4 Root Causes of Low Mood and Depression

Nutritionist Dr Marc Bubbs explains how your diet choices can positively and negatively affect your mental health.

Low mood and depression are increasing at an alarming rate in today’s modern society. The Centre for Disease Control shows 10% of people suffer from depression, but in clinical practice people struggle with low mood at much higher rates in today’s constantly connected world, seemingly fuelled by processed foods. 

The World Health Organization has estimated that by the year 2050one-third of the global population will suffer from either anxiety or depression. This is a mind-boggling statistic. How is this possible? Why are we more prone to depression today than in generations past? As with any complex condition, multiple underlying factors conspire to create an environment where low mood and depression can thrive. Let’s look at a few common root causes to better understand how things go wrong at a cellular and hormonal level.

#1 Blood Sugar and Insulin Dysfunction

Today, its estimated that 1 in every 4 adults and 1 in every 5 children are classified as overweight or obese in the UK. While the recommended intake of sugar is around 11% of a person’s daily food intake, which works out around 50g for women and 70g for men depending on how active they are, the population tends to take in more than that, with children and teenagers’ intake being the highest. 

Combined with the over-consumption of processed carbs and alcohol and you’ve got five of the top six foods in the UK diet; desserts (grain-based), breads, processed chicken, fizzy/​sugary drinks, energy drink, alcohol and pizza. 

This leads to an excessive caloric intake, which is further exacerbated by these hyper-palatable foods, meaning the cycle continues, over and over again. When your cells are constantly flooded with excess energy, they eventually say, enough is enough” and refuse to take in more energy. This is the state of insulin resistance and, further down the road, diabetes (type‑2). 

How does this relate to mood? Research from Scandinavia has uncovered a clear association between elevated HbA1c — a three-month average of your blood sugar levels — and insulin levels with increased risk of depression. 

They found that young men with insulin resistance were three times more likely to suffer from severe depression.(1) Another study in Diabetes Care of over 4,000 people showed depressive symptoms were highly associated with higher fasting and 30-minute insulin levels.(2) The authors specifically noted that antidepressant medications did not alter this association because the medications target neurotransmitters (e.g. serotonin, dopamine) and do not address blood sugar and insulin dysfunction. 

Improving blood sugars and insulin control is an important first step for reducing your risk for low mood and depression.

#2 Chronic & Systemic Inflammation #

Inflammation is another potential root cause of low mood. Low-grade systemic inflammation leads to the over-production of pro-inflammatory cytokines that are also associated with depression.(3) The prestigious New England Journal of Medicine published a review of the growing connection between chronic inflammation and the development of today’s most common chronic diseases, including depression.(4)

The current medical literature tells us that if you are overweight or obese, you likely have low-grade systemic inflammation.(5) This shouldn’t be a surprise, as inflammation is upstream” of blood sugar and insulin dysfunction. 

A diet rooted in traditional foods — rich in animal protein, healthy fats and antioxidants — will help to cool inflammation and reduce the damaging effects of reactive oxygen species (ROS) produced during the inflammatory response. Polyphenols found in coffee, dark chocolate (even red wine!), as well as vegetables are great sources of anti-inflammatory polyphenols. Extra-long chain omega‑3 fats, such as DHA and EPA, also exert powerful anti-inflammatory effects, and a poor omega‑3 to omega‑6 fats ratio is also associated with a chronic stress state and increased risk of depression. (6)

#3 Gut Dysfunction & Dysbiosis

The gut microbiota — commonly referred to as your microbiome — plays a key role in your mental health through its constant communication with the brain via the vagus nerve. Key neurotransmitters targeted by medications for improving symptoms of depression – serotonin and dopamine – are actually produced in the greatest concentrations in the gut (not the brain). 

This gut-brain axis is highlighted by research showing that if you are overweight, you’re at much greater risk of poor zonulin function, a key molecule that regulates gut permeability.(7) Poor zonulin function leads to symptoms of a leaky gut, leading to a pro-inflammatory environment that creates the cytokine storm that contributes to low mood and depression. 

You don’t need to be overweight to suffer from leaky gut. If you travel across multiple time zones, consume alcohol excessively, or chronically rely on NSAIDs – non-steroidal anti-inflammatory drugs – like ibuprofen and naproxen you’ll be much more prone to leaky gut and chronic worsen inflammation.(8,9) A dietary approach rooted in traditional foods — animal protein, healthy fats, vegetables and unprocessed carbohydrates — will help to keep blood sugar levels balanced and support a healthy gut microbiota, thus keeping systemic inflammation and low mood at bay. 

#4 A Sedentary Lifestyle #

Movement is a critical component of mental health and wellbeing. Long, busy workdays make it difficult to find time to exercise, however it should be a foundation of every mental health plan. A recent meta-analysis of 92 studies on more than 4,310 people showed that light to moderate exercise significantly reduced the incidence of depression. (10) Try adding 15 – 20 minute walks at lunch or the end of your day to increase your activity level. 

Strength training can also play a key role in mental health. Basic movements like squatting, lunging, bending, pushing, and pulling are deeply engrained in our DNA and exert tremendous positive benefit on multiple systems of the body: improving blood sugars and insulin, reducing inflammation, boosting testosterone (low levels have been associated with depression), and supporting healthy gut flora. If you’re not active, start slowly with 10 – 20 minutes of strength training 2 – 3 times weekly and focus on bodyweight type movements. 

There is no magic bullet” to fix depression. It’s a complex multi-factorial condition that is impacted by numerous systems of the body. From a biochemistry and physiology standpoint, addressing root causes like blood sugar and insulin dysfunction, chronic inflammation, dysbiosis and leaky gut and maintaining an active lifestyle are great places to start so you can raise the playing field (it’s also important to consult a qualified mental health professional to address the underlying emotional root-causes). 

Take control of your mental health by making the small changes to your nutrition, movement and lifestyle so you can get back to feeling your best. Many people and athletes alike experience low mood and depression, you’re not alone.


1. Timonen. M et al. Insulin resistance and depressive symptoms in young adult males: Findings from Finnish military conscripts. Psychosom Med 69(8):723 – 28

2. Pyykkonen AJ et al. Depressive symptoms, antidepressant medication use, and insulin resistance: the PPP-Botnia Study. Diabetes Care. 2011 Dec;34(12):2545 – 7.

3. Felger J, Lotrich FE. Inflammatory cytokines in depression: neurobiological mechanisms and therapeutic implications. Neuroscience. 2013 Aug 29;246:199-229.

4. Emerging Risk Factors Collaboration. Diabetes mellitus, fasting glucose, and risk of cause-specific death. New England Journal Medicine, Mar 2011;364;9:328 – 341.

5. G. S. Hotamisligil, N. S. Shargill, and B. M. Spiegelman, Adipose expression of tumor necrosis factor‑α: direct role in obesity-linked insulin resistance,” Science, vol. 259, no. 5091, pp. 87 – 911993

6. Larrieu T, et al. Nutritional omega‑3 modulates neuronal morphology in the prefrontal cortex along with depression-related behaviour through corticosterone secretion. Transl Psychiatry. 2014 Sep 9;4:e437.

7. Moreno-Navarrete JM et al. Circulating zonulin, a marker of intestinal permeability, is increased in association with obesity-associated insulin resistance.. PLos One 2012;7(5):e37160.

8. VanWijck K et al. Aggravation of exercise-induced intestinal injury by Ibroprofen in athletes. Med Sci Sports Exerc. 2012 Dec;44(12):2257 – 62

9. Matsui H et al. The pathophysiology of non-steroidal anti-inflammatory drug (NSAID)-induced mucosal injuries in stomach and small intestine. J Clin Biochem Nutr. 2011 Mar;48(2):107 – 11.

10. Rebar A, et al. A Meta-Meta-Analysis of the effect of physical activity on depression and anxiety in non-clinical adult populations. Health Psychol Rev. 2015 Mar 5:1 – 78