A daily serving of almonds improved depressive symptoms in diabetes, but will it work in non-diabetic depression?
Changing a single ingredient in the diet rarely makes a difference in studies of depression. Walnuts, soy, and matcha tea have all been tried without success.1-3 Instead, nutritional psychiatry research has found the best antidepressant effects with a balanced, Mediterranean-style diet.4 But a small trial of almond supplementation in diabetes shows promise.
The study was a small, randomized controlled trial of 45 Chinese adults with type-II diabetes.5 All of the subjects were counseled to adopt a low-fat diet that was rich in vegetables and protein and low in salt and carbohydrates. The control group was allowed a daily serving (300 grams) of a carbohydrate-rich food (in China, this was typically rice or noodles), while the intervention group cut that carb dish in half and replaced it with 56 grams of almonds (about half a cup).
After 3 months, those in the almond group had a significant reduction in depression on the self-reported PROMIS scale, while the average mood of the control group did not budge. The effect size was large (0.94 using Hedges’ correction for small sample sizes), although the statistical spread on that effect was wide (+/- 0.62). Importantly, the investigators did not require a diagnosis of depression to enter the trial. On average, their scores (49) fell just below the 55-point cut-off for mild depression on the PROMIS, although some had moderate or severe depression (up to 81 on the PROMIS).6
Metabolic parameters (weight and glycated hemoglobin (HbA1c)) improved significantly with both diets, although the reduction in HbA1c was larger (by 1 point) in the almond group (p < 0.01). Next, the investigators looked at changes in the gut microbiome to clarify the mechanism behind this antidepressant effect.
A diverse microbiome in the GI tract is associated with both metabolic and mental health. The gut bacteria communicate with the brain through multiple pathways, including the vagus nerve, inflammatory signaling, and short-chain fatty acids.7 In the study by Ren and colleagues,5 microbiome diversity improved in both groups, but the almond group had a significant increase in bacterial species that produce short chain fatty acids (Roseburia, Ruminococcus and Eubacterium). This type of bacteria stimulates production of the metabolic hormone glucagon-like peptide-1, which lowers appetite and regulates insulin. Supporting this hypothesis, levels of glucagon-like peptide-1 rose throughout the trial in the almond group.
Dr Aiken is the Mood Disorders Section Editor for Psychiatric TimesTM, the Editor in Chief of The Carlat Psychiatry Report, and the Director of the Mood Treatment Center. He has written several books on mood disorders, most recently The Depression and Bipolar Workbook. He can be heard in the weekly Carlat Psychiatry Podcast with his co-host Kellie Newsome, PMH-NP.
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