Do you know why you are depressed?

No? Here are four reasons why that’s good.

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There is much talk these days of mental health issues, especially depression. We hear of its paralysing effects, and the range of treatments available, and that’s good. But we need to talk more about what is causing this devastating disability, which affects staggering numbers of people across the globe.

We urgently need to broaden the discussion and explore all possible explanations, including the effects of diet.

People see a nutrition consultant for all sorts of reasons, usually to improve energy or digestion, lose weight, or correct hormonal imbalances — that sort of thing. For over fifteen years, that was my bread and butter. Helping people regain their physical health was immensely rewarding, something that never diminished with time.

Helping people regain their mental health was equally rewarding, but often took a slightly different route.

When it came to mental health, I noticed a certain pattern. Often when people sought advice for physical problems, buried within their concerns were the mental health issues that attended those problems.

Searching for clues

Each client was asked to complete a questionnaire prior to the consultation, and rarely was depression stated as a main concern. More often than not, it was slipped between the lines, like a nervous after-thought. I learned quickly not to dismiss those “secondary” issues. They would often turn out to be the main reason for the consultation.

“Do you know why you are depressed?” I would ask, to my client’s surprise and relief.

The door was opened, and we’d go through it.

“No!” Was the usual response, followed by something along the lines of:

“I shouldn’t be depressed. I love my family and my job. I don’t have any major financial problems. I don’t understand why I feel the way I feel.”

And we would both smile at the absurdity and sadness of the situation. Doing so served to relieve the undercurrent of guilt felt by my client for feeling bad when everything was good.

It was the response I hoped for. Because, like so many physical conditions, the underlying cause of the depression and/or anxiety was quite possibly diet. And if it was diet, it was just a matter of determining the specific dietary cause and correcting it.

It wasn’t always the case, of course. Sometimes there had been a clear trigger for mental health decline, and no amount of diet was going to change past trauma. But in the absence of anything obvious, I was optimistic that nutritional intervention was the answer. The effect of food on the brain is profound.

Of course it is: the brain is made out of the food you eat. It is is a wobbly mass of fat, protein, cholesterol and water, activated by vitamins, minerals, fatty acids and amino acids. Its dry weight is 60% fat.

Did you really think that what you ate had no impact on the operating system of your brain?

Work it out

There are many dietary factors that affect brain function. Below, I focus on the four that I encountered most frequently in clinic. The clues to identifying the right one(s) usually lay in the accompanying physical symptoms. If you suffer from depression and anxiety, you too might spot the clues. I hope so.

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1. Blood sugar imbalance

This was the most common cause of mood disorders that I encountered. It was also surprisingly easy to correct.

Elsa was a 24-year old jewellery designer, whose main reason for seeing me was her lack of energy. She also mentioned, on further questioning, that she had “mild” depression and mood swings. Then she revealed that she was often too low, and too tired, to get out of bed in the morning.

I felt there was quite possibly a link between Elsa’s fatigue, depression and mood swings. That link was, as it transpired, her fluctuating blood sugar levels.

A key question I always asked if I suspected blood sugar imbalance was: How do you feel if you don’t eat for at least four hours? Frequently, the mere suggestion was enough to induce panic. It was simply not possible, without experiencing tremors, headaches, light-headedness, irritability and mental confusion.

The sugar in your blood comes mainly from the carbohydrates that you eat. The more carbs you eat, the more your blood sugar (glucose) rises, and the more insulin you produce. Insulin lowers glucose levels. Protein can also cause a rise in insulin, but nothing like carbohydrate.

Keep eating sugar and carbohydrates, and you are going to have frequent spikes of blood sugar, followed by sudden drops, as insulin rushes in. These peaks and troughs can eventually lead to something called insulin resistance, when insulin loses its effect. Insulin resistance can lead to the metabolic syndrome, a condition that puts you at risk of cardiovascular disease, diabetes and stroke. There is also heightened risk of mental health conditions.

There is a high prevalence of metabolic syndrome in people with psycho-neurological disorders, including schizophrenia, bipolar disorder, depression, anxiety, ADHD and autism.

“Due to the shared nature of these conditions, treatment should address aspects of both mental health and metabolic disorders”. Nousen et al (2013)

The road to metabolic syndrome is paved with symptoms of blood sugar imbalance, including low energy and depression.

The clues were writ large in Elsa’s food diary. Breakfast was normally a chocolate croissant and a cup of tea with one sugar. Lunch was a sandwich followed by a packet of crisps (or chips, if you’re in the US). In the evening, a ready-meal followed by a rhubarb and custard dessert was the norm.

Also the norm for Elsa — but not for the human body — was the prodigious amount of snacking that occurred throughout the day. Elsa thought that these snacks would help with her energy, but they were having the opposite effect. She just loved root ginger cookies and chocolate, and her day was spent on a roller-coaster of spikes and dips in both glucose and insulin.

I persuaded Elsa to cut out all sweet foods and refined carbohydrates, such as bread, pasta, rice, pastries, and so on. She didn’t go carb-free; she ate beans and lentils as a component of meals, which always included a complete protein along with root vegetables. A complete protein includes meat, fish, eggs, cheese, yogurt. I also asked her to stick to three meals a day with no snacking in-between.

Three weeks later, a much brighter (and 2k lighter) Elsa came back to see me. She said she felt transformed, and described her mood, along with her energy levels, as “completely normal”.

2. Gluten sensitivity

Here’s one that regularly stirs up media cynicism. Gluten/wheat sensitivity is sometimes dismissed as an attention-seeking trend of the self-obsessed. This view is based on the observation that gluten sensitivity was virtually unheard of, several years ago, and now everyone seems to have it.

The truth is that not that long ago, large numbers of people were living their entire lives with gluten sensitivity, without knowing it. People just thought it was normal to be plagued with symptoms, ranging from depression to irritable bowel syndrome (the physical/mental combo again). No, it isn’t normal: there is always a cause, and gluten sensitivity is remarkably common.

In one of my previous articles — Is Gluten Messing with Your Mind? Find Out Now — I describe a client of mine, Simon. He had a combination of physical and mental symptoms. These included low energy, depression, anxiety and a long history of gastroenteritis. It turned out they were all caused by gluten sensitivity.

At least the medical profession now takes gluten sensitivity seriously. The condition has been recognized with an official medical term: non-celiac gluten sensitivity (NCGS).

The “classical” presentation of NCGS is, indeed, a combination of gastro-intestinal symptoms including abdominal pain, bloating, bowel habit abnormalities (either diarrhea or constipation), and systemic manifestations including disorders of the neuropsychiatric area such as “foggy mind”, depression, headache, fatigue, and leg or arm numbness.” Lionetti et al (2015)

Gluten is the name of a group of proteins found within certain grains, namely wheat, rye and barley. Gluten sensitivity is not the same as celiac disease, or wheat allergy, which, until recently, were the only gluten-related conditions recognised by the medical community.

Simon carried out an exclusion test to determine whether or not gluten was his nemesis. There was a significant clue in his food diary: he ate mounds of wheat, every day. Pasta and sandwiches were the foods he said he would find hardest to give up. Cravings are, unfortunately and quite cruelly, the modus operandi of a food sensitivity.

The test was positive, so it was simply a question of eliminating all gluten in order to eliminate all symptoms.

For more information about gluten sensitivity, and how to do an exclusion test, see the link below to my article.

3. Docosahexaenoic acid (DHA) deficiency

The first thing I always asked my clients, regardless of whatever they had written on their questionnaire, was: What is the main problem you would like to deal with?

My all-time favourite response was Alicia’s. Without missing a beat, she quipped: “It’s my husband. He’s a fucking bastard.”

I like a challenge, and Alicia certainly presented one. Once we’d moved on from her husband, who was interesting, we discussed her dry skin and eyes, her irregular menstruation and her joint pain. She never mentioned her anxiety during our initial consultation, and it wasn’t on her questionnaire. I had my suspicions (it didn’t take a genius), but decided to park them for the time being.

The physical symptoms of deficiency of the fatty acid DHA include dry skin, dry eyes, menstrual and other hormonal difficulties. It is strongly associated with inflammatory conditions, such as joint pain.

The psychological and neurological signs of deficiency include depression and anxiety.

The latter are hardly surprising. Different types of fat play a crucial role in the structure and function of the brain, which is the fattiest organ in the body.

DHA is an omega-3 fatty acid that is essential for normal neurodevelopment. It is the major polyunsaturated fat in the brain. There are two families of polyunsaturated fats: omega-3 and omega-6 fatty acids. They are required in more or less equal amounts. However, they compete for absorption. The modern diet, heavy on cereal grains and refined vegetable oils, is much higher in omega-6 than omega-3, creating an imbalance that affects the whole body, not least the brain.

Patients with major depressive disorder and bipolar disorder have been shown to have significantly lower blood levels of DHA compared to healthy controls. Research has found that increasing dietary intake of DHA significantly reduces depression symptom severity.

Alicia did not like oily fish or seafood, which was unfortunate because they are the only significant dietary source of DHA. Although it is true that the body can make DHA from some plant sources — nuts and seeds — the amount it is able to make is so small (less than 0.5% conversion rate) that it is considered negligible. That is why the prevailing view is that this is an “essential” fatty acid, meaning it needs to be obtained, preformed, directly from diet.

Fish for brains

You can see the problem here. Oily fish — sardines, salmon, herring, trout, mackerel, anchovies — are not top of most people’s list of favourite foods. Intake of omega-6, which replaces omega-3 in the brain, is soaring. Anything cooked in soya, corn or sunflower oil will displace omega-3.

I couldn’t persuade Alicia to eat fish, but she did agree to take fish oil capsules instead. She also eliminated all foods cooked in vegetable oils, to reduce her omega-6 intake.

What a difference I saw in Alicia when she returned. This time, she mentioned her anxiety (but not her husband). In her own words, she said she “had never felt so ‘unanxious’”. Her new-found calmness was evident. She went on to explain that all her life she had felt highly anxious about everything. She had not mentioned this anxiety previously because she didn’t see it as a health problem; having never known anything else she just thought it part of her make-up. She didn’t know that it was possible to feel differently.

4. Alterations in the gut microbiome

“The next few years of research hold the potential of uncovering intriguing connections between gut bacteria and neurological conditions that may possibly impact human health.” Mayer, E.A., et al (2014)

The microbiome — sometimes called the “second brain” — is the term for all microorganisms living in the gut.

There is a direct line between gut and brain, along which communication takes place. This line is the vagus nerve, the longest nerve in the body’s autonomic nervous system.

Who would have guessed that the gut microbiome could in any way influence your mental health. But it does, quite profoundly. The research into the human microbiome, and its role in brain function, including mood, is still emerging and is now gaining traction.

There has been a paradigm shift in neuroscience in the understanding of the link between the gut microbiome and the central nervous system. Both psychological and physical stress can affect the make up and activity of the gut microbiome. At the same time, changing the gut microbiome can affect emotional behaviour. This suggests that the gut microbiome may play a role in the development of human brain diseases such as autism spectrum disorder, anxiety and depression.

There is an established link between bowel disorders and neurological disorders.

“For example, mood disorders affect more than half of all patients with irritable bowel syndrome, with antidepressants being one of the most common pharmaceutical interventions for irritable bowel syndrome.” Rogers et al (2016)

That was written in 2016. In 2005, I met Vicky. She was preparing to get married, and as part of that preparation wanted to deal once and for all with both her digestive problems and depression, that had dogged her for years.

From her questionnaire, and from our discussion, I strongly suspected that Vicky had a bad case of dysbiosis, an imbalance between friendly and not-so-friendly bacteria and yeasts in her gut. She had constipation, excessive gas and bloating, acne, headaches, low energy, irritability and depression. Not a good look on any day, let alone your wedding day.

I focussed on making sweeping changes to her diet, which was heavy on refined carbohydrates, and supplementing with probiotics. The effects were dramatic, but took a bit of time to appear. When I saw her two months later, she reported that she felt “…phenomenal. I feel like a normal human being.

In an earlier article, How gut bacteria can lift depression. Be sure to feed them well, I give details of dietary recommendation to support the health of the microbiome. See below for the link.


Times have changed, and we talk about mental illness much more freely now, without the stigma that once confined sufferers to a silent agony. If we can accept that certain medications can alter mood by modulating brain biochemistry, the idea that chemicals found in food can do something very similar does not sound so far-fetched.

I started the publication Feed Your Brain because I saw a real need to highlight the link between diet and mental health. If you can fix your body through diet, why not your brain?

Read and share my other articles on diet and mental health:

Is gluten messing with your mind? Find out now.

How gut bacteria can lift depression. Be sure to feed them well.

How intermittent fasting with exercise can boost your brain

Your brains are in your belly, and that’s good for your mental health.

How to beat depression with vitamin D

What you learn about racism, from studying the human brain.

How to manage your stress by changing your diet.

The link between diet and depression: 5 important facts

How eating more fat can improve your memory

How three ordinary B vitamins could save you from Alzheimer’s

Why you need cholesterol for your mental health

Alzheimer’s disease and the sugar connection.

Thinking of going vegan? Read this first.