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.
The author does not accept honoraria from pharmaceutical companies but receives royalties from PESI for The Depression and Bipolar Workbook and from W.W. Norton & Co. for Bipolar, Not So Much.
References
1. Pribis P. Effects of walnut consumption on mood in young adults-a randomized controlled trial. Nutrients. 2016;8(11):668.
2. Simpson EEA, Furlong ON, Parr HJ, et al. The effect of a randomized 12-week soy drink intervention on everyday mood in postmenopausal women. Menopause. 2019;26(8):867-873.
3. Dietz C, Dekker M, Piqueras-Fiszman B. An intervention study on the effect of matcha tea, in drink and snack bar formats, on mood and cognitive performance. Food Res Int. 2017;99(Pt 1):72-83.
4. Jacka FN, O’Neil A, Opie R, et al. A randomised controlled trial of dietary improvement for adults with major depression (the ‘SMILES’ trial). BMC Med. 2017;15(1):23.
5. Ren M, Zhang H, Qi J, et al. An almond-based low carbohydrate diet improves depression and glycometabolism in patients with type 2 diabetes through modulating gut microbiota and glp-1: a randomized controlled trial. Nutrients. 2020;12(10):3036.
6. Kroenke K, Stump TE, Chen CX, et al. Minimally important differences and severity thresholds are estimated for the PROMIS depression scales from three randomized clinical trials [published online January 23, 2020]. J Affect Disord.
7. Bastiaanssen TFS, Cowan CSM, Claesson MJ, Dinan TG, Cryan JF. Making sense of … the microbiome in psychiatry. Int J Neuropsychopharmacol. 2019;22(1):37-52.
Further reading:
Subba R, Sandhir R, Singh SP, Mallick BN, Mondal AC. Pathophysiology linking depression and type 2 diabetes: Psychotherapy, physical exercise, and fecal microbiome transplantation as damage control. Eur J Neurosci. 2021;53(8):2870-2900.
Qian F, Liu G, Hu FB, Bhupathiraju SN, Sun Q. Association between plant-based dietary patterns and risk of type 2 diabetes: a systematic review and meta-analysis. JAMA Intern Med. 2019;179(10):1335-1344.
Francis HM, Stevenson RJ, Chambers JR, Gupta D, Newey B, Lim CK. A brief diet intervention can reduce symptoms of depression in young adults – A randomised controlled trial. PLoS One. 2019;14(10):e0222768.
Parletta N, Zarnowiecki D, Cho J, et al. A Mediterranean-style dietary intervention supplemented with fish oil improves diet quality and mental health in people with depression: A randomized controlled trial (HELFIMED). Nutr Neurosci. 2019;22(7):474-487.
Sánchez-Villegas A, Martínez-González MA, Estruch R, et al. Mediterranean dietary pattern and depression: the PREDIMED randomized trial. BMC Med. 2013;11:208.