What Does Sugar Do to Your Brain?

No one really thinks of sugar as a health food, do they? Most of us are quite aware that it plays a role in weight management, tooth decay and the development of Type 2 diabetes. For the last forty years, we have been sold the myth that a calorie is a calorie and that sugar is pretty harmless, however, nothing could be further from the truth. Dietary fat has been demonized and sugar was supposed to be our salvation. Coca-cola, amongst other processed food companies, markets its products as part of an “active, healthy lifestyle.”

Perhaps there has never been a better time to remember the saying: “Repeat a lie often enough and it becomes the truth.” The illusory truth effect is the tendency to believe information to be correct after repeated exposure. In this day and age of social media and “alternative facts,” I cringe at times at the information that circulates, especially in the area of nutrition. 

Mortality rates in the developed world are not affected like they once were, by infection and lack of sanitation.  Today’s health woes are instead conditions that are chronic, degenerative and metabolic in nature. One of the biggest underlying factors is the change in our dietary intake, most notably with regards to sugar consumption.

Glucose – a type of sugar – is the main energy source for every cell in the body, the brain is no exception.  Studies show the brain accounts for 60% of the body’s glucose utilization. Thinking, memory and learning are all dependent on the amount of glucose available for brain function. Although the brain needs glucose, it wreaks havoc when available in excess.

To gain a better idea of amounts, the average Canadian aged 19 and older consumes 85 grams of added sugar per day. What is more remarkable is that it is less than the 100-115 g/day in children under the age of 8! The World Health Organization’s recommends a daily maximum or no more than 50 grams, and encourages an intake of only of 25 grams for added health benefits.2

Let’s examine some of key ways that sugar impacts your brain.

  1. Addiction and overeating. Science tells us sugar is more addictive than cocaine. When we eat sugar, a neurotransmitter called dopamine is released. Not only does dopamine make us feel good, it also controls mood, behavior, learning, and memory. Consuming excess sugar long term influences both the gene expression and availability of dopamine receptors and dopamine transporter proteins. 3,4 That means it takes more and more of the substance to create the same dopamine release. In situations where sugar is not available, people experience the same withdrawal symptoms as seen in other addictions, such as nervous tremors, teeth chattering and anxiety. Additionally, chronic sugar consumption blunts the brain’s ability to trigger feelings of satiety, which leads to overeating. 5
  2. Cognitive learning and memory. A diet high in added sugar reduces the production of a brain chemical known as brain-derived neurotrophic factor (BDNF). BDNF is a protein produced by nerve cells that is needed by our brains to learn and create new memories. This critically vital protein is lower in people with already impaired glucose metabolism (diabetics and pre-diabetics) and the more it declines, the more sugar metabolism deteriorates, causing insulin resistance. 6 Insulin resistance is like the boy who cried wolf – your body’s receptors no longer respond to the presence of insulin, because it is always in the bloodstream. Insulin resistance is the first step to a whole host of other serious health problems. A reduction in BDNF levels are seen after only two months of adopting a high fat, high sugar diet. 7
  3. Depression and anxiety. Sugar consumption contributes to feelings of depression in numerous ways. Firstly, it affects what intestinal microbes grow, where 90% of your serotonin is produced. Secondly, it competes for B vitamins and folic acid, both of which are needed to produce serotonin. Thirdly, it reduces the production of BDNF, which can result in depressive mood, increased anxiety, cognitive deficiencies as well as accelerated brain aging. 8
  4. Dementia and Alzheimer’s. Alzheimer’s has been recently described as a side effect of the Western high sugar diet. 9 In one study that tracked over 5000 people over ten years conclusively showed that they had a greater rate of cognitive decline than their normal blood sugar counterparts. 10 A person with Type 2 Diabetes is twice as likely to develop Alzheimer’s. 11 Another study that investigated dietary intake of more than 1000 people. Those with the highest carbohydrate intake has 80% greater chance of developing Alzheimer’s. 12,13 Diabetes also weakens blood vessels, which can lead to multiple ministrokes in the brain, resulting in dementia. There are currently around 50 million people in the world with Alzheimer’s disease and the figure is predicted to rise to more than 125 million by 2050. 14

Sugar is bad news for brain health, period. When you do eat sugar, choose to do so, consciously and (very) occasionally. The rest of the time, reach for an apple instead a candy bar. Your brain (and the rest of your body) will thank you for it.


  1. https://en.wikipedia.org/wiki/Illusory_truth_effect
  2. https://www.who.int/mediacentre/news/releases/2015/sugar-guideline/en/
  3. Siresha Bathina and Undurti N. Das. Brain-derived neurotrophic factor and its clinical implications.Arch Med Sci.2015 Dec 10; 11(6): 1164–1178.
  4. Spangler R, Wittkowski KM, Goddard NL, Avena NM, Hoebel BG, Leibowitz SF. Opiate-like effects of sugar on gene expression in reward areas of the rat brain. Brain Res Mol Brain Res. 2004 May 19;124(2):134-42.
  5. Anaya Mitra,Blake A. Gosnell, Helgi B. Schiöth, Martha K. Grace, Anica Klockars, Pawel K. Olszewski, and Allen S. Levine  Chronic sugar intake dampens feeding-related activity of neurons synthesizing a satiety mediator, oxytocin. Peptides. 2010 Jul; 31(7): 1346–1352.
  6. Krabbe KS, Nielsen AR, Krogh-Madsen R, Plomgaard P, Rasmussen P, Erikstrup C, Fischer CP, Lindegaard B, Petersen AM, Taudorf S, Secher NH, Pilegaard H, Bruunsgaard H, Pedersen BK. Brain-derived neurotrophic factor (BDNF) and type 2 diabetes. Diabetologia. 2007 Feb;50(2):431-8. Epub 2006 Dec 7.
  7. Neuroscience. 2002;112(4):803-14.
  8.  Molteni R, Barnard RJ, Ying Z, Roberts CK, Gómez-Pinilla F.A high-fat, refined sugar diet reduces hippocampal brain-derived neurotrophic factor, neuronal plasticity, and learning. Neuroscience. 2002;112(4):803-14.
  9. https://www.theatlantic.com/health/archive/2018/01/the-startling-link-between-sugar-and-alzheimers/551528/?utm_source=feed
  10. Fanfan Zheng, Li Yan, Zhenchun Yang, Baoliang Zhong, Wuxiang Xie. HbA1c, diabetes and cognitive decline: the English Longitudinal Study of Ageing. Diabetologia April 2018, Volume 61, Issue 4, pp 839–848
  11. https://www.cnn.com/2011/09/19/health/diabetes-doubles-alzheimers/index.html
  12. T. Ohara, Y. Doi, T. Ninomiya, Y. Hirakawa, J. Hata, T. Iwaki, S. Kanba, Y. Kiyohara. Glucose tolerance status and risk of dementia in the community: The Hisayama Study. Neurology, 2011; 77 (12): 1126
  13. https://www.nih.gov/news-events/news-releases/higher-brain-glucose-levels-may-mean-more-severe-alzheimers
  14. 14. https://www.telegraph.co.uk/science/2017/02/23/alzheimers-could-caused-excess-sugar-new-study-finds-molecular/
Tasleem Kassam