Depression is typically thought of as a biochemical-based imbalance or a psychologically-rooted problem. On the contrary, nutrition can play a key role in the onset as well as severity and duration of depression.
Many of the noticeable changes in food patterns that precede depression are strikingly similar to biological symptoms of depression, such as loss of appetite, change in taste, or cravings for “comfort” food that usually high in sugar or fat.
When carbohydrates are consumed, it triggers the pancreas to produce insulin, which in turn helps us utilise glucose in our cells to produce energy. However, high glycaemic index (GI) or glycaemic load (GL) foods, such as sugary snacks or refined grain-based desserts, will trigger an insulin roller-coaster ride and thus create more stress for the body to deal with. The Women’s Health Initiative found that higher GI foods were associated with increased risk of depression (Gangwisch et al 2015). The study also showed that progressively higher consumption of dietary added sugars was associated with increasing odds of incident depression. Moreover, a higher consumption of lactose, fibre, non-juice fruit, and vegetables was significantly associated with lower odds of incident depression, and non-whole/refined grain consumption was associated with increased odds of depression. A meta-analysis and systematic review found no significant association between either dietary GI or GL and odds of depression in cross-sectional studies, but they did find a significant positive association between dietary GI and depression in cohort studies, and that a significant effect of a high-GL diet consumption on risk of depression was seen in clinical trials (Salari-Moghaddam et al 2019).
Hence, eating low GI foods, such as whole grains, root vegetables, and legumes will be more likely to provide a sustained and lasting effect on brain chemistry, mood and energy level than high GI foods.
What about protein? Humans need nine essential amino acids, meaning we cannot produce them from other sources. These are histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Tryptophan is the precursor to serotonin, the neurotransmitter that regulates our mood, sleep and appetite. Dopamine and adrenaline’s precursor, tyrosine, although not an essential amino acid, is still an important amino acid, as has been shown in depletion studies that tyrosine-free subjects were less content, more apathetic, had significant differences in decision-making tasks and disrupted affect/reward-based processing characteristic of clinical depression (Harmer et al 2001).
The National Health and Nutrition Examination Survey from 1971-1975 found that increased intake of protein demonstrated a protective effect among men but a deleterious effect among women (Wolfe et al 2011). The same National Health and Nutrition Examination Survey for the years 2007-2014 found that total protein intake and protein intake from milk and milk products might reduce the risk of depressive symptoms in United States adults (Li et al 2020). Another national survey of the United States and South Korea showed that when the proportion of calories intake by protein increased by 10%, the prevalence of depression was significantly reduced both in the United States and South Korea, and that the low protein intake groups had significantly higher risk for depression than the normal protein intake groups in both countries (Oh et al 2020).
Are fats bad for mental health? Well, that depends on what types of fat we are talking about. Most of us have heard of the omega-3 fatty acids EPA and DHA, and that regular consumption of these polyunsaturated fatty acids (PUFA) are good for our hearts and brains.
A meta-analysis in 2019 showed an overall beneficial effect of omega-3 polyunsaturated fatty acids on depression symptoms, and when compared with placebo, pure EPA or EPA formulations demonstrated clinical benefits with a dose of <1g/day, whereas pure DHA and DHA-formulations did not exhibit such benefits (Liao et al 2019). However, the data is inconsistent for certain groups such as pregnant women, with one meta-analysis demonstrating no difference in depression scores when they were given omega-3 fatty acids as a monotherapy for treatment of depression (Liu et al, 2017), while another showed significantly improved depressive symptoms in perinatal women (Zhang et al, 2020). When looking at actual fish consumption, large studies show that high-fish consumption can reduce the risk of depression (Li et al 2016, Grosso et al 2016, Yang et al 2018).
There is some discussion whether the effect may be due to taking omega-3 fatty acids as a supplement rather than as a dietary “food package” such as oily fish, and the preventive role of omega-3 PUFA may depend on other factors such as overall diet quality and the social environment.
Not only is the absolute level of omega-3 PUFA important, the ratio of omega-6 to omega-3 seems to be a determining factor for the development of depression as well. A 7-year prospective study showed that the omega 6:3 PUFA ratio is associated with an increased risk for mood disorders in young people at ultra-high risk of depression (Berger et al 2017). Similar findings of increased risk of depression and suicide risk were noted in smaller studies on pregnant women and older adults (Vaz et al 2014, Kiecolt-Glaser et al 2007, Hoge et al 2019).
Shall we avoid foods high in omega-6 fatty acids? Some of these foods are part of a healthy diet, such as walnuts, sunflower seeds, tofu and eggs, and when eaten as whole foods, are beneficial to our overall health. However, highly processed and refined industrial seed and vegetable oils should be avoided, and healthy oils such as olive oil, avocado oil and cold-pressed nut and seed oils can be used instead. Monounsaturated fatty acids have also shown some benefit in
The worst combo is a combined high-sugar, high-fat diet, which has been associated with more depressive symptoms (Vermeulen et al 2017). Such high calorie obesogenic diets are not only nutrient-poor a lot of the times, but also contribute to metabolic disturbance, oxidative stress and inflammatory processes that may be linked to neuroinflammation, the hallmark feature of brain disorders (Melo et al 2019).
In summary, nutritional compounds might modulate depression associated biomarkers. In this context, several healthy foods such as olive oil, fish, nuts, legumes, dairy products, fruits, and vegetables have been inversely associated with the risk of depression and might also improve symptoms. In contrast western dietary patterns including the consumption of sweetened beverages, fried foods, processed meats, baked products have been shown to be associated with an increased risk of depression in longitudinal studies. Diet and nutrition offer key modifiable targets for the prevention of mental disorders (Khanna et al, 2019)
Article first written for and first published by ASLM https://www.lifestylemedicine.org.au/
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