You may have heard of friends and family trying the keto diet. It's a strict, high-fat diet with varying levels of protein and generally very low levels of carbohydrate.
The keto diet was first used as a treatment for pediatric drug-resistant epilepsy to reduce seizures in the 1920s. It's still used for help prevent seizures in the U.S. when medications alone aren't enough. However, it can also help you lose weight if you stick with the plan long term. It may also provide other health benefits that come with weight loss.
If you're wondering if the keto diet is right for you, our registered dietitians explain the eating plan and its pros and cons.
What is the keto diet?
The ketogenic or keto diet includes eating high-fat, low-carbohydrate foods to reach ketosis. In ketosis, the body uses fat for fuel, instead of sugar (glucose). This produces acids known as ketones.
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What are the basic rules of the keto diet?
There are several different styles of keto diets. Each calls for eating different amounts of fat, protein and carbs in a day.
Classic Keto Diet
This is the original and best-studied of the different diet strategies. It's recommended that you work with a registered dietitian as it's the strictest, most difficult diet to follow.
- This diet is very in high fat, very low in carbs and relatively low in protein.
- All foods must be weighed on a scale to achieve a relative weight distribution of 4 grams of fat for every 1 gram of combined protein and carb eaten throughout the day. In other words, you will likely need to avoid all carb-rich foods (like pasta, potatoes, fruit, etc.). Also, for every serving of protein-rich food, you need four servings of a fatty food (heavy cream, avocado, olive oil, full fat cheese, etc.).
- A typical meal might look like half an avocado with a small piece of salmon cooked in a lot of olive oil with a side salad. It will all be topped with a cream sauce made with heavy cream and cheese. You would need to eat all of the oils and creams.
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Modified Keto Diet
This is a modified form of the classic keto diet, allowing slightly more protein and carbs.
- This diet generally still requires a scale for weighing food. It's defined by a ratio closer to 3 grams of fat for every 1 gram of combined protein and carb (generally with a focus on more protein than carbs). In other words, you'll still avoid most carb-rich foods except for maybe one or two servings per day. For every serving of a protein- or carb-rich food, you'll need three servings of very high-fat food.
Modified Atkins Diet
This diet is the more user-friendly keto diet and likely the most popular. It's a high-fat, low-carb diet where you can choose to eat as much protein as you like.
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What foods can you eat on the keto diet?
Here's a list of foods you should eat on the keto diet:
- Dairy and unsweetened dairy alternatives such as full fat cheese, plain full fat yogurt, cottage cheese and unsweetened plant-based milk.
- Low-carb vegetables like leafy greens, peppers and broccoli.
- Other plant-based foods including nuts, seeds and avocados.
- Oils and fats like olive and coconut oils, as well as whole olives and avocados.
- Moderate amounts of high protein foods such as seafood, meat, poultry and eggs.
- Sometimes small amounts of berries can be eaten.
These diets generally avoid all starchy foods (pasta, rice, potatoes, bread, corn, peas, beans and legumes). Desserts and any other high-carb foods are also not part of the diet. Fruits can sometimes be included if they are high in fiber, such as raspberries.
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What are the pros and cons of the keto diet?
Here are some benefits of the keto diet for your health:
- Helps with weight loss: Research suggests that the keto diet helps people cut calories because the diet doesn't include many foods that people are likely to overeat. However, it can be difficult to transition off of the keto diet without regaining weight. That's because people typically start eating more high-carb foods. Some data supports going from the keto diet to the Mediterranean diet or MIND diet may help maintain healthier weight once weight loss goals are achieved.
- Benefits people with type 2 diabetes: Some people with diabetes find that reducing their carb intake can help with blood sugar and medication management.
- Epilepsy management: Data shows that the keto diet can have positive effects for people with epilepsy in helping with seizure management.
Some cons of the keto diet include:
- Can lead to nutrient deficiencies: The keto diet is very low in carbs which means you can't eat many fruits and vegetables. That can lead to low levels of vitamins A, E and B6, as well as folate, calcium, magnesium, and potassium.
- Possible negative effects on heart health: There are mixed results in studies that examine the specific effects of the keto diet on heart health. This is likely because much of it depends on individual food choices. Generally, foods high in saturated fat and a high-fat diet have negative consequences on heart health factors such as your lipid panel.
- Constipation and other gastrointestinal (GI) troubles: Constipation is likely the greatest long-term complication of the keto diet because of a low fiber intake. Fiber is a form of carb that is digested not by our human cells, but by the microbes in our gut. Any high-fiber foods (like beans, whole grains, and certain fruits) are also high in carbs, which is not typically part of the keto diet. An ongoing diet that is low in fiber (including the typical Western diet) may leave you at higher risk for certain cancers like colon cancer.
Learn tips for diarrhea and constipation relief
What are some side effects of the keto diet?
Before starting the keto diet, you should get a blood test to look at your lipids. You should then take another blood test after three to six months on the keto diet.
Some people will actually find that their high-density lipoproteins (HDL) – the good cholesterol – go up and their triglycerides go down. But some people won't see a positive shift in those markers and may find their low-density lipoproteins (LDL) – the bad cholesterol – go up to unhealthy levels.
There can be issues with bone health when people switch to low-carb keto diets. Researchers see that markers for bone breakdown are higher and markers for bone building are lower. This is a common side effect in kids who are fed the keto diet to treat epilepsy.
Also, when people start the keto diet, they go through the keto flu. Keto flu symptoms appear a few days after starting the diet. This eventually goes away once your body adjusts to your eating changes. People on the keto diet also tend to lose more salt/sodium than those on a higher carb diet and may need more salt than the average person.
Most people following a strict keto diet should take a multivitamin with minerals to ensure they're meeting those vitamin and mineral needs. The diet itself generally is not enough.
Does the keto diet improve brain functions, such as learning and memory?
The keto diet can show positive results for helping the brain. It's been used for years to treat epilepsy. Researchers are looking to see if the keto diet can help treat age-related brain decline and potentially Alzheimer's disease. There are mixed results on if the keto diet can help those with neuromuscular diseases such as Parkinson's disease.
There are many different theories as to why the keto diet may be beneficial for brain health. These include the direct benefit from the presence of ketone bodies, especially one called beta hydroxybutyrate. Other theories suggest a possible benefit in changing the microbiome for certain conditions, like epilepsy.
Is the keto diet good for athletes?
Our bodies use multiple energy systems to exercise. The type of energy system used depends on the exercise intensity and duration. At lower intensities, our bodies use a mix of both burning fat and carbs for fuel. When we transition to high intensities (such as a scheduled workout), our bodies start to rely primarily on carbs.
Most studies involving endurance athletes showed the keto diet hurts their performance. The keto diet has also been shown to increase losses of lean tissue when compared to a higher-carb diet.
The bottom line is that the keto diet impairs athletic performance and are not recommended for athletes because they restrict carbs.
Read about how the keto diet can improve aging muscles and brain health
What other eating plans might be right for me?
If the keto diet doesn't sound like the right fit for you, you may want to consider one of these other eating plans.
Intermittent fasting
This weight-loss trend dates back to ancient times where fasting helps heal the body. The idea behind intermittent fasting is that by restricting food, our bodies will more quickly tap into fat stores for energy. It's not necessarily an eating plan that outlines what types of foods to eat but instead focuses on when to eat. There are a couple of different ways to implement intermittent fasting.
Explore intermittent fasting benefits and how it works
Mediterranean diet
This way of eating focuses on whole, plant-based foods and healthy fat. The Mediterranean diet's methods are scientifically proven to reduce the risk of chronic conditions like heart disease.
Learn more about the Mediterranean diet
MIND Diet
Short for "Mediterranean-DASH Intervention for Neurodegenerative Delay," this diet is similar to the Mediterranean diet, but with stricter requirements for what you can eat. It emphasizes eating more vegetables, fruits (specifically berries), high-fiber foods, beans, nuts, seafood, poultry and olive oil. The MIND diet can possibly help reduce the cognitive decline associated with aging. It also may help slow disease progression for conditions like Parkinson's disease.
Check out healthy eating recipes from our Good Food is Good Medicine blog
This blog was medically reviewed by our registered dietitians Erin Nella, Angela Salas and Kathryn Ward.
