How what you eat affects how you think

Have you ever noticed that your mood takes a nosedive after indulging in a packet of potato chips or a sugary soda?  

Or you feel tired after lunch when you had a white bred sandwich or something accompanied by white rice?

Or maybe you feel a sudden surge of energy followed by a crash after a meal of fast food?

It’s not just your imagination – what you eat can have a profound effect on your health, including your mental health.

This is because most processed food is not ‘balanced’ in the way your body needs food to be.

One area of growing concern is how processed food affects mental health, the gut-brain connection and the impact on hormones, mood and emotions.

The Gut-Brain Connection

Your gut and your brain are connected by a complex network of nerves, hormones, and chemicals. This means that what happens in your gut can have a direct impact on your mental health.

In fact, your gut is sometimes called your “second brain” because it produces many of the same neurotransmitters that are found in your brain, including serotonin, dopamine, and gamma-aminobutyric acid (GABA).

These neurotransmitters are essential for regulating mood, sleep, and appetite.  Interestingly, your gut produces more than 90% of your body’s serotonin which plays a crucial role in regulating your mood.

The connection between your gut and brain is mediated by the vagus nerve, which allows for bidirectional communication.  In other words, communication to, and from, your brain.

Recent studies have shown that the gut microbiota, which are the microorganisms that live in our gut, play a crucial role in this connection.

This means that when you eat processed foods you have a direct effect on your gut biota which can result in:

Reduced Diversity of Gut Microbiome

Your gut is home to trillions of bacteria, which make up what is known as your gut microbiome. These bacteria play a crucial role in your overall health, including your mental health.

A diet high in processed foods, can reduce the diversity of the gut microbiome which, in turn, can lead to a reduction in beneficial bacteria which then allows harmful bacteria to take over.

Increased Inflammation

Processed foods are nearly always high in sugar, refined carbohydrates, and unhealthy fats. These types of foods contribute to inflammation in the body, including in the gut.

Chronic inflammation can lead to a range of health problems, including mental health issues such as depression and anxiety. 

One thing you may not realise is that bloating, and even obesity, are an indication of inflammation in your body.  It is a message from your body that so often gets overlooked.

Impaired Gut Barrier Function

The gut barrier is a protective layer that lines the gut and prevents harmful substances from entering the bloodstream. A diet high in processed foods, can impair the function of the gut barrier. This can lead to a condition known as leaky gut syndrome, where harmful substances leak into the bloodstream and cause inflammation throughout the body, including in the brain.

Why your gut hormones and neurotransmitters are important

Think of your hormones and neurotransmitters as chemical messengers that send information around your body to different organs, tissue and cells.

These different messengers have different messages and only communicate to the relevant ‘receiver’.

When your gut bacteria are out of balance then these substances in your gut are directly affected.

Then, depending on what happens to the messages, other hormones and organs within your body can be indirectly affected. 

There is the potential for multiple comprehensive effects to the way your body functions when your diet consists mostly of processed food. 

This is why so many people can have different experiences when they eat the same processed foods.

How processed food affects your hormones and neurotransmitters

There are so many ways you can be affected when you eat mainly processed food that I am only going to elaborate on three here:

Insulin resistance

Processed foods are often high in refined carbohydrates and sugar, which can cause a spike in blood sugar levels.

This can lead to insulin resistance, where your body becomes less responsive to insulin.

Insulin resistance has been linked to a range of health problems, the most common being type 2 diabetes.  It is also linked to mental health problems which include depression and anxiety.

Disruption of the HPA Axis

Your hypothalamic-pituitary-adrenal (HPA) axis is a complex system responsible for the regulation of hormones such as cortisol, which is your body’s main stress hormone.

When you eat a diet that is high in processed foods, you disrupt the HPA axis, leading to an overproduction of cortisol.

High levels of cortisol can lead to chronic stress, which has been linked to a range of mental health problems.

Reduction in serotonin

Serotonin is a neurotransmitter that is often referred to as the “feel-good” hormone. It plays a crucial role in regulating mood, appetite, and sleep.

When you eat a diet that is high in processed foods, you can reduce production of serotonin, which in the long term can lead to a range of mental health problems, including depression and anxiety.

You may even notice a change in your mood after eating certain foods, or observe it in the people around you.

Some specific processed foods that can disrupt gut hormones and impact mental health include:

Processed food as a whole will affect your gut bacteria but here are some which are more prevalent in most people’s diet.  Even reducing these can make a difference to how you feel.

Sugar and artificial sweeteners

Consuming large amounts of sugar can cause a rapid spike in blood sugar levels, which can lead to a corresponding spike in insulin levels.

This can cause a crash in blood sugar levels shortly after, leading to feelings of fatigue, irritability, and anxiety.

In addition, long term high sugar consumption affects insulin production and can lead to insulin resistance and diabetes.

Processed meat

Processed meats like deli meat, hot dogs, salami and sausages contain high levels of nitrates and nitrites, which can damage the cells lining the digestive tract and disrupt the balance of gut bacteria.

Trans fats

Trans fats are often found in processed foods like packaged snacks, fast food, and fried foods.

These fats can contribute to inflammation in the body and can interfere with the production of hormones such as serotonin, dopamine, and norepinephrine.  These hormones are responsible for regulating mood, motivation, and emotion, and imbalances can lead to mental health problems.

Highly processed grains

Highly processed grains like white bread and white pasta are stripped of their natural fibre and nutrients, which can negatively impact gut health and hormone production.


Too much salt can lead to dehydration, which can cause feelings of fatigue and low energy. This can also lead to imbalances in electrolytes, which can affect the functioning of your nervous system.

Additives and preservatives:

Processed foods often contain a variety of additives and preservatives to extend their shelf life and enhance their flavour.

These additives can have negative effects on your mental health. For example, some food dyes have been linked to hyperactivity and other behavioural problems in children.

Additionally, some preservatives, such as sodium nitrate, have been linked to an increased risk of cancer.

It is really important to read food labels and avoid processed foods that contain artificial additives and preservatives.

Nutrient deficiencies

Processed foods are often low in essential nutrients, such as vitamins, minerals, and fibre. These nutrients are crucial for maintaining optimal mental health.

Studies have shown that consuming foods that are rich in omega-3 fatty acids can help reduce symptoms of depression and anxiety.

When you consume processed foods, you don’t provide your body with the nutrients it needs to function properly.

This can lead to overall nutrient deficiencies which can, in turn, have negative effects on our mental health.

The most common mental health effects of processed food

So, what are the most common mental health effects of eating a diet high in processed food?

Here are a few:

Depression and anxiety

Diet can play a crucial role in the development of depression. Studies have shown that a diet that is high in processed foods is associated with an increased risk of depression. This is because processed foods can lead to inflammation and impaired gut health, which can disrupt the gut-brain connection and affect mood-regulating hormones like serotonin.

Depression is a complex disorder that is caused by a range of factors, including genetics, environment, and lifestyle so it may be necessary to address a number of different factors in this instance.

Behavioural issues

While the exact cause of attention-deficit/hyperactivity disorder (ADHD) is not known, diet is thought to play a role in the development and management of the disorder.

Similar to depression and anxiety, studies link a diet high in processed foods to an increased risk of ADHD symptoms. This is likely due to the impact that processed foods have on the gut-brain connection and the production of neurotransmitters like dopamine and serotonin.

Many parents report behavioural issues with their children which, by managing diet, they are able to mitigate. 

Specific research may not be available for different behaviours but, given the association between gut biota and behaviour, it may be worth investigating if you are trying to manage behaviour in your children, or for yourself.

Fatigue and Irritability

You may even experience this and not really connect it with your food.

When insulin levels spike and then crash, it can cause fatigue and irritability, making it harder to concentrate and stay focused.

If you usually feel tired after lunch, make a note of what it was you had for lunch and try something different the next day.

Brain Fog

Processed foods can also cause inflammation in the body, which can affect cognitive function, leading to “brain fog” and difficulty thinking clearly.

Similar to fatigue, if you have difficulty thinking after lunch you may like to test out how you feel when you have a variety of different foods.

Addiction: Processed foods are often designed to be addictive, with high levels of sugar, salt, and unhealthy fats. This can lead to a cycle of cravings and binge eating, which can negatively impact mental health.

What Can You Do?

If you’re concerned about the impact of processed food on your mental health, there are a few things you can do:

Choose whole foods

Opt for whole foods like fruits, vegetables, whole grains, and lean proteins. These foods are packed with nutrients that can support mental health and reduce inflammation in the body. 

Choosing whole foods will also help to reduce your risk of other negative health consequences such as risk of obesity, type 2 diabetes, and cardiovascular disease.

Limit processed foods

Try to limit your intake of processed foods like sugary snacks, fast food, and pre-packaged meals. Instead, focus on cooking at home using fresh, whole ingredients.

Pay attention to how you feel

Keep track of how you feel after eating certain foods. If you notice that you feel tired, irritable, or anxious after eating processed foods, it may be time to make a change.

Get help

Sometimes just changing things yourself can work and make a huge difference.  Often though, there are a number of factors as well as diet and if you don’t think you can do it all on your own then find someone to help you.

Healthy Eating is Easy! can get you started on the path of eating food which is more beneficial for your gut.

It is important to note that mental health is complex and multifaceted, and diet is just one factor that can influence your well-being.

If you’re struggling with mental health issues, it’s essential to seek professional help and support from a qualified healthcare provider.


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