Even though it’s hotter than a pistol, the ketogenic diet is nothing new. While the ketogenic diet as we know it has been around since the beginning of the 20th century, some would say keto (which, physiologically, closely resembles a state of fasting) has roots that run as deep as 500BC. Heck, there’s even reference to the therapeutic potential of fasting in the New Testament of the Bible. (No, Jesus wasn’t going around telling people to limit carbs to 30 grams a day or anything.)

Fascinating history aside, keto is synonymous with hype—some worthy, some far-fetched, and some the topic of heated debate. Along those lines, you’ve got outspoken people on both sides of the fence: evangelists and cynics. And while the former is quick to tout the potential benefits of keto, the skeptics continue to raise questions about if the keto diet is safe.

Does it cause the potentially lethal ketoacidosis? Does it really raise cholesterol? Is it truly bad for your heart? Doesn’t your brain NEED carbs? Keto burns muscle, right? Does keto put you at risk of dangerous nutrient deficiencies? Is the keto flu inevitable?

Let’s get to the bottom of these questions. And, let’s answer the burning question: Is the keto diet safe?

Does keto cause ketoacidosis?

When it comes to the topics of “is the ketogenic diet safe”, the biggest question—which is unfortunately perpetuated by the medical community—usually circles back to something called diabetic ketoacidosis, a dangerous pathological condition that occurs almost exclusively in cases of uncontrolled diabetes.

Basically, people have heard about this potentially life-threatening condition that sounds an awful lot like ketosis, which is a byproduct of a very-low-carb ketogenic diet. They then automatically think keto puts them at risk. Simply put, diabetic ketoacidosis is a completely different physiological state than nutritional ketosis, or dietary ketosis, which occurs during prolonged fasting or severe carbohydrate restriction (i.e., the ketogenic diet).

You see, ketoacidosis is a state of uncontrolled ketone production. And it’s often accompanied by very high concentrations of blood glucose. This is typically a concern in cases of severely uncontrolled diabetes when ketone bodies are produced in massive supraphysiological quantities.¹ Subsequently, the body’s acid-base buffering system is overwhelmed, and pH levels drop significantly (more acidic). This can have serious consequences.

On the flipside, during fasting or while following the ketogenic diet (very low carbohydrate intake), the regulated and controlled production of ketone bodies causes the harmless physiological state known as nutritional ketosis. Unlike diabetic ketoacidosis, blood pH remains tightly buffered within a normal range during dietary ketosis.

If you want to geek out for a moment, normal insulin and glucagon function is crucial in the process as ketone bodies essentially limit their own production (negative feedback loop) thanks to the help of these hormones. This is why ketoacidosis is most commonly a concern with type 1 diabetics, who don’t have normal insulin function.

To better illustrate, let’s lay out some numbers to put it into perspective:²

• Under “normal” conditions (eating a carb-containing diet), ketone levels are typically less than 0.3 mmol/L, blood glucose is between 80 – 120 mmol/L, and blood pH is 7.4 in an otherwise healthy individual.
• With the ketogenic diet, blood ketone levels typically range from 0.5 – 8 mmol/L, blood glucose is usually between 60 and 120 mmol/L, and blood pH remains normal (7.4) in an otherwise healthy individual.
• In the case of diabetic ketoacidosis, ketone levels exceed 25 mmol/L, blood glucose reaches levels over 200 mmol/L, and pH drops below 7.3.

As you can see, ketone levels can be up to 50 TIMES higher in uncontrolled ketoacidosis compared to the levels typical with the keto diet (i.e., dietary ketosis).

For an otherwise healthy individual, a well-formulated keto diet does not cause ketoacidosis (plus the keto diet is safe). By no means is that meant to make light of diabetic ketoacidosis, which unequivocally is a serious, life-threatening complication.

Doesn’t the brain need carbs to function?

Under normal conditions when you’re not fasting and consuming a mixed diet including carbs, your central nervous system (CNS)—including your brain—only uses glucose for fuel. You see, the CNS cannot use fat as an energy source per se because free fatty acids cannot cross the blood-brain barrier. This is why the brain usually uses only glucose. In addition to the brain, red blood cells also require about 20 grams of glucose per day.

By extension, it’s why most people think you need carbs (at least 130 grams per day is the typical recommendation). After all, dietary carbohydrates directly provide glucose. But the truth is that there is no clear requirement for dietary carbohydrates in adults. In other words, there’s no such thing as an essential carbohydrate. On the other hand, we know there are both essential fats (e.g., omega-3s) and amino acids (i.e., protein), as well as water and micronutrients (e.g., vitamins, minerals).

In the absence of dietary carbohydrate (such as fasting or starvation) or during severe carbohydrate restriction (such as the ketogenic diet), the body is “forced” to find an alternative energy source to meet the energy demands of the CNS: Ketones. Ketones being a byproduct of high levels of fat burning and created by the liver through a process called ketogenesis.

Under these conditions, about 80% of the brain’s energy needs can be met from ketones. The remaining energy can be derived through a process called gluconeogenesis. This is where the body creates glucose from amino acids (protein) and glycerol (fat) metabolism. Keep in mind that when most people are following a ketogenic diet, they’re also eating about 20 – 30 grams of dietary carbohydrate per day.³

Now, just because the body has the capacity to create and ability to use this alternate fuel for glucose doesn’t mean ketones are somehow preferred or optimal fuel for the brain as some might suggest. Certainly, there may be instances where that may be true (e.g., drug-resistant epilepsy). However, that does not make it the rule.

Interestingly, a main reason a minimum carbohydrate intake is set is to prevent ketosis. This recommendation can be traced back to the misconception about nutritional ketosis discussed above. Even though there is debate about whether dietary carbohydrates are essential for adults in the present day environment where most of us are faced with an abundance of food options, many researchers would argue that dietary carbohydrate was indeed essential for the evolution of humans to accommodate the increased metabolic demands of a growing brain.⁴

Does the keto diet burn muscle?

You may have noticed above that the body can create glucose (via gluconeogenesis) from amino acids (i.e., protein). While it’s indeed true, it has led to the misconception that low-carbohydrate diets “burn muscle,” which are made up of amino acids, for fuel. In fact, the most prominent exercise physiology textbook claims, “A low-carbohydrate diet sets the stage for a significant loss of lean tissue as the body recruits amino acids from muscle to maintain blood glucose via gluconeogenesis.”⁵

Fortunately for keto dieters, this doesn’t seem to inherently be the case. In fact, some would argue that ketones protect lean body mass by preventing catabolic (i.e., breakdown) activity.^1,6 Indeed, one commonly cited study by the keto crowd showed that a very-low-carbohydrate diet resulted in a significant reduction in fat mass and a concomitant increase in lean body mass in normal-weight men.⁷

However, in a recent review study published in the International Journal of Sport Nutrition and Exercise Metabolism, Tinsley and Willoughby found that “the majority of studies report decreases in fat-free mass in individuals following a ketogenic diet.”⁸ They did cite several concerns, including how studies measured fat-free mass (which includes lean muscle) and the fact that many studies did not include resistance training, which is one of the most powerful tools for preserving muscle when dieting.

It’s important to keep in mind that fat-free mass also includes weight like body water and glycogen (stored carbohydrate). We’d expect both of these to be lower with a very-low-carbohydrate ketogenic diet. In other words, that would explain at least part of the reduction in fat-free mass.

With that being said, several studies have shown that combining a ketogenic diet with resistance training may lead to reduced body fat while maintaining (or even increasing) lean muscle.^9–12 With that in mind, here’s some practical advice if you’re worried about “burning muscle” with the ketogenic diet:

• Don’t cut calories too drastically.
• While keto is not typically considered a “high-protein” diet, strive for the upper end of the protein limits (about 20 – 25% of calories).
• Lift weights.

Does the keto diet cause nutrient deficiencies?

When you focus on severely cutting carbs like keto does, you tend to reduce your menu of plant-based foods fairly dramatically. That means you’ll eliminate whole grains, legumes, tubers, and fruit, and you restrict your intake of nuts and seeds. In order to stay under the 20- to 30-gram daily quota of carbs, you even have to be careful with the types and amounts of vegetables you choose.

Obviously, these whole, plant-based foods are a far cry from the ultra-refined processed foods that keto banishes. However, THE rule (< 30 grams of carbs per day) is THE rule. And by severely limiting your intake of these types of foods, you run the risk of not getting enough key vitamins, minerals, fiber, and phytonutrients provided by them. You may have noticed I’ve used the term “well-formulated” when talking about the ketogenic diet. Basically, a well-formulated keto diet goes beyond just carbs, fat, and protein. It takes into consideration vitamin and mineral needs, and it emphasizes eating a variety of whole foods, including nutrient-dense foods like fish, eggs, meat, nuts, seeds, low-carb vegetables, and even certain fruits (e.g., avocados). In general, as keto continues to rise in popularity, we’re seeing this trend toward a whole foods-based approach evolve. In fact, many in the Paleo community are embracing keto, and in short, Paleo can be summed up with slogans like “Eat REAL food” and “Don’t eat processed garbage.” The ketogenic diet has also been applied to the Mediterranean lifestyle. In other words, ketogenic guidelines (very-low-carbohydrate, high-fat) can be applied to popular diets/lifestyles like Paleo and Mediterranean, which consistently rank highly for diet quality and health outcomes.¹³

Is it possible to run into nutrient deficiencies (especially for certain vitamins, minerals, and fiber) with a ketogenic diet? Sure, and it may be even more likely due to a limited menu. But the fact of the matter is that most people who aren’t keto have a number of nutrient deficiencies, including vitamins D, E, and K, magnesium, potassium, fiber, and omega-3s to name a few. In other words, nutrient deficiencies aren’t specific to keto. They are a concern for EVERYONE.

What is the keto flu?

If you’re keto, thinking about trying keto, or have gone keto before (or questioning “Is the keto Diet Safe”), chances are you’re familiar with something that people often refer to as “keto flu.” The keto flu refers to a constellation of issues that some (not all) people experience when embarking on the ketogenic diet, including:

• Brain fog
• Headache
• Nausea
• Muscle cramps
• Increased heart rate
• Fatigue
• Lethargy
• Feeling light-headed
• Difficulty sleeping
• Sugar cravings
• Digestive discomfort
• Constipation

Fortunately, a well-formulated ketogenic diet addresses many of the factors that seem to contribute to the keto flu. That being said, each person is different, adaptation periods vary, and by no means is a ketogenic diet a perfect fit for everyone. Having said that, here’s a list of 12 tips to mitigate the keto flu (click on the link for details):

1. Make sure you’re getting enough fat.
2. Make sure you’re eating enough calories.
3. Make sure your protein intake isn’t too high.
4. Make sure you’re keeping your carbs low.
5. Stay hydrated.
6. Replenish electrolytes (especially sodium, potassium, and magnesium).
7. Make sure you’re getting enough fiber.
8. Exercise.
9. Watch your alcohol intake.
10. Experiment with exogenous ketones.
11. Try intermittent fasting.
12. Stick with it!

Is the keto diet safe for heart health?

For most people, the low-fat mantra has permeated their lives. Even though that ideology has been debunked, many are still stuck in the rut that too much fat is bad—especially for heart health. Along those lines, the ketogenic diet is very high in fat, so it must be “bad” for your heart, right?

WRONG.

Does a high-fat ketogenic diet raise cholesterol? YES. However, the increase in cholesterol is experienced with keto is usually a result of:

1. Higher levels of HDL cholesterol, which is typically classified as “good” cholesterol. Generally speaking, higher levels of HDL are associated with better heart health outcomes (i.e., lower cardiovascular disease risk); and
2. An increase in the size and volume of LDL cholesterol particles (i.e., large, fluffy LDL particles). Unlike small, dense LDL particles, which are considered to be a predictor of coronary heart disease, large, fluffy LDL particles are considered to reduce cardiovascular disease risk.^2,14

In other words, although LDL cholesterol is traditionally viewed collectively as “bad,” the size and density of the LDL particles matters. Large, fluffy particles (which tend to increase with keto diets) reduce the risk of cardiovascular disease. On the other hand, small, dense LDL particles have a higher artery-clogging properties.

Unfortunately, typical cholesterol panels only measure collective LDL particle number—not particle size and/or density. So, an increase in LDL is viewed as “bad.” However, that doesn’t tell the whole story.

Further, high-fat ketogenic diets seem to be particularly effective at lowering triglycerides, which is also very important for reducing the risk of cardiovascular disease. Keto is also extremely effective at lowering insulin levels, which is another important metric for cardiovascular and metabolic health.

While there’s no question that dietary fat can have a direct impact on cholesterol levels, what many people don’t realize is that insulin activates a key enzyme (the very same enzyme targeted by popular statin medications) involved in the body’s synthesis of cholesterol. Practically speaking, comprehensive review studies show that the ketogenic diet has a more favorable impact on markers of cardiovascular health than the more commonly recommended low-fat diet.^15–18

Is the keto diet sustainable?

This is probably the biggest rub not just against keto but any diet. In fact, it’s why most people “fail” when it comes to weight-loss maintenance.¹⁹ One could argue that sticking with a keto diet is even more difficult because it’s so extreme.

Along those lines, a U.S. News and World Reports panel of experts argue that it’s so extreme that it bears being ranked last among a list of popular diets. While there’s some research to corroborate that assessment, some studies have shown that adherence for low-carb diets doesn’t seem any worse than low-fat diets. In other words, keto doesn’t seem particularly more or less sustainable than other restrictive diets.

And now that it’s more popular, it’s possible that sustainability may be less of an issue. In other words, one of the greatest benefits of keto may be the buy-in. Popularity means more positive social support and accountability. It also means that keto-friendly foods and menu options are likely to increase. That all usually adds up to increased adherence. BUT, just because you read about someone being keto for years doesn’t mean it will be “easy” or “right” for you.

Is the keto diet safe?

As a take-home point, many of the questions and concerns about keto are misguided and inaccurate. But does that make the keto diet safe? Does that make it the best approach for everyone? In the case of the latter, certainly not. If anything, it highlights the significance of finding what works best for you personally.

In the case of the former, even though we can safely dismiss many of the common concerns, the longest trials investigating the safety of the ketogenic diet in humans have lasted six months.^15,20,21 These studies provide encouraging evidence of the safety of the ketogenic diet; however, there is uncertainty about the long-term effects beyond these time periods.

While I’m all about collecting more data to help expand our knowledge base and provide peace of mind, I have to admit that a diet that emphasizes whole foods—whether ketogenic or not—seems like a DRAMATIC step in the right direction for most people. Regardless if that means a ketogenic Paleo diet or a ketogenic Mediterranean lifestyle, if it means abandoning the traditional Western-style diet that relies heavily on ultra-refined processed foods for Real Food, I think it’s a good thing.

But that comes with a caveat: IF you tolerate it well. Don’t force a square peg into a round hole. Keto is not for EVERYONE. Just like low fat is not for everyone. Just like Paleo is not for everyone.