Association, not causation
Several experts weighed in on the study results in a statement from the U.K. nonprofit organization, Science Media Centre.
Gunter Kuhnle, PhD, professor of nutrition and food science, University of Reading (England), cautioned that the study only offers information on association – not causation.
“It is very possible that people with depression change their diet and might decide to consume foods that are easier to prepare – which would often be foods considered to be ultraprocessed,” Dr. Kuhnle said.
What’s most interesting is that the association between UPF intake and depression was driven by a single factor – artificial sweeteners.
“This supports one of the main criticisms of the UPF concept, that it combines a wide range of different foods and thereby makes it difficult to identify underlying causes,” Dr. Kuhnle added.
“There are currently no data that link artificial sweetener use to mental health, despite most of them having been available for some time. It is also important to note that there are a wide range of different artificial sweeteners that are metabolized very differently and that there might be reverse causality,” Dr. Kuhnle commented.
Paul Keedwell, MBChB, PhD, consultant psychiatrist and fellow of the Royal College of Psychiatrists, said this is an “interesting and important finding, but one that raises more questions. At this stage, we cannot say how big an effect diet has on depression risk compared to other risk factors, like family history of depression, stress levels, and having a supportive social network.”
Dr. Keedwell noted that the investigators carefully excluded the possibility that the effect is mediated by obesity or lack of exercise.
“However, an important consideration is that a diet based on ready meals and artificially sweetened drinks might indicate a hectic lifestyle or one with shift work. In other words, a fast-food diet could be an indirect marker of chronic stress. Prolonged stress probably remains the main risk factor for depression,” Dr. Keedwell said.
Keith Frayn, PhD, professor emeritus of human metabolism, University of Oxford (England), noted that the relationship between artificial sweeteners and depression “stands out clearly” even after adjusting for multiple confounding factors, including BMI, smoking, and exercise.
“This adds to growing concerns about artificial sweeteners and cardiometabolic health. The link with depression needs confirmation and further research to suggest how it might be brought about,” Dr. Frayn cautioned.
The NHS II was funded by a grant from the National Cancer Institute. Dr. Chan reported receiving grants from Bayer and Zoe and personal fees from Boehringer Ingelheim, Pfizer, and Freenome outside this work. Dr. Keedwell and Dr. Kuhnle disclosed no relevant financial relationships. Dr. Frayn is an author of books on nutrition and metabolism.
A version of this article first appeared on Medscape.com.