The ketogenic, or keto, diet has been steadily at the forefront of the health community for a while now. It’s one of the most popular dietary approaches for weight loss. The keto diet also offers a number of other purported benefits, which continue to draw in many followers looking to make changes to their health.
Understanding the basics of the keto diet, including certain variations, current evidence, as well as potential benefits and side effects, is key to success when considering this way of eating.
What is the keto diet?
While the keto diet gained mainstream popularity more recently, it actually has a much longer history than many people may realize. In fact, the keto diet was developed and used to manage symptoms of epilepsy, a seizure disorder, among children in the early 1920s. It was initially used by Russel Wilder, a physician at the Mayo Clinic for this purpose.1,2
The keto diet was designed to be a very low carbohydrate, high fat diet. In the context of helping kids with epilepsy, researchers knew that fasting was effective for improving severe seizures in a matter of days.
Of course, fasting is only appropriate and feasible for a short time, so the keto diet was developed as an alternative, more sustainable, eating approach that limited carbs.
Limiting the amount of carbs (which the body and brain use as a primary energy source), puts the body in a state called ketonemia. This is when there is a high level of ketones in the bloodstream. Ketonemia was found to be as effective in treating seizures as a total water fast. This prolonged state is called nutritional ketosis today.2
Today, some physicians still use the keto diet as part of the therapeutic plan for children and adults with severe epilepsy, though typically along with anti-seizure medications that have since been invented. But the keto diet is much more widely known as a weight loss diet among the general population.
For the purposes of weight loss and other potential health benefits, today’s mainstream keto diet is usually designed to be 55-60% fat, 30-35% protein, and 5-10% carbohydrates. Carbs are limited to 20-50 grams per day, depending on individual energy needs.2
Keto Diet Foods
While the keto diet is restrictive, there are many foods you can still eat. Here is a list of foods to eat:
- Red meat
- Pork and pork products
- Plain Greek yogurt
- Heavy cream
- Nuts and seeds
- Non-starchy vegetables
- Berries, in small quantities
- Shirataki noodles
- Coffee and tea
- Sugar substitutes
Foods to avoid on keto include:
- Grains: rice, oatmeal, quinoa
- Fruit and fruit juice
- Beans and legumes
- Starchy vegetables
- Sugar-sweetened foods and beverages
- Milk and sweetened yogurt
The primary goal for restricting these foods is to put the body into a metabolic state of ketosis, which is the underlying reason behind its weight loss successes.
What is ketosis?
The keto diet helps the body achieve a state of ketosis. This is when it switches from using carbs to using fats and ketone bodies as its primary fuel source.
When carb intake is reduced to under 50 grams per day, insulin secretion significantly decreases and the body enters a catabolic state. Glycogen stores are depleted, which forces the body to find an alternative source of energy or ketone bodies, through the processes of gluconeogenesis and ketogenesis.3
Ketogenesis is the production of ketone bodies. Specifically, these include acetoacetate, beta-hydroxybutyrate, and acetone, which are used to make ATP and replace glucose for energy.4
While in a metabolic state of ketosis, the body experiences low blood sugar and blood insulin levels. This reduces the storage of fat and glucose. Ketosis will be maintained for as long as dietary carb intake stays very low.
Ketosis vs. Ketoacidosis
Note that while both are metabolic conditions, ketosis is not the same as ketoacidosis. The latter is a dangerous state in which ketones become problematic when metabolism is abnormal. When ketones build up in high amounts in the blood, this leads to metabolic acidosis. If ketoacidosis is not treated and reversed, it can quickly become life-threatening.
Diabetic ketoacidosis (DKA) is a potentially deadly condition most commonly experienced among individuals with type 1 diabetes, but can occur in alcoholics and other individuals who undergo long periods without food. DKA is a combination of severe metabolic acidosis and insulin resistance, when there is no insulin to limit production of ketones or allow glucose into the cells for energy.
The difference is that in ketosis, metabolism is normal and the ketone bodies are able to be properly regulated with insulin. The process occurs at a rate at which the body makes the alternate energy sources as needed.
The body actually switches between using glucose and ketone bodies for energy regularly, without us really knowing it. Ketone bodies are regularly used during fasting periods, such as sleeping overnight. But once ketone bodies become the primary energy source, this is when a state of ketosis has been achieved.
Ketogenic diet for weight loss
The primary reason the keto diet is used by the general population today is to promote weight loss. Some of the most well-known ketogenic, or low-carb, diets are Atkins and the South Beach Diet.
Low-carb ketogenic diets have been shown to be effective in helping people lose weight, at least in the short term. There are a few main reasons for this.
First, a keto diet tends to increase satiety due to the higher intake of fat and protein. These two macronutrients keep you fuller for longer than carbs (especially those carbs that are more refined, like white breads and snack foods). As a result, people generally consume fewer overall calories, which supports weight loss.
Keto diets also appear to reduce appetite as a result of hormonal changes. Some research has found that individuals on a keto diet did not experience an increase in appetite-stimulating hormones as is typically expected with lower calorie intake.
A 2013 study published in the European Journal of Nutrition observed that people on a keto diet for 8 weeks saw an average of 13% body weight loss. Appetite hormones ghrelin and leptin were suppressed during the study and the participants reported feeling less hungry.5
It appears that following a keto diet can also increase metabolism, subsequently increasing the amount of calories burned naturally. When the body switches to using fat for energy, there is an increase in lipolysis – or fat breakdown – and a reduction in the amount of fat stored in the body.
Likely for all of these reasons and more, many people who adopt a ketogenic diet experience rapid weight loss within the first two weeks. The primary reason behind this is because the keto diet does also have a diuretic effect, which promotes water loss and reduces weight quickly, as is the case with many diets.
Losing weight quickly can be very motivating for many, helping them stick to the diet longer. As you stay on the diet, hunger declines, and weight decreases further because fewer overall calories are being consumed.
Based on current evidence, most health professionals don’t advocate following a keto diet for a prolonged period of time or as a life-long diet pattern. Enough research is available to support keto used by the general population for short periods, for which it has been shown to promote weight loss and preserve lean muscle mass.
For example, researchers of a 2003 study published in the New England Journal of Medicine found that significant weight differences were no longer present after one year of a low-fat or low-carb diet.6
Other health benefits of ketogenic diet
While overall weight loss is the predominant reason that most people today turn to the keto diet, it does have a few other purported health benefits that may be attractive.
For example, keto diets may be more effective at pinpointing abdominal fat, which is known to be a stubborn area many people want to target for weight loss. A 2004 study found that people who followed a very low-carb diet were more likely to lose fat around their abdominal cavity when compared to those on a low-fat diet.7
The keto diet may also help lower triglycerides, which are fat molecules that circulate in your blood. Having high levels of fasting triglycerides – meaning your levels are high even after you haven’t eaten in awhile – is a risk factor for heart disease.8
A low-carb diet seems to work in this scenario because high fasting triglyceride levels among people with sedentary lifestyles seems to be driven largely by high carb consumption.9
Oppositely, studies have shown that drastically reducing the amount of carbs eaten can drastically reduce fasting triglyceride levels.10-12
Having a higher HDL or “good” cholesterol, relative to your LDL or “bad” cholesterol levels, is another biomarker for improved heart health. A keto diet may help improve HDL levels, primarily due to the high percentage of fat included in the eating pattern. Studies have observed that HDL levels rise substantially on healthy, low-carb diet patterns, while low-fat diets only trigger a small increase in HDL.6,13-15
To go along with this, some studies have found that low-carb diets can also reduce the overall amount of LDL particles in your bloodstream, while increasing the size of the ones that are left circulating. It appears that smaller LDL particles are linked to a higher risk for heart disease, whereas larger particles have a lower risk.16,17
High blood pressure, a risk factor for heart and kidney disease, may also be alleviated with use of a keto diet, at least in the short term. In a 2007 randomized trial, researchers found that obese and overweight women who followed a low-carb diet experienced a greater reduction in metabolic effects like high blood pressure, compared to those who followed the Zone (an anti-inflammatory low-carb diet), Ornish (emphasizes “good” vs. “bad” carbs), or LEARN (approximately 60% carbs) diets.18,19
There is evidence that a well-planned keto diet can be beneficial for people who are seeking better blood sugar management or who have insulin resistance.20 Reducing carb intake lowers both blood glucose and insulin levels. In fact, a keto diet can be so effective in this regard that people who take insulin or other medications to help manage their blood sugar levels may need to cut their dosing dramatically.21-23
Potential side effects
A number of possible long and short term side effects have been observed with the keto diet that are worth considering.
Perhaps the most frequent complaint is what has been called the “keto flu”. This is a group of symptoms that seems to appear early on in the adoption of a very low-carb diet. Common symptoms of keto flu can include nausea, dizziness, fatigue, headaches, insomnia, constipation, and trouble exercising.24
These appear to result from the hormonal shifts, change in blood sugar levels, and electrolyte imbalances triggered by drastic reduction of carb intake. The good news is that symptoms usually resolve within the first few days or weeks of dietary adherence. General recommendations for alleviating symptoms include drinking enough water and supplementing electrolytes.
As for the longer term, the keto diet comes with several concerns from health and medical professionals. The main reason that there is such hesitation over recommended usage of a keto diet for a prolonged period of time is that there isn’t enough evidence to support its effectiveness or safety, especially when it comes to a wide variety of populations.
Ketogenic diets are low in fiber, a critical nutrient for health, especially aimed at digestion. Inadequate fiber intake is already common in Western populations. Fiber is only found in plant foods, which are also a major source of carbohydrates and of course limited.
Furthermore, there is concern that very low-carb keto diets come with a heightened risk for nutrient deficiencies. It seems likely that this diet pattern would be lacking in vitamin D and the B vitamins, calcium, zinc, magnesium, phosphorus, and selenium. Micronutrient supplementation is a good idea on a keto diet to help reduce the risk for these deficiencies, especially if the diet is followed for longer periods of time.25,26
In a 2018 study published in the Lancet Public Health, researchers examined self-reported dietary intake of 15,428 adults ages 45-64 years, over a period of 25 years. Using this data, all-cause mortality risk was also assessed. It was concluded that those with the lowest risk of mortality reported getting between 50-55% of their calories from carbohydrates, a much larger portion than the 5-10% of carbs usually eaten on a keto diet. Additionally, when animal foods replaced carbs, mortality risk also increased. On the other hand, mortality risk decreased when plant foods replaced animal protein.27
Another common concern around following a keto diet for a longer period is that it could increase risk for heart disease. However, as previously discussed, it does seem more common for keto diets to lower blood fats associated with heart disease risk. Still, more research is needed on the effects of a keto diet on heart health over a longer period.
Animal studies have also indicated that a keto diet may promote fat accumulation in the liver, resulting in inflammation and other potential issues.28,29
Intermittent fasting Ketogenic Diet
As the keto diet has retained its popularity, intermittent fasting eating patterns have also gained public attention. Some health gurus have even combined the two for an ultimate weight loss regimen. Dr. Joseph Mercola, a well-known natural health and weight loss physician, is one of those gurus. He recommends the combination of keto and fasting to help promote fat burn, while incorporating plenty of high fat foods to improve metabolic health.30,31
Intermittent fasting is a pattern in which you have designated eating periods and fasting periods. There are several approaches, such as fasting for a full 24 hours at a time, or fasting for 8-16 hours or more at a time while consuming food only within the other window.
Dr. Mercola says fasting allows your body more time to digest and absorb what you eat, alleviating extra stress on the digestive system, and boosting weight loss without drastically reducing the overall amount of calories you normally eat.
This combined approach may be popularized by Mercola, but what does scientific evidence say? Some research indicates that fasting may help you reach ketosis faster. It may also help boost metabolism and increase thermogenesis, burning more fat. Fasting and keto may work together to reduce appetite and prevent overeating.32-35
Still, while combining the two may be helpful for some, it’s not for everyone and more research is needed to determine the best approaches and applications of the two together.
Interestingly, a combination of keto and intermittent fasting has also been studied for potential benefits in multiple sclerosis. A 2020 randomized controlled trial found that this eating pattern may modulate immunity, reduce the severity of the disease, and even promote remyelination among mice.36
Tips for success
The keto diet can be difficult to sustain, and is not appropriate for everyone. There are a few things to keep in mind when considering a keto diet.
First, it’s important to remember that the most evidence around the safety and effectiveness of a keto diet is in the short-term. A keto diet can help boost weight loss and may even have other short-term benefits in terms of heart health biomarkers, blood sugar management, and fat loss. However, a keto diet is not generally recommended for a prolonged period as health effects are unknown. Plus, weight loss does eventually plateau on this diet.
Second, the quality of the foods consumed on a keto diet are also key for sustainability, maintenance of weight loss, and overall health. Due to the higher risk for nutrient deficiencies and electrolyte imbalances on a keto diet, it may be a good idea to use a multivitamin and mineral supplement. A keto diet is not a free-for-all to consume all the fatty foods you want. Choosing high-quality foods, like poly- and monounsaturated fats, is critical to success.
Lastly, working with a health and nutrition professional, such as a physician and a registered dietitian, is always smart when considering making a drastic change to your diet. This is especially important for people who have existing medical conditions or who are on medications, to make sure that adopting a keto diet is appropriate and safe for you.