When it comes to the elimination phase of the low FODMAP diet, soy is listed on many “avoid” lists. But is soy always a no-go for those eliminating FODMAPs for their IBS? The short answer: it depends! Soybeans are high in fermentable carbohydrates called oligosaccharides – mainly galacto-oligosaccharides (GOS) as well as some fructans.
There are a few factors that can alter the FODMAP content in soy-based foods, making some low FODMAP and others high FODMAP. Talk about confusing! As a registered dietitian at Ignite Nutrition who works with IBS patients daily, I get questions about soy all the time – Is tofu high FODMAP? What about soy sauce? What soy ingredients should we be wary of on labels? The list goes on!
Today we’ll be reviewing which soy products should be avoided during the elimination phase and which are considered safe. Let’s get started!
Manufacturing and Maturity
There are two main factors that affect the FODMAP content in our soy foods – how the soy is processed and the maturity of the soybeans themselves.
For starters, soy can be processed in a variety of different ways. That’s why we have so many diverse soy products on the market. It’s amazing what can be made from one plant! Some soy products are made from fermented soybeans, which actually helps to break down the FODMAP content. Other soy products are made from primarily the fat of the soybean, meaning the carbohydrate content is extremely low – ie. no FODMAPs! We’ll outline these foods in the next section, as well as soy foods that aren’t always so safe.
Secondly, soybeans that are mature contain more FODMAPs than young, immature soybeans. Most soy foods are made from the older soybeans, but that doesn’t necessarily mean they’re a trigger, as FODMAPs can be processed out later on. We can also just eat the young soybeans as is – they are called edamame and they are delicious! Edamame is considered low FODMAP at about 1 cup (without the shells).
Fermented Soy Products: Low in FODMAPs
As mentioned above, foods made by fermenting soybeans are generally much lower in FODMAPs and are considered safe at certain portions. Some examples of fermented soy products include:
- Miso paste – typically used in Japanese-style miso soup and asian cuisine, this fermented soybean paste is super flavourful and low FODMAP at 2 tablespoons.
- Tempeh – Tempeh is a solid meat substitute that cooks up similar to tofu. It is made from cooking soybeans and then partially fermenting them. It is considered low FODMAP at 100 grams (about 1 slice), but can be high in oligosaccharides in larger portions.
- Soy sauce – Soy sauce is also low FODMAP at 2 tablespoons, as fermenting the soybeans prior to production helps to break down the oligosaccharides in them.
Soy oils & fats
During the production of some soybean products, the carbohydrates in the soybean are completely removed, leaving the oil, fat, and/or protein behind. This means the end product is low FODMAP, as there are generally no fermentable carbohydrates remaining! Some examples of this include:
- Soybean oil – All oils are low FODMAP, including soybean oil. There are no carbohydrates in oils, therefore no FODMAPs!
- Soy lecithin – During the production of soybean oil, a byproduct called soy lecithin is made and gets used as an additive in many other food products. It is often added to food as an emulsifier. It is made of a combination of fat and oil, so thought to be low FODMAP (although not officially tested by Monash University yet).
What about tofu?
There’s no doubt that when we think about soy, we often think about tofu. Tofu is indeed one of the most common uses of soy, especially in the vegetarian and vegan communities. When it comes to FODMAPs, not all tofu is created equal. The processing method determines the FODMAP content:
- Regular tofu – Regular tofu is made by coagulating soy milk and then pressing the remaining curds into a block. This removes a great deal of water from the block, which can also help to remove FODMAPs. Because galacto-oligosaccharides and fructans found in soy are water soluble, some of them also get drained off as the tofu is pressed.
- Silken tofu – The production of silken tofu also starts in the same way. Soy milk gets coagulated, creating a soft and spongy block of tofu. However, the process stops there with silken tofu – none of the excess water gets drained off, meaning the high levels of FODMAPs also remain.
To clarify, silken tofu is high FODMAP, while regular tofu is low FODMAP at ⅔ cups.
Soy milk & yogurt
Soy milk and yogurt can be made in a couple ways – either from whole/hulled soybeans or from soybean protein. Soy milk made from soy protein is low FODMAP at 1 cup, but can be difficult to come by. This also goes for soy yogurt – if it is made from soy protein it is lower in FODMAPs. Be sure to check the ingredients list on the back of any soy-based milk alternatives. Due to the confusion, I find that most of my patients prefer to choose other dairy alternatives like almond milk, rice milk, or lactose-free dairy. No need to make it complicated!
Whole Soybeans & Soy Flour
Finally, it is important to avoid the highest sources of soy during the low FODMAP elimination phase – whole soybeans and soy flour. The production of these foods leaves the GOS and fructans intact, meaning they are high FODMAP and may cause IBS symptoms. Some gluten-free products do contain a small amount of soy flour. However, if it isn’t the main flour in the mix (ie. further down on the ingredient list), you may be able to tolerate a small amount. This is completely individualized and may be best explored with supervision from a dietitian!
Soy comes in many different shapes, sizes, and varieties. Rather than banning all soy on the low FODMAP diet, it is more important to pay attention to the type of soy. You may be unnecessarily restrictive!
Soy can be an excellent alternative to animal protein, especially for plant-based eaters. Check out the Monash University app to learn more about the recommended serving sizes for soy-based foods.
Keep in mind, after the elimination phase of the low FODMAP diet, you can challenge foods that contain oligosaccharides to determine whether those particular FODMAPs are triggers for you. It is highly recommended to work with a dietitian through the various phases of the low FODMAP diet for IBS.