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Does Cooking Vegetables Lead to a Loss of Minerals Such as Magnesium?

Cooking Vegetables

Most people could benefit from eating more vegetables. Sadly, a study found that only 12% of people eat the recommended 2 to 3 cups of vegetables daily, along with 1.5 to 2 cups of fruit. Even worse, the most popular vegetables people eat are potatoes and ketchup!

One reason we need to eat more vegetables is that they’re a rich source of vitamins, minerals, and phytonutrients with antioxidant and anti-inflammatory activity. Plus, unlike animal foods, they’re rich in fiber that supports a healthy gut microbiome.

When people do eat their vegetables, they may eat them raw or cooked. One problem with eating cooked vegetables is cooking, especially with lots of water or for a long period of time, reduces the vitamin content. For example, vitamin C and some B-vitamins are unstable when you heat them. Some of the vitamins may leach into the cooking water and get poured down the sink.

Vegetables are also rich in minerals such as calcium, magnesium, and zinc. For example, leafy greens are an excellent source of magnesium while calcium is abundant in broccoli. It’s a myth that you can only get calcium from dairy foods. Tofu, beans, lentils, leafy greens, seafood, and some fruit is also rich in calcium. Plus, some packaged foods, such as orange juice and some non-dairy milk products, contain added calcium.

What happens to these minerals when you cook mineral-rich foods? Some research suggests that cooking reduces the mineral content of foods. According to the textbook Chemical and Functional Properties of Food Components, cooking vegetables reduces the content of zinc by 20 to 40% and magnesium by 15 to 70%. Those are significant losses.

Yet other studies show that cooking leads to minimal loss of minerals. The same can’t be said for cooking meat at high temperatures. One study found that grilling and broiling led to the loss of 40% of the meat’s minerals and B-vitamins. So, there is some concern that cooking foods, especially for long periods and at high heat, reduces the available minerals.

The Cooking Method Matters

How much of the mineral content of a food you lose when you cook it depends on the food and how you prepare it. One of the better cooking methods is steaming. Because you use only a small amount of water, there’s less opportunity for minerals to leach out of the food and into the cooking water. Interestingly, microwaving with a small amount of water may be the best method to preserve the mineral content of foods. Studies show microwaving retains almost all the minerals in a food.

Even if you cook food in liquid, you can retain most of the minerals by saving the liquid and using it in another recipe. Why discard vitamins and minerals? You can add the liquid to soups, stews, and smoothies, for example. No need to waste it!

Where mineral loss is substantial is when manufacturers process cereal grains. This involves milling the grain to create a fine flour. Not only does the milling process reduce the fiber content of cereal grains, it lowers the vitamin and mineral content of the finished product. In fact, the loss of magnesium when flour is processed to make white bread approaches 90%. That’s why manufacturers of white bread and cereals often add vitamins and minerals back into the finished product. The goal is to make up for some of the nutrients lost due to milling and processing.

Avoiding Mineral Deficiencies

It’s concerning that people don’t eat enough fruits and vegetables to get sufficient fiber and minerals. Some studies suggest that 40% of the population may have low tissue levels of magnesium, a mineral necessary for over 300 chemical reactions in the human body. Magnesium is important for blood pressure regulation, heart health, blood glucose control, muscle health, and healthy bones. A standard magnesium blood test isn’t reliable for identifying magnesium deficiency at the tissue level. If blood levels fall, the body releases more magnesium from tissue stores, so blood magnesium levels look normal, but tissue levels are low. The gold standard test for measuring tissue levels of magnesium is called the magnesium red blood cell test.

To ensure you’re getting enough important minerals, like zinc, magnesium, and calcium, eat a variety of raw and cooked plant-based foods and realize the mineral content of produce varies. The quantity of minerals in plants varies depending on the soil they’re grown in, so some vegetables may have higher quantities of minerals than others. That’s especially true of some of the trace minerals, like selenium. By eating more raw foods and using cooking methods that don’t use high heat or lots of water, you can better ensure you’re getting enough minerals in your diet.

The Bottom Line

Depending on the food and cooking method, exposing vegetables to heat can reduce its mineral content. Losses will be greatest if you cook them in a lot of water. Surprisingly, microwaving in light water may be the best method for preserving the mineral content of food and steaming a close second. Enjoy cooked veggies but save a little room for some raw ones too. You don’t have to worry about mineral loss when you don’t cook them. You also avoid the inevitable loss of vitamin C and some B-vitamins by munching on veggies raw. Make sure you’re eating a variety of fruits and vegetables too. The more you diversify what’s on your plate, the greater array of vitamins, minerals, and phytonutrients you’ll get. Switch some of the starchy carbs you currently eat for nutrient-dense whole foods in a wealth of colors. It’s a surefire recipe for upgrading your diet!

 

References:

  • com. “Only 1 in 10 American adults eat enough fruits and vegetables, says the CDC”
  • USDA Table of Nutrient Retention Factors. Release 6.
  • Chemical and Functional Properties of Food Components. Third Edition. CRC Press. 2007.
  • 2018 Sep; 10(9): 1202. Published online 2018 Sep 1. doi: 10.3390/nu10091202.
  • Mayo Clinic. “Boost your calcium levels without dairy? Yes you can!”
  • com. “Magnesium Blood Test, RBC”

 

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