Correcting Silly Headlines: Grapes Won't Prevent Alzheimer's

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Reporters have turned yet another study's underwhelming results into exaggerated headlines about the cognitive benefits of fruit consumption. Let's take a closer look at the paper in question.

We've reached a point where you must assume everything the media says about nutrition is false. This is a drastic but necessary assumption given the ridiculous headlines that routinely populate our news feeds. I've covered several such stories in recent months: dementia-fighting blueberries, dementia-promoting processed foods, and pesticides that supposedly counteract the nutritional benefits of eating produce.

The list of dubious nutrition stories is enormous, and it's time to add another article to the collection: “Eating grapes can extend your life by 5 years and reduce Alzheimer’s risk, study says,” The New York Post reported earlier this month. What did the researchers find? The Post continued:

The study was performed on female mice that were fed high-fat Western-pattern diets, with half of the mice receiving grape supplements. Scientists then compared the brain, liver and metabolic health of the two groups. Antioxidants found in grapes can reduce the risk of Alzheimer’s disease by improving neuron function. The study also found that the grape supplements extended the lifespan of the mice.

The researchers actually conducted two studies. They divided 40 female mice into four groups of 10, each consuming a standard or high-fat diet with or without a grape supplement (see Table 1). After 13 weeks, the animals were euthanized and “liver was collected for biomarker analysis, determination of genetic expression … and histopathological examination.” In the second study, two groups of mice (100 animals in each group) were put on a high-fat diet, though one of them received a grape supplement.

The authors reported “subtle yet intriguing responses” to the grape supplement in both studies. You can review all the gritty statistical details in section 3 of the paper. For reasons we'll explore, the results are anything but intriguing and tell us very little about human nutrition.

What the media missed

While most of the headlines stressed the study's finding that consuming grapes reduces the risk of Alzheimer's, here's what the authors actually wrote:

We have yet to investigate the effects of grapes on gene expression related to Alzheimer’s disease in our mouse model. However, using the same model, we have shown behavior changes and modulation of gene expression in mouse brain as a result of dietary grape administration.

If you click over to that earlier study, you'll see that the results are much messier than the authors implied. For example, buried deep in the “discussion” section was this conclusion about the impact of the same grape supplement on memory:

These data strongly suggest memory decline due to consumption of a [high-fat diet], but only weakly suggest any improvement due to the addition of grape to the diet.

The authors also cited this clinical trial to bolster their findings, which concluded that grapes “have a protective effect on brain metabolism.” However, there were only 10 participants in the trial, leading the authors of the study to acknowledged that “the size of the sample hinders generalizability and future larger studies will be important to confirm the results.” In other words, we have one uncertain animal model based on another uncertain animal model that cites a tiny clinical trial, which itself has to be replicated. These are underwhelming results, to put it politely.

Keep in mind that we still don't know what causes Alzheimer's Disease. In fact, we know even less than we thought we did a month ago, thanks to a recent study that challenged one of the leading hypotheses about how the disease develops. Diet may play some role, but this has not been demonstrated in humans. It's therefore highly speculative to suggest that any single nutritional intervention has a clinically significant impact.

Grapes prevent liver disease?

That leads us to another important point. The researchers noted “that grape powder supplementation of the diets does not have an effect on mouse body weight.” The result held across all four groups of mice. This is quite important because non-alcoholic fatty liver disease (NAFLD) is most commonly diagnosed in obese patients, and systemic inflammation associated with obesity is the prime suspect that may link diet to Alzheimer's disease. Moreover, physicians treat NAFLD with a prescription for diet and exercise to promote weight loss.

The study authors were aware of the problem this presents for their hypothesis, because they argued that “the overall ramifications of body mass and health are complex.” This is simply not true. There is a clear dose-response relationship between obesity and disease. The bigger you get, the greater your risk.

Supplementation is mostly useless

Medical authorities routinely tell the public to avoid vitamin supplementation and consume a balanced, nutritious diet. Outside of a few select groups with specific medical conditions, nobody benefits from taking supplements. The overall quality of your diet is what matters, and the same logic applies here. If you subsist on fast food and rarely exercise, you are laying the groundwork for several nasty diseases, most notably heart disease and diabetes.

Righting your metabolic ship requires sustained lifestyle changes—far more than adding 300 grams of grapes to your diet [1]. That's not the sexy result reporters love to turn into headlines, but it is the truth. Deal with it as you will.


[1] This serving is roughly equivalent to the dose mice in the study consumed.