Soybeans and soy products CAN be sources of oligosaccharides, especially of GOS (some fructans, too). But not all soy products are significant sources. It helps to understand two things about fructans and GOS: 1) they are fibers, so soy foods that have less fiber have less FODMAPs 2) They are water-soluble, so any processing method that involves soaking soybeans in water and draining away the water will reduce FODMAPs. Consuming the soaking water means we are consuming the FODMAPs.
- Soy beans--Not suitable.
- Soy milk--In the US, soy milk is usually made by combining whole soybeans and water. It is likely to be high in FODMAPs. (There are a couple of suitable US products that might be suitable, although they haven't been measured in the lab. Visit me on Pinterest to see them.) In Australia, soy milk made from isolated soy protein is more available. It has been measured in the lab at Monash University and it is considered suitable for a low FODMAP diet.
- Soy yogurt--probably high in FODMAPs because the main ingredient is soy milk (see above)
- Soybean oil--No carbohydrates here, so no FODMAPs. Fine for the elimination phase.
- Soybean lecithin--Not a source of FODMAPs. Suitable for the elimination phase.
- Tofu block, floating in water, unseasoned--In the US, this might be called soft, firm, or extra firm tofu. This type of tofu has been measured and is low in FODMAPs. Tofu is made by coagulating soy milk, cutting it into blocks, pressing, and draining off the resulting liquid. The GOS/FODMAP is in the liquid, which is not consumed. Suitable for the elimination phase of the diet.
- Silken tofu--This type of tofu is made by coagulating soy milk. Instead of being pressed and drained, the whole thing is packaged and ultimately consumed. I have not seen FODMAP composition data on this type of tofu, but it stands to reason the FODMAPs are still in it, so it is probably not suitable for the elimination phase of the diet.
- Soy sauce--Soy sauce has been measured in the lab and is low in FODMAPs. This probably goes for tamari sauce, too. Teriyaki sauce probably has garlic in it, so it is probably not suitable.
- Soy vegetarian crumbles, nuggets, burgers, etc.--These products vary, but it is likely that they all contain fiber from the whole soybeans they are made with; in addition, most will be seasoned with onions and garlic. These are not suitable for the elimination phase of the diet.
- Soy protein powder--FODMAP status probably varies depending on processing. If the product has any fiber showing up in the nutrition facts I would assume it is not low-FODMAP. Soy protein isolate could potentially be low FODMAP if it is very pure, but actual FODMAP status is unknown.
Soy products that are not suitable for the elimination phase of the IBSFree diet could be reintroduced when challenging GOS/oligosaccharides. Hope this sheds some light on soybeans!