Potential mechanisms
Although scientists can’t say for certain how UPFs affect brain health, there are several theories. UPFs may influence an inflammatory immune response, which has been linked to depression and dementia. Consumption of highly processed foods may also disrupt the gut microbiome, Dr. Chan said, which, in turn, may increase depression risk.
“This is an important potential mechanism linking ultraprocessed food to depression since there is emerging evidence that microbes in the gut have been linked with mood through their role in metabolizing and producing proteins that have activity in the brain,” he said.
In addition, with UPFs that contain aspartame, there could be a more direct link to brain function. In the gastrointestinal track, the sweetener is quickly broken down into methanol, aspartic acid, and phenylalanine. All three enter the bloodstream, cross the blood-brain barrier, and are neuroactive.
“Phenylalanine is a precursor for neurotransmitters in the brain, and aspartic acid activates the glutamate excitatory neurotransmitter receptor,” Dr. Bhide said. “The effects we’ve seen could be due to these metabolites that have a direct effect on the brain function.”
Time to act?
Some researchers are building a case for classifying UPFs as addictive substances. Others are calling for additional research on UPF safety that is conducted outside the food industry.
There has also been some discussion of placing warning labels on UPFs. However, there is disagreement about what information should be included and how consumers might interpret it. The question of which food products are UPFs and which are not also isn’t settled. The NOVA system may be widely used, but it still has its detractors who believe it misclassifies some healthy foods as ultraprocessed.
Dr. Chan and other experts say the research conducted thus far requires additional corroboration to inform appropriate public health interventions. That would likely take the form of a large, randomized trial with one group of participants eating a healthy diet and the other consuming large amounts of UPFs.
“This type of study is extremely challenging given the number of people that would have to be willing to participate and be willing to eat a very specific diet over a long period of time,” Dr. Chan said. “I am also not sure it would be ethical to assign people to such a diet, given what we already know about the potential health effects of UPFs.”
Dr. Thiagarajan and others have called on funding agencies to direct more grant monies toward studies of UPFs to better understand their effect on brain health.
“Given the magnitude of the problem and given that there is a fair bit of evidence that points to a potential causal link, then we damn well better put money into this and get to the bottom of it,” she said.
Others are looking to the FDA to increase the agency’s scrutiny of food additives. While some additives such as artificial sweeteners have a place in diets of people with diabetes or obesity, Dr. Bhide suggests it may be wise for healthy individuals to reduce their daily intake of UPFs.
“Our data raise this to a different level because of the transgenerational transmission, which has never been shown before,” he said. “We are saying that the FDA should look in preclinical models at germ cells and maybe transgenerational transmission before approving any food additive.”
A version of this article first appeared on Medscape.com.