People diagnosed with depression, or who are susceptible to depressive symptoms, may benefit from eating more fibre, fish and grains as a measure to alter the gut-brain axis, a new report by some of Europe’s leading experts suggests.
Led by Professor Ted Dinan from APC Microbiome Ireland and the University College Cork, the expert team reviewed the interplay between diet, mood and the microbiome as part of the EU FP7 project MyNewGut – a five year multidisciplinary initiative set up to investigate the role of our gut microbiome in obesity and behavioural disorders.
“Depression is a highly prevalent disorder which exerts a major economic impact in all European countries,” noted the authors – adding that the condition is “not only the common cold of psychiatric disorders but one of the most prevalent medical conditions.”
“There is now over-whelming evidence to support the fact that gut microbes have a major impact on central neurochemistry and behaviour, especially stress related disorders such as depression,” they said, noting that recent studies have shown that people with depression have alterations to their gut microbiome (known as gut dysbiosis), but that the reason for this dysbiosis is uncertain.
Dinan and colleagues noted that over recent decades, dietary patterns in Europe and elsewhere have undergone major changes – with increased intakes of red meat, high fat foods, and refined sugars.
“It is possible that a poor quality diet may bring about the altered microbiota observed in depression,” noted the team. “Narrowing of dietary diversity with reduced intake of essential nutrients can reduce availability of substrates for specific microbial growth and this could contribute to the intestinal dysbiosis of depression.”
Such ‘Westernisation’ of diets together with sedentary lifestyles results in modifications to the gut microbiota, which could partially contribute to the increasing incidence of chronic inflammatory disorders, such as cardiovascular disease, obesity, inflammatory bowel disorder and depression, the team said.
“If we are to improve the nutritional value of food and positively impact mental health, we need to more fully understand the biological interactions between the food and microbiota,” wrote the experts.
New recommendations: The evidence
The new recommendations, published in Clinical Nutrition, come after an in-depth review of the science linking diet, our gut bacteria and mood – an area the team say is a ‘new paradigm’ in understanding and potentially treating depression.
They noted that individuals who consume a Mediterranean diet have lower rates of depression, adding that a recent study suggests that a Mediterranean diet may have antidepressant properties.
“Assuming this to be the case, which components of the Mediterranean diet mediate the effects? Highly levels of polyphenols or polyunsaturated fatty acids are obvious candidates,” conclude the authors, noting that long-chain omega-3 fatty acids such as are docosahexaenoic acid (DHA) are vital building blocks of the brain and have been consistently linked with depression.
“In countries where there is a high consumption of fish there are lower rates of depression,” noted the team – who added that multiple trials of omega-3 supplementation have shown a benefit, though others have had ‘mixed results’.
“At this point it seems reasonable to recommend fish in the diet of patients with depression but there is insufficient data to recommend omega-3 PUFAs as either a mono or adjunctive therapy in the disorder,” the team concluded.
Dinan and colleagues also noted that fermented foods including probiotics have long been associated with a health benefit – but only recently has that benefit been extended to mental health.
“The principal rationale for the use of probiotics in treating major depression rests on their potential for suppressing the pro-inflammatory component of depression,” said the team noting that although many claims for probiotics have not been substantiated, one area where benefit has been established is for IBS.
“Several placebo controlled studies indicate that a bifidobacteria is highly effective in treating the condition,” said the team. “This is of relevance given the fact that up to 40% of patients with IBS have co-morbid depression and many bifidobacteria have anti-inflammatory activity.”
The team added that further ‘psychobiotic’ studies in depressed patients are urgently required.
While probiotics may not yet have enough clinical evidence, the expert recommendations say that prebiotics and fibres do.
“Prebiotics are fibres metabolised by the microbiota and capable of increasing the levels of good bacteria such as bifidobacteria,” the recommendations state – noting that a number of clinical trials have assessed the efficacy of certain prebiotics on psychological outcomes with ‘promising results’.
Further, they noted that high fibre diets are associated with fewer symptoms of depression.
“When analysed by the source of fibre, diets higher in total fibre (more than 27 g per day), and fibre from vegetables and breads/cereals (mostly whole grain) were associated with a 42%, 46%, and 41% reduced likelihood of having depressive symptoms, respectively,” the team noted.
“We in the MyNewGut consortium recommend that patients with depression or vulnerability to depression should be encouraged to enhance a plant-based diet with a high content of grains/fibres and fish,” concluded the team.
Source: Clinical Nutrition
Volume 38, Issue 5, October 2019, Pages 1995-2001, doi: 10.1016/j.clnu.2018.11.010
“Feeding melancholic microbes: MyNewGut recommendations on diet and mood”
Authors: Timothy G.Dinan, et al