his own book, “The Detox Mono Diet: The Miracle Grape Cure and Other Cleansing Diets.” The terms “miracle” and “detox” when used in connection with diets smack of quackery.
Other promoters of grape consumption may shy away from making specific claims about cures but do imply that grapes have special health properties. For example, the popular site “Healthline” features an article entitled “The Top 16 Health Benefits of Grapes.” It is noteworthy that 13 of these start with the word “may.” Such as “May aid heart health, “May have anticancer effects,” “May benefit eye heath,” “May support bone health,” “May slow signs of aging and promote longevity,” “May have anti-obesity effects,” and “May support sleep.” Of course, each of these could just as well start with “May not.” For each one of the claims they dredge up some laboratory finding and imply unfounded human relevance. For example, they may tout that resveratrol, one of the 1600 or so compounds that are present in grapes, reduces the multiplication of cancer cells in a test tube. Many compounds will do that “in vitro” but never pan out “in vivo.” And the studies use far more resveratrol than is available in grapes.
The three claims that do not begin with “may” are “Packed with Nutrients, ” “High in antioxidants” and “Easy to add to your diet.” The first two are overstatements. Grapes are not particularly high in any nutrient. A cup has only 5% of the daily value of vitamin C, 6% of potassium and an inconsequential amount of protein or fiber. Grapes do contain a variety of antioxidants, but the same can be said for most other plant products and the exact value of antioxidants in the diet is far less clear than is commonly implied. But the one claim that cannot be contested is about grapes being easy to add to the diet. Sure, by all means do include grapes in the diet, make them one of the five to seven servings of fruits and vegetables that we should be consuming every day. And if you want your pet mice to live longer, give them some freeze-dried grape powder.