What are FODMAP Carbohydrates?
Saccharides can be broken into different types of carbohydrates depending on their chain length. FODMAPs are small-chain carbohydrates that are commonly malabsorbed in the small intestine and can trigger digestive distress in those who experience visceral hypersensitivity (a sensitive gut), such as in irritable bowel syndrome (IBS). It is important to note that foods containing FODMAPs can be healthy, do not cause painful gastrointestinal (GI) symptoms in those with a healthy gut, and should be enjoyed liberally in those who can tolerate them.
The Low FODMAP Diet: Who Might Benefit?
Food intolerance is common as it impacts about 15-20% of the global population.1 For those living with IBS (a chronic GI condition that presents with bloating, abdominal pain, and alternation in bowel habits) a diet low in FODMAP carbohydrates is showing great promise for symptom management. IBS impacts up to 20% of Americans.2 Food-related symptoms are common in IBS. In fact, one survey of nearly 200 patients with IBS revealed that up to 84% perceived eating any food resulted in digestive distress.3 Similar to IBS, people with celiac disease and inflammatory bowel disease may also experience food-related GI symptoms. Research has shown that reducing FODMAP carbohydrates may benefit symptom control in people living with these conditions when IBS symptoms prevail.4,5
Despite patient complaints of food-related GI symptoms in IBS, for years the medical community had very little to offer in regard to nutritional intervention to calm gut pain. There was little science to support the use of diet for therapeutic benefit in IBS until the novel low FODMAP diet was introduced by a research group at Monash University in Melbourne, Australia, in 2005 (referenced in the previous article). With growing interest and numerous randomized controlled trials to date, the low FODMAP diet has been shown to be an effective therapy, managing GI symptoms in more than 50% of IBS patients.6,7
As outlined in the lead article, the low FODMAP diet is a 3-phase nutritional approach. Despite its high degree of effectiveness, it is a nuanced diet with a high level of dietary modification that should involve the help of a FODMAP knowledgeable registered dietitian nutritionist for best compliance and improved success rate.8
How do FODMAPs Cause GI Distress in IBS
IBS is a digestive condition characterized in part by a hypersensitive intestine. Poorly absorbed FODMAP carbohydrates can produce varying degrees of osmotic effects in the gut (water is pulled into the intestinal tract) due to their small size, contributing to luminal distention which can trigger GI symptoms in those with IBS. Moreover, gut microbes feast on these unabsorbed carbohydrates producing gas, short-chain fatty acids and various metabolites. The stretching of the intestinal tract via the extra water and gas in the gut prompts cramping and gut symptoms. Gut microbe-derived metabolites via FODMAP fermentation may also play a role in symptom induction, but this area needs to be studied further.9
How do Soy-based Foods Fit a Low FODMAP Diet?
There are many soy-based foods that are suitable for the low FODMAP diet such as firm tofu, soy cheese, plain tempeh, edamame, soybean oil, soy sauce, miso, and some soymilk.10 Food processing, fermentation, and maturity of the plant can impact the FODMAP content of soyfoods. For low and high FODMAP soyfoods examples, see Table 1.
Table 1: Low and High FODMAP Soy-based Foods
Unknown FODMAP Status: Natto, soynuts, soynut butter
Because FODMAPs are water-soluble carbohydrates, draining off the liquid, as is done with firm tofu, reduces the FODMAP content compared to silken tofu. The liquid contains the water-soluble oligosaccharides from the soybeans. The fermentation process utilized to make tempeh reduces its FODMAP content.11 Natto, a fermented soybean dish, has yet to be tested for FODMAPs and soy yogurt has been tested as high FODMAP.
Products that utilize soy protein versus the whole soybean will be lower in FODMAP carbohydrates as well. For example, soymilk made with the whole soybean is high FODMAP versus soymilk made with isolated soy protein which is low FODMAP.10,12 Isolated soy protein may be lower in FODMAPs if the protein component is only present (i.e., there is no residual fiber that may contain oligosaccharides in the product), but this ingredient has yet to be formally tested. Textured vegetable soy protein is high FODMAPs.10 Soynuts and soynut butter contain the whole mature soybean and are likely high in FODMAPs. As previously mentioned, the maturity of a plant may also play a role in the FODMAP content of the food. For example, edamame has less FODMAPs than the mature soybean.
Consuming an alpha galactosidase enzyme supplement with 300 GALU (galactosidic units) along with foods such as soybeans that have high amounts of galacto-oligosaccharides has been shown to mitigate IBS symptoms.13 This over-the-counter supplement may offer another way for those with IBS to expand their soy intake but should be done under the supervision of a healthcare provider.
The low FODMAP diet is a 3-phase, evidence-based nutritional intervention utilized for IBS symptom management. There are many soy-based foods that are low FODMAP and suitable for consumption during the elimination phase of the diet. As an individual goes through the reintroduction and personalization phase of the diet to identify his/her personal triggers, more soyfoods may be incorporated in the diet as tolerated. FODMAP intolerance is variable per person and the goal of the diet is to provide as much diet variety as possible to enhance food-related quality of life and overall health, while managing GI distress. The oligosaccharides component of soybeans offer prebiotics (food for beneficial probiotic microbes in the gut) which may positively impact the individual’s gut microbiome and health. Alpha galactosidase enzyme supplements with the consumption of a soy-rich meal may offer improved tolerance to high FODMAP soyfoods in those with IBS.
- Lomer MC. Review article: the aetiology, diagnosis, mechanisms and clinical evidence for food intolerance. Aliment Pharmacol Ther. 2015;41(3):262-275. doi:10.1111/apt.13041
- Canavan C, West J, Card T. The epidemiology of irritable bowel syndrome. Clin Epidemiol. 2014;6:71-80. Published 2014 Feb 4. doi:10.2147/CLEP.S40245
- Bohn, et al. Self-reported food-related gastrointestinal symptoms in IBS are common and associated with more severe symptoms and reduced quality of life. Am J Gastroenterol. 2013;108:634-41
- Cox SR, et al. Effects of Low FODMAP Diet on Symptoms, Fecal Microbiome, and Markers of Inflammation in Patients With Quiescent Inflammatory Bowel Disease in a Randomized Trial. Gastroenterology. 2020;158(1):176‐188.e7. doi:10.1053/j.gastro.2019.09.024
- Roncoroni L, et al. A Low FODMAP Gluten-Free Diet Improves Functional Gastrointestinal Disorders and Overall Mental Health of Celiac Disease Patients: A Randomized Controlled Trial [published correction appears in Nutrients. 2019 Mar 06;11(3):]. Nutrients. 2018;10(8):1023. Published 2018 Aug 4. doi:10.3390/nu10081023
- Eswaran S, et al. A randomized controlled trial comparing the low FODMAP diet vs. modified NICE guidelines in US adults with IBS-D. Am J Gastroenterol. 2016;111:1824- 1832
- Halmos EP, et al. A diet low in FODMAPs reduces symptoms of irritable bowel syndrome. Gastroenterology. 2014;146(1):67-75.e5. doi:10.1053/j.gastro.2013.09.046
- Tuck C, et al. Implementation of the low FODMAP diet in functional gastrointestinal symptoms: A real-world experience. Neurogastroenterol Motil. 2020;32(1):e13730. doi:10.1111/nmo.13730
- McIntosh K, et al. FODMAPs alter symptoms and the metabolome of patients with IBS: a randomized controlled trial [published correction appears in Gut. 2019 Jul;68(7):1342]. Gut. 2017;66(7):1241-1251. doi:10.1136/gutjnl-2015-311339
- Tuck C, et al. Fermentable short chain carbohydrate (FODMAP) content of common plant-based foods and processed foods suitable for vegetarian- and vegan-based eating patterns. J Hum Nutr Diet. 2018; 31:422–435 https://doi.org/10.1111/jhn.12546
- McNamara L. Food processing and FODMAPs - what you need to know. Food processing and FODMAPs - A blog by Monash FODMAP | The experts in IBS - Monash Fodmap. https://www.monashfodmap.com/blog/food-processing-and-fodmaps-what-you/. Published February 7, 2017. Accessed June 27, 2020.
- Taylor L. Eating vegan on a low FODMAP diet. A blog by Monash FODMAP | The experts in IBS - Monash Fodmap. https://www.monashfodmap.com/blog/eating-vegan-on-low-fodmap-diet/. Published November 25, 2014. Accessed June 20, 2020.
- Tuck C, et al. Increasing symptoms in irritable bowel symptoms with ingestion of galacto-oligosaccharides are mitigated by α-galactosidase treatment. Am J Gastroenterol. 2018;113(1):124-134. doi:10.1038/ajg.2017.245