Feeling blue or anxious?
Start to feel better by changing your diet! The SMILES study published in 2017 by Jacka, F.N., O’Neil, A., Opie, R, et. al. tested the hypothesis that dietary changes can alleviate symptoms of depression and anxiety (1). The SMILES study was conducted over a 12 week period and was a single blind randomized control trial with a parallel control group. The 67 participants were randomized into either the dietary intervention group or the control group who received social support. At the beginning of the study, all participants took four tests; Montgomery-Asberg Depression Rating Scale (MADRS), Hospital Anxiety and Depression Scale (HADS), Profile of Mood States (POMS), and Clinical Global Impression-Improvement (CGI-I). The MADRS is an interviewer-rated scale that consists of 10 items and each item is rated on a 6-point scale. Higher scores relate to more severe symptoms. The HADS is a self-reported questionnaire and POMS is a mood assessment. Lastly, CGI-I measures the change in symptoms between starting and finishing the trial.
Participants in the dietary intervention group met with a dietitian for seven 60 minute sessions. During the session, participants received individualized diet advice and how to implement the advice into daily practice. Dietary advice was based on the Australian Dietary Guidelines and Dietary Guidelines for Adults in Greece which included 5-8 servings of whole grains daily, 6 servings vegetables daily, 3 servings fruit daily, legumes 3-4 servings weekly, 2-3 low-fat and unsweetened dairy daily, 1 serving raw or unsalted nuts daily, fish twice per week, 3-4 servings red meat weekly, chicken 2-3 servings weekly, eggs up to 6 per week, and 3 Tbsp olive oil daily. Participants were also encouraged to consume less sweets, refined grains, fried foods, fast foods, processed meats, sugary drinks, and alcohol.
The control group received social support through the ‘befriending’ protocol. Participants had seven 60 minute sessions with a research assistant where they either had conversations on neutral topics, examples include weather or current events, or engaged in activities, such as board games. The research assistant was to keep the participant engaged and feeling positive.
Researchers found that the participants who received dietary intervention had significantly less depressive and anxiety symptoms. They also had significant improvements in dietary patterns including eating an extra 1.21 servings whole grains per day, 0.46 servings of fruit per day, 0.52 serving daily per day, 0.42 servings legumes per week and 1.12 servings fish per week. There was also a decrease in undesirable foods of 21.76 servings per week.
In subsequent research, Chen, Guo-Qiang et. al. published a meta-analysis that examined the relationship between the Dietary Inflammatory Index (DII) and mental health, including depression (2). Researchers discovered a positive linear correlation of a 1-unit increase on the DII and a 6% increase in symptoms of depression. Researchers proposed a few potential mechanisms. First, a diet that promotes inflammation is associated with elevated inflammatory markers such as cytokines. These inflammatory markers can interfere with neurotransmitter metabolism and neural flexibility which can lead to depression and or anxiety. Second, a pro-inflammatory diet can cause an oxidant-antioxidant imbalance which leads to increased levels of reactive oxygen and nitrogen species. Excess reactive oxygen and nitrogen species promotes DNA damage that is associated with increased depression and anxiety. Lastly, a pro-inflammatory diet can affect the microbiome-gut-brain axis. The microbiome modulates the immune system by regulating neurotransmitter production and controls neuroendocrine pathways that can influence mental health.
Consuming a diet rich in fruits, vegetables, nuts, whole grains, fish, and healthy fats helps to reduce inflammation (3). Eliminate inflammatory causing foods including refined carbohydrates, fried foods, sugar sweetened beverages, such as soda, red and processed meats, margarine, shortening and lard.
Even though fish contains anti-inflammatory omega-3 fatty acids, consuming fish is not recommended on a whole food plant based diet. Fish contains a higher amount of amino acids than plant proteins that causes the body to produce more IGF-1 (insulin-like growth factor 1) (4). High levels of IGF-1 is associated with an increased cancer risk due to the nature of stimulating cell division and growth. Fish is similar other animal proteins in being high in cholesterol and saturated fat while lacking in fiber and phytochemicals. Heavy metals, such as mercury, PCBs (polychlorinated biphenyls), pesticides and insecticides are also to be concentrated in fish. Plant based sources of omega-3 fatty acids include flaxseed, chia seed, walnuts, and edemame (5).
- SMILES (Supporting the Modification of lifestyle in Lowered Emotional States) [Jacka, F.N., O’Neil, A., Opie, R. et al. A randomised controlled trial of dietary improvement for adults with major depression (the ‘SMILES’ trial). BMC Med 15, 23 (2017). https://doi.org/10.1186/s12916-017-0791-y]
- -Chen, Guo-Qiang, Chun-Ling Peng, Ying Lian, Bo-Wen Wang, Peng-Yu Chen, and Gang-Pu Wang. “Association Between Dietary Inflammatory Index and Mental Health: A Systematic Review and Dose–Response Meta-Analysis.” Frontiers in Nutrition 8 (2021).
Author: Misty Hildenbrand, Registered Dietitian