Nutrition, Brain Function and Mental Health

10 November 2020

Good nutrition is important for both our mental and physical health. Following a healthy diet can protect and support your mental health.


Our brain needs to be fed regularly with the right mix of nutrients in order for it to work properly. The brain relies on a steady supply of glucose as its primary fuel.

Where does the glucose that our brain needs come from?

  • The carbohydrates we eat (like oats, high fibre cereals, bread, Provitas, rice, pasta, cous cous, etc.)
  • Starchy vegetables (like potatoes, sweet potatoes, butternut, pumpkin, peas and corn)
  • Legumes (like lentils, chickpeas, kidney beans, black-eye-beans, etc.)
  • Fruit
  • The milk sugar (lactose) found in milk and yoghurt
  • Sugary foods, drinks and treats (high GI therefore limit consumption)

Carbohydrates, starchy vegetables, legumes, fruit, milk and sugar all get digested into glucose, which is then absorbed into our blood stream. This blood glucose supplies our brain with the energy that it needs to function, concentrate and focus. We need to focus on including foods that are also digested into glucose slowly such as fruit, vegetables, and cereals (also called Low Glycaemic Index or Low GI foods) to help to control the rate of glucose supply to your brain and body.

However, food with a Low Glycaemic Index can only supply our brain and body with glucose for 2.5 – 3 hours, which is why it is important to eat breakfast and then regular meals every 2.5 – 3 hours up until supper time.

Not having enough glucose in the blood can make us feel weak, tired and ‘fuzzy’ minded. This can happen when we don’t have enough carbohydrate-containing foods, with very restrictive diets and with erratic eating patterns.

However, if we include an excess of glucose that our body does not require, the surplus will be stored as fat. It is therefore important to limit sugary foods, drinks and treats as they do not supply our body with any important nutrients other than glucose, and they provide our body with a very short-lived supply of energy (high GI). Foods to limit include: chips, crisps, pies, puddings, cake, sweets, chocolate and cold drinks.

Fats and oils

Our brains are made up of about 50% fat and our cells need fats to maintain their structure, therefore an adequate supply of fats are needed to maintain health.

Focus on including monounsaturated fats such as: avocado, olive oil, olives, canola oil, almonds, cashew nuts, macadamia nuts, peanuts, peanut butter, peanut oil, avocado oil, pecan nuts, hazel nuts, pistachio nuts, sesame seeds and margarines made with olive or canola oil. It is important to only use monounsatured fats when cooking.

Polyunsatured fats should also be included in the diet and include: margarines, seeds (like pumpkin, sunflower, linseeds), sunflower oil, reduced fat mayonnaise and salad dressings.

Try to reduce your intake of saturated fat (found in: fatty meats, chicken skin, butter, cream, full cream milk and full fat yoghurt, coconut and palm kernel oil). Trans fats (found in fried foods, fried take-aways, hard brick margarines, coffee creamers, processed meats and foods) should also be limited.

Omega-3 fish oils

Omega-3 fish oils (found in oily fish) may help with depression. Fish high in Omega-3 oil include: sardines, pilchards, mackerel, herring, anchovy, salmon and trout.

Aim for a minimum of 2 portions of oily fish per week or alternatively an omega-3 fish oil supplement may be taken daily. If you feel you are missing elements from your diet, it is a good idea to consult with a doctor or dietician prior to taking supplements.


Try and include protein at most meals and snacks together with carbohydrates, as this helps to keep us feeling full and prevent overeating. Tryptophan is an amino acid (one of the building blocks of protein) and research suggests that it may be helpful as it is a component of serotonin. Serotonin is a messenger chemical in the brain which improves mood.

Good sources of tryptophan include: fish, chicken, eggs, lean meat, cottage cheese, legumes, dairy products and seeds. If you are a vegetarian or vegan, it is important to ensure you are also getting enough protein from plant sources; if you’re not sure – speak to a dietician.


Evidence shows that even slight dehydration may affect your mood. Since we know that the brain contains water, it makes sense to drink plenty. Aim for 6 – 8 glasses (1.5 – 2 litres water per day).

Caffeine may affect your mood and may lead to withdrawal headaches and to a low or irritable mood when the effects of caffeine wear off. Drinks such as coffee, black tea, green tea, cola, energy drinks and chocolate all contain caffeine and should be limited.

Vitamins and minerals

When you don’t eat enough nutrient-rich foods, your body may lack vitamins and minerals, often affecting your energy, mood and brain function. These are some of the key vitamins and minerals which can impact you if you not including them in your diet:

  • Low levels of iron can make us feel weak, tired and lethargic all the time. Red meat, liver, chicken and fish can reduce our risk of developing iron-deficiency anaemia.
  • Low levels of B-vitamins can make us feel tired, depressed and irritable. Whole wheat bread and cereals, liver, meat, chicken, fish, eggs, lower fat dairy, legumes, potatoes, nuts and a wide variety of fruit and vegetables should be included to ensure an adequate intake of B-vitamins.
  • Low folate can increase our chance of feeling depressed and is particularly important in the elderly. Include liver, broccoli, spinach, kale, cabbage, asparagus, citrus fruit, beef, chicken, fish, legumes (dried beans & lentils), yeast extracts like Marmite, potatoes, whole wheat bread and cereals.
  • Low selenium may increase the incidence of feeling depressed and other negative mood states. Include brazil nuts, seafood, kidney, liver, meat, chicken, lentils and avocado pear.

Key points to remember:

  • Eat regularly throughout the day
  • Include low GI carbohydrates that keep you fuller for longer and make sure that your brain has a steady supply of energy
  • Add lean proteins that help to prevent overeating
  • Monounsaturated fats and polyunsaturated fats are important during meal-times.
  • Include omega-3 fatty acids in your diet
  • Drink plenty of non-caffeinated fluid throughout the day
  • Include a wide variety of fresh foods, fruit and vegetables daily to make sure that you get enough micronutrients to help your brain to function properly

If you are concerned about your eating habits, seeing a COPE Therapist who has an interest in eating issues could be beneficial for you.

If you are concerned about your diet structure, getting enough vitamins or minerals, your health as it relates to your diet, and your nutrition, seeing a dietician can help.

Written by:

Written by Brindy Watson, Registered Dietician, RD(SA)