Low-FODMAPs Diet Not Working? An RD Shares 7 Possible Reasons Why + What To Do

FODMAPs tend to be short carbohydrate chains and are easily fermentable by bacteria in the small intestine. Fermentation increases gas production and draws water into the colon, which leads to distention, bloating, stomach pain, gas, and discomfort, ultimately resulting in constipation or diarrhea.

While the diet typically helps 50% to 80%2 of people who follow it, there are still others who don't get these positive results. If you're among these people, it can be frustrating and confusing. Here are some reasons that may explain why the diet didn't work for you and additional things you can consider trying. 

Even if you are being careful about hidden sources of FODMAPs, it is important to remember that FODMAPs can have a bucket-like effect, which means, when you eat carbohydrates with FODMAPs you slowly add to the bucket and gradually get closer to a threshold after which symptoms start to appear. The threshold varies from one person to another. So, if you eat half a cup of roasted broccoli with two Brussels sprouts and sprinkle 2 tablespoons of pine nuts on top, you could trigger symptoms even though all are within the allowed portion limit for each food.

For the diet to be successful, you must follow the initial elimination plan fully for at least 2 weeks. If you slip often and eat foods that are not allowed intentionally or by accident, you're probably not going to get the anticipated results. The studies that have looked at its efficacy usually have qualified dietitians instructing participants on the diet, so you may want to reach out to a professional to make sure you're following it correctly. 

On the low-FODMAPs diet, you can eat rice, white potato, corn, quinoa, and other starches. While these carbohydrates are not considered FODMAPS, they can still be difficult to digest. Digestion involves enzymes produced by the stomach, pancreas, and intestinal cells, with the support of the liver and gallbladder. People who don't produce enough enzymes, possibly due to aging, the use of proton-pump inhibitors, current or past gut infections, gut inflammation, or for any other reason, will not be able to digest starches with long carbon chains like these. These long-chain carbohydrates eventually get fermented by gut bacteria and will have the same effect as foods that contain FODMAPs.

If you are following a low-FODMAPs diet, you probably eat these carbohydrates, sometimes even in excess to make up for the ones that have been eliminated. Try removing all grains and starches, including white potato, quinoa, corn, buckwheat, oats, and others for two weeks and see if that makes a difference.

Sugars and carbohydrates, whether they are low or high in FODMAPs, feed yeast. It's possible that your symptoms are related to yeast overgrowth. Yeast is part of your gut flora and is kept within a normal healthy range thanks to good healthy gut bacteria. Antibiotics that wipe beneficial bacteria can lead to yeast overgrowth. Estrogen promotes the growth of yeast3, and the use of hormonal contraceptives can affect yeast balance in the gut. If you have a history of yeast infections, it's possible that you still have a yeast imbalance in your gut.

Try removing all sugars and carbohydrates for two weeks, and see how that makes you feel. This includes sugars allowed on the low-FODMAPs and natural sugars including maple syrup, cane sugar, grapes, bananas, and other fruit.

Nuts, seeds, leafy greens, oils, raw vegetables, meats, in addition to all sugars and grains can trigger bloating, pain, discomfort, diarrhea, or constipation. Although these foods don't have high levels of the fermentable carbohydrates and are allowed on the low-FODMAPs diet, they can still cause a reaction.

High fat intake can slow down gastric emptying and give you the feeling of indigestion and bloating. If your liver and gallbladder don't make and release enough bile salts, you may not absorb fats and oils properly, which will lead to diarrhea or loose stool.

If you have followed the low-FODMAPs diet strictly but didn't feel significant improvement in your symptoms, it's possible you have an immune response to foods that are allowed. You may be reacting to salmon, chicken, blueberries, cucumber, parsley or any other "safe" low-FODMAP food. Or your immune system may be reacting to the casein in dairy, not just the lactose. If the diet made you feel worse, you may have started eating a food that you have a sensitivity to more often because it's allowed on the diet, and that ended up backfiring.

If cutting out or reducing grains, sugars, dairy, nuts, raw vegetables, and other potential problematic foods still doesn't help, consider food sensitivities next. Consult with a dietitian who can help you identify and test your own individual food sensitivities.

The low-FODMAPs diet can reduce histamine levels4 in the body. While this is a point in favor of the diet, if you have histamine intolerance, you're probably still taking in too much histamine from food without knowing it. Aged hard cheeses, vinegar, tomato, eggplant, spinach, bone broth, and canned tuna are high in histamine, despite being low in FODMAPs. And eggs, strawberries, oranges, banana, pineapple, some nuts, tomatoes, eggplant, spinach, and shellfish can stimulate your body to make more histamine. Leftover foods, even a day or two later, can accumulate enough histamine to trigger symptoms. On top of that, having food sensitivities means that your body is releasing histamine, along with other immune compounds, as a reaction to foods, regardless of their histamine or FODMAPs levels.

If you have stomach pain, bloating, diarrhea, and loose stool in addition to these other symptoms, you may need to adjust your diet further. Remove the foods that contain or release histamine mentioned above for two weeks, and eat only same-day-cooked meals. A diet that is both low in histamine and FODMAPs is challenging, so you might want to consult with a dietitian who can help you address both. Consider consulting with a medical professional who can help diagnose and manage histamine intolerance. 

The low-FODMAPs diet tends to help people who have SIBO. However, they may need additional dietary restrictions, such as removing all starches, grains, legumes, and sugars. People with SIBO also have a hard time with the reintroduction phase. Because the presence of bacteria in the small intestine isn't addressed with the elimination diet alone, adding back foods that are easily fermented will bring on the symptoms again.

If you suspect that you may have SIBO, consult with a health practitioner who can help you diagnose the condition. Eradicating the bacteria, whether through a specific type of antibiotic or through herbal supplement protocol, is necessary to be able to reintroduce some of the foods that were eliminated on the plan.

The diet can affect the composition of the gut microbiome, which can lead to other health implications later. One study found that following the low-FODMAPs diet for 21 days reduced total bacteria abundance6 in the gut. Another study found that four weeks on the low-FODMAPs diet reduced bifidobacteria7, a beneficial type of bacteria that prevents infections and produces B vitamins and short-chain fatty acids (SCFA). Eating nutrient-rich, high-fiber foods like apples, pears, cauliflower, celery, onion, garlic, artichoke, and others is important for maintaining a healthy gut and preventing many chronic diseases.