Problem foods and beverages

Seven foods cause about 90% of all food intolerance reactions:

• Milk and milk products which contain the milk proteins casein and whey and the milk sugar lactose which are common allergens
  • Fermented milk products such as kefir and yoghurt can be more easily digestible
  • Goat and sheep milk can be more digestible than cow’s milk
• Wheat and other grains with gluten, including barley, rye, spelt and oats
  • Celiac disease is the more extreme case of wheat allergy, however wheat and gluten can also cause milder intolerances which can cause low grade inflammation and which test negative on a gluten intolerance (celiac) test
• Eggs
• Soy
• Fish
• Shellfish
• Nuts
  • Ground nuts: peanuts
  • Tree nuts: such as walnuts, almonds, pine nuts, brazil nuts, and pecans

Almost any food can trigger an intolerance however. Less common ones include:

• Corn
• Gelatin
• Meat – beef, chicken, mutton, and pork
• Seeds, often sesame, sunflower, and poppy
• Spices, such as caraway, coriander, garlic, and mustard
• Celery

Sicherer, S.H. and Sampson, H.A. (2018). Food allergy: a review and update on epidemiology, pathogenesis, diagnosis, prevention, and management. [online] Journal of Allergy and Clinical Immunology, 141 (1), pp. 41–58.

• Anxiety
• Fatigue
• Brain fog
• Mood swings
• Depression
• Insomnia

Ranges from asymptomatic to the following:

• Bloating
• Diarrhea
• Cramping
• Gas
• Raised heart beat immediately after eating

An undiagnosed intolerance can cause a situation of chronic inflammation leading to gut issues, poor digestion and absorption, which can contribute to or exacerbate mental health conditions such as depression and anxiety Jansson-Knodell, C.L., White, M., Lockett, C., Xu, H. and Shin, A. (2022). Associations of food intolerance with irritable bowel syndrome, psychological symptoms, and quality of life. [online] Clinical Gastroenterology and Hepatology, 20 (9), pp. 2121–2131

Allergies

Unlike a food intolerance, severe food allergies such as peanut allergy and celiac disease (allergy to gluten) can be identified with a blood test, and are a far more serious condition than a sensitivity or intolerance.

Intolerances and sensitivities

To identify an intolerance or sensitivity, you can take a food intolerance test, which is usually a pin-prick blood test, however the reliability and accuracy of these have been questioned.

Another cheaper and possibly more reliable but more time consuming method is to follow an elimination diet, in which you eliminate potentially all allergenic foods from your diet for two to four weeks, and then systematically reintroduce them one by one, taking note of any symptoms in a food and mood journal during both elimination and reintroduction phase.

If you feel better during the elimination phase, but start to feel unwell or develop symptoms during the reintroduction phase, it is a strong indication that you are allergic or intolerant to a specific food Turnbull, J.L., Adams, H.N. and Gorard, D.A. (2015). Review article: the diagnosis and management of food allergy and food intolerances. [online] Alimentary Pharmacology & Therapeutics, 41 (1), pp. 3–25.

A urine test can check for casein, whey and lactose intolerance.

Gluten is a protein found in:

• Wheat (including wheat varieties like spelt, kamut, farro and durum, bulgur and semolina)
• Barley
• Rye
• Triticale
• Oats (unless they are “gluten free”)

Biesiekierski, J.R. (2017). What is gluten?. [online] Journal of Gastroenterology and Hepatology, 32 (Suppl 1), pp. 78–81.

When you are sensitive to gluten, consuming it can trigger an immune response, leading to inflammation Biesiekierski, J.R., Jonkers, D., Ciacci, C. and Aziz, I. (2025). Non-coeliac gluten sensitivity. [online] The Lancet, 406 (10518), pp. 2494–2508.

• This is usually due to an inability to properly digest gliadin, a protein found in gluten
• Undigested gliadin produces gliadorphin which acts as a neuropeptide
  • Neuropeptides cause the release of neurotransmitters such as adrenaline, noradrenaline and dopamine affecting mood, and possibly causing anxiety and depression
  • Gliadorphin is an opioid peptide, which has an effect on motivation, emotions and attachment behaviour Asokan, V., Jha, D.K. and Aranganathan, V. (2026). Pharmacological and neurobehavioral evaluation of the bifunctional opioid peptide gluten exorphin B5. [online] Biochemical Pharmacology
• Left undiagnosed, a gluten sensitivity can damage your gut lining and prevent the optimal absorption of nutrients
• In some people, gliadin can produce a similar effect to the antibodies that attack the thyroid gland in autoimmune conditions
  • While one condition has nothing to do with the other, the symptoms are often the same – fatigue, loss of enthusiasm, mild to moderate depression, unexplained weight gain and hair loss
  • In cases where these symptoms are present but thyroid tests all prove to be normal, always recommend that clients have a gliadin sensitivity test Piticchio, T., Frasca, F., Malandrino, P., Trimboli, P., Carrubba, N., Tumminia, A., Vinciguerra, F. and Frittitta, L. (2023). Effect of gluten-free diet on autoimmune thyroiditis progression in patients with no symptoms or histology of celiac disease: a meta-analysis.
• Studies have shown that gluten sensitivity can cause disorders in the digestive system and gut, but also in the following areas attaining to mental health:
  • Brain
  • Mood
  • Spinal cord
  • Peripheral nerves

  Giuffrè, M., Gazzin, S., Zoratti, C., Llido, J.P., Lanza, G., Tiribelli, C. and Moretti, R. (2022). Celiac disease and neurological manifestations: from gluten to neuroinflammation. [online] International Journal of Molecular Sciences, 23 (24), 15564.

Possible mental health symptoms of gluten sensitivity

• Lethargy
• Poor focus
• Depression
• Anxiety
• Craving for gluten-containing products
• Irritability
• Autistic symptoms
• Brain fog
• Insomnia

Nagarajappa, P., Chavali, S.M. and Mylavarapu, M. (2023). Pathological manifestations of gluten-related neuro-psychiatric disorders and the impact of gluten-free diet in a pediatric age group: a systematic review. [online] Cureus, 15 (10), e47062.

Gluten sensitivity has also been (controversially) implicated in some neuropsychiatric disorders, including:

• Schizophrenia
  • Schizophrenia’s original name was “Bread Madness” on account of the observation that schizophrenic patients who eat gluten have a higher degree of neurological symptoms and schizophrenic exacerbation Kelly, D.L., Lee, C.M., Vyas, G., Buchanan, R.W., Roche, D.J., Harrington, V., Rowland, L.M., Wijtenburg, S.A., Adhikari, B.M., Sathyasaikumar, K.V., Kochunov, P., Talor, M.V., Waltz, J., Liu, F., Hare, S., Adams, H.A., Schwarcz, R., Salem, D., Gold, J.M., Clark, S.M. and Eaton, W.W. (2026). Randomized double-blind inpatient study of a gluten-free diet for negative symptoms in people with schizophrenia. [online] Schizophrenia Research, 289, pp. 33–45.
• AutismCroall, I.D., Hoggard, N. and Hadjivassiliou, M. (2021). Gluten and autism spectrum disorder. [online] Nutrients
• Peripheral neuropathyZis, P. and Hadjivassiliou, M. (2019). Treatment of neurological manifestations of gluten sensitivity and coeliac disease. [online] Current Treatment Options in Neurology
• AtaxiaZis, P. and Hadjivassiliou, M. (2019). Treatment of neurological manifestations of gluten sensitivity and coeliac disease. [online] Current Treatment Options in Neurology
• Attention deficit hyperactivity disorder (ADHD)Slim, M., Rico-Villademoros, F. and Calandre, E.P. (2018). Psychiatric comorbidity in children and adults with gluten-related disorders: a narrative review. [online] Nutrients

Wheat also contains carbohydrates called fructans and proteins called lectins both of which can be irritating to the gut and cause intolerances.

Celiac disease is a far more serious condition than gluten sensitivity, and involves an allergy to gluten.

It is a serious auto-immune disease, and occurs when the body mounts an immune attack because it mistakes gluten for a dangerous toxin and aims to destroy it, damaging the small intestine in the process.

When this occurs, food can’t be properly broken down, and nutrients can’t be absorbed.

This can lead to a deficiency in various key amino acids and micronutrients, which can affect neurotransmitters such as serotonin, dopamine and GABA which can lead to:

• Depression
• Anxiety and panic
• Sleep issues
• Poor attention
• Poor memory
• Apathy
• Irritability

Sharma, N., Singh, K. and Senapati, S. (2021). Celiac disease poses significant risk in developing depression, anxiety, headache, epilepsy, panic disorder, dysthymia: a meta-analysis. [online] Indian Journal of Gastroenterology, 40 (5), pp. 453–462.

Fermentable, Oligo-, Di-, Mono-saccharides and Polyols (FODMAPs) are short chain carbohydrates that are poorly absorbed in the small intestine. They can be found in a range of different foods:

• Oligo-saccharides: e.g. fructans (found in wheat, rye and some vegetables) and galacto-oligosaccharides (found in pulses and legumes)
• Di-saccharides: e.g. lactose (found in mammalian milk)
• Mono-saccharides: e.g. free fructose (found in honey, some fruit and fruit juices)
• Polyols: e.g. sorbitol and mannitol (found in some fruits and vegetables)

Whelan, K., Martin, L.D., Staudacher, H.M. and Lomer, M.C.E. (2018). The low FODMAP diet in the management of irritable bowel syndrome: an evidence-based review of FODMAP restriction, reintroduction and personalisation in clinical practice. [online] Journal of Human Nutrition and Dietetics, 31 (2), pp. 239–255.

A full list can be found here.

Patients with IBS suffering from bloating, abdominal pain and diarrhoea often show improvement in these symptoms by following the FODMAP diet Black, C.J., Staudacher, H.M. and Ford, A.C. (2022). Efficacy of a low FODMAP diet in irritable bowel syndrome: systematic review and network meta-analysis. [online] Gut, 71 (6), pp. 1117–1126.

There is often a correlation between IBS and mental health symptoms such as depression, anxiety, lethargy, irritability, etc.

Dairy can cause several types of intolerance.

Casein intolerance

Casein is a milk protein found in dairy products, and is a common allergen which some people have a hard time digesting. Its metabolite casomorphin can affect the brain and cause mental health symptoms, having opioid like properties Thiruvengadam, M., Venkidasamy, B., Thirupathi, P., Chung, I.M. and Subramanian, U. (2021). β-Casomorphin: a complete health perspective. [online] Food Chemistry, 337, 127765.

• Casomorphin, like gliadorphin is an opioid neuropeptide
• It affects behaviour by attaching to opioid receptors in the brain
• Abnormal opioid activity leads to behavioural problems as well as deficits in attention and social communication which are features of autism, and is also implicated in Parkinson’s disease and schizophrenia Quan, L., Xu, X., Cui, Y., Han, H., Hendren, R.L., Zhao, L. and You, X. (2022). A systematic review and meta-analysis of the benefits of a gluten-free diet and/or casein-free diet for children with autism spectrum disorder. [online] Nutrition Reviews, 80 (5), pp. 1237–1246.
• Casomorphin has been consistently shown to be elevated in postpartum psychosis Lindström, L.H., Nyberg, F., Terenius, L., Bauer, K., Besev, G., Gunne, L.M., Lyrenäs, S., Willdeck-Lund, G. and Lindberg, B. (1984). CSF and plasma beta-casomorphin-like opioid peptides in postpartum psychosis. [online] American Journal of Psychiatry, 141 (9), pp. 1059–1066.
• The link between depression and casomorphin is uncertain, however tests have shown that people with depression tend to have more casomorphin than non-depressed people

Lactose intolerance

If you have a deficiency of the enzyme lactase, then you cannot properly digest the lactose found in dairy products.

Patients with IBS are more likely to suffer from lactose intolerance.

Patients with IBS and gut sensitivity tend to have higher levels of anxiety Misselwitz, B., Butter, M., Verbeke, K. and Fox, M.R. (2019). Update on lactose malabsorption and intolerance: pathogenesis, diagnosis and clinical management. [online] Gut, 68 (11), pp. 2080–2091.

Legumes, which include beans, peas, lentils and peanuts, are a healthy source of complex carbohydrates, protein and fibre, but some people find them difficult to digest and can have intolerance reactions.

The two adverse or ‘toxic’ factors contained in legumes are lectins and phytates. Both are termed by some nutritionists as ‘anti-nutrients’, because they can prevent the absorption of nutrients.

• Lectins are a type of protein which bind to carbohydrates, and have been implicated in a number of mental health problems
  • Deposits of lectins in the brain are associated with dementia and schizophreniaKonozy, E.H.E. and Osman, M.E.M. (2024). From inflammation to immune regulation: the dual nature of dietary lectins in health and disease. [online] Heliyon, 10 (20), e39471.
• Phytates found in beans/seeds serve the purpose of allowing beans/seeds to be stored over winter as they prevent premature germination
  • Phytates can affect mental health because they block absorption of iron, zinc, calcium and other minerals which are key to producing and modulating key neurotransmitters and, in the case of calcium, nerve impulse conduction along nerve cells Gibson, R.S., Raboy, V. and King, J.C. (2018). Implications of phytate in plant-based foods for iron and zinc bioavailability, setting dietary requirements, and formulating programs and policies. [online] Nutrition Reviews, 76 (11), pp. 793–804.
• Soaking legumes for 8 – 12 hours can significantly reduce phytate levels

Trans fats, or trans-fatty acids, and some saturated fats, can be detrimental to mental health. Both trans-fatty acids and saturated fats can make your brain cells hard and rigid and interfere with the brain’s ability to process information quickly Muth, A.K. and Park, S.Q. (2021). The impact of dietary macronutrient intake on cognitive function and the brain. [online] Clinical Nutrition, 40 (6), pp. 3999–4010.

Trans fats

Trans fats, or hydrogenated fats, are bad fats, with no health benefits whatsoever:

• They are found in processed or fried foods and certain vegetable oils such as hydrogenated vegetable oils
• Trans fats compete with, damage and block the conversion of healthy Essential Fatty Acids such as GLA, DHA, EPA and prostaglandins, preventing them from doing their vital brain-protecting work Sánchez-Villegas, A., Verberne, L., De Irala, J., Ruíz-Canela, M., Toledo, E., Serra-Majem, L. and Martínez-González, M.A. (2011). Dietary fat intake and the risk of depression: the SUN Project. [online] PLoS ONE, 6 (1), e16268.
• Trans fats are implicated in Alzheimer’s disease by contributing to beta amyloid production in the brain Barnard, N.D., Bush, A.I., Ceccarelli, A., Cooper, J., de Jager, C.A., Erickson, K.I., Fraser, G., Kesler, S., Levin, S.M., Lucey, B., Morris, M.C. and Squitti, R. (2014). Dietary and lifestyle guidelines for the prevention of Alzheimer’s disease. [online] Neurobiology of Aging, 35 (Suppl 2), pp. S74–S78.

Trans fats or hydrogenated fats are found in most:

• Crackers
• Crisps
• Cakes
• Sweets
• Biscuits
• Doughnuts
• Processed cheese

Processed oils such as:

• Corn
• Safflower
• Sunflower
• Peanut
• Canola
• Rapeseed

The wrong type of saturated fats

Higher saturated fat is associated with cognitive decline, as well as depression Ruan, Y., Tang, J., Guo, X., Li, K. and Li, D. (2018). Dietary fat intake and risk of Alzheimer’s disease and dementia: a meta-analysis of cohort studies. [online] Current Alzheimer Research, 15 (9), pp. 869–876., Firth, J., Gangwisch, J.E., Borisini, A., Wootton, R.E. and Mayer, E.A. (2020). Food and mood: how do diet and nutrition affect mental wellbeing?. [online] BMJ

However, saturated fats are not all created equal. Indeed there are bad saturated fats, from unhealthy sources (from the produce and processing of industrially raised meat and poultry), and good saturated fats, from healthy sources (grass fed, free range, organic, unprocessed produce of meat, poultry and dairy, coconut oil, avocado, nuts, dark chocolate, etc.) Astrup, A., Magkos, F., Bier, D.M., Brenna, J.T., de Oliveira Otto, M.C., Hill, J.O., King, J.C., Mente, A., Ordovas, J.M., Volek, J.S., Yusuf, S. and Krauss, R.M. (2020). Saturated fats and health: a reassessment and proposal for food-based recommendations: JACC State-of-the-Art Review. [online] Journal of the American College of Cardiology, 76 (7), pp. 844–857. While the wrong types of saturated fats should be avoided, due to their negative health consequences, the right types of saturated fats and cholesterol are essential for optimal mental health.

Most processed foods, in a box, can or bottle are full of artificial food additives and chemicals to flavour, colour, texture and preserve your food.

In high concentrations, some of these additives and chemicals can contribute to adverse mental health symptoms, such as hyperactivity and depression, and should be avoided:

• Monosodium glutamate
• Food colourings Miller, M.D., Steinmaus, C., Golub, M.S., Castorina, R., Thilakartne, R., Bradman, A. and Marty, M.A. (2022). Potential impacts of synthetic food dyes on activity and attention in children: a review of the human and animal evidence. [online] Environmental Health, 21 (1), 45.
• Sodium benzoate-rich beverages as seen in carbonated drinks are associated with ADHD-like behaviour in college students Lange, K.W., Lange, K.M., Nakamura, Y. and Reissmann, A. (2023). Nutrition in the management of ADHD: a review of recent research. [online] Current Nutrition Reports, 12 (3), pp. 383–394.

• Non-organic meats
  • Beef, chicken, etc. can contain growth hormone, antibiotics, and pesticide and herbicide residue which can be detrimental to our mental health
• Organ meats
  • Liver, thymus, kidneys
  • Organ meats
    • Are high in cadmium, which is a non-essential carcinogenic metal, which bioaccumulates at all levels of the food chain, with particularly high levels found in organ meats
    • High levels of cadmium are associated with depressionCybulska, A.M., Grochans, S., Kamińska, M.S., Bosiacki, M., Skonieczna-Żydecka, K. and Grochans, E. (2021). Are cadmium and lead levels linked to the development of anxiety and depression? A systematic review of observational studies. [online] Ecotoxicology and Environmental Safety, 216, 112211.
• Fish
  • Large ocean fish
    • Tuna, swordfish, shark, tilefish can contain high levels of mercury which can be damaging to mental health
  • River fish
  • Heavy metals such as mercury, lead and aluminum levels are positively correlated with maternal fish consumption
    • The mean levels of these heavy metals is higher in the hair of autistic children
  • Fish consumption is also associated with consumption of cadmium through pollution and is positively associated with depression Yang, Y., Kim, Y. and Je, Y. (2018). Fish consumption and risk of depression: epidemiological evidence from prospective studies. [online] Asia-Pacific Psychiatry, 10 (4), e12335.
• Non-organic fruit and vegetables
• Soy
  • Soy can be damaging to the gut through a component called the trypsin inhibitor
    • Trypsin is the enzyme we need to digest protein effectively
    • Soy not only inhibits the process, but is itself high in protein
    • The inability to digest it can cause stress on the pancreas and lead to pancreatitis
    • Chronic pancreatitis can cause mental distress including anxiety
  • Soybeans and their food products (Tofu) have been investigated for potential benefit against Alzheimer’s disease, however current evidence shows that soybeans can lead to cognitive impairment Cui, C., Birru, R.L., Snitz, B.E., Ihara, M., Kakuta, C., Lopresti, B.J., Aizenstein, H.J., Lopez, O.L., Mathis, C.A., Miyamoto, Y., Kuller, L.H. and Sekikawa, A. (2020). Effects of soy isoflavones on cognitive function: a systematic review and meta-analysis of randomized controlled trials. [online] Nutrition Reviews, 78 (2), pp. 134–144.
  • Soy has been said to cause anxiety (possibly due to soy’s estrogenic effects)
  • Soy has been associated with ADD and learning
  • Soy has also been linked to thyroid problems, the symptoms of which include lethargy, malaise and fatigue Otun, J., Sahebkar, A., Östlundh, L., Atkin, S.L. and Sathyapalan, T. (2019). Systematic review and meta-analysis on the effect of soy on thyroid function. [online] Scientific Reports, 9 (1), 3964.

Sugar can act as a stimulant, giving a boost of energy and a burst of serotonin. However the consumption of sugar can also be addictive, can cause blood sugar imbalances, mood swings, anxiety, concentration and attention issues, etc.

In the UK, together we eat 4 million kilos of sugar and 2 million kilos of chocolate every week Amoutzopoulos, B., Steer, T., Roberts, C., Collins, D. and Page, P. (2020). Free and added sugar consumption and adherence to guidelines: the UK National Diet and Nutrition Survey (2014/15–2015/16). [online] Nutrients, 12 (2), 393.

Types of sugar

• Refined sugar
  • Added to coffee, tea, in yoghurt, over fruit, cereal etc.
  • Found in sugar-rich foods and beverages such as biscuits, pastries, confectionery, sodas, culinary sauces
  • Read the label and watch out for hidden sugars, particularly in pasta, breads, sauces and drinks sweetened with refined sugar
• “Healthier” sugars
  • Maple syrup
  • Molasses
  • Honey
  • Unconcentrated fruit juices
  • Stevia
    • A natural plant-based sweetener, but which can still trick your body into craving more sugar
  • Sugar alcohols
    • Xylitol
• Products made from refined flour
  • White pasta
  • Pizza
  • White bread
  • Bagels
  • Rolls
  • Wraps
• Artificial sweeteners
  • Aspartame
  • Sucralose
  • Saccharin
  • Erythritol
  • Sorbitol
  • Maltitol

Consuming refined sugar, even just from one can of soda, has been shown to cause the following mental health symptoms, especially in children:

• Difficulties in concentration and attention
• Irritability
• Depression
• Aggression
• Anxiety

Hu, D., Cheng, L. and Jiang, W. (2019). Sugar-sweetened beverages consumption and the risk of depression: a meta-analysis of observational studies. [online] Journal of Affective Disorders, 245, pp. 348–355.

Regular sugar consumption has been shown to correlate with the following issues:

• Lower IQ
• Aggression
• Anxiety
• Hyperactivity
• Attention deficit
• Depression
• Eating disorders
• Lethargy and fatigue
• Learning difficulties
• Mood swings

Farsad-Naeimi, A., Asjodi, F., Omidian, M., Askari, M., Nouri, M., Pizarro, A.B. and Daneshzad, E. (2020). Sugar consumption, sugar sweetened beverages and attention deficit hyperactivity disorder: a systematic review and meta-analysis. [online] Complementary Therapies in Medicine, 53, 102512.

Sugar can cause nutritional deficiencies:

• Sugar contains no nutrients, but merely provides us with a short term burst of energy
  • 90% of the vitamins and minerals have been removed through processingRennie, K.L. and Livingstone, M.B. (2007). Associations between dietary added sugar intake and micronutrient intake: a systematic review. [online] British Journal of Nutrition, 97 (5), pp. 832–841.
  • Consuming refined sugar causes magnesium to be lost through the urine Gottfried, S. (2013). The Hormone Cure. New York, NY: Scribner, p. 147.
  • Refined sugar causes a depletion in chromium, which ironically is essential to balancing blood sugar Amen, D. (2013). Unleash The Power Of The Female Brain. New York: Harmony Books, p. 134.
• Sugar depletes the body’s stores of vitamins and minerals, especially B vitamins, which are essential for mental healthRennie, K.L. and Livingstone, M.B. (2007). Associations between dietary added sugar intake and micronutrient intake: a systematic review. [online] British Journal of Nutrition, 97 (5), pp. 832–841.

Sugar sensitivity

If you have sugar sensitivity, you will be more susceptible to sugars in your food and beverages.

Symptoms of sugar sensitivity related to mental health include:

• Depression
• Anxiety
• Being easily stressed
• Anger and irritability
• Cravings/addiction for sugary food

Westwater, M.L., Fletcher, P.C. and Ziauddeen, H. (2016). Sugar addiction: the state of the science. [online] European Journal of Nutrition, 55 (Suppl 2), pp. 55–69.

People with sugar sensitivity tend to have low base levels of the neurotransmitter serotonin, and low beta-endorphins. They tend to crave sugar to make themselves feel better, because the consumption of sugar has the following neurochemical effects:

• Increases dopamine, the pleasure and motivation neurotransmitter, and therefore can be addictive
• High blood sugar can help the absorption of tryptophan and its conversation to serotonin
• Increases endorphins in the brain, particularly in the nucleus accumbens (referred to as the hedonic “hot spot”)

Avena, N.M., Rada, P. and Hoebel, B.G. (2008). Evidence for sugar addiction: behavioral and neurochemical effects of intermittent, excessive sugar intake. [online] Neuroscience & Biobehavioral Reviews, 32 (1), pp. 20–39.

Effects of sugar consumption on the brain and moods include:

• Consuming sugar can make you temporarily feel high, feel good
• Consuming sugar can temporarily give you better impulse control
  • Controlled activities that rely on executive functions (such as attention, reasoning, planning, self control) which override urges, emotions and automatic responses
  • Executive functions, unlike other cognitive functions, seem highly susceptible to glucose fluctuations
  • Evidence shows that self-control failure may be more likely when glucose is low, or glucose transport to the brain from the body is low
  • Some studies have linked criminal behaviour to decreased glucose processing in the brain Vadillo, M.A., Gold, N. and Osman, M. (2016). The bitter truth about sugar and willpower: the limited evidential value of the glucose model of ego depletion. [online] Psychological Science, 27 (9), pp. 1207–1214.
  • Self-control relies on glucose as a limited energy source: willpower is more than a metaphor Hagger, M.S. et al. (2016). A multilab preregistered replication of the ego-depletion effect. [online] Perspectives on Psychological Science, 11 (4), pp. 546–573.
• Consuming sugar can make you temporarily feel less sensitive to pain Stevens, B., Yamada, J., Ohlsson, A., Haliburton, S. and Shorkey, A. (2016). Sucrose for analgesia in newborn infants undergoing painful procedures. [online] Cochrane Database of Systematic Reviews, 7, CD001069.
• However, after a sugar high, your body compensates by removing sugar from the blood, resulting in a crash in blood sugar and a crash in serotonin and beta endorphins which then can make you feel down Wyatt, P., Berry, S.E., Finlayson, G., O’Driscoll, R., Hadjigeorgiou, G., Drew, D.A., Khatib, H.A., Nguyen, L.H., Linenberg, I., Chan, A.T., Spector, T.D., Franks, P.W., Wolf, J., Blundell, J. and Valdes, A.M. (2021). Postprandial glycaemic dips predict appetite and energy intake in healthy individuals. [online] Nature Metabolism, 3 (4), pp. 523–529.

Caffeine can be over-stimulating particularly to people who are very sensitive to it, and can contribute to sleep issues, anxiety, hyperactivity, attention and concentration deficits.

Caffeine can increase serum lactate and can deplete serotonin and melatonin, aggravate the symptoms of PMS, deplete B and C vitamins, potassium, magnesium, calcium and zinc, all of which can contribute to anxiety and insomnia.Wikoff, D., Welsh, B.T., Henderson, R., Brorby, G.P., Britt, J., Myers, E., Goldberger, J., Lieberman, H.R., O’Brien, C., Peck, J., Tenenbein, M., Weaver, C., Harvey, S., Urban, J. and Doepker, C. (2017). Systematic review of the potential adverse effects of caffeine consumption in healthy adults, pregnant women, adolescents, and children. [online] Food and Chemical Toxicology, 109 (Pt 1), pp. 585–648.

In the UK, together we drink 1.5 billion caffeinated drinks per week (including coffee, tea and cola) Holford, P. (2004). Patrick Holford’s New Optimum Nutrition Bible. London: Piatkus, p. 4..

In the US, 85% of Americans consume at least 1 caffeinated beverage per day with average daily consumption of 1.8 drinks Mitchell, D.C., Knight, C.A., Hockenberry, J., Teplansky, R. and Hartman, T.J. (2014). Beverage caffeine intakes in the U.S.. [online] Food and Chemical Toxicology, 63, pp. 136–142.

Caffeine is contained in varying amounts in:

• Coffee
• Tea
• Sodas such as coke
• Chocolate

Of these, the only ones to categorically avoid are sodas, as they have no nutritional value and are full of sugars and chemicals. Coffee, tea and dark chocolate however, can contain a multitude of polyphenols and phytochemicals which, in moderation, can be beneficial to mental health.

You have to be the judge how caffeine affects you, and whether you need to avoid it altogether, or maybe just reduce the quantities you consume.

Caffeine does however have harmful effects on the development of the brain of the foetus which is why it is contraindicated in pregnancy. The defects seen include anencephaly (being born without a brain, or lesser types of brain deformity). It is also believed to damage the serotonin system in the developing foetusJahanfar, S. and Jaafar, S.H. (2015). Effects of restricted caffeine intake by mother on fetal, neonatal and pregnancy outcomes. [online] Cochrane Database of Systematic Reviews, 2015 (6), CD006965.

In the UK, we drink 120 million alcoholic drinks per week together NHS England Digital (2024). Health Survey for England, 2022 Part 1: adult drinking. [online] Available at: https://digital.nhs.uk/data-and-information/publications/statistical/health-survey-for-england/2022-part-1/adult-drinking [accessed 20 Sep. 2026].

The US fares better than the UK in terms of alcohol consumption:

• 30% do not drink, another 30% consume less than 1 drink/week
• The highest 10% consume 74 million drinks/week

World Health Organization. (2018). Global Status Report on Alcohol and Health. [online] Luxembourg: World Health Organization. Available at: http://www.who.int/substance_abuse/publications/global_alcohol_report/en/ [accessed 21 Sep. 2026].

Alcohol can be detrimental to mental health:

• Alcohol lowers executive brain function Stavro, K., Pelletier, J. and Potvin, S. (2013). Widespread and sustained cognitive deficits in alcoholism: a meta-analysis. [online] Addiction Biology, 18 (2), pp. 203–213.
• Alcohol raises cortisol, the stress hormone
• Even one glass of wine can impact your sleep, reducing the amount of restorative deep and REM sleep you get
• Alcohol can disrupts hormone balance and exacerbate symptoms of PMS in females
• Alcohol can cause nutritional deficiencies (zinc, magnesium, B vitamins, vit c, EFA, antioxidants)Jophlin, L., Liu, T.Y. and McClain, C.J. (2024). Nutritional deficiencies in alcohol use disorder/alcohol-associated liver disease. [online] Current Opinion in Gastroenterology, 40 (2), pp. 112–117.
• Alcohol can negatively impact the metabolism of tryptophan which is essential for serotonin production
• Alcohol can contribute to reactive hypoglycemia
• Alcohol can damage the gut

As with certain caffeine containing beverages, certain alcoholic beverages have health benefits which can offset the presence of alcohol, but only in small doses. For instance a glass of red wine contains a number of polyphenols, phytochemicals, and antioxidants such as resveratrol.