Is the Keto Diet Safe? How to Avoid Common Issues

Is the Keto Diet Safe? How to Avoid Common Issues
  • The ketogenic diet is more popular than ever, but is keto safe? There are a few common downsides to a strict keto diet, and some situations where you may be better off modifying keto by eating some carbs.
  • Keto can cause mild to dangerous side effects, including muscle cramping, decreased metabolic flexibility, gut issues, and insomnia. It can also be tough to get enough fiber on a keto diet.
  • If you’re an athlete or have autoimmune issues, you may be better off eating a modified ketogenic diet, like cyclical ketosis or targeted keto.
  • Nutrition varies from person to person. Use this article to figure out what carb intake and type of keto diet is best for you.

The ketogenic diet is more popular than ever, but is keto safe? As word spreads about eating a high-fat and low-carb, more and more articles tout the benefits of a keto diet. And rightfully so: ketosis (your body’s fat-burning mode) can help you lose weight, upgrade your brain, soothe inflammation, and more.

That said, a lot of proponents of the keto diet don’t talk about the negative side effects of keto or whether the keto diet is safe. There are a few possible safety issues to keep in mind when you follow a ketogenic diet.

“In the early, early days, I would do hardcore keto for long periods of time,” says Bulletproof founder Dave Asprey. “At first, I felt good, but over time I developed problems from that, including leaky gut, food allergies, and my sleep quality went down, but if I’m never in ketosis my life absolutely sucks.”

This article will cover common problems with keto, how to avoid any dangerous side effects, and when it might be good to modify your keto diet by adding in extra carbs.

Is the keto diet safe?

man in bed unable to sleepGenerally, a ketogenic diet is perfectly safe. However, there are a few things to watch for when you’re eating keto.

Dehydration and muscle cramps

Carbs require water for storage. Fat does not. On a keto diet, you store less water, and your kidneys actively expel sodium instead of holding onto it. That means it’s easy to get dehydrated eating keto, especially during the first few weeks. With dehydration and low electrolytes, your muscles can start cramping, too.

Do this: Double down on magnesium, sodium, and potassium, your body’s three main electrolytes, and make sure you drink extra water. This is particularly important if you work out while on keto. Staying hydrated will also help you avoid symptoms of the keto flu.

Decreased metabolic flexibility

A lot of people report struggling to process carbs when they eat a strict keto diet long-term, which makes sense. If you hardly ever eat carbs, you have no need to keep your insulin pathways running. It’s like keeping the lights on during the daytime — a waste of energy.

Your body seems to downregulate insulin (the hormone that tells your cells to use carbs for fuel) after you’ve been strict keto for a while. Some parts of your body thrive on glucose, like the glial cells in your brain that handle repair and immune function. If your cells are great at using fat for fuel and terrible at using carbs, you won’t run at full power.

On an episode of the Bulletproof Radio podcast, Mark Sisson, author of “The Keto Reset Diet,” recommends using keto as a strategy, for a couple of weeks at a time, to reset your metabolism. This, he says, will improve your metabolic flexibility and your metabolic efficiency.

“In doing so, everything good in your life improves. You decrease inflammation. You increase your muscle mass. You increase the amount of energy you have… There are a lot of things that happen as a result of this metabolic flexibility and this metabolic efficiency,” explains Sisson. (Listen to Sisson talk about metabolic flexibility here.)

Another way to reach maximum metabolic flexibility is with a cyclical ketogenic diet, where you eat carbs one day a week in order to go in and out of ketosis regularly.

Do this: Experiment with carb cycling (aka cyclical keto) by eating 150 grams of quality carbs one day a week.

Download Now: 7-Day Cyclical Keto Diet Meal Plan & Recipe Book for Beginners

Not enough fiber

If you’re eating fewer than 20 grams of carbs a day, it can be hard to get enough fiber. Low fiber intake can contribute to constipation,[1] irritable bowel syndrome (IBS),[2] and an increased risk of colon cancer.[3] Plus, fiber boosts your fat-burning ability and strengthens your gut.

Do this: Be sure most of your carbs on a keto diet come from leafy, colorful, fiber-rich vegetables. (Even then, sometimes it’s tough to get enough fiber.) This is where a modified keto diet like the cyclical ketogenic diet (aka carb cycling) may be a better option. It gives you the flexibility to eat the types of foods our ancestors thrived on, like tubers, that support a healthy gut.


There isn’t research on keto and sleep problems, but some people report waking up in the middle of the night on keto. If you find you have trouble sleeping on keto (and Bulletproof sleep hacks don’t help), you may be better off eating some high-quality carbs at night.

These issues are common on strict keto, and are a big part of the reason why the Bulletproof Diet includes some quality carbs.

Do this: Take 1 teaspoon of raw honey before bed.

When to modify a keto diet

woman doing pull-ups outdoorsIn addition to the potential problems with keto listed above, there are specific situations where you may do better on a modified keto diet that includes some carbs.

Intense exercise

The jury is still out on keto and exercise. Some studies have found that keto-adapted athletes do just as well as high-carb athletes,[4] while other studies find that keto athletes suffer decreased performance.[5]

Do this: If you work out a lot and you find you don’t have as much energy to push through tough workouts on a keto diet, consider trying targeted keto. With targeted keto, you selectively eat carbs to boost your workout performance, and end up back in ketosis a few hours later.

Thyroid and autoimmune issues

If you have an autoimmune condition like hypothyroidism or Hashimoto’s, you may be better off doing a cyclical ketogenic diet. Cutting carbs too much can decrease thyroid hormone production in some people,[6][7], although other research has found that keto is fine for your thyroid,[8] and the decreased inflammation from keto could actually be good for it.[9] This is another example of individual variation.

Do this: If you have an autoimmune disease, work with your doctor to find out how keto affects you.

It’s worth noting that nutrition varies a lot from person to person. Some people do really well on a full keto diet, while others do much better when they eat more carbs. The key is to experiment and see how you feel. Find your ideal carb intake today, and play around until you find a diet that works well for you.

If you’ve got more questions, read our FAQ guide to keto here.

Thanks for reading!

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