Mood and dietary sugars

This content is authored by Registered Dietitian, Juliette Kellow.

Mood

Mood describes the way a person feels at a particular time and covers a wide range of emotions. Feelings such as happiness or contentment contribute to a positive mood, while sadness or frustration contribute to a negative one.

Many factors can affect mood, including genetics, upbringing, life experiences, environment, and lifestyle choices. Diet also plays a role, as the brain, which regulates emotions and mood, needs a steady supply of energy, nutrients, and fluids to work effectively.

Hydration and brain function

Maintaining good hydration is particularly important. Around 75% of the brain is made up of water, and even mild dehydration can affect how we feel. Studies show that negative emotions such as anger, depression, and tension can increase with just 1% dehydration (1).

Nutrients that support mood

Many nutrients play a role in supporting brain health. For example, vitamins B1, B3, B6, B12 and C, folate, biotin, and magnesium contribute to normal psychological functioning – the mental processes such as emotion, perception, thinking, and memory (2).

Carbohydrates and mood

The brain relies on glucose – its preferred source of energy (3) – which comes from the breakdown of carbohydrates during digestion. Indeed, carbohydrates contribute to the maintenance of normal brain function (2).

How do carbohydrates affect mood?

Carbohydrates also appear to have an indirect role in the production of serotonin, a chemical in the brain (neurotransmitter) that helps regulate mood, sleep, and appetite. Low serotonin levels, or reduced serotonin activity, are often linked with depression and anxiety (4). Serotonin is made from an amino acid (a building block of protein) called tryptophan.

When carbohydrates are eaten, insulin is released, which helps to move amino acids (except tryptophan) into the muscles. This allows more tryptophan to enter the brain, supporting serotonin production. The extent of this effect depends on several other factors, including the type of carbohydrate consumed (this influences how quickly insulin is released) and the composition of the meal – for example, protein-rich foods provide other amino acids that compete with tryptophan for entry into the brain (5).

Around 90-95% of the body’s serotonin is made in the gut. Dietary fibre – a form of indigestible carbohydrate – has an important role in this process. Beneficial gut bacteria ferment fibre, producing short-chain fatty acids such as butyrate and acetate, which stimulate cells lining the gut to produce and release serotonin. Although serotonin made in the gut cannot cross into the brain, it can influence mood indirectly through the vagus nerve, which carries signals from the gut to the brain (5).

Despite clear biological pathways, more research is needed to confirm how carbohydrates affect mood and to understand the mechanisms involved.

Do dietary sugars specifically affect mood?

It is a popular misperception that sugars cause large fluctuations in blood glucose levels, causing short-term mood swings or ‘sugar crashes’, leading to irritability, anger, anxiety, and stress. There is a lack of scientific evidence to support this, and recent findings challenge the idea of sugars-induced mood swings (6, 7).

Is there a link between diet, dietary sugars, and depression?

Low mood is common and usually temporary, but when it persists for weeks or months, it may indicate depression (depressive disorder). The World Health Organization estimates that more than one in 20 adults – around 332 million people worldwide – live with depression, with more women affected than men (8).

Depression has no single cause. It can result from a combination of stressful life events (e.g., bereavement, relationship difficulties, or financial strain), family history, hormonal changes such as menopause or the postnatal period, loneliness, chronic illness, or substance use (9).

Evidence linking diet to depression remains unclear. While observational studies suggest less healthy diets may be associated with a higher risk of depression (10, 11), more research is needed to confirm if they cause the condition.

Some studies also suggest a link between dietary sugars and depression, although all are observational (12, 13, 14). This means it is not clear whether sugars contribute to depression or are consumed more frequently because of it.

The impact of mood on eating habits and dietary sugars intakes

Symptoms of low mood and depression can affect appetite and energy levels, leading to changes in eating habits. Poor sleep, headaches, and digestive issues such as constipation are also common (15). Some antidepressants may further alter appetite or cause side effects such as nausea, dry mouth, constipation, or diarrhoea (16), which may influence diet over time.

Whether negative emotions, low mood, or depression result in higher intakes of sugars remains uncertain. One large study from the UK Biobank, which included more than 100,000 people, found that people with depression or anhedonia (loss of pleasure) consumed more energy-dense foods, free sugars, and lactose (milk sugars) than those without depression. This suggests that these foods might be used to cope with a low mood (17).

Anecdotally, several factors may explain higher intakes of sugars in those with low mood. Sweet foods and drinks may be consumed to maintain energy levels or combat tiredness. Or there may be a greater reliance on ‘comfort foods’ such as biscuits, chocolate, or ice cream, which are often linked to positive memories (18).

Summary

The link between mood and dietary sugars is complex. Carbohydrates provide glucose – an essential fuel for the brain – and contribute to the production of serotonin in the brain and gut. However, the impact this has on mood is difficult to measure.

While some evidence suggests an association between high intake of sugars and depression, it remains unclear whether sugars play a causative role or are consumed in response to low mood. Many factors influence how we feel, and further research is needed to clarify how diet and sugars fit into this broader picture.

References

1. Liska, D et al. Narrative Review of Hydration and Selected Health Outcomes in the General Population. Nutrients. 2019;11(1):70.

2. European Commission. EU Register of Health Claims. Available at: https://food.ec.europa.eu/food-safety/labelling-and-nutrition/nutrition-and-health-claims/eu-register-health-claims_en

3. Mergenthaler, P et al. Sugar for the brain: the role of glucose in physiological and pathological brain function. Trends Neurosci. 2013;36(10):587.

4. NIH. StatPearls. Physiology, Serotonin. 2023. Available at: https://www.ncbi.nlm.nih.gov/books/NBK545168/

5. Tang J et al. A Comprehensive Review of Nutritional Influences on the Serotonergic System. Advances in Nutrition. 2025; (11):100524.

6. Van de Rest O, et al. Effects of glucose and sucrose on mood: a systematic review of interventional studies. Nutr Rev. 2018;76(2):108-116.

7. Muijs L T, et al. Glucose variability and mood in adults with diabetes: A systematic review. Endocrinol Diabetes Metab. 2020;4(1):e00152.

8. World Health Organization. Depressive Disorder (Depression). Available at: https://www.who.int/news-room/fact-sheets/detail/depression

9. NHS. Causes – Depression in Adults. Available at: https://www.nhs.uk/mental-health/conditions/depression-in-adults/causes/

10. Li Y et al. Dietary patterns and depression risk: A meta-analysis. Psychiatry Res. 2017;253:373-382.

11. Gianfredi V et al. Association between dietary patterns and depression: an umbrella review of meta-analyses of observational studies and intervention trials. Nutrition Reviews. 2023; 81(3):346-359.

12. Zhang L et al. Association between dietary sugar intake and depression in US adults: a cross-sectional study using data from the National Health and Nutrition Examination Survey 2011-2018. BMC Psychiatry. 2024;24(1):110.

13. Hu D, Cheng L, Jiang W. Sugar-sweetened beverages consumption and the risk of depression: A meta-analysis of observational studies. J Affect Disord. 2019;245:348-355.

14. Xiong Jet al. Association of sugar consumption with risk of depression and anxiety: a systematic review and meta-analysis. Front Nutr. 2024;11:1472612.

15. NHS. Symptoms – Depression in adults. Available at: https://www.nhs.uk/mental-health/conditions/depression-in-adults/symptoms/

16. NHS. Antidepressants. Available at: https://www.nhs.uk/medicines/antidepressants/

17. Dobai T, et al. Consumption of High-Energy Food and Sugar Shows a Strong Positive Association with Low Mood in Control Subjects and Depressed Patients. Nutrients. 2025;17(16):2594.

18. Spence C. Comfort food: A review. Int. J. Gastron. Food Sci. 2017;9:105-109.