A bidirectional relationship has been found between T2DM and depression; depression increases the risk of the development of T2DM while T2DM increases the risk of depression. Therefore management of mental health is an important aspect of diabetes treatment.
In China, a low-fat diet (LFD) is recommended for prevention and control of type 2 diabetes to help improve blood glucose levels. However, a meta-analysis has suggested a reasonable low-carb diet (LCD) is more beneficial for T2DM. Most studies support a protective effect of a low fat-high carb diet on depression but for T2DM patients carbohydrate is believed to be the greatest dietary contributor to blood glucose rise so it is important to explore what diet regimen is beneficial to both depression and glycometabolism.
Nuts, as part of LCD, have been shown to effectively improve glycosylated hemoglobin (HbA1c) levels and fasting blood glucoses (FBG) in T2DM patients. The almond is the most consumed and studied nut and its prebiotic properties have been shown to contribute to increased production of short-chain fatty acids (SCFAs) in the gut microbiome, which can promote the secretion of glucagon-like peptide 1 (GLP-1), an important regulator of microbiota–gut–brain signalling in health and stress-related psychiatric illnesses.
The current randomised controlled trial was carried out to compare the effects of an almond rich low carb diet (a-LCD) with a low-fat diet (LFD). This is one of only a few studies which have reported whether a diet regimen is beneficial to both depression and glycometabolism in T2DM patients.
Forty-five participants with T2DM were enrolled from a diabetes club and the Endocrine Division of the First and Second Affiliated Hospital of Soochow University, China. They were randomly allocated to either an intervention or control group. The control group adopted an LFD while the a-LCD group consumed 56 g/day almond in place of 150 g carbohydrate.
The participants completed each dietary intervention for three months. The indicators for depression and biochemical indicators including glycosylated hemoglobin (HbA1c), gut microbiota, and GLP-1 concentration were assessed at the baseline and third month and compared between the two groups.
The resulting data revealed a low carb diet significantly improved depression and HbA1c (p <0.01). Meanwhile, a-LCD significantly increased the short chain fatty acid (SCFAs)-producing bacteria Roseburia, Ruminococcus and Eubacterium. What's more, the GLP-1 concentration in the a-LCD group was higher than that in the LFD group (p <0.05).
The authors conclude that the a-LCD could exert a beneficial effect on depression and glycometabolism in patients with T2DM.
The report states: "We speculate that the role of an a-LCD in improving depression in patients with T2DM may be associated with it stimulating the growth of SCFAs-producing bacteria, increasing SCFAs production and GPR43 activation, and further maintaining GLP-1 secretion. In future studies, the SCFAs and GPR43 activation should be further examined."
In this study, the a-LCD also decreased weight (p <0.05) and BMI (p <0.05) of patients with T2DM, suggesting the effectiveness of the diet in improving weight and BMI. The authors suggest this may be because nuts have rich energy density and high fat which may reduce gastric emptying rate and increase satiety.
There are several limitations of the study. One of the limitations is that it was conducted in a T2DM population with and without depression, which may limit the a-LCD effect on depression. Further studies that examine the effects of an a-LCD in patients with diabetes with clinical depression are required to understand the effectiveness of the current findings. The study did not monitor the dynamic changes of depression over the three-month period; therefore could not find the earliest time point for improvement in depression.
Almonds are rich in dietary fiber, polyphenols, and unsaturated fatty acids that may be protective against the development of depression.
Various interventions, along with two recently published cohort studies, have concluded higher nut consumption is associated with lower depression scores. A cohort study in Tianjin, China, indicated that nut consumption may be beneficial in the prevention of depressive symptoms.
In a large, parallel-group, multicenter, RCT using a Mediterranean diet supplemented with 30 g mixed nuts (15 g walnuts, 7.5 g hazelnuts, and 7.5 g almonds) including 7447 participants for 3 years, the result indicated that the inverse association with depression was not significant in the whole cohort. However, when the analysis was restricted to participants with T2DM, a 40% lower risk of depression was reported.
Wang. X., 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"