Do You Really Need to Give Up Kale, Cauliflower, and Other Cruciferous Vegetables When You Have Hypothyroidism?

If you have hypothyroidism (underactive thyroid), you may have been told to avoid cruciferous vegetables — such as kale, cauliflower, broccoli, cabbage, and Brussels sprouts.

Cruciferous vegetables have been shown, in certain situations, to interfere with how your thyroid gland uses iodine. Using iodine effectively is necessary for normal thyroid function.

It’s not clear, though, if eating cruciferous vegetables in moderation has any harmful effects on thyroid function in people without thyroid disease. And many people with hypothyroidism can safely incorporate these foods into their diet.

Here’s what you need to know about cruciferous vegetables and hypothyroidism — the effects these veggies can have on your thyroid, whether you should avoid them, and how to weigh the risks and benefits of eating them.

How Cruciferous Vegetables Affect Your Thyroid

Cruciferous vegetables belong to a group of related plants, and include the following produce:

• Bok choy
• Broccoli
• Brussels sprouts
• Cabbage
• Cauliflower
• Collard greens
• Kale
• Kohlrabi
• Mustard greens
• Turnips and turnip greens

These vegetables are chemically unique in many ways, including their high level of sulfur-containing compounds called glucosinolates, which give them their distinctive smell.

But glucosinolates and other chemicals in these veggies are considered goitrogens, which means they may interfere with the production of thyroid hormone — mostly by disrupting your thyroid’s use of iodine. Your thyroid uses iodine for normal production of thyroid hormone, and if it can’t access iodine properly or if there isn’t enough iodine in your body, your thyroid hormone level will drop.

For most people, goitrogens shouldn’t be a concern, and eating cruciferous vegetables can lead to a number of health benefits, including a reduced risk of several types of cancer.

“They’re not necessarily harmful if you have a normally functioning thyroid,” says Luis O. Rustveld, PhD, RD, a dietitian and assistant professor at the Baylor College of Medicine in Houston.

In fact, Dr. Rustveld says, many concerns that people have about cruciferous vegetables stem from animal studies showing that they can trigger hypothyroidism. One such study, in which researchers observed thyroid gland enlargement in rabbits eating cabbage, was published in 1928 and led to the discovery of dietary goitrogens.

According to researchers at Oregon State University, normal consumption of foods containing goitrogens doesn’t seem to increase the risk of hypothyroidism in humans — unless someone is deficient in iodine. Iodine deficiency, Rustveld adds, is extremely rare in the United States, largely due to iodine supplementation in salt and other food items.

Researchers have found that collard greens, Brussels sprouts, and certain varieties of Russian kale contain enough goitrogens to potentially interfere with iodine uptake in healthy people when eaten in large quantities, according to a study. But other cruciferous vegetables — including broccoli, turnips, and most types of kale — didn’t contain enough goitrogens to pose a significant risk to people with normal thyroid function.

Cruciferous vegetables aren’t the only dietary source of goitrogens, Rustveld notes. They’re also present in soy, spinach, strawberries, peaches, and peanuts.

Can You Safely Eat Cruciferous Vegetables?

If you have hypothyroidism, you may want to consider limiting your intake of cruciferous vegetables, says Rustveld.

“If you have an underactive thyroid or iodine deficiency, you should avoid juicing cruciferous vegetables,” he adds, since juicing makes it easy to ingest large quantities of produce.

You should also be sure to cook cruciferous vegetables if you have hypothyroidism. “Cooking cruciferous vegetables lessens their goitrogenic properties,” says Rustveld. “It reduces the effect of goitrogens on the thyroid, so they don’t cause any problem” in normal quantities, he adds.

But you don’t have to overcook your veggies until they’re mushy; normal cooking or steaming should do the trick.

Another good rule of thumb: People with hypothyroidism shouldn’t consume more than half a cup of cooked cruciferous vegetables each day, Rustveld says.

Weighing the Risks and Benefits of Cruciferous Veggies

When deciding whether you should eat cruciferous vegetables when you have hypothyroidism, the first thing to consider is the advice of your doctor, says Rustveld.

It’s also important to keep tabs on how well your treatment for hypothyroidism is working, he says. If your thyroid levels are normal, you may have more room for choices in your diet.

If your doctor leaves the decision to you, you should consider the potential benefits of these vegetables along with their risks.

Don’t underestimate the nutritional value of these vegetables, urges Rustveld. “Cruciferous vegetables are a rich source of nutrients — fiber, all kinds of vitamins, phytonutirents, antioxidants,” he says.

The bottom line: “Check with your doctor, but if you want to consume them because you like them, and if you cook them well, then you should be okay.”