The ketogenic diet is a low-carb, high-fat diet commonly used for weight loss.
Restricting carbs and increasing fat intake can lead to ketosis, a metabolic state in which your body relies primarily on fat for energy instead of carbs.
However, the diet also carries risks you should be aware of.
Here are seven keto diet dangers to know about.
1. The keto diet may lead to the keto flu
Carb intake on the keto diet is typically limited to fewer than 50 grams per day, which can come as a shock to your body.
As your body depletes its carb stores and switches to using ketones and fat for fuel at the start of this eating pattern, you may experience flu-like symptoms.
These include headaches, dizziness, fatigue, nausea, and constipation — due in part to dehydration and electrolyte imbalances that happen as your body adjusts to ketosis.
While most people who experience the keto flu feel better within a few weeks, it’s important to monitor these symptoms throughout the diet, stay hydrated, and eat foods rich in sodium, potassium, and other electrolytes.
Summary: As your body adjusts to using ketones and fats as its primary energy source, you may experience flu-like symptoms at the beginning of the keto diet.
2. The keto diet may stress your kidneys
High-fat animal foods, such as eggs, meat, and cheese, are staples of the keto diet because they don’t contain carbs. If you eat a lot of these foods, you may have a higher risk of kidney stones.
That’s because a high intake of animal foods can cause your blood and urine to become more acidic, leading to increased calcium excretion in your urine.
Some studies also suggest that the keto diet reduces the amount of citrate released in your urine. Given that citrate can bind to calcium and prevent the formation of kidney stones, reduced levels of it may also raise your risk of developing them.
Additionally, people with chronic kidney disease (CKD) should avoid keto, as weakened kidneys may be unable to remove the acid buildup in your blood from these animal foods. This can lead to a state of acidosis, which can worsen the progression of CKD.
Moreover, lower protein diets are often recommended for individuals with CKD, while the keto diet is moderate to high in protein.
Summary: Eating many animal foods on the keto diet can lead to more acidic urine and a higher risk of kidney stones. This acidic state can also worsen the progression of chronic kidney disease.
3. The keto diet may cause digestive issues and changes in gut bacteria
Since the keto diet restricts carbs, meeting your daily fiber needs can be difficult.
Some of the richest sources of fiber, such as high-carb fruits, starchy vegetables, whole grains, and beans, are eliminated from the diet because they provide too many carbs.
As a result, the keto diet can lead to digestive discomfort and constipation.
A 10-year study in children with epilepsy on the ketogenic diet found that 65% reported constipation as a common side effect.
What’s more, fiber feeds the beneficial bacteria in your gut. A healthy gut may help boost immunity, improve mental health, and decrease inflammation.
A low-carb diet lacking in fiber, such as keto, may negatively affect your gut bacteria — although current research on this topic is mixed.
Some fiber-rich keto-friendly foods include flax seeds, chia seeds, coconut, broccoli, cauliflower, and leafy greens.
Summary: Due to its carb restrictions, the keto diet is often low in fiber. This may trigger constipation and adverse effects on gut health.
4. The keto diet may lead to nutrient deficiencies
Since the keto diet restricts several foods, incredibly nutrient-dense fruits, whole grains, and legumes, it may fail to provide recommended amounts of vitamins and minerals.
Suggested read: The carnivore diet: Benefits, downsides, and sample menu
In particular, some studies suggest that the keto diet doesn’t provide enough calcium, vitamin D, magnesium, and phosphorus.
A study that evaluated the nutrient composition of common diets revealed that very low-carb eating patterns like Atkins, which is similar to keto, provided sufficient amounts for only 12 of the 27 vitamins and minerals your body needs to obtain from food.
Over time, this may lead to nutrient deficiencies.
Notably, guidelines for clinicians who manage people on a very low-calorie keto diet for weight loss recommend supplementing with potassium, sodium, magnesium, calcium, omega-3 fatty acids, psyllium fiber, and vitamins B, C, and E.
Keep in mind that the nutritional adequacy of this diet depends on the specific foods you eat. A diet rich in healthy low-carb foods, such as avocados, nuts, and non-starchy vegetables, provides more nutrients than processed meats and keto treats.
Summary: Some studies suggest that keto provides insufficient vitamins and minerals, including potassium and magnesium. Over time, this could lead to nutrient deficiencies.
5. The keto diet may cause dangerously low blood sugar
Low-carb diets like keto have been shown to help manage blood sugar levels in people with diabetes.
In particular, some studies suggest that keto may help decrease hemoglobin A1c, a measure of average blood sugar levels.
However, individuals with type 1 diabetes may be at a high risk of more episodes of low blood sugar (hypoglycemia), which is marked by confusion, shakiness, fatigue, and sweating. Hypoglycemia can lead to coma and death if not treated.
A study in 11 adults with type 1 diabetes who followed a ketogenic diet for over two years found that the median number of low blood sugar events was close to 1 per day.
Individuals with type 1 diabetes typically experience low blood sugar if they are taking too much insulin and not consuming enough carbs. Thus, a low-carb keto diet may increase the risk.
Suggested read: 9 best keto supplements to take
Theoretically, this could also happen to individuals with type 2 diabetes who take insulin medications.
Summary: Although low-carb diets have been shown to improve blood sugar control in people with diabetes, they may also increase your risk of low blood sugar events — especially if you have type 1 diabetes.
6. The keto diet may damage bone health
The keto diet is also associated with impaired bone health.
Several animal studies link the keto diet to decreased bone strength, likely due to losses in bone mineral density, which may occur as your body adapts to ketosis.
A 6-month study in 29 children with epilepsy on the keto diet discovered that 68% had a lower bone mineral density score after going on a diet.
Another study in 30 elite walkers determined that those who followed keto for 3.5 weeks had significantly higher blood markers for bone breakdown levels than those who ate a diet higher in carbs.
All the same, more extensive research is warranted.
Summary: The keto diet may reduce your bone mineral density and trigger bone breakdown over time, though further studies are needed.
7. The keto diet may increase your risk of chronic diseases and early death
The ketogenic diet’s effect on your risk of chronic illness, such as heart disease or cancer, is hotly debated and not entirely understood.
Some evidence suggests that high fat, low carb diets focusing on animal foods may lead to poor health outcomes, while diets emphasizing vegetable sources of fats and proteins provide benefits.
A long-term observational study in over 130,000 adults linked animal-based low-carb diets to higher death rates from heart disease, cancer, and all causes.
On the other hand, vegetable-based low-carb diets were associated with a lower death rate from heart disease and all causes.
Another study in over 15,000 adults found similar results but tied both low and high-carb diets to a greater all-cause death rate, compared with moderate-carb diets in which carbs comprised 50–55% of total daily calories.
Yet, more substantial studies are needed.
Summary: While research is mixed, some evidence suggests that low-carb diets focusing on animal foods may lead to higher death rates from heart disease, cancer, and all causes.
While the keto diet is linked to weight loss and other health benefits in the short term, it may lead to nutrient deficiencies, digestive issues, poor bone health, and other problems over time.
Due to these risks, individuals with kidney disease, diabetes, heart or bone ailments, or other medical conditions should speak to their healthcare provider before trying the keto diet.
You may also want to consult a dietitian to plan balanced meals and monitor your nutrient levels while on this diet to help minimize the risks of complications and nutrient deficiencies.