Fix Your Gut With Fiber! – Doctor Reveals What To Eat Daily For Long-Term Health | Dr. Karan Rajan

The Power of Green Bananas

Dr. Rajan begins the discussion with green bananas, a food not widely recognized for its gut benefits. Unlike ripe bananas that are high in sugar, green bananas contain a significant amount of resistant starch, which behaves like a prebiotic fiber. Resistant starch passes through the small intestine undigested and reaches the colon, where it ferments and nourishes beneficial gut bacteria, particularly those producing butyrate. Butyrate plays a crucial role in feeding colon cells and maintaining intestinal health. Although green bananas offer these gut-friendly compounds, Dr. Rajan rates them as an A-tier food primarily because high levels of resistant starch might be abrasive or cause discomfort in people with sensitive guts. Despite this caveat, green bananas, along with similarly prepared foods like day-old rice or cooled potatoes, are excellent options for improving gut microbiota health.

The Importance of Daily Fiber Intake

A notable part of the episode explores why Dr. Rajan personally aims for 50 grams or more of fiber daily. Population data and subsistence societies consuming over 100 grams per day demonstrate some of the lowest rates of chronic diseases. Fiber intake is connected to a remarkable assortment of benefits beyond gut health, including improved mood, skin integrity, immune resilience, metabolic regulation, glucose control, insulin sensitivity, and cholesterol management. He emphasizes that benefits increase with fiber intake beyond the commonly recommended 30 grams per day, although with diminishing returns at very high intakes.

Dr. Rajan also shares his observations from personal experiments and from clinical evidence that soluble fibers can lower LDL cholesterol by binding bile acids in the intestines, facilitating their excretion. This mechanism has a direct impact on reducing cardiovascular disease risk, highlighting how fiber supports heart health.

Ranking Common Fiber Sources

Next, the conversation moves into evaluating popular fiber sources and supplements. Psyllium husk, a viscous fiber known for improving bowel regularity and promoting satiety, is rated as an A-tier option. Although it effectively helps with both constipation and diarrhea through its bulk-forming properties and capacity to absorb water, Dr. Rajan notes that pure psyllium lacks the diversity of prebiotic fibers found in whole foods. It also has a less pleasant texture, which can decrease user adherence. Still, for many, it is a practical, clinically supported supplement to support digestion and cholesterol management.

On the other end, dark chocolate—especially those with 70% or higher cocoa content—earns a respectable B tier. While it is rich in antioxidants, polyphenols, and some fiber, the amount can vary depending on cocoa concentration and added sugar content. It is best seen as a tasty adjunct rather than a primary fiber source, useful when mixed into smoothies or desserts for added polyphenols and dietary diversity.

Dr. Rajan also highlights practical strategies for increasing everyday fiber intake, including combining familiar ingredients like apples, oats, chia seeds, raspberries, and nuts to reach or surpass 30 grams in a single meal. He encourages listeners to use such combinations to simplify the challenge of meeting fiber goals and reinforce the importance of dietary diversity.

Plant-Based Protein, and the Gut

Dhru Purohit and Dr. Rajan expand on the importance of plant-based fibers combined with complementary proteins, as exemplified by staples like beans, legumes, brown rice, chickpeas, and vegetables such as carrots, sweet potatoes, and broccoli. These foods not only provide a range of prebiotic fibers that ferment throughout the length of the colon, but they also deliver essential nutrients, antioxidants, and complete proteins when combined correctly.

Dr. Rajan relates some of his own dietary evolution from a vegetarian lifestyle through raw foodism to a more omnivorous diet, observing how reductions in fiber-rich foods can negatively affect gut comfort and overall health. Despite personal variations, the core message remains: a fiber-rich diet supports a flourishing microbiome, which in turn is linked to systemic health benefits.

Emerging Gut Health Products

The discussion turns to new products entering the market, including Dr. Rajan's own fiber supplement, which he is launching through his startup, LOM Science. This product aims to combine multiple prebiotic fibers with clinical validation, better taste, and ease of use than traditional supplements like psyllium. It targets the entire colon by including a blend of fast, medium, and slow-fermenting fibers to support diverse gut bacteria, delivering benefits beyond bowel regularity, potentially affecting immunity and the gut-brain axis.

In contrast, the duo critiques popular prebiotic sodas and fiber gummies widely marketed as easy ways to boost fiber intake. These products typically rely heavily on fast-fermenting fibers like inulin and fructooligosaccharides, which may cause excessive gas, bloating, and discomfort—especially in individuals with sensitive guts or irritable bowel conditions. Consequently, Dr. Rajan ranks these options lower, generally at a C tier, emphasizing that while they may marginally contribute to fiber intake, they are not substitutes for whole foods and diverse fiber sources. These products also carry concerns regarding additives, sugar content, and user experience.

Non-Nutritive Sweeteners and Artificial Additives

Artificial sweeteners common in diet sodas and some gut health products come under review, discussed for their ambiguous effects on gut microbiomes. Dr. Rajan explains that many fears around artificial sweeteners are dose-dependent; typical consumption in humans is far below levels associated with adverse effects in laboratory studies. Moreover, when used as part of weight loss efforts, these sweeteners may indirectly improve gut health by improving metabolic and inflammatory status following weight reduction. He advises caution for individuals with chronic gut sensitivity, suggesting moderation, while highlighting the need for more research in specific populations.

Daily Habits for Supporting Gut Health

Beyond diet, Dr. Rajan stresses the foundational role of consistent health behaviors, highlighting oral hygiene's connection to gut health. The mouth hosts a complex microbiome that influences the rest of the digestive tract and systemic health markers like heart disease risk. His recommendations include avoiding alcohol-based mouthwashes regularly, flossing, tongue scraping, and electric toothbrushing as strategies to nurture oral microbes beneficially. These simple practices earn an S-tier designation, reflecting their wide-reaching impact on overall health.

Fiber Is Not a "Scam"

Throughout the episode, Dr. Rajan challenges common misconceptions such as the idea that fiber is unnecessary or only correlated with health outcomes rather than causative in them. He reinforces that a substantial body of randomized controlled trials, meta-analyses, and mechanistic studies document fiber's vital role in producing short-chain fatty acids that drive multiple health pathways. While fiber is not essential for survival in the narrow sense, its absence correlates strongly with chronic disease risk and poorer quality of life across populations.

Circadian Rhythm

One of the more unique insights offered revolves around meal timing. Late-night snacking, particularly on high-calorie, low-fiber foods, is ranked as F tier because it conflicts with circadian rhythms governing digestion and microbiome activity. The gut's digestive capacity peaks midday, while eating late inhibits key processes like the migrating motor complex—a cleansing mechanism crucial for intestinal health. Improper meal timing also promotes indigestion, acid reflux, and poor sleep, all of which negatively impact gut and overall health.

Practical Morning Routines

Dr. Rajan shares his personal morning routines to meet fiber and health goals, ranging from simply adding fiber supplements to black coffee on some days to a robust, fiber- and protein-rich overnight oats breakfast on others. Dhru Purohit complements this with his own protein-fiber smoothie strategy, reinforcing that individualized consistent habits are essential for sustainable results.

In closing, Dr. Rajan emphasizes that no single food or supplement can make or break gut health overnight. Rather, longevity in consistent, balanced behaviors—consistent fiber intake, thoughtful supplementation, oral care, meal timing, and dietary diversity—offer the best prospects for long-term gut and systemic health. This episode provides a well-rounded, science-grounded, and practical roadmap for listeners seeking to "fix" their gut and enhance life quality through mindful fiber consumption and daily habits.