Why Eating Nuts Upsets Your Stomach

So you went on a health kick and started eating more nuts. You pack pecans as a mid-morning snack, you slather almond butter on apple slices, and you top your salads with chopped walnuts.

You did all of this to be healthier, but instead of feeling better, you feel bloated, gassy, and uncomfortable after eating. What’s the deal?

You’re wondering why eating nuts upsets your stomach so much.

I know how you feel. The same thing happened to me. Not only did eating nuts upset my stomach, but my mouth and throat would get itchy after eating certain nuts, like walnuts or pecans. Many people get serious digestive issues from eating nuts and assume they must eliminate them from their diet.

Barring the possibility of food sensitivities or allergies (in which case, you DO want to eliminate them), there is a way to prepare nuts that makes them easier to digest. It took me years to find this out, but ever since, I have been able to enjoy eating my cashews and walnuts and pecans and almonds (and all those other delicious nuts) in moderation without these annoying reactions.

Why Raw Nuts Mess Up Your Digestion

It turns out that raw nuts contain many compounds that impair digestion, including phytates to tannins. Phytates and tannins both work by binding up minerals so they are unable to ignite the enzymatic reactions that tell a seed or nut to sprout until it is safe to do so.

Every plant has to find a way to protect itself and ensure its progeny will survive.

In this case, if an animal eats the nut, it could pass through the digestive system unharmed and possibly have a chance to sprout and grow a whole new plant.

Unfortunately, for humans, this means we can’t digest nuts very well or fully absorb the minerals from them. Phytate is like a magnet for minerals, binding them up until the seed has started to germinate. We’re talking important minerals like calcium, magnesium, iron, zinc, and copper.

I was so fascinated by this finding, that I did an entire research presentation on the topic in college looking specifically into phytates and how they impact mineral absorption in humans. Some animals (like rats and birds) can digest phytates, but humans lack the enzyme (phytase) to make it happen.

When these nuts or seeds are specially prepared, by soaking or sprouting or fermenting, most of these compounds break down or are leached out, making nuts easier to digest.

Through soaking, you trick the nut into thinking it’s time to germinate. Phytate begins to break down, releasing the minerals it was holding onto to fuel the enzymes that the seed requires to grow into a new plant. Only, you’re gonna eat the nut before it has a chance to grow. I’ll save you from any further nerdy explanations and organic chemistry.

What’s cool about it is that traditional cultures (and even some animals) figured this out long ago. It’s not just nuts and seeds, but also grains and legumes that are subject to special preparation.

  • Ever notice how squirrels will gather seeds and bury them for later?
  • What about how acorns were soaked by Native Americans before being consumed?
  • Or how the Scottish would soak their oats overnight before cooking and save leftovers in a wooden “porridge drawer” in the kitchen, which would ferment and be eaten over the course of the week?

Maybe you didn’t know those things, but there is a reason humans and some animals go out of their way to prep nuts before eating.

Similar preparation techniques can be used so you can eat nuts without getting an upset stomach – without burying almonds in the yard or building a special drawer for your kitchen.

The following recipe is originally from Nourishing Traditions, a great cookbook that delves into the foods of traditional cultures. My favorite nut to use in this recipe is cashews, but you can use whatever you like. Hands on prep time is less than 5 minutes, though you will need to leave your oven on for about a day. I usually start the soaking process in the morning or right before bed.

Crispy Nuts

Prep Time: 2 minutes

Total Time: 24 hours


  • 4 cups (1 pound) raw cashews
  • 1 Tablespoon sea salt (it looks like a lot, but go with it)
  • filtered water (enough to cover nuts)


  1. Place cashews and salt into a large non-reactive bowl, such as pyrex, ceramic, or stainless steel.
  2. Soak nuts for 6-7 hours. They will plump up considerably.
  3. Drain off water (do not rinse).
  4. Spread in a single layer on a non-reactive pan, such as a pyrex/glass or stainless steel baking pan.
  5. Dehydrate in a slow oven ~200 degrees F for 12-24 hours, turning once or twice. They are done when the nuts are crisp.
  6. Let cool and store in an airtight container.

NOTE: For nuts other than cashews, you may let the nuts soak for longer and dehydrate at a lower temp for better results (150 degrees or less). Cashews do better at a slightly higher temperature and shorter soaking time, otherwise they can develop off-flavors.