The Problems with Eating Kale

author avatar Dr. Eric Berg 11/06/2023

Kale is such an incredible health food, and it is part of many healthy diets. I end up eating a lot of this cruciferous vegetable every single day, whether it is in my salads or smoothies. I love it for its incredible vitamin and nutrient content, and the way it fixes up the body and keeps it healthy. But did you know that for some people, there can also be some problems with eating kale?

In this article, I'll share with you two of the major kale side effects.

I will cover:

Let's start by reviewing the incredible health benefits of kale and other cruciferous vegetables.

Close-up photo of thumb and fingers holding a kale leaf on a kale plant growing in a field.


Why I love kale

As you may know, I am a big kale lover. I promote it in a lot of my videos, because I think it is a wonderful nutrient-dense superfood.

Kale is a cruciferous vegetable. Other veggies in this family include Brussels sprouts, cabbage, broccoli, collard greens, bok choy, and other leafy greens.

This vegetable is amazing. Below are some of its top health-promoting qualities:

  • It has anti-cancer properties. It can help support your body in fighting off cancer and staying healthy.

  • It is anti-estrogenic. This means that it can help prevent excess estrogen activity in the body, which is important for avoiding health problems.

  • It cleans up the liver. Kale and other cruciferous vegetables are so good for the liver. They help remove fat from the liver, decongest the gallbladder, and promote bile production.

  • It is loaded with nutrients. Cruciferous vegetables like kale are packed with vitamins, minerals, and other nutrients. For example, it is high in vitamin A, vitamin C, and vitamin K.

I recommend adding kale to your diet, whether that comes in the forms of salads, smoothies, kale chips, or kale juice.

Curly kale salad with tomatoes and cheese on a yellow plate and placemat with fork on a table.

It can be such a convenient option for loading up your diet with disease-fighting, nutrition-packed foods. You can blend it, drink it up, and be good for the day in just a few easy steps. Get my favorite kale shake recipe here.

But that being said, there can be some problems with eating kale for a small portion of the population.

Let's go into two of the major kale side effects that can occur.


The two main kale side effects

There are a few side effects that can occur when people eat cruciferous vegetables, including kale.

Here are the two major issues that come up:


1. It can deplete iodine

Periodic table concept for iodine element, orange square showing atomic number and name.

The problem:

There are certain phytonutrients found in cruciferous vegetables that inhibit the absorption of iodine. They are known as goitrogens. When iodine absorption is blocked, this can lead to some problems, especially in the thyroid gland. The thyroid gland relies on iodine to make its thyroid hormones.

Without enough iodine or thyroid hormones, thyroid function can become impaired. So that is one of the potential problems of eating too many foods that are rich in goitrogens, such as cruciferous vegetables.

This tendency of cruciferous vegetables to deplete iodine in the thyroid gland scares many people off of kale. But in fact, kale is not really poison to your thyroid. It would take eating so much kale to make that a real problem – more than most people would ever be able to consume in a day.

And the only people who really might have a small problem with kale and iodine are people who already have hypothyroidism. Hypothyroidism means they already have low thyroid function and low levels of thyroid hormones.

The solution:

Luckily, there is a really easy solution if this problem ever comes up (and that is very rare). Just add sea kelp to your diet.

Sea kelp is a great source of healthy iodine and will prevent any iodine deficiency issues. Boom. Problem solved.


2. It can be hard on digestion.

Woman in a striped shirt holding her hands to her stomach with bloating and digestive problems.

The problem:

Kale is full of fiber. So much so that sometimes it can disrupt the digestive system.

Your digestive system is filled with microbes. Four to five pounds of microbes, actually. And all of these microbes feed on fiber.

When you introduce large amounts of fiber (like with cruciferous vegetables), you can overwhelm your microbes. As a result, you can get bad bloating and constipation. And that is not a good thing.

If you are bloated all the time due to too much fiber, you won't feel good, you won't lose weight, and you won't sleep well. As much as you have heard that fiber is good for you, if it is causing you problems it will actually make your health worse.

The solution:

One issue may be that you are eating too much too fast. The amount of fiber in kale is new to a lot of people and they aren't used to digesting it. Anything that is a sudden change just might be too much for your body to handle.

So instead of going straight to drinking 20 cups of kale smoothie a day, start slow. And then gradually increase your intake over time so that your microbes have a chance to adapt.

And if you still get bloated or constipated after you eat kale (or other cruciferous vegetables), then switch it up. Go for spinach instead, and use other vegetables in your salads.

Read this article for more information on fiber and how to reduce this kind of problematic bloating.


The bottom line

Kale can be a wonderful addition to a healthy diet. It is a really good source of important vitamins and nutrients, and it has many great health benefits.

Fresh raw curly kale with silverware on rustic background of shovel and dirt soil.

But for as healthy as this vegetable may be, a small portion of the population has a hard time tolerating it. The majority of people will do just fine with it, and can load up their salads, shakes, smoothies, juices, stir-fries, and more with it. But for some, kale can pose a few problems.

To review, these are the two major potential issues:

  1. It can deplete iodine. This only really happens for people who already have hypothyroidism and have a problem with their thyroid and iodine. Luckily, taking sea kelp (a healthy source of iodine) is a quick solution that works wonders for anyone with hypothyroidism issues.

  2. It can be hard to digest, causing bloating and constipation. This is not true for the majority of people. Only 20% or so of the population just can't digest it well, especially when they are eating too much. Those people can either start slow with their intake, or turn to other veggies like spinach instead.

If you are one of the people who has some problems with kale, it is okay to avoid it. There are many other vegetables you can turn to to get all your nutrients and health benefits, including other cruciferous vegetables (like cabbage, Brussels sprouts, etc.) or spinach.

And for the rest of us, we can keep loving kale and eating it all we want!

Do you eat kale? Have you ever experienced kale side effects? Share your thoughts on these problems with eating kale in the comments section below.

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Disclaimer: Our educational content is not meant or intended for medical advice or treatment.

Editor’s Note: This post has been updated for quality and relevancy.

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