What does this study tell you about grapes?

Discovering how particular foods can increase your chances of a healthier life is very rewarding. It’s one of the reasons I love researching and writing about new scientific health breakthroughs. So when I learned of a new study looking at how grapes might deliver health benefits through gut biome changes, my interested was immediately piqued.

Having previously looked at the mechanisms by which eggs, nuts and other foods work to make you healthier, I’d hoped to learn the same about grapes. Unfortunately, I found the latest study quite disappointing.

There’s no doubt about the health benefits of grapes, both red and white. Grapes contain a number of different B vitamins and antioxidants, and are also a good source of fibre. In the new study, Dr John Pezzuto and his co-authors sought to investigate the potential of grapes to modulate the human microbiome.

They did so by enrolling 41 people – 22 female and 19 male – to partake in a two-week dietary regime. This regime involved a restricted diet supplemented by three servings of grapes per day, followed by a 30-day ‘no grapes’ period.

The effect of grapes on the biome

Using faecal samples obtained before and after the trial, the researchers found that except for a subgroup of females ages 29 to 39, grape consumption did not significantly alter the overall diversity of the microbiome in the study population.

They did, however, observe changes in the abundance of certain gut bacteria. The levels of some gut bacteria, such as Holdemania spp., decreased, while those of others, such as Streptococcus thermophiles, increased.

In some individuals, these level changes remained even after the 30-day post-trial ‘washout’ period. That suggests that the effects of eating grapes on the biome can be long-lasting and/or delayed.

What does that mean in practical terms?

That’s a question I found myself asking, and one I didn’t feel this study answered very well.

The study showed that eating grapes three times a day for two weeks changed bacteria levels in the gut biome. Without questioning the research, I think it’s not unreasonable to assume that would be the case regardless of the food involved. I was also somewhat concerned by the small sample size – 29 seems a little low, although, again, I cannot claim expertise here.

What bothered me perhaps most of all about this study was the form of grapes consumed. I wondered what types of grapes had been consumed and found the answer to be ‘grape powder’. Really?

I can’t claim to have even heard of grape powder. In this case, it was “a freeze-dried powder manufactured under the auspices of the California Table Grape Commission”.

The authors claimed there was a good reason for this. It would “assure the consistency and continuity of experimental and clinical research concerning the biological and physiologic potential of grapes”.

The grape powder serves as a surrogate for fresh grapes, the authors contend. The powder comprises “fresh seeded and seedless red, green and black grapes that are ground and freeze dried”.  This allows them to retain their bioactive compounds.

As true as I’m sure that is, the use of grapes in powdered form still made me a bit angry. (Does that make them grapes of wrath?) It should also be noted that the California Table Grape Commission provided partial funding for this study.

In conclusion …

“Further research is required to determine if these responses are responsible for or related to any of the health benefits.” That sentence, referring to the change in gut biome after grape consumption, forms part of the study’s conclusion.

It may sound a little bit inconclusive but, in fairness, most scientific studies call for further research. Usually, though, they come after demonstrating a link of some description, at least. This study appears to reveal very little.

The authors conclude that “it does seem logical to expect changes of these types are profound enough to have significance”.

I’m sure that’s true, but I feel none the wiser as to the significance. Perhaps that’s just me. Perhaps this time I’m just experiencing a case of sour grapes.

Are you a grape lover? Do you prefer white or red grapes? Let us know via the comments section below.

Also read: Why eating a fibre-rich diet can boost your mood

Health disclaimer: This article contains general information about health issues and is not advice. For health advice, consult your medical practitioner.

Andrew Gigacz
Andrew Gigaczhttps://www.patreon.com/AndrewGigacz
Andrew has developed knowledge of the retirement landscape, including retirement income and government entitlements, as well as issues affecting older Australians moving into or living in retirement. He's an accomplished writer with a passion for health and human stories.


  1. Andrew, you are correct in questioning the use of “grape powder” as a substitute for real grapes. The argument could’ve been that at least the “grape powder” is available all year round. I can quickly see another more natural version of the grapes that keeps fairly well and is available all year round and can be consumed with ease, for some people more than three times a day. With or without meals.
    There is always a wine that will please the palate of any tastes. In the servings as discussed in this study, probably as beneficial to the stomach biome as any other food.

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