Did you know that your mental clarity increases when you are hungry and decreases when you are full? If you are surprised by this idea, remember the last “food coma”/mental dullness you have experienced after a heavy meal.

Studies show that fasting and hunger leave you hyper-vigilant and energetic. It makes much sense from an evolutionary point of view: it keeps you active towards your goal of finding food. In lab testing, vigilance, cognition, and memory scores also improve after intermittent fasting.

This sharpness of your brain has a lot to do with its fuel source. In 2017, Yamagata & al proposed the “selfish brain” theory. Its crucial need for energy makes your brain using up to 65% of circulating glucose ahead of other organs. Once you stop eating for a while, nature provides a strong back-up: ketogenesis. Ketone bodies production is your body’s capacity to utilize fat as an alternative fuel source when glucose is not available. These ketones are a lot more efficient at producing energy for your brain, promote neuroplasticity, improve insulin signaling. Your brain becomes sharper.

Frequent eating, as well as reliance on simple sugar-rich foods, reduce the body’s ability to burn fat to produce ketone bodies. This metabolic “inflexibility” leads to impaired mitochondrial function and energy imbalances, the cause of many modern chronic diseases and brain fog.

The good news is that metabolic flexibility, and brain alertness, are quickly restored with fasting or Time-Restricted Feeding.