The more bacon and sausages we eat the more likely we are to suffer from depression, warns a new study.
Researchers exploring the effects of ultra-processed foods – such as ice cream, ham, sausages, bacon, crisps, mass-produced bread, breakfast cereals and biscuits – also found artificially sweetened drinks to be directly associated with depression risk.
The study, which focused on a group of more than 31,000 American women, provides undeniable evidence of the association between poor diet and depressive tendencies.
The research, published in JAMA Open, focused both on the general connections between ultra-processed foods as well as the individual types of foods.
Ultra-processed foods (UPF) typically have five or more ingredients and tend to include additives and ingredients not suited to home cooking such as preservatives, emulsifiers (E-numbers), sweeteners and artificial colors or flavors.
UPF tends to have longer shelf lives and include foods such as fizzy drinks, fruit-flavored yogurts, instant soups, and some alcoholic drinks including whisky, gin, and rum.
The foods often contain high levels of saturated fat, salt and sugar and, when we eat them, we have less room in our diets for more nutritious foods like fruit and vegetables.
It has also long been suggested that the additives in these foods could be responsible for negative health effects.
American researchers in the latest study – a collaborative group approved by the Brigham and Women’s Hospital and the Harvard T.H. Chan School of Public Health in the United States – sought to identify the links between UPF and depression.
They looked at the Nurses’ Health Study II – conducted between 2003 and 2017 – of middle-aged women free of depression at baseline.
The participants’ diets were assessed using food frequency questionnaires (FFQs) every 4 years.
Consumption of UPF was measured using the NOVA classification, which groups foods according to the degree of their processing.
In a secondary process, the researchers also split the different UPFs into categories such as ultra-processed grain foods, sweet snacks, ready meals, fats and sauces, dairy products, savory snacks, processed meat, drinks and artificial sweeteners.
The study team also defined depression in two categories: a strict definition requiring clinically diagnosed depression and regular antidepressant use and a broader definition requiring clinical diagnosis and/or antidepressant use.
Results were adjusted for depression risk factors including age, calorie intake, BMI, physical activity, smoking status, alcohol intake, median family income, social network levels, marital status, sleep duration and pain.
The study cohort included a total of 31,712 women aged between 42 and 62 at the beginning of the study.
The researchers found that women who ate a higher proportion of UPF had greater BMIs, were more likely to smoke, had an increased prevalence of comorbidities like diabetes and hypertension and were less likely to exercise regularly.
A total of 2,122 cases of the strict definition of depression were found and 4,840 using the broader definition.
They found that, compared to those with the lowest intake of UPF, those with the highest reported consumption of ultra-processed foods had an increased risk of depression in both definitions.
When looking at the specific UPF types most likely to lead to depression, the study team found that only artificially sweetened drinks and artificial sweeteners were associated with a greater risk of depression.
Additionally, the researchers found that those who reduced UPF intake by at least three servings per day had a lower risk of depression compared with those who maintained a stable intake throughout each four-year period.
The researchers, led by Dr. Raaj Mehta, of the Harvard Medical School and Massachusetts General Hospital, suggested the links between artificial sweeteners and depression could be to do with how they are processed in the brain.
Dr. Mehta said: “These findings suggest that greater UPF intake, particularly artificial sweeteners and artificially sweetened beverages, is associated with increased risk of depression.
“Although the mechanism associating UPF to depression is unknown, recent experimental data suggests that artificial sweeteners elicit purinergic transmission in the brain, which may be involved in the etiopathogenesis (the cause or development) of depression.
“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.”
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