Blood sugar and carbohydrate imbalances

The brain needs glucose to function. And it needs a lot of it, in a steady supply:

• In a resting state, the brain consumes up to 60% of our daily glucose intakeMergenthaler, P., Lindauer, U., Dienel, G.A. and Meisel, A. (2013) ‘Sugar for the brain: the role of glucose in physiological and pathological brain function’, Trends in Neurosciences, 36(10), pp. 587–597
• The brain particularly likes a steady and sustainable release of sugar, and works best when there is constant access to a source of glucose – not too high, not too low
• Glucose lights up the reward circuits of the brain, and prompts the release of feel good chemicals such as dopamine, serotonin, endorphins and endocannabinoidMergenthaler, P., Lindauer, U., Dienel, G.A. and Meisel, A. (2013) ‘Sugar for the brain: the role of glucose in physiological and pathological brain function’, Trends in Neurosciences, 36(10), pp. 587–597

Effects of sugar consumption on the brain and moods:

• Consuming sugar can create temporary feelings of bliss
• Consuming sugar can give you temporary 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 brainVadillo, 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’, Psychological Science
  • Self-control relies on glucose as a limited energy source: willpower is more than a metaphor
• Consuming sugar can make you feel less sensitive to pain, especially childrenPepino, Y.M. and Mennella, J.A. (2005) ‘Sucrose-induced analgesia is related to sweet preferences in children but not adults’, Pain, 119(1–3), pp. 210–218.
• 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 downQin, D., Qi, J., Shi, F., Guo, Z. and Li, H. (2025) ‘Sugar Addiction: Neural Mechanisms and Health Implications’, Brain and Behavior
• Therefore it is important to consume sugar in the form of complex carbohydrates (beans, pulses, whole grains, starchy vegetables, etc.) instead of refined carbohydrates (processed, refined sugars and flours), as they take longer to digest and allow for balanced blood sugar and a steady release of glucose for the brainArshad, M.T., Maqsood, S., Altalhi, R., Shamlan, G., Mohamed Ahmed, I.A., Ikram, A. and Abdullahi, M.A. (2025) ‘Role of Dietary Carbohydrates in Cognitive Function: A Review’, Food Science & Nutrition

While the brain needs glucose to function, too much glucose can be toxic for nerve cells and damage them, causing inflammation in the brain.Watt, C., Sanchez-Rangel, E. and Hwang, J.J. (2020) ‘Glycemic Variability and CNS Inflammation: Reviewing the Connection’, Nutrients

If you eat a diet high in fast assimilating sugars, such as refined carbohydrates and foods with a high glycemic index (the glycemic index measures how quickly and how much a food raises blood glucose levels) which cause a rapid rise in blood sugar levels, especially when you eat these alone without protein or fat, you may get a sugar high, which may feel great at first, due to the glucose effect on the reward chemicals in the brain, but then can produce mental health symptomsWatt, C., Sanchez-Rangel, E. and Hwang, J.J. (2020) ‘Glycemic Variability and CNS Inflammation: Reviewing the Connection’, Nutrients such as:

• Irritability
• Depression
• Anxiety
• Poor memory
• Poor concentration and attention
• Hyperactivity  (ADD and ADHD)

Usually, after a period of high blood sugar caused by quick-release sugars such as refined carbohydrates on their own, your blood sugar plummets, which can also happen if you skip meals. Then you can suffer from mental health related symptoms of low blood sugar.

As mentioned above, the brain needs a large amount of the body’s glucose to function (60%).Lack of glucose to the brain can lead to the following symptoms:

• Brain fog and fuzzy thinking
• Exhaustion
• Anxiety
• Irritability
• Psychosis
• Dizziness
• Insomnia
• Poor concentration and attention
• Poor memory
• Depression
• Aggression
  

Verhulst, C.E.M., Fabricius, T.W., Nefs, G., Kessels, R.P.C., Pouwer, F., Teerenstra, S., Tack, C.J., Broadley, M.M., Kristensen, P.L., McCrimmon, R.J., Heller, S., Evans, M.L., Pedersen-Bjergaard, U. and de Galan, B.E. (2022) ‘Consistent Effects of Hypoglycemia on Cognitive Function in People With or Without Diabetes’, Diabetes Care, 45(9), pp. 2103–2110.

If you have sugar sensitivity, you will be more susceptible to blood sugar fluctuations.

Symptoms of sugar sensitivity related to mental health include:

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

Qin, D., Qi, J., Shi, F., Guo, Z. and Li, H. (2025) ‘Sugar Addiction: Neural Mechanisms and Health Implications’, Brain and Behavior

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
• Can help the absorption of tryptophan and its conversion to serotonin
• Increases endorphins in the brain, particularly in the nucleus accumbens (referred to as the hedonic “hot spot”)

However a while after consuming sugar, their blood sugar crashes, and they will crave more sugar to compensate for the loss of feel good chemicals. They will seek to eat more sugar, and the cycle repeats.Qin, D., Qi, J., Shi, F., Guo, Z. and Li, H. (2025) ‘Sugar Addiction: Neural Mechanisms and Health Implications’, Brain and Behavior

Diets high in refined carbohydrates such as white sugar, white flour, high glycemic index foods, can cause blood sugar imbalances:

• Through processing, complex carbohydrates are turned into simple ones which are essentially pre-digested
• They are fast-releasing sources of energy and have a high glycemic load prompting a rapid increase in blood sugar which usually leads to a subsequent rapid fall in blood sugarArshad, M.T., Maqsood, S., Altalhi, R., Shamlan, G., Mohamed Ahmed, I.A., Ikram, A. and Abdullahi, M.A. (2025) ‘Role of Dietary Carbohydrates in Cognitive Function: A Review’, Food Science & Nutrition
• The problem is that we often crave rapid sugar in the form of junk food, as it makes us feel better temporarily, giving us quick energy, and lighting up our reward circuits
• However the effects don’t last, and the crash after eating highly refined carbohydrates can be very unpleasant
• Spikes and slumps in blood sugar from the consumption of refined carbohydrates can lead to mood swings, low energy, and don’t allow for the steady release of energy which your brain requiresArshad, M.T., Maqsood, S., Altalhi, R., Shamlan, G., Mohamed Ahmed, I.A., Ikram, A. and Abdullahi, M.A. (2025) ‘Role of Dietary Carbohydrates in Cognitive Function: A Review’, Food Science & Nutrition

As well as diets low in proteins and fats:

• Consuming protein and fats with carbohydrates slow down the digestion process and ensure a more steady and even release of blood sugar, which is better for the brain
• Diets low in proteins and fats can lead to more unstable blood sugar levels

Fasting, dieting or skipping meals can lead to unstable blood sugar levels.

Eating refined carbohydrates rather than complex ones can lead to blood sugar imbalances.

Human tolerance to sugar starts in the womb. Babies of mothers who have diabetes, start their life with a genetic predisposition towards insulin resistance and can subsequently pass these genes on to the next generation.

Genetic factors also play a role how people perceive and tolerate the taste of sweetness. Those genetically more sensitive to sweet tastes can eat less sugar to achieve the same perception of sweetness, while those genetically less sensitive to sweet tastes may need to eat more sugar to achieve the same perception of sweetness.Hwang, L.-D., Lin, C., Gharahkhani, P., Cuellar-Partida, G., Ong, J.-S., An, J., Gordon, S.D., Zhu, G., MacGregor, S., Lawlor, D.A., Breslin, P.A.S., Wright, M.J., Martin, N.G. and Reed, D.R. (2019) ‘New insight into human sweet taste: a genome-wide association study of the perception and intake of sweet substances’, The American Journal of Clinical Nutrition, 109(6), pp. 1724–1737.

Insulin resistance

When carbohydrates cause an increase in blood sugar, the pancreas releases insulin to mop up the glucose in the blood and carry it out of the bloodstream, into the cells.

However, when blood sugar is chronically high due to a diet high in sugar and refined foods, the pancreas keeps pumping out more and more insulin, which then has the effect of numbing our cells’ sensitivity to insulin, i.e., the cells refuse entry to insulin. This can lead to a condition called “insulin resistance” which is a precursor to diabetes.

Insulin resistance means that we are no longer able to adequately regulate our blood sugar, which can remain chronically high as a result.

Chronically high blood sugar and insulin resistance can then lead to inflammation, throw other hormones and neurotransmitters out of balance, and lead to a rapid degeneration of the brain, mood and mental health.Rahman, M.S., Hossain, K.S., Das, S., Kundu, S., Adegoke, E.O., Rahman, M.A., Hannan, M.A., Uddin, M.J. and Pang, M.-G. (2021) ‘Role of Insulin in Health and Disease: An Update’, International Journal of Molecular Sciences

HPA imbalance

There is a correlation between adrenal or HPA dysfunction, and blood sugar imbalance, as well as sugar sensitivity:

• Hyperactivity of the HPA (hypothalamic-pituitary-adrenal) axis can contribute to hyperinsulinemiaJanssen, J.A.M.J.L. (2022) ‘New Insights into the Role of Insulin and Hypothalamic-Pituitary-Adrenal (HPA) Axis in the Metabolic Syndrome’, International Journal of Molecular Sciences
  • A condition in which there are excess levels of insulin circulating in the blood relative to the level of glucose, often mistaken for diabetes or hyperglycaemia
  • Its symptoms include
    • Weight gain
    • Sugar cravings
    • Intense and frequent hunger
    • Difficulty concentrating
    • Fatigue
    • Anxiety and panic
• Conversely, blood sugar dysregulation can impact insulin and cortisol which then has a disruptive impact on the HPA axis
• A primary role of cortisol is to regulate blood sugar availability
  • Glucose is needed for ATP production (ATP is the fundamental energy unit of the cell)
  • If blood sugar drops, cortisol is secreted to bring it back up to a normal range, in order to provide for energy production

Thyroid imbalance

• Hypothyroidism tends to co-exist with type 1 and 2 diabetes
• Hypothyroidism is linked with various hormonal biochemical and nervous abnormalities which may contribute to hypoglycaemia
• Hypothyroidism is linked with low growth hormone and cortisol responses to insulin-induced hypoglycaemia and this prevents adequate counter regulatory protectionEom, Y.S., Wilson, J.R. and Bernet, V.J. (2022) ‘Links between Thyroid Disorders and Glucose Homeostasis’, Diabetes & Metabolism Journal, 46(2), pp. 239–256.

Having an infection, being ill or very stressed can result in blood sugar imbalances:

• Stress activates the hypothalamic-pituitary-adrenal (HPA) axis, and elevates cortisol
• Elevated cortisol increases glucose production within liver cells which increases blood glucose
• Elevated cortisol inhibits insulin secretion from pancreatic beta cells as well as muscles
• This can lead to impaired glucose tolerance and insulin resistance

Kaur, J., Gandhi, J. and Sharma, S. (2025) ‘Physiology, Cortisol’, in StatPearls