Negative Aspects of a Ketogenic Diet

In this Article (Index)

A critical review of the risks and adverse health effects of the Ketogenic Diet

• Keto Diet Short-Term Side Effects
• Keto Flu
• Constipation
• Long-term Side Effects
• Kidney stones
• osteoporosis
• Glucose intolerance and Insulin Resistance
• Cautions and Counterindications
• The Risks of Being Fat

Keto Diet Short-Term Side Effects

Masood and Uppaluri (2018) and Batch, Lamsal, Adkins, Sultan, and Ramirez (2020) (1, 2) looked into the side-effects of a keto diet and mentioned a group of symptoms that are usually are known collectively as "keto-flu" because they resemble those of influenza:

Keto Flu

• Nausea
• Vomiting
• Dizziness
• Headache
• Fatigue
• Insomnia
• Constipation
• Low tolerance to exercise and training

These adverse effects occur on short diets and usually clear up after a few days, but sometimes can also last a few weeks. They respond well to an adequate fluid intake and a correct electrolyte balance (Visit our Do I need eight glasses of water a day? webpage for more information on keeping hydrated).

These symptoms occur as the body adapts to a lower level of glucose and turns to ketone bodies as a primary energy source.

Constipation

The keto diet causes a shift in your food intake. It eliminates most carbohydrates and this may also lead to a drop in the amount of fiber consumed. Some "high" carb foods such as potatoes, onions, and oatmeal, for instance, are rich in fiber: these three have roughly 2% fiber -2 g per 100 g serving, and eliminating them from your diet reduces your fiber bulk.

The lack of fiber combined with an increased loss of fluids and some key electrolytes such as magnesium during the first days of ketosis may cause constipation.

This can be avoided by eating more fiber.

• Green, leafy vegetables such as kale, spinach, arugula that, by the way, are magnesium-rich too.
• Fiber-rich seeds (flax, chia, wheat bran).
• Drinking more water (Read more about Drinking water and Constipation).

Long-term Side Effects

A regular ketogenic diet is short, not more than 24 weeks. But long diets may involve health risks, as is the case of children treated with a keto diet to control seizures and neurological disorders.

Russel Wilder created the keto diet to treat pediatric epilepsy in 1921 and it was Wilder who coined the term "ketogenic diet." Some studies tracked the health effects of long term keto dieting in children (not in adults), and their findings are listed below (2).

• Hyperlipidemia (High cholesterol)
• Hepatic steatosis (fatty liver)
• Increase in Kidney stones
• Osteoporosis
• Impaired growth
• Hypoproteinemia (low levels of protein in the blood)
• Vitamin and mineral deficiencies

Nevertheless, the risks do not appear to be deadly because a study by Kosinski and Jornayvaz (2017) (3) found that subjects following a low-carb, high-protein diet were not affected "with higher mortality after 12 years of follow-up."

We will look into each of these adverse effects below.

Does a keto diet increase Cholesterol and Triglycerides?

The high quantity of fat required by a Keto Diet can cause some concern regarding the potential increase of blood lipids (cholesterol and triglycerides).

But the effect is the opposite; according to Paoli (2014) (4), most studies showed that a keto diet reduces total cholesterol and increases the "good" HDL-cholesterol. It also reduces triglycerides.

Regarding the "bad" LDL-cholesterol, the keto diet "increase[s] the size and volume of LDL-C particles which is considered to reduce cardiovascular disease risk since smaller LDL particles have a higher atherogenicity."

This means that unlike smaller LDL particles, the larger ones don't provoke the buildup of deposits on arterial walls.

The lower blood glucose levels caused by a low carb keto diet mean lower insulin levels that, in turn, hinder the activation of an enzyme that synthesizes cholesterol (the enzyme is called HMGCoA), resulting in a lower output of cholesterol.

However, a long-term 22 weeks diet in mice produced high levels of blood lipids, an outcome that is completely different from the one found in human subjects.

Several studies have reported different outcomes in rodents in comparison to humans.

However, the Keto Diet reduces all-cause mortality rate

Despite the risks mentioned further up, a 2024 study using data from 43,776 adult Americans conducted between 2001 and 2018 found that following a ketogenic diet (KD)lowered the death risk (mortality) due to all causes and cardiovascular (CVD) causes: "adherence to a KD exhibits potential in reducing all-cause mortality risk while not posing an increased threat of CVD-related fatalities."(10)

How long is it safe to be in ketosis?

Dashti (2004) (5) studied 83 obese subjects that followed a ketogenic diet for 24-weeks.

All of them lost weight and showed improvements in their total cholesterol, HDL, LDL, Triglycerides, and blood sugar levels.

The scientists concluded that "the present study confirms that it is safe to use a ketogenic diet for a longer period of time than previously demonstrated."

The ketogenic diet and cardiovascular disease

We have not found studies indicating any negative side-effects regarding heart disease, such as heart palpitations.

On the contrary, the effects reported are positive ones (For more details, visit our Keto Diet Review page).

Fatty Liver

The same long term (22-week) study found that mice developed hepatic steatosis or fatty liver (3).

Kosinski and Jornayvaz (3) reviewed three meta-analyses (studies that group other studies to find statistical correlations that link different variables) involving mice and found that the KD provokes liver inflammation or fatty liver (Non-alcoholic Fatty Liver Disease or NAFLD).

Studies involving human subjects have not managed to replicate these findings. So the case is open whether a Keto Diet can induce, or on the contrary, improve NAFLD in humans (Haghighatdoost, 2016) (6).

KD as a treatment for NAFLD in humans?

Haghighatdoost also found that low-carb diets reduced liver fat content in subjects with NAFLD.

Protein intake and the kidneys

Kidney Stones

One of the negative effects on the kidneys is due to an excessive intake of protein. But this shouldn't be the case with a Keto Diet.

Because, as Paoli (2014) (4) points out that "a ketogenic diet is not, strictly speaking, a Low carb ⁄ High Protein; Keto Diet is mainly a very low carbohydrate diet with a normal amount of protein."

Yet even though the ketogenic diet is a very low-carb, moderate-protein, and high-fat diet, those who follow it may tend to ingest more protein than recommended, or increase ingestion to levels higher they normally eat.

This excess protein may be avoided by following the protein intake values set down in your ketogenic diet macros.

The problem is that the extra protein will be broken down into their amino acid building blocks, which in turn, can be converted into glucose.

Extra glucose will lower ketones, increase insulin levels, and interfere with ketosis.

The breakdown of additional proteins produces nitrogen in a toxic form: ammonia. The liver converts ammonia into urea, which is almost non-toxic and soluble in water. The kidneys then excrete the urea into the urine.

Uric acid, on the other hand, is the result of the breakdown of nucleic acids and purines. The latter is very common in different kinds of foods: animal-based protein, red meat, organ meats, and shellfish. It is also excreted in the urine.

However, high production of uric acid may generate an acid load that acidifies the urine and makes it easier for uric acid stones to form in the kidneys.

Approximately 1 in every 20 children on an epileptic keto diet suffer from kidney stones, and they are treated with potassium citrate to prevent them (7).

Other kidney issues

Is there a risk of kidney pain during ketosis?

The protein component of a keto diet results in higher amounts of amino acids, which may trigger high blood pressure.

People suffering from renal insufficiency, metabolic syndrome, or obesity-related health conditions may be more susceptible to the high blood pressure side effects.

As a positive note, Paoli (4) mentioned that a "very low carb keto diet" reverted diabetic kidney damage in mice.

Osteoporosis and stunted growth

Some studies with rats, (4) revealed that a keto diet causes a reduction in a hormone known as IGF-I or IGF-1 (insulin-like growth factor 1).

As its name suggests, it is a protein very similar in its structure to insulin. It promotes growth in children and correct body functions in adults.

So it may have an impact on children following long-term ketogenic diets.

Rat studies also show that a Keto diet impairs bone mass density. These mice studies lasted 4-weeks (a very long time in comparison to their lifespan).

But "recently published articles suggested that there is not a negative effect on bone health" (4).

Vitamin deficiencies

Vitamin deficiencies in long-term keto diets (such as those used in epileptic children) may arise from the lack of fresh fruits and vegetables in their very low-carb diet.

Supplementation should cover any vitamin or mineral needs. Raw and cooked veggies should be part of your keto diet.

Glucose intolerance and Insulin Resistance

Risk factor for diabetics

The review by Kosinski and Jornayvaz (3) found that a ketogenic diet produces insulin resistance and glucose intolerance in rodents.

This finding is supported by a recent study (Grandl, 2018) (8) using mice. It found that there may be an increased risk of insulin resistance caused by a keto diet which could lead to Type 2 diabetes.

But, once again, the keto diet in humans produces better control of sugar levels leading to a reduction in the use of antidiabetic medications in subjects with type-2 diabetes (3).

Paoli suggests moving gradually out of a ketogenic diet and into a normal diet. This gradual phase-out transition will avoid sensitization and any harmful effects on glucose metabolism (4).

Dutta et al. (2020) (9) indicated cautiously that "the KD has a valuable role in the long-term management of at least some subtypes of T2DM. However, critics argue that KD is not superior to other forms of low-calorie diets with regards to weight loss, glycemic control, and reversal of diabetes."

Masood and Uppaluri (1) recommended that diabetic patients adjust their hypoglycemic medication dosage before starting this diet. There is a risk that these subjects may experience episodes of hypoglycemia (low blood sugar).

Cautions and Counterindications

Masood and Uppaluri (1) also list a series of conditions that may interact with a ketogenic diet. Don't follow a ketogenic diet if you suffer from liver failure, pancreatitis, porphyrias, or disorders of fat metabolism.

General Diet Recommendations

Most people who lose weight are likely to find it difficult to keep the weight off. You can improve your chances by adopting a lifelong commitment that includes a balanced diet and more physical activity.

• Increased, frequent, and regular physical activity of at least moderate intensity.
• Healthy eating following the Dietary Guidelines for Americans, emphasizing a reduction in total calories, lower fat consumption, and an increase in vegetables, fruits, and whole grains.

Even a modest weight loss (5 - 10 percent of body weight, 10 - 20 pounds) will improve your health and lower the health risks associated with being overweight.

Unless medically indicated, weight loss after the first two or three weeks of dieting should not exceed a rate of three pounds, or approximately one and one-half percent of body weight per week.

More rapid weight loss may increase the risk of developing gallbladder disease.

People who are considered medically appropriate for more rapid weight loss should have their progress monitored by a physician.

Very low-calorie diets (less than 800 kcal per day) are designed to promote rapid weight loss in people whose obesity has resulted in or has put them at medical risk of developing serious health complications. Rapid weight loss may also be associated with some medical problems. A weight loss program should include medical supervision to minimize risks associated with rapid weight loss.

People undergoing weight loss can experience physical changes in the body (dizziness, interruptions in the menstrual cycle, and hair loss, for example) that may indicate more serious conditions. People noticing such changes should talk immediately to their primary care physician.

Children and adolescents, pregnant or breastfeeding women, and people with significant health problems such as bulimia, heart disease, kidney disease, diabetes, or psychiatric disorder, should not begin this ketogenic diet program without written authorization by their primary care provider.

People under treatment for other conditions or taking medications prescribed by their health care provider should tell their providers that they have begun this diet because, in some cases, adjustments to medications or modifications to the weight loss program may be appropriate.

The Risks of Being Fat

Obesity is a far worse risk factor

We have seen that there are several potential negative side-effects, some of them have been studied in mice with conflicting outcomes to studies performed on humans.

It is important to know and assess these health risks before embarking on a ketogenic diet (or any other diet). It is also important to discuss the matter with your physician.

However, being obese involves a series of health risks such as type 2 diabetes, metabolic syndrome, insulin resistance, glucose intolerance, high blood sugar levels, and the chronic low-level inflammation associated with increased risks of osteoporosis.

Visceral or abdominal fat is associated with cardiovascular disease, high blood pressure, dementia, asthma, cancer (colorectal and breast cancers), and type 2 diabetes risk.

We discuss these risks in our "The Dangers of Belly Fat" webpage.

Dangers of Belly Fat

Visceral fat has been linked to many health conditions: diabetes, dementia, asthma, cardiovascular disease, and several types of cancer. Abdominal fat is a silent killer.

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So, the "cons" of a keto diet should also be weighed against the "cons" of obesity, because many of the negative aspects of a ketogenic diet have not yet been definitively proved for humans, but those of obesity are real and life-threatening.

If you are interested, we discuss the Keto Diet and its benefits in detail in our "Ketogenic diet" webpage:

Keto Diet: A Review

Ketogenic diet: what is it? Its benefits? The chemistry and the truth behind it: it does help you lose weight and body fat quickly and with few side-effects.

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