It is widely recognized that food can positively impact mood due to its cultural, nostalgic, or traditional significance. However, the body's blood glucose response also plays a crucial role in how food affects a person's mood. The glycemic index (GI) categorizes carbohydrates based on their rate of digestion, absorption, metabolism, and subsequent impact on blood glucose and insulin levels. Research suggests that high GI foods, such as sugary drinks and pastries, can negatively affect mood in the short and long term.

In the short term, consuming high-GI foods can lead to rapid fluctuations in blood glucose levels. This triggers the release of counter-regulatory hormones, such as cortisol, adrenaline, growth hormone, and glucagon, which work to restore blood glucose levels to normal. These physiological responses may result in changes in anxiousness, irritability, and hunger. 

Over the long term, unhealthy glucose responses due to consistent high-GI food intake can have a negative impact on normal insulin responses. This can potentially lead to insulin resistance, prediabetes, and eventually type 2 diabetes. Human and animal studies have suggested a potential connection between mood disorders (particularly depression) and insulin resistance. A 3-year prospective cohort study involving 69,954 participants concluded that a high-GI diet could be a risk factor for depression in postmenopausal women. Similarly, two cohort studies with 85,500 participants found a significant positive association between high-GI diets and depression.

Insulin plays a role in regulating neuronal signaling and plasticity, and unhealthy insulin metabolism in the brain may alter dopamine turnover, which can contribute to anxiety and depressive-like behaviors. Animal models of insulin resistance have shown an increased risk of depression-like behaviors, possibly due to dysregulated mitochondrial function, neuroinflammation, and reduced neurogenesis. Unhealthy insulin metabolism is also associated with dysregulation of glucocorticoids in the hypothalamic-pituitary-adrenal axis, which can be associated with some mood disorders.

The Netherlands Study of Depression and Anxiety (NESDA), a longitudinal multisite study involving 601 adults aged 18 to 65 without a lifetime history of depression or anxiety disorders, observed that a moderate clinical increase in insulin resistance measurements (e.g., high triglyceride to high-density lipoprotein ratio) corresponded to an 89% increase in the incidence rate of major depressive disorder over a 9-year follow-up period. The researchers suggest that insulin resistance is a risk factor for developing major depressive disorder in both men and women. 

Promoting normal blood glucose and insulin metabolism can potentially support a healthy mood. Along with a nutrient-dense, low-GI diet, adequate intake of specific nutrients like magnesium may help to promote normal blood glucose metabolism and overall mood health simultaneously. 

By Danielle Moyer, MS, CNS, LDN