While the keto diet may not be as popular as it once was, it remains firmly in the mainstream, appearing on the list of the top 15 most common eating patterns of 2024, according to an International Food Information Council survey of 3,000 adults. Much has been written about the pros and cons of the keto diet, but this divisive eating pattern continues to inspire strong reactions. Proponents claim it has transformed their health, while critics warn that the extremely low-carb, high-fat diet could lead to long-term health issues. So, who’s right? Is the keto diet safe?
The reality is that, despite its popularity, the keto diet is often misunderstood—even by those who claim to follow it. It involves more than simply cutting out bread and calling it a day. Contrary to popular belief, it isn’t an all-you-can-eat bacon buffet either. Overall, the keto diet requires a significant lifestyle change that alters how your body produces energy. Most importantly, while it may offer some benefits for specific groups, it is not suitable for everyone and shouldn’t be marketed as a quick and easy weight loss solution.
To clarify how this extreme eating plan functions, we consulted two dieticians and a cardiologist to discuss the keto diet, its potential risks, and who—if anyone—it is best suited for.
Experts Featured in This Article
- Abigail Collen, MS, RD, CDN: Registered dietician and nutritionist at the Mount Sinai Health System.
- Gabrielle Gambino: Senior clinical dietitian of Advanced Heart Failure Service at NewYork-Presbyterian.
- Karen Aspry, MD, MS, FNLA, FACC: Cardiologist with the Cardiovascular Institute, certified lipidologist, and co-chair of the American College of Cardiology Prevention Council, Nutrition, and Lifestyle Workgroup.
What Is the Keto Diet?
In simple terms, the ketogenic (keto) diet is a highly restrictive, high-fat, low-carb eating pattern. A typical macronutrient ratio on the keto diet consists of about 70% fat, 15-20% protein, and just 5-10% carbohydrates. This means carb intake can be as low as 20-50 grams per day on a standard 2,000-calorie diet. High-fat foods such as meat, eggs, butter, cheese, avocado, oils, and nuts are commonly consumed on the keto diet.
“Keto is a low-carb diet that shifts the way the body uses energy,” explains Abigail Collen, MS, RD, CDN. The diet forces the body to rely on fat rather than carbohydrates for energy. “When there’s not enough sugar in the body from carbs, it becomes reliant on other types of energy created from the breakdown of fats and fatty acids,” she adds.
In essence, the human body typically uses carbohydrates for energy, breaking them down into glucose (or blood sugar), which is then absorbed into the bloodstream for fuel. When carbs are limited, the body produces ketone bodies from fat, which serve as an energy source—a process known as ketosis.
The keto diet was initially implemented in the 1920s to improve epilepsy symptoms and reduce seizures. It is still utilized today for this purpose. The theory is that by shifting the energy source to ketone bodies, the way cells metabolize energy is altered, which may decrease brain excitability and remove metabolites linked to seizure activity. Although it appears effective, more research is needed to fully understand the mechanisms involved.
It’s Not Your Typical Low-Carb Diet
Many people underestimate the extent of carbohydrate restriction required to achieve true ketosis. “A lot of people think they are on a keto diet when it’s actually more accurately classified as a low-carb diet,” notes Karen Aspry, MD, MS, FNLA, FACC. “To really enter ketosis, there has to be a very low carb amount and a very low protein amount.”
On the keto diet, daily protein intake is limited to just 1.2 to 1.5 grams per kilogram of body weight. Consuming more protein can inhibit ketosis. Aspry adds that some individuals may claim to follow the diet while eating high-protein foods, which could prevent them from achieving ketosis.
It’s also important to mention that the state of ketosis can lead to unpleasant symptoms, commonly referred to as the “keto flu,” which may include nausea and headache.
Is the Keto Diet Safe?
The keto diet may be safe for short-term use for the average healthy adult, but it is not suitable for everyone.
“There are risks, particularly with long-term adherence to a high-fat diet,” warns Gambino. “This eating pattern may increase the risk of developing or exacerbating cardiovascular diseases, liver issues, kidney stones, and nutritional deficiencies if not properly followed or if the individual is genetically predisposed to these conditions.”
Certain groups should particularly avoid the keto diet, including:
- Individuals with liver, thyroid, pancreas, or kidney issues.
- Those who have had their gallbladder removed (the organ that helps break down fat).
- People with type I diabetes, who are at greater risk for ketoacidosis—a dangerous condition caused by low glucose levels and altered acid-base balance.
- Athletes engaged in endurance sports, as the diet may not provide sufficient energy and could lead to dangerously low blood sugar levels during exercise.
- Pregnant individuals, since important nutrients like folic acid, often found in fortified grains, may be excluded from the keto diet.
What Are the Risks of the Keto Diet?
According to our experts, here are the most notable risks associated with the keto diet’s low-carb, high-fat eating pattern:
It Goes Against Standard Guidelines for Healthy Eating
“The keto diet is inherently unbalanced when compared to the standard guidelines for healthy eating,” explains Gambino. “Keto meal plans typically feature a very high percentage of dietary fat. People can easily overindulge in animal-based saturated fats, processed foods, and sodium-laden items while staying within the keto macronutrient guidelines.”
The keto diet diverges significantly from the Dietary Guidelines for Americans (DGA), which recommend limiting saturated fat to less than 10% of daily calories and keeping sodium intake below 2,300 mg.
“Increased dietary fat intake, combined with decreased consumption of whole grains, fruits, and vegetables, may elevate the risk of developing kidney stones, liver issues, and heart diseases,” Gambino notes. It could also heighten the likelihood of nutritional deficiencies.
It Can Hurt Your Gut Health
Fiber is crucial for gut health, and the keto diet’s restriction on foods like beans, lentils, and starchy vegetables makes it difficult to obtain adequate fiber.
“Nutrition science supports plant-rich and fiber-rich diets in reducing cardiometabolic diseases and mortality from all causes,” explains Dr. Aspry. “To maintain gut health, it’s essential to consume fiber-rich, phytonutrient-rich foods.”
The elimination of whole grains, which are important for gut health, is another issue with the keto diet. “Whole grains significantly reduce inflammation and promote gut health,” Dr. Aspry states. “I tell patients to consider them as scrubbing brushes for the gut, removing cholesterol, toxins, and bacterial overgrowth.”
It Increases Saturated Fat Intake and LDL Cholesterol Levels
Boosting fat intake isn’t inherently negative, provided that the sources are healthy, unsaturated fats—like those from olive oil, avocados, and nuts—that can help elevate “good” HDL cholesterol levels.
However, the keto diet often encourages high consumption of saturated fats from sources like butter, fatty cuts of meat, cheese, and processed meats, such as bacon. Dr. Aspry cautions that a rise in unhealthy saturated fats can increase “bad” LDL cholesterol levels, which has been linked to a higher risk of heart disease.
There is ongoing debate among experts regarding the connection between saturated fat, LDL cholesterol, and heart problems. However, Dr. Aspry emphasizes, “All data show that LDL levels are causally related to cardiovascular disease. Lowering LDL cholesterol reduces risk; raising it increases risk.”
She cites a large cohort study from the UK Biobank, which involved 100,000 participants on a low-carb, high-fat diet. The study found that these participants had significantly higher LDL cholesterol levels and more than double the risk of cardiovascular events. While this observational study does not prove causality, it underscores the need for further research into the long-term effects of the keto diet.
Gambino adds that other studies have indicated that cholesterol levels can worsen with long-term adherence to the keto diet, especially among those genetically predisposed to cholesterol management issues.
Are There Any Benefits to the Keto Diet?
One of the primary attractions of the keto diet is weight loss. It has developed a reputation for delivering rapid weight loss. While many people experience a significant drop in weight in the initial weeks, the reasons might be different than expected.
Collen explains, “The rapid weight loss many observe is largely due to water weight and, to some extent, dehydration. Carbohydrates are stored in the body with water. The keto diet depletes carbohydrate stores and the associated water.”
However, whether this weight loss is sustainable remains questionable. “While it may facilitate short-term weight loss, for many individuals, this diet is too difficult to maintain over the long haul,” Gambino notes. Once carbs are reintroduced into the diet, weight may return. This isn’t inherently negative—weight alone is not an accurate measure of health. However, if weight loss is a primary motivation for adopting the keto diet, it is crucial to be aware of this potential rebound.
If individuals still wish to pursue a ketogenic eating pattern, it’s essential to do so mindfully and with the support of a healthcare professional. They can assist in crafting a balanced plan that incorporates whole foods, adequate fiber, and sufficient vitamins and minerals.
Ultimately, the keto diet may offer benefits for specific populations, such as those with epilepsy, but the risks for the general population may outweigh the potential benefits. When it comes to weight management, many experts argue that sustainable lifestyle changes—not extreme eating patterns—are the most effective way to promote long-term health.
In Summary
The keto diet has garnered significant attention for its low-carb, high-fat approach to weight loss and health management. However, many misconceptions surround its practice, including its long-term safety and efficacy. While it may be beneficial for certain individuals—especially those with epilepsy or specific metabolic conditions—it poses considerable risks for others, particularly if followed improperly. A well-rounded diet focused on whole foods and proper nutrient intake is generally the best choice for overall health.
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