The brain is one of the most energy-demanding organs in the body. Although it accounts for only 2% of body weight, it consumes nearly 20% of the body’s energy. Because of this high demand, the brain relies on stable and well-regulated metabolism.

Modern dietary patterns, especially those high in refined carbohydrates, added sugars, and ultra-processed foods, can disrupt this balance. Repeated glucose spikes force the body to release increasing amounts of insulin to maintain normal blood sugar. Over time, tissues, including those in the brain, become less responsive to insulin’s signals, leading to insulin resistance.

How Insulin Resistance Impacts Brain Health

Research consistently shows that insulin resistance is linked to early changes in cognitive function, even in people without noticeable memory concerns. Higher insulin resistance is associated with lower performance in verbal memory, reduced executive function such as planning and mental flexibility, lower overall cognitive scores, and faster loss of brain tissue in regions responsible for learning and memory. These changes can appear years before diabetes develops and long before cognitive impairment becomes clinically apparent.

Importantly, improving metabolic health makes a meaningful difference. Long-term studies show that better glycemic control is associated with slower cognitive decline, underscoring the deep link between metabolic function and brain health.

Key Labs for Evaluating Insulin Resistance

Because insulin resistance often develops well before blood sugar becomes abnormal, a broader lab panel can be helpful in identifying early metabolic stress. Useful markers include:

• Fasting insulin: A blood test that measures how much insulin the body produces in a fasting state; rising levels suggest reduced insulin sensitivity.
• HOMA-IR: A calculated score that uses fasting glucose and fasting insulin to estimate insulin resistance.
• Fasting glucose: A measurement of blood sugar after an overnight fast that offers helpful context but often remains normal early on.
• Hemoglobin A1c (A1c): A marker reflecting average blood sugar over the past two to three months that may remain normal despite significant insulin resistance.
• Triglycerides and HDL cholesterol: A lipid pattern in which high triglycerides and low HDL strongly correlate with early insulin resistance.
• Continuous glucose monitoring (CGM): A wearable device that tracks glucose levels throughout the day and night, revealing patterns and spikes that single blood tests cannot detect.

Together, these markers provide a clearer picture of metabolic function than glucose alone.

Dietary Strategies to Support Insulin Sensitivity

Dietary patterns play a central role in improving insulin sensitivity and preventing the metabolic imbalance that affects brain health. Helpful approaches include:

• Increasing fiber-rich foods: Vegetables, legumes, nuts, seeds, and intact whole grains slow glucose absorption, support the gut microbiome, and improve glycemic control.

• Reducing overall carbohydrate load (especially refined carbohydrates): Lower-carbohydrate and lower–glycemic index approaches reduce post-meal glucose spikes and insulin demand, improving insulin sensitivity over time.
• Prioritizing protein at meals: Protein improves satiety, stabilizes blood sugar, and supports weight management. Both plant and animal proteins can be effective as part of a balanced eating pattern.
• Choosing healthy fats: Monounsaturated and polyunsaturated fats found in olive oil, nuts, seeds, avocados, and fatty fish improve insulin sensitivity and reduce inflammation.
• Minimizing ultra-processed foods: Ultra-processed foods promote overeating, weight gain, and higher diabetes risk, even when macronutrients appear similar to whole foods. Reducing these foods lowers metabolic stress.
• Supporting balanced eating patterns: Regular meal timing, avoiding large evening meals, and eating fiber or protein before carbohydrates can help create smoother post-meal glucose responses.

These strategies reduce metabolic burden, improve insulin responsiveness, and help protect long-term brain health.

Conclusion

Insulin resistance, fueled in part by modern dietary patterns, emerges early, progresses quietly, and meaningfully affects cognitive performance and brain structure. The good news is that insulin resistance responds to nutritional and lifestyle changes. Supporting metabolic health is one of the most powerful ways to support brain health across the lifespan.

-Carey Kunz, ND, IFMCP

Director of Education at FMP Essentials

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