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.”

• 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.”

Takeaway

Some 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.

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

“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.

Takeaway

Adults 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

Takeaway

While 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

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.

Takeaway

Studies 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

“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

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

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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

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.”

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

“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.”

Takeaway

Long-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.

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.

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.

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

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.

• Pancreatitis, which can affect the production of enzymes that help you digest proteins and fats

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• Liver failure, since a keto diet may worsen liver damage

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• 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

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• 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

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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.”

Takeaway

The 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.