by Daniel Brouse
August 26, 2025
Fasting has gained popularity in recent years as a supposed way to detox, lose weight, or improve longevity. However, the science tells a more complex story. While short periods without food may not be harmful for everyone, prolonged fasting--especially beyond 12 hours--can negatively affect your health in significant ways.
Going without food for more than half a day disrupts the delicate balance of gut bacteria, which play a central role in overall health. When your gut microbiome is weakened, it compromises your immune system and can lead to systemic issues throughout the body. Research shows that disruptions in gut bacteria are linked to inflammation, poor digestion, and weakened disease resistance.
This imbalance doesn't stop at digestion. A compromised gut microbiome has cascading effects on:
The gut-brain axis, influencing mood, cognition, and mental health.
The liver and kidneys, which become stressed without a steady supply of nutrients.
The stomach and intestines, where prolonged fasting can reduce protective mucosal lining and impair digestion.
The cardiovascular system, as fasting can disturb electrolyte balance and blood pressure regulation.
Neurological function, since the brain depends on steady glucose and nutrient delivery to operate optimally.
Rather than fasting, a more sustainable and health-supportive approach is eating four small meals per day. These meals should prioritize whole, non-processed foods rich in fiber, vitamins, and minerals. Most importantly, they must include complete proteins--nutrients essential for maintaining muscle, supporting cellular repair, and sustaining immune function.
Complete proteins are found in meat, dairy, and eggs. At least one small meal each day should include them to ensure the body receives the full range of essential amino acids. Notably, certain beneficial gut bacteria can only be supported through the consumption of bovine protein, highlighting the unique role animal proteins play in human health.
While fasting may sound like a quick fix for health or weight loss, the risks often outweigh the benefits. Extended fasting undermines gut health, weakens immunity, and stresses vital organs. A diet of four balanced small meals, rich in unprocessed foods and complete proteins, provides a safer and more effective foundation for long-term health and vitality.
The gut microbiome goes through several important shifts over the course of a day, and these changes are closely tied to the body's circadian rhythm. When fasting periods extend too long, this rhythm can be disrupted, throwing off the natural balance of microbial populations. These daily microbial cycles play a central role in regulating the sleep–wake cycle--certain populations become more active in the morning to help the body wake up, while others support rest and recovery at night. Coffee also connects into this system: research shows that drinking about two cups in the morning is associated with longer lifespan and multiple health benefits. Interestingly, these benefits appear to be strongest when coffee and a healthy morning gut microbiome are working in harmony.
Equally critical is the role of gut bacteria in nutrient metabolism. Most vitamins--especially B vitamins and vitamin K--depend on good gut bacteria for proper absorption and utilization. Without a healthy microbiome actively working throughout the day, even a nutrient-rich diet can fall short because your body simply can't metabolize those vitamins effectively.
So while shorter fasting windows (12 hours or less) might be manageable for some, extending beyond that risks weakening both circadian balance and vitamin metabolism--two foundations of overall health.
COVID, fasting, and other conditions can destroy good gut bacteria, resulting in a compromised immune system. Gut bacteria play several key roles in maintaining health, including communicating with the immune system and producing essential vitamins. Without healthy gut bacteria, even a vitamin-rich diet may not be effective--your body cannot properly metabolize most vitamins without them.
Most people first develop beneficial gut bacteria through their mother's breast milk. Once lost, however, good gut bacteria are very difficult to reestablish. Ideally, breastfeeding for at least six months provides the foundation, but for adults, this is obviously not an option.
To rebuild a healthy microbiome, the body needs the right conditions:
Diversity of bacteria: 300–500 different strains.
Chemical building blocks for fermentation.
Ample dietary fiber, which is crucial for sustaining bacterial health.
It's important to note that juicing and blending often remove or destroy much of the fiber. The best dietary sources of fiber include:
Beans and legumes
Whole grains
Brown rice
Popcorn
Nuts
Baked potatoes with skin
Berries
Bran cereal
Additionally, resistant starch is especially beneficial for gut bacteria. Good sources include cooked and cooled rice or potatoes, as well as whole grains like barley and oats.
Understanding Good Gut Bacteria
Gut Reactions: How Microbial Triggers, COVID-19, and Climate Feedback Loops Drive Chronic Illness
Guide To Edible Plants and Health Foods
NAD+ Plus Immune Boosting Diet