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The definition of a fad diet is a diet that is popular for a time, without being a standard dietary recommendation, and often promising unreasonably fast weight loss or other nonsensical health improvements for those who adopt it.

Many people think that ketogenic diet fits this definition. Not only that, but some claim that the diet may actually be causing harm in those who choose to follow this high-fat eating plan.

You may have heard one of a number of criticisms of keto: that’s it’s “too high in unhealthy fat”, that it “doesn’t contain enough micronutrients”, or that it will lead to unwanted side effects like the dreaded “keto flu” or bad breath.

Generally, there is a lack of scientific evidence to support these criticisms. And in fact, the keto diet has been shown to improve health under a wide variety of conditions.

Low-carb diets are far from dangerous for most people, and probably have more health benefits than risks.

Common Myths About the Ketogenic Diet

Despite the research, there are many myths floating around about the dangers of the ketogenic diet. Some of these have arisen due to long-held misconceptions about nutrition. Below, we’ve listed some of the most commonly cited dangers, their source, and evidence against them.

Eating Too Much Fat Will Give You Heart Disease

Much of our worn-out nutritional conventions tell us that if we consume too many fatty foods, we will cause a build up of cholesterol in our arteries and increase our risk of heart disease.

In this light, it would make sense to be fearful of keto. The keto diet advocates high fat intake: fat makes up around 85% of the total calories in the diet. This means eating a lot of meats, cheeses, oils, fatty fish, butter, eggs, and nuts.

However, it is disingenuous to lump all fats together. There are several different types of fat, including saturated, unsaturated, and trans fat. Each of these has a very different role to play in disease risk.

We have typically been advised to limit consumption of saturated fat. This recommendation was the result of epidemiological data which found an association of saturated fat consumption with heart disease; an association that has recently been questioned. In fact; some comprehensive studies have found an inverse association between saturated fat consumption and death from heart disease.Deghan2017

Along with no elevated risk from increasing saturated fat consumption on keto, there is evidence that a high-consumption of unsaturated fats (also advocated on keto) is associated with better health.

Upping your intake of unsaturated fats from foods like avocados, fish, nuts and seeds may reduce cardiovascular disease risk factors, lower blood pressure, and improve blood lipids.Appel2005

The only fat consistently linked to greater disease risk are trans fats—partially hydrogenated fats found mainly in vegetable oils, processed snacks, baked goods, and margarine.Mozaffarian2009

What about cholesterol? High cholesterol levels are a suspected culprit in heart disease, and so the thinking goes that a diet higher in fat and cholesterol will increase your risk. The relationship, however, isn’t quite as linear as it might seem.

Some studies have shown a weak correlation between the amount of cholesterol in one’s diet and cholesterol levels in the blood.Kratz2005 There is also some evidence that different people may have widely varying responses to dietary cholesterol. There is also more than one “type” of cholesterol—often separated as LDL cholesterol (the “bad”) and HDL cholesterol (the “good”).

More important than total cholesterol levels might be the LDL to HDL ratio. The ketogenic diet may favorably impact this ratio by increasing blood HDL and reducing LDL through the consumption of poly and monounsaturated fats from healthy sources.

Images of the different kinds of fats: avocados, nuts, steak and coconut. And the bad kinds of trans fat, chips and cookies.

Eating Lots of Fat Will Make You Fat

Our long held fear or fat is due in some part to the fact that some people believe that eating fat (the macronutrient) will directly cause you to gain fat (body fat). A low fat diet, therefore, should cause reduced body fat and prevent weight gain. This thinking is completely unscientific.

Put simply: any excess energy consumed in the diet—whether from protein, carbohydrates, or fat—will end up stored as body fat (or muscle glycogen).

In fact, dietary fat may be the least likely to stimulate body fat storage.

This is because unlike fat, carbohydrates and protein stimulate the release of insulin. Insulin is a “pro-growth” hormone which tells our cells to take up nutrients for utilization or, if not used, storage.

If dietary fat invariably caused an increase in body fat, you’d expect the keto diet to promote weight gain. This is completely the opposite of what is seen in the literature. There is consistent and strong evidence that ketogenic diets are an effective therapy for weight loss.Paolia2013

In the absence of an overconsumption of calories, the ketogenic diet won’t lead to increased body weight. What is more, high-fat diets are actually shown to be more satiating (appetite-suppressing) than other mixed diets,AdamPerrot2006 and therefore may promote reduced caloric intake and weight loss as a byproduct.

Will My Electrolyte and Water Levels Become Imbalanced?

If you have read anything about keto, you’ve likely heard the term “keto flu” mentioned once or twice.

Keto flu isn’t an actual virus, but instead, is the name given to the constellation of symptoms that some people experience soon after adopting a low-carb ketogenic diet. Many of these symptoms include muscle cramps, constipation, brain fog, and low-energy. Why do these occur?

In part, these keto “side effects” happen due to an imbalance of electrolytes. When one starts keto and drastically reduces their carbohydrate intake, insulin and glucose fall, as does muscle glycogen (initially). As a result, a large amount of water is lost, taking with it essential minerals.

These shifts are likely temporary, and can even be resolved or prevented through targeted electrolyte and mineral supplementation. There is likely no long-term health impact from any of the manifestations of the “keto flu” and, once you’ve adapted to the diet, they’re unlikely to happen again.

Keto Will Worsen My Exercise Performance

Athletes are always looking for a leg up, and diet is often one of the first things to be experimented with. Many people caution against the use of ketogenic diets for athletes for fear they it will worsen performance or even lead to a loss of muscle mass.

A fear of worse performance is rooted in the well-accepted idea that carbohydrates are the primary and preferred source of fuel for exercise—high intensity exercise, at least. If you want strength, speed, and power, high-carb is the way to go.

This consensus is still accepted by most.

However, in sports involving body composition or ultra-endurance (think marathon running), ketogenic diets might actually provide an advantage.

A study of keto-adapted runners found that these athletes had a superior ability to burn fat compared to athletes consuming a diet with around 600 grams of carbohydrates daily.Volek2016 Interestingly, they were also able to burn the most amount of fat while exercising at 70% of the maximal capacity. Usually, max fat burning occurs at around 55% of one’s maximal effort.

Much more research needs to be done on how ketogenic diets affect endurance capacity.

In regards to the “losing muscle” critique, there is simply no evidence to support it. People think that since keto is a “moderate protein” diet, it won’t have enough muscle-building foods to promote gains in lean muscle mass.

But research shows that low-carbohydrate diets that contain a sufficient amount of calories can maintain and even increase muscle mass in normal individuals and in athletes who are in the midst of a training program.Wilson2017,Paoli2012,Gregory2017

Will Keto Lead to a Nutrient Deficiency?

Those who say that keto isn’t a “complete” diet are most likely the same people who think that keto is mainly a butter and bacon-based diet. This is far from an accurate representation of the composition of most ketogenic diets.

Keto also calls for the elimination of several foods that, while rich in micronutrients, are also high in carbs. Examples include many fruits, potatoes and other starches, and fortified whole grains and bread. This brings up the possibility that a ketogenic diet that limits consumption of these foods will result in micronutrient deficiencies. There is also the discussion of fiber intake, which may drop a bit when you go keto.

A major flow exists in this argument: keto diets contain plenty of micronutrient-rich food groups. Non-starchy veggies, mushrooms, some fruits, leafy greens, and avocados—these food sources provide a wealth of micronutrients. High-quality meat and dairy also contain high levels of trace minerals and vitamins.

Adopting a ketogenic diet means you should work to incorporate plenty of the above foods (and others) into your diet to ensure a wide array of nutritional intake from diverse food groups.

Overall, a well-planned ketogenic diet plan is likely far more nutrient-rich than a typical american diet.

Will I Develop Ketoacidosis?

Ketoacidosis is not a legitimate concern for someone on a ketogenic diet.

To understand why this is, it’s important to understand the difference between ketosis and ketoacidosis—sometimes referred to as diabetic ketoacidosis (DKA) because it occurs commonly in individuals with type 1 and sometimes type 2 diabetes.

Ketosis is a metabolic state where ketones in the blood are elevated. This is typically achieved through fasting, exercise, or a ketogenic diet and is the result of the body burning fat for energy.

Blood levels of ketone bodies during a state of ketosis typically can reach anywhere from 0.5mM to 8mM, though the latter may only be achieved through extended (i.e. >3 weeks) of fasting.

Ketosis is a natural and safe physiological response to low energy availability.

Ketoacidosis, on the other hand, is an adverse physiological state that happens when both blood sugar levels and ketone bodies are elevated. How does this happen?

In diabetics who fail to produce enough insulin, blood sugar can’t be taken up by muscles. At the same time, the signal for the body to stop breaking down and releasing fat (insulin) is absent. This leads to increased ketone production in the liver while glucose is also high—which normally can’t occur.

Ketone levels rise dramatically during ketoacidosis—leading to the blood becoming more acidic. This is a life-threatening condition that requires medical care.

In sum: the ketogenic diet does not increase your risk for developing ketoacidosis.

Will I Mess up My Hormones?

When it comes to the keto diet and hormones, cortisol and thyroid are of interest. Both are super important for a wide array of physiological functions.

Cortisol is largely involved in our stress response, sends signals to break down fat and protein, and helps to modulate sleep and blood pressure. While it’s important, elevated cortisol over a long period of time can increase the risk for disease.

Why might a ketogenic diet raise cortisol levels? As noted earlier, the ketogenic diet may lead to increased water loss, also causing a loss of sodium. If sodium levels in the body drop too low, the brain will send signals to our adrenal glands to increase levels of hormones that regulate fluid balance. Cortisol is released along with these hormones.

If a ketogenic diet contains too little sodium, cortisol levels may increase over time.DeHaven1980 However, a well-formulated keto diet containing adequate sodium likely won’t alter cortisol levels to a significant extent.Volek2002

What about thyroid function?

The thyroid hormones control metabolism, digestion, protein synthesis, and bone growth, among other functions. Some studies have indicated that T3, also known as “active thyroid”, might go down on a ketogenic diet.Kose2017

However, lower T3 may in fact not represent impaired thyroid function, but rather an improved sensitivity to thyroid hormones. The hypothesis is that the ketogenic diet may increase thyroid sensitivity, thus making the body more responsive to a similar or lower amount of thyroid hormones.

Unfortunately, there are a lack of long-term studies on the ketogenic diet investigating the effects on thyroid function, and more research needs to be done in this area.

Should You Try Keto?

If some of these common myths were holding you back from experimenting with the ketogenic diet, we hope to have convinced you that may of them are unfounded or at least less-risky than the media and uninformed health professionals might want you to believe.

As with all lifestyle changes, adopting a ketogenic initially comes with some risks, but these are generally minor, and are mostly due to the fact that the body needs a period of adaptation once this diet is initiated.

The side effects of a keto diet are mostly short term will likely resolve after a few weeks. If you’re making sure to get high-quality fats and a variety of nutritious whole foods in your diet, you likely have nothing to worry about.

Keto might be different, but it surely isn’t dangerous. If you are concerned about potential health consequences, consult a healthcare professional before trying out keto. Perhaps find a nutritionist or dietitian who is well-versed in the keto diet who might be able to provide you with some tips.

And as always, it’s important to remember that the ketogenic diet isn’t going to be the best diet for everyone. It works wonders for many people, perhaps it could for you.

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