BOSTON, Massachusetts, November 13, 2023 (ENS) – Everybody knows what ultra-processed foods are – sweet snacks, ready-to-eat meals, fats and sauces, ice cream, savory snacks, cookies and chips, ham, sausages, mass-produced bread, breakfast cereals, instant soups, sodas, and artificial sweeteners. They can tickle the tastebuds, but new research that followed 31,000+ U.S. women over a 14 year period has linked eating ultra-processed foods with risk of depression.
The scientific team from Massachusetts General Hospital and Harvard Medical School, Harvard T.H. Chan School of Public Health, and Brigham and Women’s Hospital in Boston published their findings in September in the “Journal of the American Medical Association.”
In their introduction, the authors sketch their method. “We conducted a prospective study in the Nurses’ Health Study II between 2003 and 2017 among middle-aged females free of depression at baseline,” they explain.
Diet was assessed using validated food frequency questionnaires every four years. The scientists estimated ultraprocessed food intake using a classification that groups foods according to the degree of their processing.
The researchers used two definitions for depression: first, a strict definition requiring self-reported clinician-diagnosed depression and regular antidepressant use, and second, a broad definition requiring clinical diagnosis and/or antidepressant use.
The researchers accounted for some of the many known and suspected risk factors for depression, including: age, total caloric intake, body mass index, physical activity, smoking status, menopausal hormone therapy, total energy intake, alcohol, comorbidities such as diabetes and hypertension, median family income, social network levels, marital status, sleep duration, and pain.
Their cohort included 31,712 females, aged 42 to 62 years at baseline, non-Hispanic White females. The data they contributed was 95 percent self-reported to the researchers, as structured clinical interviews were too expensive to conduct, the authors explained.
They concluded that, “Participants with high ultra-processed food intake had greater body mass index, higher smoking rates, and increased prevalence of comorbidities like diabetes, hypertension, and dyslipidemia and were less likely to exercise regularly.”
“We identified 2,122 incident cases of depression using the strict definition and 4,840 incident cases using the broad definition. Compared with those in the lowest quintile of UPF consumption, those in the highest quintile had an increased risk of depression, noted for both strict definition and broad definition,” they wrote.
Next, they examined the association of specific ultra-processed food components with risk of depression.
They found that only artificially sweetened beverages and artificial sweeteners were associated with greater risk of depression.
Nevertheless, processed meats can be very damaging. N-nitroso compounds are cancer-causing substances responsible for some of the adverse effects of processed meat consumption. They are formed from sodium nitrite that is added to processed meat products to prevent the development of microbiological organisms that cause food poisoning and to provide the bright red color in meat products like sausage, ham, and salami.
Dropping Ultra-processed Foods Helps
In an exploratory analysis, those who reduced their ultra-processed food, UPF, intake by at least three servings a day were at lower risk of depression compared with those with relatively stable intake in each four-year period.
“These findings suggest that greater UPF intake, particularly artificial sweeteners and artificially sweetened beverages, is associated with increased risk of depression,” the researchers report.
They admit that “the mechanism associating UPF to depression is unknown,” but cite recent experimental data suggesting that artificial sweeteners elicit “purinergic transmission in the brain,” which may be involved in the underlying cause of depression.
Purinergic receptors, also known as purinoceptors, are a family of plasma membrane molecules that are found in almost all mammalian tissues.
Within the field of purinergic signalling, these receptors are involved in learning and memory, locomotor and feeding behavior, and sleep.
The authors themselves evaluate the strengths and weaknesses of their work. “Strengths of our study include the large sample, prospective design, high follow-up rate, ability to adjust for multiple confounders, and extensively validated dietary assessment tools,” they write.
“This study had limitations,” they continue. “The cohort primarily included non-Hispanic White females. Additionally, without structured clinical interviews, misclassification of the outcome may be considered.”
Still, even with its weaknesses, the study suggests that depression can be eased with a change in diet.
Featured image: Two obese women in front of a supermarket display of processed meats. June 14, 2023 (Photo by Gilbert Mercier)