Pricey Mark: Keto and selenium deficiency – one thing to worry?

Dear Mark,
A friend of mine just found out that I’ve been on a keto diet for the past few months and they told me to stop right away and have my selenium levels checked. They said I might have a heart attack because of keto. Now I’m freaking out a bit. Help?

Don’t freak out. Let’s look at the evidence.

What is selenium and why do we need it?

Selenium is an essential trace element that we get from our diet. Enzymes, called selenoproteins, play a number of important roles throughout the body. In particular, selenoproteins in the thyroid facilitate the conversion of T4 to T3. Selenoproteins require adequate selenium intake.

Selenium deficiencies can be very serious. Selenoproteins act as antioxidants. Without enough selenium – or truly selenoproteins – to provide protection, heart muscle cells can suffer free radical damage. This is the case with Keshan’s disease, a potentially fatal cardiomyopathy (disease of the heart muscle). Keshan is a region in China where selenium has been removed from the soil. As a result, residents suffered a high rate of heart disease before a supplement program was introduced. Selenium deficiency can also lead to male infertility, as a selenoprotein known as GPx4 protects sperm from oxidative stress.

However, your friend may want to know that, barring serious flaws, the jury is still ignorant of selenium’s role in cardiovascular disease. Some, but not all, observational studies have shown that low selenium levels are a risk factor for cardiovascular disease. Others have found that high selenium levels can also be a problem. Selenium supplementation does not appear to prevent heart disease, but clinical studies have mainly been conducted in adult men who are already getting enough selenium from their diet.

In any case, selenium deficiencies are rare, except in certain parts of the world where the soil is significantly depleted. Most adults in the United States are given at least twice the recommended daily allowance. So your friend’s baseline seems shaky already, but let’s do our diligence here and ask if you’re at higher risk after following a keto diet.

Is there any evidence that keto causes selenium deficiency?

Yes, especially for children who have been prescribed a therapeutic ketogenic diet to treat hard-to-treat epilepsy.

As of 2020, there have been at least 66 documented cases of selenium deficiency in children on a therapeutic ketogenic diet. Three deaths were attributed to low selenium cardiomyopathies. A fourth child died after QT prolongation (essentially abnormal heartbeat). However, QT prolongation can be triggered by acidosis, so selenium may not be the culprit here.

It is unclear how common selenium deficiency is in pediatric epilepsy patients on keto. A study of 110 children found that almost half of them were low in selenium. None of them showed evidence of cardiomyopathy as a result. Another study tracked 91 children who followed a variant of the keto diet and received vitamin and mineral supplements, including selenium, for 12 months. Selenium levels decreased over time, and some children ended up falling below the recommended range.

So it is clear that selenium deficiency is a risk for these children. However, current medical opinion suggests that with adequate monitoring and supplementation, nutritional deficiencies can be managed and, moreover, the risk of serious adverse events is low.

What about healthy adults?

I haven’t seen any evidence that selenium deficiency is a problem in healthy adults following ketogenic diets, let alone heart problems.

This is the deal: It is incredibly easy to include selenium in your diet, keto, or otherwise. The recommended daily dose for selenium is 55 µg per day. Here is just a selection of the selenium content of common foods:

  • A 5-ounce can of tuna: 103 µg
  • 113 grams of Koho salmon: 43 µg
  • 4 ounces skinless chicken breast: 31 µg
  • 4 ounces 80% lean ground beef: 23 µg
  • 2 ounces beef liver: 20 µg
  • 1 large egg: 15.4 µg

You can see most keto dieters exceed the daily recommended allowance without trying. If you are concerned, eat a Brazil nut. Yes, only one. A single Brazil nut contains 90.6 µg selenium.

Why are children with epilepsy at risk?

It boils down to the specific type of keto diet that they are prescribed. All of the children in the above studies followed a therapeutic ketogenic diet designed for hard-to-treat epilepsy. This diet is very different from a primal keto diet. and that’s the crux of the matter.

Therapeutic keto diets usually follow a 4: 1 ratio, which means that for every four grams of fat, the child gets 1 gram of carbohydrates and proteins combined. In other words, you need to restrict carbohydrates and protein so much that they only make up 20 percent of your food intake. In fact, the goal is to get the most protein you need to keep your ketone levels as high as possible. As you can imagine, the diet is difficult to follow. It also increases the risk of nutrient deficiencies and related health problems. (Hence the growing interest in “modified Atkins” diets, which could be just as effective at a 2: 1 or even 1: 1 ratio that allows for more protein.)

The keto diet that the average person follows for health, weight loss, or longevity reasons, is likely nowhere near as strict as a 4: 1 therapeutic diet, and it shouldn’t be. The version of keto that I recommend in The Keto Reset Diet and Keto for Life is high in protein and includes a colorful variety of plant-based foods to cover your nutritional basics.

All in all, I’m not worried about that. Any version of a primal keto diet that contains meat is high in selenium. To calm your mind, you can always ask your doctor for a selenium test, but that seems to be an exaggeration in my book.

One final note: as with any vitamin or mineral, it is possible to get too much selenium. Don’t eat a cup of Brazil nuts a day because your boyfriend worried you. Just eat your regular, balanced diet and you should be ready to go.

About the author

Mark Sisson is the founder of Marks Daily Apple, godfather of the Primal Food and Lifestyle movement, and the New York Times best-selling author of The Keto Reset Diet. His latest book is Keto for Life, which describes how he combines the keto diet with an original lifestyle for optimal health and longevity. Mark is also the author of numerous other books, including The Primal Blueprint, which is credited with the growth of the Primal / Paleo movement in 2009. After three decades of researching and educating people about why food is the key component to achieving optimal wellbeing, Mark launched Primal Kitchen, a real food company, the Primal / Paleo, Keto and Whole30-friendly kitchen staples manufactures.

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