Are Kale Smoothies Really That Healthy?

QUESTION

My son-in-law has started drinking a smoothie every day. He includes two whole cups of kale, about a cup of berries and a few other ingredients. Is it healthy for him to drink this everyday? He never even ate greens before, and it sure seems like a lot of kale!

ANSWER

Yes! There is nothing a dietitian loves more than hearing about people who decide to regularly eat greens! Cruciferous vegetables, such as kale, Brussels sprouts and broccoli, are especially nutritious because they are such a rich source of antioxidants, vitamins C, E and K, folate and fiber. Cruciferous veggies also contain sulfur-containing substances called glucosinolates, which give them their pungent aroma. Some studies have linked the compounds in glucosinolates to lower risk for certain types of cancer, such as colorectal and breast cancer. However, glucosinolates can also interfere with the absorption of iodine, a nutrient that is crucial for thyroid health. For this reason, people with hypothyroidism (low thyroid), should check with their doctors before adding large amounts of raw kale or other cruciferous veggies to their diet. Note: When these veggies are cooked, they do not pose the same risk. In addition, some people have been hesitant to add kale to their diets because of a recent report based on the observation of a biologist that linked the veggie to increased levels of the heavy metal thallium in the blood. Cruciferous vegetables can accumulate toxic metals if they are grown in contaminated soil near a cement or coal-burning plant. Consuming thallium-contaminated kale that is grown in the US is possible, but it is unlikely. This type of poisoning would cause such symptoms as vomiting, diarrhea and temporary hair loss. Like other foods, kale is safe to consume in moderation. If a person has hypothyroidism, he/she should take thyroid medication on an empty stomach to ensure its absorption. Anyone using the blood thinner warfarin (Coumadin) should speak to a doctor or registered dietitian about incorporating a consistent amount of kale (and other cruciferous veggies) into the diet since this food is rich in vitamin K, which impacts the effectiveness of this medication. As you probably know, berries are also superfoods, packed with antioxidants and vitamins. Eating half a cup of blueberries or strawberries at least three times a week has been shown to lower blood pressure and risk for heart attack. You don’t mention whether your son-in-law includes some type of liquid in his smoothie. I recommend that he include a source of protein and fat such as full-fat or 2% plain Greek yogurt and/or 2% milk in his smoothie. If he’s vegan, he can use almond milk and/or coconut yogurt. The fat will help him absorb the fat-soluble vitamins A, D, E and K found in kale. The protein will keep him feeling full all morning, so he’ll be less tempted to snack on doughnuts or pastries. Your son-in-law has definitely started a healthy new habit, so congratulate him!