Increasing Bacteroidetes in your gut comes down to three main levers: eating more fiber (especially prebiotic types), choosing certain protein sources, and exercising regularly. Bacteroidetes and Firmicutes together make up over 90% of your gut bacteria, and the ratio between them is linked to metabolic health, body weight, and inflammation. Here’s what actually works to shift the balance.
Why Bacteroidetes Matter
Bacteroidetes are specialists at breaking down complex carbohydrates and proteins that your own digestive enzymes can’t touch. Their genomes are packed with enzymes that can process a huge range of substrates from plant, algal, and animal sources. When they ferment these compounds, they produce short-chain fatty acids that fuel the cells lining your colon, regulate appetite hormones, and help control blood sugar.
A higher ratio of Firmicutes to Bacteroidetes has been consistently linked to obesity, while people at a healthy weight tend to carry more Bacteroidetes. That said, the goal isn’t to maximize Bacteroidetes at all costs. Certain Bacteroidetes species have pro-inflammatory properties and are associated with inflammatory bowel disease. The sweet spot is a diverse, well-fed gut community where Bacteroidetes hold their fair share.
Prebiotic Fiber Is the Strongest Lever
The most reliable way to boost Bacteroidetes is feeding them what they thrive on: prebiotic fiber. A study in the British Journal of Nutrition found that a 1:1 mixture of inulin and oligofructose dose-dependently increased Bacteroidetes groups. The higher the dose (up to 20% of the diet in animal models), the greater the shift. This held true in both lean and obese subjects, suggesting prebiotics can help normalize the reduced Bacteroidetes numbers often seen in obesity.
Inulin is found in chicory root, garlic, onions, leeks, asparagus, and Jerusalem artichokes. Oligofructose occurs naturally in many of the same foods. You don’t need a supplement to get meaningful amounts, though concentrated inulin powders are widely available if your diet falls short.
Resistant Starch
Resistant starch is another potent fuel source for beneficial gut bacteria, including Bacteroidetes. It passes through your small intestine undigested and ferments in the colon. The richest sources by concentration are raw potato starch (about 63% resistant starch), green banana flour (around 44%), and high-amylose corn starch (about 46%).
Most clinical trials showing gut benefits use at least 15 grams of resistant starch per day. One study found that 30 grams of raw potato starch daily for 12 weeks increased beneficial bacteria and improved blood sugar responses in elderly participants. Lower doses, around 5 grams per day, improved digestive symptoms but didn’t produce measurable changes in short-chain fatty acid levels. So if you’re adding resistant starch to your routine, aim for the higher end. Cooked and cooled potatoes, slightly green bananas, and cooked-then-cooled rice all contain meaningful amounts in whole-food form.
Protein Sources Make a Difference
Both plant and animal protein can increase Bacteroidetes, but through different mechanisms and with different trade-offs.
Soy milk consumption increased the abundance of Bacteroidetes while reducing Firmicutes, a shift associated with lower obesity risk and better metabolic markers. Plant proteins in general tend to promote a more favorable overall microbial profile.
Animal protein also raises Bacteroidetes levels, but in a less clean way. High-meat diets increase bile-tolerant species like Bacteroides, Alistipes, and Bilophila. Bilophila in particular has been linked to inflammation. A high-beef diet was shown to increase both Bacteroides and Clostridia while decreasing certain beneficial Bifidobacterium species. So while animal protein does technically boost some Bacteroidetes members, the broader microbial shifts are less favorable than what you see with plant-based proteins.
If your goal is a healthier Bacteroidetes-to-Firmicutes ratio, emphasizing plant proteins like soy, lentils, and beans gives you the microbiome shift without the inflammatory side effects.
Exercise Shifts the Ratio
Physical activity independently changes your gut microbiome composition, even without dietary changes. A seven-week intense training program in competitive swimmers decreased the proportion of Firmicutes while increasing Bacteroidetes, along with improved overall microbial richness.
Intensity matters. High-intensity functional training produced the greatest reductions in the Firmicutes-to-Bacteroidetes ratio across multiple study groups. High-intensity exercise was also linked to beneficial shifts in Bacteroidetes alongside improved lactate metabolism and better protein and carbohydrate utilization by gut microbes. Moderate exercise showed benefits too, but the effect was smaller. The research points toward regular vigorous activity, things like interval training, competitive sports, or intense circuit workouts, as the most effective exercise strategy for shifting this ratio.
Processed Food Works Against You
Bacteroidetes have acquired genes over evolutionary time, sometimes from environmental bacteria, that let them break down complex compounds found in whole, minimally processed foods. Diets heavy in processed and hygienic foods deprive your microbiota of the substrates these bacteria specialize in degrading. When you eat a diet low in diverse plant fibers and high in refined carbohydrates, you’re essentially starving the organisms you want to grow while feeding simpler, less beneficial species that can thrive on sugar and processed starch.
The practical takeaway is straightforward: dietary diversity matters as much as any single food. Eating a wide variety of vegetables, legumes, whole grains, nuts, and fermented foods gives Bacteroidetes a broader range of complex carbohydrates to work with.
What About Probiotic Supplements?
Most commercial probiotics contain Lactobacillus and Bifidobacterium strains, not Bacteroidetes. You won’t find Bacteroides in a standard supplement. However, several Bacteroidetes species are being developed as next-generation probiotics, including Bacteroides thetaiotaomicron, Bacteroides uniformis, and Bacteroides acidifaciens. These are being studied for their potential to prevent or alleviate obesity, liver disease, diabetes, and colitis.
These next-generation probiotics aren’t widely available to consumers yet, and there’s some caution around them. Unlike Lactobacillus and Bifidobacterium, Bacteroides species show greater uncertainty about their potential to cause infections in vulnerable people. For now, the most reliable path to higher Bacteroidetes is feeding the ones already in your gut rather than trying to introduce new ones through supplements.
A Practical Plan
- Add prebiotic fiber daily. Garlic, onions, leeks, asparagus, and chicory root are the richest whole-food sources of inulin and oligofructose.
- Include resistant starch. Aim for 15 grams or more per day from cooked-and-cooled potatoes, green bananas, or raw potato starch mixed into smoothies.
- Favor plant protein. Soy, lentils, chickpeas, and black beans shift the ratio toward Bacteroidetes without the inflammatory trade-offs of high meat intake.
- Exercise at higher intensities. Interval training and vigorous workouts produce the biggest microbiome shifts.
- Eat a wide variety of whole plants. Diversity of fiber types matters because Bacteroidetes carry enzymes for a broad spectrum of complex carbohydrates.
Changes in gut microbiome composition typically become measurable within two to six weeks of sustained dietary shifts, based on the timelines used in most clinical trials. Consistency matters more than perfection. A diet that regularly includes diverse fiber sources, plant proteins, and resistant starch will do more for your Bacteroidetes levels over time than any single superfood.