The review, conducted by researchers associated with the University of Illinois Urbana-Champaign looked at studies with cognitive function endpoints that included dietary interventions with omega-3 supplementation, studies using probiotic organisms and studies using prebiotics.
The endpoints included anxiety, depression, stress, major coping strategies and one that studied an endpoint termed as ‘psychosocial health.’
Diet quality affects mood
The researchers looked at six studies that investigated how different diets affected the subjects’ mood states.
“The habitual intake of specific food groups has been associated with stress and depression. Specifically, sweets and fast-food are consumed more frequently in stressed and depressed individuals. Contrarily, fruits and vegetables are consumed less frequently by depressed individuals,” they wrote.
The primary mode of action that they derived from the studies using altered diets is the low production of butyrate in the guts of individuals consuming little fiber from fruits and vegetables. Through a complicated mechanism involving the gut mucosal layer, this tends to degrade the barrier function of the gut and lead to chronic low level inflammation.
“Inflammation is characteristic of depression. Thus, SCFAs [short chain fatty acids] may indirectly influence mood by modulating intestinal permeability and systemic lipopolysaccharide circulation,” they wrote.
Six studies included in the review used dietary modifications including low fat, high carb diets, personalized nutritional support, omega-3s supplementation and comparing low glycemic load and high glycemic load diets. The authors found some support for omega-3s’ mood benefits, as well as data backing the effect of diets low in saturated fat.
Paucity of prebiotics data
On the prebiotic front, the researchers noted that few studies are available in this area. The most commonly studied prebiotics for mood support are fructooligosaccharides and galactooligosaccharides, they said.
Three trials using these ingredients showed positive effects, which the authors attributed mostly to the ability of these ingredients to foster the growth of bifidobacteria. In their view, high dosages of at least 5 grams a day may be necessary to show these effects.
“Bifidobacteria may promote health benefits by producing B vitamins, antioxidants, and polyphenols; and aiding immune system function by inducing the production of immunoglobulins. Additionally, bifidobacteria contribute to the production of lactate and acetate, which can be utilized by other bacteria in the gastrointestinal microbial community to produce butyrate, a phenomenon known as cross-feeding,” they wrote.
Mixed results in probiotic studies
The biggest chunk of studies included in the review had to do with probiotics. Thirteen studies in all were included, all which used strains of either Bifidobacterium or Lactobacillus. The studies were a mixed bag, with some showing improved quality of life scores and less depression. But few showed measurable benefits on lessening anxiety.
Overall, the authors said the whole field is still in its early days, but researchers seem to be on the right track. Much more data is needed to be able to fully sketch out the relationships between the gut and the brain.
“High-quality diets, prebiotics, and probiotics may beneficially affect mood. Habitual diets rich in dietary fiber and omega-3-polyunsaturated fatty acids may be linked to reduced risk of developing symptoms of depression, anxiety, and stress; however, additional studies are necessary. Certain probiotics may enhance mood, but their influence on the gastrointestinal microbiota requires further investigation,” they concluded.
Source: Nutritional Neuroscience
Published online ahead of print, 2018 Jul 9:1-14. doi: 10.1080/1028415X.2018.1493808.
“A review of dietary and microbial connections to depression, anxiety, and stress”
Authors: Taylor AM, Holscher HD