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 (1Trusted Source).
However, the diet also carries risks you should be aware of.
Here are 7 keto diet dangers to know about.
1. 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 (2Trusted Source).
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 (3Trusted Source).
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 (3Trusted Source).
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. 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 excretion of calcium in your urine (4Trusted Source, 5Trusted Source).
Some studies also suggest that the keto diet reduces the amount of citrate that’s 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 (5Trusted Source).
Additionally, people with chronic kidney disease (CKD) should avoid keto, as weakened kidneys may be unable to remove the acid buildup in your blood that results from these animal foods. This can lead to a state of acidosis, which can worsen the progression of CKD.
What’s more, lower protein diets are often recommended for individuals with CKD, while the keto diet is moderate to high in protein (6Trusted Source).
SUMMARY
Eating a lot of 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. May cause digestive issues and changes in gut bacteria
Since the keto diet restricts carbs, it can be difficult to meet your daily fiber needs.
Some of the richest sources of fiber, such as high carb fruits, starchy vegetables, whole grains, and beans, are eliminated on 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 (7Trusted Source).
What’s more, fiber feeds the beneficial bacteria in your gut. Having a healthy gut may help boost immunity, improve mental health, and decrease inflammation (8Trusted Source).
A low carb diet that’s lacking in fiber, such as keto, may negatively affect your gut bacteria — although current research on this topic is mixed (8Trusted Source).
Some keto-friendly foods that are high in fiber 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 negative effects on gut health.
4. May lead to nutrient deficiencies
Since the keto diet restricts several foods, especially nutrient-dense fruits, whole grains, and legumes, it may fail to provide recommended amounts of vitamins and minerals.
In particular, some studies suggest that the keto diet doesn’t provide enough calcium, vitamin D, magnesium, and phosphorus (9Trusted Source).
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 (10Trusted Source).
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 (11Trusted Source).
Keep in mind that the nutritional adequacy of this diet depends on the specific foods that 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. 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 levels of hemoglobin A1c, a measure of average blood sugar levels (12Trusted Source, 13Trusted Source, 14Trusted Source).
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 2 years found that the median number of low blood sugar events was close to 1 per day (15Trusted Source).
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.
Theoretically, this could also happen to individuals with type 2 diabetes who are taking insulin medications.
6. May damage bone health
The keto diet is also associated with impaired bone health.
Several studies in animals 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 (16Trusted Source, 17Trusted Source).
In fact, 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 the diet (18Trusted Source).
Another study in 30 elite walkers determined that those who followed keto for 3.5 weeks had significantly higher levels of blood markers for bone breakdown, compared with those who ate a diet higher in carbs (19).
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. 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 that focus on animal foods may lead to poor health outcomes, while diets that emphasize vegetable sources of fats and proteins provide benefits (20Trusted Source, 21Trusted Source).
A long-term observational study in over 130,000 adults linked animal-based low carb diets to higher rates of death from heart disease, cancer, and all causes (21Trusted Source).
On the other hand, vegetable-based low carb diets were associated with a lower rate of death from heart disease and all causes (21Trusted Source).
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 (22Trusted Source).
Yet, more substantial studies are needed.
SUMMARY
While research is mixed, some evidence suggests that low carb diets that focus on animal foods may lead to higher death rates from heart disease, cancer, and all causes.
The bottom line
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.
Last medically reviewed on March 25, 2020
How we reviewed this article:
HISTORY
Medically reviewed by Kathy W. Warwick, R.D., CDE, Nutrition — By Lizzie Streit, MS, RDN, LD on March 25, 2020