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Probiotics are the synergistic bacteria in your gut that help you digest your food. Prebiotics are what probiotics eat—fermenting them, and then producing short-chain fatty acids (food for the colon) as byproducts. 

There’s been an enormous amount of research recently on the various health benefits of probiotics—which types and strains are best, etc. 

Prebiotics get less attention. Most probiotic supplements contain them (though not all), but they were originally found in food, of course. 

Prebiotics in Food

Good prebiotic sources include a number of foods on the high FODMAP list, including asparagus, artichoke, onions, garlic, honey, wheat, barley, rye, peas, beans, cow’s milk, and dandelion. 

FODMAPs are often problematic for those with SIBO, as they will feed the bacterial overgrowth. Prebiotics can be a problem for those with SIBO for the same reason. 

Fortunately there are some prebiotic foods that are not on the high FODMAP list. These include tomatoes, oats, bananas, chia seeds, seaweed, and chicory. Unripe bananas and cold oats in particular fall into the overlapping category of resistant starches. 

Are Prebiotics Enough? 

There are some studies out there, though not a lot, that isolate the effects of either prebiotics, or the short chain fatty acids they produce, without throwing probiotics into the mix. These studies generally look at supplement sources rather than food-based sources, but the results are fairly compelling when it comes to gut health. 

This study shows that prebiotics alone (without probiotics) are effective for chronic constipation to increase bowel transit, improve stool consistency and decrease bloating. 

This study also argues that prebiotics, and the short chain fatty acids they produce, lead to improved immune function and improved integrity of the gut barrier. 

Short chain fatty acids (SCFA) are primarily acetate, propionate and butyrate. I wrote more here on the specific health benefits of butyrate. In general, SCFAs also aid in regulating glucose levels, probably because insulin resistance and the microbiome are so intimately related.

This study specifically explored using the prebiotic inulin to control prediabetic and diabetic glucose levels, and demonstrated that at 10 grams daily for 6 weeks or longer, the effects were significant.

Compounding the glucose regulation effect, this study showed that prebiotic supplementation in obese children helped to control appetite, which surely also improves blood sugar levels as well. 


Fermentation produces gas, of course. The simpler (shorter chain) prebiotics get fermented faster, and the prebiotics found in supplements tend to be simpler. They can thus produce gas as a side effect. Even those who don’t have SIBO may be susceptible to this, though of course SIBO would make the symptom more pronounced. 

If you’re susceptible to gas from prebiotic supplements (even at the amount found in typical probiotic supplements), and particularly if you’re FODMAP sensitive, I’d recommend getting evaluated for SIBO. In the meantime, you might do better with the food-based prebiotic sources such as resistant starches, tomatoes, chia seeds, seaweed, and chicory. 

In many cases of overt gut pathology, though, in my experience more rapid improvements can be seen with direct probiotic supplementation (without the prebiotics, if they produce symptoms. Though if they don’t, leave the prebiotics in).