The 12 biggest Keto diet dangers to know

While it may seem like the ketogenic diet has only become mainstream within the past decade, the diet has been around since the 1920s as a treatment for epilepsy. The keto diet, often used for weight management, typically reduces carbohydrate intake to less than 50 grams (g) per day and calls for moderately increased protein and fat intake. However, it may not be safe for everyone, and the potential dangers of keto can lead to some harmful or unwanted side effects.

“The keto diet can certainly be effective for quick weight loss,” says Kim Yawitz, RD, a registered dietitian nutritionist and gym owner in St. Louis. “Weight loss of up to 10 pounds in just a couple of weeks is common, although some of this is water weight.”

However, minimizing carbs and focusing on fats and proteins changes the body’s fuel source from carbs to an alternative fuel called ketones — a process known as ketosis. This can have a range of effects on the muscles, kidneys, and bowels, as well as affecting blood sugar, nutrient intake, and more.

1. Significant Muscle Loss Can Be a Side Effect of Keto

“Muscle loss on the ketogenic diet is an ongoing area of research,” says Edwina Clark, RD, a Washington, DC–based dietitian in private practice. “Small studies suggest that people on the ketogenic diet lose muscle even when they continue resistance training. This may be related to the fact that protein alone is less effective for muscle building than protein and carbohydrates together after exercise.”

One study explored body composition on keto and highlighted that while the keto diet significantly reduced fat mass, it also reduced muscle mass. Several causes may contribute to muscle loss, including:[1]

• The body storing less sugar, or glycogen, in the muscles, which may cause fatigue during the workout and throughout recovery
• Not getting enough protein for adequate muscle recovery
• A change in how the muscles access energy, as the body has switched to using ketones as fuel
• Lower insulin levels, which might affect how muscles make proteins

“Loss of muscle mass as we age has a number of serious consequences,” notes Clark. “Muscle is metabolically active and helps boost daily energy expenditure and mitigate age-related weight gain.”

Losing muscle mass can decrease functional strength and increase the risk of falls, notes Clark. Falls are the top cause of death from injury in older populations, according to the Centers for Disease Control and Prevention.[2]

TakeawaySome people may lose muscle mass while on the keto diet, which can decrease functional strength and increase the risk of falls, especially as you age.

Is the Keto Diet Okay for People With Diabetes?

2. Keto Can Put Stress on the Kidneys and May Give You Kidney Stones

Kidney stones are a well-noted potential side effect of the ketogenic diet. A systematic review of data from 2,795 people on keto diets found that 7.9 percent of the adults developed kidney stones.[3]

And while little firm evidence shows that short-term keto dieting affects kidney function, some studies link a long-term focus on increased intake of animal and saturated fats to albuminuria, a sign of kidney disease that means too much of a protein called albumin leaves the body in the urine.[4]

“If you’re going to do keto, there’s a better and a worse way to do it. Loading your plate with meats, and especially processed meats, may increase your risk of kidney stones and gout,” advises Yawitz. “High intake of animal proteins makes your urine more acidic and increases calcium and uric acid levels. This combination significantly increases the risk of developing kidney stones,” warns Yawitz.

Supplementing with potassium citrate may reduce the risk of kidney stones for some people, but it does not address all potential kidney concerns associated with the keto diet.[3]

TakeawayAdults on the keto diet who consume high levels of animal protein — especially processed foods — have a higher risk of developing kidney stones.

3. The Possibility of Low Blood Sugar Can Make Keto Risky for People With Diabetes

Keto dieting can be risky for some people with diabetes, especially those with type 1 diabetes. Low-carb intake can lead to a dangerous condition called diabetic ketoacidosis, as well as extremely low blood sugar, or hypoglycemia. Plus, the research is mixed and generally based on individual case studies and observation, meaning it’s hard for doctors to apply their findings widely. Further research is needed into whether keto dieting is recommended for people with type 1 diabetes.[5]

The same goes for people with type 2 diabetes. While following the keto diet to manage type 2 diabetes can support better blood sugar and weight management, as well as less dependence on medications, it still risks hypoglycemic episodes, especially for those on insulin. It can also lead to nutritional deficiencies and constipation.[6]

Plus, the keto diet omits certain food groups known to benefit those with this disease. For example, research suggests that eating 150 g of whole grains daily can help control blood sugar and HbA1C and improve insulin resistance.[7] However, whole grains are off-limits on the ketogenic diet.[8]

If you have diabetes and really want to try keto, speak to your diabetes specialist along with a dietitian about the risks and benefits for your specific situation.[5]

TakeawayWhile the ketogenic diet may help control blood sugar in some people with diabetes, it may also increase the risk of hypoglycemia, particularly in those with type 1 diabetes. It’s important to talk with your doctor about the benefits and risks of the diet before getting started.

4. Because It’s Hard to Follow, Keto Can Lead to Yo-Yo Dieting

The keto diet can be extremely regimented and very difficult for many people to stick to. As a demonstration, a single baked potato provides 33.7 g of carbs, and one slice of white bread provides 12.4 g of carbs.[9][10] That’s a combined 46.1 g of carbs. With a typical keto diet allowing around that amount daily, you get very little wiggle room for any other food with carbs if you eat a single potato and one slice of white bread in a day. Additionally, some carb sources are not so obvious, including legumes and certain dairy products, like full-fat milk.[11]

Sticking with such a restrictive diet long-term can be difficult, leaving you open to weight regain and the cycle of yo-yo dieting. “Chronic yo-yo dieting appears to increase abdominal fat accumulation and diabetes risk,” notes Clark.

“Studies have shown that the ability to stick to a diet is more important for long-term success than the type of diet that’s followed,” says Yawitz.[12] “Keto is incredibly restrictive and is particularly tough for those who have frequent social engagements or are prone to carb cravings.”

In contrast, the Mediterranean diet allows you to eat carbs, including as many fruits and veggies as you want, along with whole grains. Not to mention, the Mediterranean diet has been linked to a number of other health benefits, including a lower risk of Alzheimer’s and Parkinson’s disease, certain types of cancer, and heart disease.[13]

TakeawayStudies have shown that people are unlikely to adhere to ketogenic diets that are not medically supervised. Additionally, restrictive diets like keto can lead to yo-yo dieting, which may increase fat accumulation and diabetes risk over time.

5. The Ketogenic Diet Can Lead to Dehydration and a Loss of Electrolytes

Dehydration is a possible side effect of the keto diet because you’ll have less glycogen available. Glucose is the sugar in your bloodstream that holds water, meaning you may lose fluids and electrolytes while cutting out carbs. This can put extra pressure on your kidneys.[8]

“Suddenly and drastically reducing carbohydrates sets your body up for a double whammy of sorts,” says Yawitz. “The brain’s favorite fuel is glucose, which is most easily created from carbohydrates. In very low-carb diets, the brain has to adjust to using ketones from digested fats for energy. To add to this discomfort, your kidneys release more electrolytes as insulin levels fall.”

Additionally, your total body water decreases as carbohydrates become depleted on a keto diet, notes Clark. The result? What’s known as the keto flu, which can cause constipation, nausea, headache, fatigue, irritability, cramps, and other symptoms.

Don’t fret: Many of these symptoms last only a few days or weeks. Make sure to drink plenty of fluids to help your body cope with these symptoms. And call your doctor if symptoms — especially nausea — are prolonged, advises Yawitz.

Takeaway

Dehydration and low electrolytes are possible side effects of keto, so stay hydrated. Symptoms of keto flu tend to get better without treatment, but speak to a doctor if they don’t.

6. Because Keto Severely Limits Carbs, You May Develop Nutrient Deficiencies

Many of the carbs people eat come from fruits, vegetables, nuts, seeds, and whole grains.[14] Restricting your intake of those foods for the keto diet can have a knock-on effect on the nutrients you get too. You might not consume enough essential vitamins, minerals, and plant compounds.[15]

Keto diets might also be low in fiber, given how much of your fiber you get from fruits, vegetables, and whole grains. As fiber is a vital nutrient for gut health and regular pooping, you might need to supplement it, although this may work against the intended effects of a keto diet.[16]

Low-carb diets have a high risk of being low in the following nutrients:[16]

• Vitamin A
• Vitamins B1, B6, and B9
• Calcium
• Vitamin E
• Magnesium
• Iron
• Zinc
• Potassium, which may result from increased urination[17]

Multivitamin supplements can offset some of these deficiencies, but they don’t often provide plant compounds like flavonones and anthocyanins that you can only get from fruits and vegetables.

Takeaway

Low fruit and veggie intake while on keto can mean you don’t get enough fiber, potassium, or other nutrients. Taking a multivitamin and sticking to low-carb fruits and vegetables like avocados and spinach can help you top up your nutrition while staying within your carb limit.

7. Digestive Problems Are Common on Keto

Keto dieting can lead to constipation and diarrhea.[15] “Many of the richest sources of fiber, like beans, fruit, and whole grains, are restricted on the ketogenic diet,” says Clark. “As a result, ketogenic eaters miss out on the benefits of a fiber-rich diet, such as regular laxation and microbiome support. The microbiome has been implicated in everything from immune function to mental health.”

Indeed, in a year-long study, the authors noted constipation as a very common side effect in children who were put on ketogenic diets for epilepsy treatment.[18] Diarrhea was also among the most common adverse effects, and Yawitz notes that “some people have difficulty digesting large amounts of dietary fat, which can lead to greasy diarrhea.”

In people who don’t fully absorb fats, the fats travel to the colon. Here, they break down into fatty acids, which trigger fluid release by the colon, leading to watery poop.[19]

Other causes of diarrhea on the keto diet include processed low-carb foods like shakes and bars that may contain sugar alcohols. These sugar alcohols can ferment in the gut and cause gastrointestinal discomfort.[20]

Yawitz suggests limiting foods labeled “sugar-free” if you’re prone to gas or diarrhea when you eat them.

You may want to gradually adjust your carbs downward and your fats upward.

“Also build your diet around [naturally] high-fiber, low-carb foods like avocado and nonstarchy vegetables such as broccoli, cauliflower, and asparagus,” Yawitz says. Other keto-friendly foods that can help you get more fiber include chia seeds, almonds, and coconut.

Takeaway

Reduced fiber intake, processed low-carb foods, and increased fat intake can increase your risk of bowel changes on keto. To help prevent this, focus on naturally high-fiber, low-carb foods, and make diet changes gradually. Also, avoid processed foods labeled “low-carb” or “sugar-free” if diarrhea is a problem.

8. Your Period on Keto Might Undergo Some Changes

“Periods may become irregular or stop altogether on the keto diet,” says Yawitz. “This is more common in women who follow the diet long term and experience significant weight loss. The change is typically due to drops in key reproductive hormones, including gonadotropin-releasing hormone, follicle-stimulating hormone, luteinizing hormone, estrogen, and progesterone.”

Long-term disruption of menstruation can bring on serious side effects, including low bone density. “This is because estrogen is very important to bone health,” says Yawitz. “Studies have also found that prolonged menstrual irregularity increases risk of cardiovascular disease, depression, anxiety, and sexual dysfunction. It’s important to contact your ob-gyn if your cycles become irregular or if you stop having periods.”[21]

However, females with polycystic ovary syndrome (PCOS) might find that the keto diet helps regulate their periods.

“For some women with PCOS, the ketogenic diet may actually help regulate hormones and improve menstrual cycles,” notes Yawitz. These findings align with more recent studies showing that the keto diet can significantly reduce the LH/FSH ratio, a key marker of hormonal imbalance in PCOS.[22]

“Researchers believe this effect may be due to improved insulin sensitivity, which helps normalize endocrine function,” suggests Yawitz. “That said, the authors emphasized the need for more research, especially on the diet’s long-term impact.”

TakeawayLong-term adherence to the keto diet, especially when coupled with significant weight loss, can lead to irregular periods or their discontinuation. Over time, disruption of menstruation can lead to health effects such as decreased bone density. However, studies also show that the keto diet may help to regulate and improve menstrual cycles in women with PCOS. More research on the subject of the keto diet’s impact on menstruation is necessary.

9. Keto Could Cause Your Blood Sodium to Dip

The keto diet can lead to low blood sodium.

“When you start the keto diet, you lose sodium and other electrolytes in the urine, due to reductions in insulin,” says Yawitz.[23] “This is a major contributor to symptoms of keto flu.”

Be sure to replenish sodium through your diet, especially if you exercise or sweat a lot. “This can help ward off more serious side effects of long-term sodium deficiencies,” says Yawitz. These include lethargy and confusion, and in extreme cases, seizures, coma, and death.[24]

Takeaway

Your body gets rid of more sodium on the keto diet, so it’s a good idea to replace the lost sodium via the foods you eat.

10. Keto May Lead to High Cholesterol and an Increased Risk of Heart Disease

The ketogenic diet doesn’t put a cap on saturated fat, which has been associated with adverse health effects. However, Yawitz recommends choosing high-quality, unsaturated fats from plants instead.

“There’s a big difference nutritionally between bacon and almonds,” says Yawitz. “The ketogenic diet doesn’t typically put a limit on saturated fat, but the quality of fat counts. As much as possible, people set on keto should emphasize plant-based, unsaturated fats like nuts, seeds, olive oil, and avocado, which have even been shown to protect the heart.”

Yawitz advises that this is especially important in light of research linking low-carb, high-fat diets to an increased risk of heart disease.

One large study found that people who reported eating a diet in which carbs made up less than 25 percent of total daily energy, and fat more than 45 percent, had higher levels of low-density lipoprotein cholesterol (LDL, or “bad”) cholesterol and apoB — both markers tied to heart disease.[25]

In fact, cases of dangerously high cholesterol were nearly twice as common in people on a low-carb, high-fat diet, compared with those following a standard diet. The cardiovascular risks appeared to be even greater among those with already elevated LDL cholesterol levels.

If you have high cholesterol or other risk factors for heart disease, you should speak with your doctor before beginning the keto diet. This is because the diet may — but doesn’t have to — include large amounts of saturated fat.

Another possible impact of the keto diet on heart health is for people who take the anti-clotting drug warfarin to manage a heart condition. To balance the nutrient deficiency that can occur after ditching many high-carb fruits and vegetables, you might suddenly end up eating much more leafy greens than before. However, these provide a considerable amount of vitamin K, which can interfere with how warfarin works if you sharply increase your leafy green intake. While this may not necessarily be a bad thing, let your doctor know if that’s the case.

If a person with diabetes takes a drug called SGLT-2 inhibitors to treat heart failure, starting the keto diet may trigger a dangerous condition called normoglycemic acidosis, as well as reduce the effectiveness of the medications.[26]

Takeaway

Studies are conflicted on how the keto diet affects blood cholesterol, but some people have a risk of a rapid increase in “bad” cholesterol. Also, people taking certain medications to treat heart disease should speak to a doctor before trying the keto diet.

11. The Keto Diet May Weaken Your Bones

The keto diet may reduce the amount of calcium your body can absorb, increase the amount it excretes, and increase the amount that moves from the bones into the blood. As calcium is central to bone development, and you get it from your diet, studies have looked at whether these effects on calcium levels can impact bone health.[27]

Bone consistently breaks down, so that the body can reabsorb it in a process known as bone metabolism. The bone metabolism of different populations responded to the keto diet in varying ways, according to one review.[28]

“Research on the keto diet’s impact on bone health remains somewhat mixed. Some studies suggest that certain groups, such as children with epilepsy or women who lose more than 10 percent of their body weight, may be more vulnerable to bone loss while on the diet,” says Yawitz. “However, a 2023 systematic review of seven studies found no significant changes in bone density among participants following a keto diet.”[28]

Yawitz warns that, overall, larger and longer-term studies are needed to better understand the potential impact of the keto diet on bone health. Although Clark agrees that high-quality research doesn’t fully back the keto diet’s effects on bone health, she does advise that the keto diet excludes some calcium-rich foods, which may contribute to calcium deficiency.

“To overcome this, I recommend incorporating low-carb, calcium-rich foods like tofu, kale, sunflower seeds, and collard greens to support bone health on the keto diet,” advises Clark. “Regular weight-bearing exercise and adequate vitamin D are also important for promoting bone health.”

Takeaway

Most adults don’t need to worry about bone health on the keto diet, and it has even improved bone health for some. However, specific populations, including children and women, have shown signs of bone metabolism issues in previous studies.

12. Keto Can Be Unsafe if You Have Certain Medical Conditions

Clark suggests that the keto diet can be safe on a short-term basis. “However, it needs to be carefully managed to ensure nutrient adequacy and minimize adverse side effects, and is contraindicated for some groups,” adds Clark.

You’ve already learned about the potential dangers of keto for people with diabetes, kidney problems, and those taking certain heart disease medications. However, other health conditions may also make the keto diet unsafe for some people, including:[15]

• Pancreatitis, which can affect the production of enzymes that help you digest proteins and fats[29]
• Liver failure, since a keto diet may worsen liver damage[30]
• Rare disorders of ketogenesis, like primary carnitine deficiency, carnitine palmitoyltransferase deficiency, pyruvate kinase deficiency, or carnitine translocase deficiency, which make it much harder than usual for the body to use fat deposits for energy[30]
• Porphyrias (a rare group of disorders caused by a buildup of porphyrins in the body), since carbohydrates are necessary to prevent the condition from coming back; porphyrins are responsible for the production of hemoglobin in red blood cells[30][31]

Speak to a clinician if you’re considering the keto diet while living with any of these health conditions.

Yawitz also suggests avoiding keto dieting if you’re pregnant or breastfeeding. “Pregnant women should avoid it due to potential risks, including a possible link to neural tube defects, and because weight loss diets during pregnancy are not recommended,” she cautions. “There’s also limited research on keto’s safety during breastfeeding, so it’s best to steer clear unless prescribed by a doctor for medical reasons.”

TakeawayThe keto diet can be unsafe for people with certain health conditions. Always speak with your doctor before starting a restrictive diet like keto.

Is the Keto Diet Safe?

Yawitz says that although the diet carries some significant risks, it can be safe for managing certain conditions under the direct supervision of a medical professional.

“The ketogenic diet has long been used to manage certain medical conditions, such as epilepsy, particularly when the health risks of the condition outweigh those of the diet itself,” Yawitz advises. “In these cases, patients typically follow the diet under close medical supervision, often working with both a physician and a registered dietitian to ensure they meet their nutritional needs.”

When followed properly and under medical guidance, the keto diet can be a safe and effective option for some individuals. However, Yawitz cautions that many people adopt the diet for weight loss without professional oversight, even though safer, more sustainable approaches are available.

The Takeaway

• If you’re thinking about trying the ketogenic diet, run it by your doctor first, whether or not you have preexisting health conditions. It’s also helpful to consult a registered dietitian nutritionist who can help you create a meal plan you can stick to.
• People with kidney disease or a history of disordered eating should avoid the diet, and people with diabetes may want to avoid it as well. If you have risk factors for heart disease, you’ll want to speak with your doctor before considering the diet.
• Women who are pregnant or lactating should talk to their healthcare practitioner before trying any new diet, including keto.

EDITORIAL SOURCES

Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.

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