Blueberry Trial Finds Gut Changes, No Proven Mood Benefit
A randomized, double-blind pilot trial found that daily blueberry powder consumption changed the abundance of certain gut bacterial enzyme genes in older adults, but did not significantly improve depressive symptoms compared with a placebo, according to researchers at Hebrew SeniorLife’s Marcus Institute.
Published in The Journal of Nutrition, Health and Aging, the study examined 18 sedentary adults aged 65 and older experiencing mild depressive symptoms. Researchers investigated whether a daily dietary intervention could affect mood and gut microbial functions.
Over three months, ten participants consumed 48 grams daily of freeze-dried wild blueberry powder, equivalent to approximately two cups of fresh blueberries. Eight participants received a visually and calorically matched placebo powder.
Depression Scores Show Limited Improvement
Depressive symptom assessments showed numerical improvements in both groups during the 90-day intervention. Participants consuming blueberries demonstrated a more consistent reduction in symptom severity scores than those receiving the placebo.
However, the between-group difference did not reach statistical significance. The small sample of 18 participants limits conclusions about whether blueberries improve depressive symptoms.
The findings therefore do not establish that eating blueberries prevents or treats clinical depression, despite the apparent favorable trend in the intervention group.
Blueberries Alter Gut Microbial Functions
Whole-genome shotgun sequencing identified changes in genes associated with six bacterial enzymes among participants consuming blueberry powder.
Researchers found no corresponding changes in overall gut bacterial species abundance. Circulating short-chain fatty acids, including butyrate and propionate, also remained unchanged between groups.
One affected enzyme was Polyamine Transporting ATPase (EC 3.6.3.31), an enzyme complex implicated in metabolic pathways associated with gamma-aminobutyric acid (GABA).
GABA is an inhibitory neurotransmitter involved in regulating nervous system activity and anxiety. However, detecting changes in microbial genes associated with these pathways does not establish that blueberry consumption increased GABA production or directly changed brain function.
Larger Clinical Trials Remain Necessary
The trial suggests that dietary blueberries may influence the functional genetic profile of gut microorganisms without substantially changing which bacterial species are present.
Larger clinical trials are needed to establish whether these microbial changes consistently occur in older adults and whether they produce clinically meaningful improvements in depressive symptoms.
