Beyond digestion, dietary fiber feeds specific gut bacteria. These bacteria produce butyrate, a compound our bodies struggle to extract from food directly. Butyrate is essential for the proper function of mitochondria in the cells lining our gut, which helps maintain a strong gut barrier.

The goal of fiber is to feed gut bacteria that produce butyrate, a key acid for gut health. However, you can bypass this. Being in a ketogenic state directly provides beta-hydroxybutyrate (a ketone) to the gut, strengthening the microbiome without requiring high fiber intake.

When you cook and then cool starchy foods like beans, potatoes, or bread, you create "retrograde starch." This process transforms simple carbohydrates into complex resistant starches, which are a powerful food for your gut bacteria. This enhances the food's nutritional quality and lowers its glycemic index.

Instead of adhering to a strict diet label like vegan or pescatarian, Dr. Bolsiewicz advises focusing on nutrient quality. A gut-healthy, anti-inflammatory diet is achieved by consistently consuming these four "workhorses," which support the microbiome and calm the immune system, regardless of the diet's name.

In a head-to-head study, a diet high in fermented foods like yogurt and kimchi significantly increased microbiome diversity and lowered markers of inflammation. A high-fiber diet did not consistently produce these effects, suggesting that introducing live microbes is a more direct strategy for improving gut health and immune status in Western populations.

If you experience gas and bloating from beans, it’s not because the beans are bad for you; it's because your gut microbiome lacks the strength to digest their dense fiber. Treat your gut like a muscle: start with small amounts and gradually increase your intake to build its capacity.

Increasing fiber intake may not improve gut health if an individual's microbiome is already depleted. Research suggests many people in the industrialized world have lost the specific microbes needed to break down diverse fibers. Without these microbes, the fiber passes through without providing benefits, highlighting the need to first restore microbial diversity.

Unlike the complex fibers from whole foods, purified prebiotics can cause a bloom of a small number of bacteria specialized in consuming that single fiber type. This can lead to an overall decrease in microbial diversity as these few specialists outcompete other microbes. A wide variety of plant foods is a safer approach to fostering a diverse gut ecosystem.

Contrary to popular low-carb diet advice, consuming starchy carbohydrates in the evening can significantly improve sleep quality. Carbs help lower cortisol, the body's stress hormone, which needs to be low at night for restorative sleep. This explains why many low-carb dieters struggle with sleep disruption.