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.

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.

A promising longevity therapy involves rejuvenating mitochondria. Since mitochondria and their DNA are passed down maternally, a potential source for a transplant is a younger relative in the same maternal line (e.g., a sister's child), providing a biologically matched and youthful source of the organelles.

The benefits of fermented foods aren't limited to live probiotics. Dead microbes, or "postbiotics," still have cell walls that can "tickle" your immune cells as they pass through the gut, sending signals that help calm down inflammation.

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.

While effective for short-term weight loss, there is little scientific evidence that a long-term ketogenic diet promotes longevity. Sinclair expresses concern over the lack of plant-based polyphenols, which are crucial for activating the body's anti-aging pathways.

Urolithin A, a postbiotic that promotes mitochondrial health, is naturally produced from foods like pomegranates. However, individual gut bacteria variability means production differs widely. Direct supplementation provides a more reliable and consistent dose to achieve its benefits.

Constant daily intake of some longevity molecules can have counteracting side effects. For example, taking resveratrol every other day showed a greater lifespan extension in mice than daily intake. Pulsing supplements provides a hormetic stress without constant interference.