We live in a world where food is constantly at our fingertips. Despite the explosion of new diets over the last few decades, rates of metabolic syndrome, insulin resistance, and chronic inflammation continue to climb. The issue is that many of these new “diets” focus on narrowing caloric intake, or counting macronutrients, while overlooking fundamental cellular and metabolic processes that are influenced by how often we eat. Doing one 24-hour fast per week is an evidence-based strategy that provides measurable results in terms of insulin sensitivity, inflammation, and cognitive function. Regarding a weekly 24-hour fast, this essay will take a look into glycolysis and fat burning, insulin sensitivity, and the role autophagy plays in our body, along with potential risks and misconceptions. 

Throughout a 24-hour fast, your body taps into different forms of energy. Usually, you use the glucose from what you last ate for the first 0-4 hours, glycogen, a stored form of glucose found in the liver, for hours 4-12, a combination of fat and glycogen for hours 12-18, and mostly fat for hours 18-24 as glycogen levels run low. Due to how humans evolved, the excess glycogen and fat that most people store in their bodies prevent them from burning muscle until well after these 24 hours are over. By depleting the body's glycogen stores during the first 18 hours, we force ourselves to burn fat for energy.

Not only do 24-hr fasts deplete our glycogen stores, but they are also very good at reducing insulin resistance, the gateway to Type 2 diabetes. Today, most people's bodies are used to constantly eating carbohydrates, which means that their insulin levels are consistently elevated. Over time, chronic high levels of insulin can lead to an exhausted pancreas and higher levels of insulin resistance, which eventually cause the loss of insulin-producing cells, leading to Type 2 diabetes. By giving your body a 24-hour reset, you allow your pancreas to rest and your cells to become more sensitive to insulin again, so once you begin eating again, you can respond to insulin more effectively. 

When we aren’t constantly feeding our bodies food, we force ourselves to rely on what we already have in our bodies. Autophagy, which directly translates to “self-eating,” is a catabolic process where our cells identify and break down damaged proteins, organelles, and accumulated cellular debris. This process is strongly upregulated during nutrient deprivation, like fasting, as the body switches from using external nutrients to repairing and reusing what we already have. By removing misfolded/toxic proteins, such as beta-amyloid and tau, which accumulate in the brain, higher levels of autophagy contribute to preventing neurodegenerative diseases such as Alzheimer’s. Through clearing out harmful aggregates, autophagy promotes healthier neuronal function and decreases the speed at which age-related cognitive decline progresses. Not only this, but in the early stages of cancer development, autophagy acts as a protective mechanism by removing damaged organelles and DNA-defective cells before they become malignant. This limits oxidative stress and chronic inflammation, while maintaining genome stability, which are all known to lower cancer risk. 

Despite all of the previously listed health benefits, it is important to know that fasting is not for everyone, and one should consult with their healthcare provider before making any dietary lifestyle changes. Fasting is not safe for everyone, and it is especially NOT recommended for individuals with Type 1 diabetes, pregnant or breastfeeding women, and people with a history of eating disorders. While fasting, it is important to continue drinking plenty of fluids and, if needed, consume electrolytes to maintain normal physiological functions. Some may have the worry that a 24-hour fasting period will slow the body's metabolism by triggering “starvation mode,” but it is important to note that drops in BMR (basal metabolic rate) are typically only seen after over 72 hours of fasting. By incorporating a weekly 24-hour fast, individuals can give themselves a chance to rest and reset, setting them on the fast track to good health.