Processed Food Still Doesn't Cause Dementia

Subsisting on fast food, soda, and candy is not a wise way to live. None of these foods are inherently harmful, though they should be consumed in moderation as part of a balanced diet. Studies have confirmed this conclusion repeatedly over the years, and we all know it from experience. But this isn't satisfactory for many people. Some researchers and the reporters who cover their work insist that consuming processed food, especially the "ultra-processed" variety, just has to be risky. Consider this recent report from CBS News:

Eating highly processed foods like instant noodles, sugary drinks or frozen meals may be linked to a faster rate of cognitive decline. That's according to new research presented ... at the Alzheimer’s Association International Conference in San Diego. The study examined the diets and cognition of more than 10,000 middle-aged and older adults in Brazil.

The paper hasn't been published yet, so we shouldn't say anything definitive about the results. But notice that the media coverage hasn't changed despite this dearth of information about the study. The exaggeration becomes even more apparent when we examine how sparse the existing evidence is. There is still no solid scientific reason to believe processed food uniquely contributes to cognitive decline.

What did the study find?

We don't have much information, but we know that the study was epidemiological; participants who consumed “the most” processed food—at least 20 percent of their caloric intake—experienced a 25 percent faster rate of decline in executive function over six to 10 years. There's nothing necessarily wrong with that study design. One of the authors also reasonably cautioned CBS that

… her study didn’t attempt to examine the underlying reasons for cognitive decline, and it does not conclude that consumption of ultra-processed food is a direct cause. Rather, it found a correlation between the two.

Here we have the skeleton of an accurate, informative news report: a summary of the study results with a qualified conclusion. Now, compare this information to the additional details included in the story, particularly this quote from the same researcher:

'Independent of the amount of calories, independent of the amount of healthy food that you try to eat, the ultra-processed food is not good for your cognition,' said Claudia Suemoto, an author of the study and assistant professor of geriatrics at the University of Sao Paulo Medical School.

All Suemoto's team found was an association, yet she insisted that any amount of “ultra-processed” food is harmful regardless of how many calories you get from other sources. But how does she know? Her paper can't tell us that, as she acknowledged, and previous epidemiological studies have not provided any more compelling evidence.

It's certainly true that a poor diet can damage your heart and blood vessels, and problems in the vascular system may contribute to dementia. But this hasn't been shown in humans. The results of animal models are sometimes cited as substitute evidence, though this may be altogether inappropriate. Rats typically don't develop the sort of vascular damage linked to cognitive decline unless they receive a surgical or pharmaceutical intervention that causes it.

Even then, the experience of our poor rodent stand-ins may not tell us much about our risk because they “are phylogenetically very distant from humans,” a team of researchers explained in 2016. As ACSH co-founder Dr. Beth Whelan used to say, rats and mice aren't little people. The bigger issue is that we still don't know for certain what causes Alzheimer's.

Moderation is everything

This isn't to say that nutrition has no effect on cognitive health. It probably does, but my money is on the hypothesis that overall diet quality is what matters. Contrary to USA Today's foolish coverage of this new study, two cookies once a week as part of a diverse diet won't harm your health. However, eating 2,000 calories worth of Oreos every day for years almost certainly will do some damage. Moderation is a virtue, as Aristotle said. If philosophy isn't your thing, here's the same message from ACSH contributor and nutrition scientist David Lightsey:

It is the totality of the diet, not the cherry-picked fried chicken variable, that may affect your health and aging ...

What does "ultra-processed" mean?

The other extreme we should avoid is the temptation to demonize entire food classes. Terms such as “processed” and “ultra-processed” have become synonyms for “bad” in the extensive vocabularies of many health journalists, but these definitions are unjustifiably broad. According to the Academy of Nutrition and Dietetics:

Processed food has a bad reputation as a diet saboteur … But processed food is more than boxed macaroni and cheese, potato chips and drive-thru hamburgers. It may be a surprise to learn that whole-wheat bread, homemade soup or a chopped apple also are processed foods.

Many other items help make the same point: pasteurized and vitamin-fortified milk or juice, cereal with added fiber, and canned tuna. Even deli meats, which the academy calls “heavily processed,” aren't especially troubling based on their nutrition labels. In contrast, consuming "unrefined" sugar instead of high-fructose corn syrup will not reduce your risk for obesity and diabetes. Too much sugar is too much sugar, no matter the source. As my colleague Dr. Chuck Dinerstein pointed out last year, "there is not a direct linear relationship between processing and food’s nutritional value."

The key is to pay attention to the nutrients you're actually eating instead of the buzzwords we use to identify them. All this squabbling about cookies, fried chicken, or some other no-no dish is nothing more than a distraction.