The ketogenic diet has gained considerable popularity in recent years, becoming the most Googled diet in the United States in 2020, with 25.4 million unique searches. This surge in consumer interest has fueled the rapid growth of the "keto" food industry, valuing the global ketogenic diet market at $9.57 billion in 2019. Celebrities, health magazines, and documentaries have further propelled the ketogenic diet into popular culture.
However, with the increased interest in this diet, researchers are working to understand the impact of this pattern of eating on patients’ health. There is evidence of benefit, especially regarding weight loss, but there are also risks and concerns.
What is the Ketogenic Diet?
The ketogenic diet is a very-low-carbohydrate, high-fat diet that involves a drastic reduction in carbohydrate intake. The mainstay of the ketogenic diet is that dietary carbohydrates are kept very low, with varying levels of protein and fat. The classic ketogenic diet is defined as a diet with one gram protein per kilogram of body weight, 10-15g carbohydrates per day, and the remaining calories from fat. The goal of the diet is to induce ketosis.
Under ordinary circumstances, the body primarily relies on carbohydrates for energy production. Insulin functions to extract and store energy derived from glucose. When the body has reduced carbohydrates available, insulin secretion is reduced. Initially, stored glucose in the form of glycogen is available for fuel, but after three to four days, this is depleted. Stored fat then becomes the most readily available fuel, and its breakdown into free fatty acids provides the raw materials for ketone production in the liver. Ketone production is primarily seen in times of starvation and prolonged exercise, but is also a function of adherence to a very-low carbohydrate diet.
History of the Ketogenic Diet
The first modern use of starvation for the treatment of epilepsy was noted in 1911. Two physicians in Paris reported that seizures were less severe in period of starvation. While this was the origin for the ketogenic diet, it wasn’t until 1921 that any physician tried to generate ketosis. Dr. Rollin Woodyatt noted that under conditions of starvation, acetone, and beta-hydroxybutyric acid appear. Woodyatt also uncovered that acetone and beta-hydroxybutyric acid were observed if patients ate a low carbohydrate diet. Around the same time, Dr.
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In the 1970s, nutritional ketosis was introduced as an idea for weight loss by Dr. Robert Atkins. In his book published in 1972, he describes how reducing carbohydrates “creates a unique chemical situation in the body…ketones are excreted, and hunger disappears.” Although the Atkins diet was one of the first, many other low carb diets have been popularized since the 1970s, from the South Beach Diet to variations of the Paleo and Mediterranean diets. While the details of low-carbohydrate diets may have changed, they have remained a mainstream option for weight loss.
How the Ketogenic Diet Works
The keto diet aims to force your body into using a different type of fuel. Burning fat seems like an ideal way to lose pounds. Because the keto diet has such a high fat requirement, followers must eat fat at each meal. In a daily 2,000-calorie diet, that might look like 165 grams of fat, 40 grams of carbs, and 75 grams of protein. Some healthy unsaturated fats are allowed on the keto diet - like nuts (almonds, walnuts), seeds, avocados, tofu, and olive oil.
All fruits are rich in carbs, but you can have certain fruits (usually berries) in small portions. Vegetables (also rich in carbs) are restricted to leafy greens (such as kale, Swiss chard, spinach), cauliflower, broccoli, Brussels sprouts, asparagus, bell peppers, onions, garlic, mushrooms, cucumber, celery, and summer squashes.
Potential Benefits of the Ketogenic Diet
There is evidence that the ketogenic diet is an effective weight loss therapy. However, the exact mechanisms behind this weight loss remain unclear. For example, in a review of thermodynamic principles of weight loss, Feinman and Fine explain that low-carbohydrate diets have decreased insulin fluxes causing an increased rate of lipolysis. In other words, insulin inhibits lipolysis, and decreased insulin in low-carb diets causes increased fat breakdown. This theory is demonstrated in a study that follows 15 subjects for 12 weeks. The first six weeks they ate a low-carbohydrate diet and the next six weeks a low-fat diet.
Another proposed weight loss mechanism is with decreased carbohydrate intake, the body will have to undergo increased amounts of gluconeogenesis to provide glucose to the brain. Gluconeogenesis is an expensive metabolic process. Theoretically, restricting carbohydrates depletes glucose stores, and increases gluconeogenesis.
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Another mechanism of weight loss is theorized to be direct appetite suppression. In a study with 17 men, subjects were given a high protein diet with two weeks of high-carb and two weeks of moderate-carb intake. During the low-carb, ketogenic diet phase, the participants reported significantly decreased hunger, leading the authors to hypothesize that ketosis itself may suppress hunger.
With these mechanisms in mind, numerous studies have evaluated the keto diet’s weight loss efficacy. There are many examples of randomized controlled trials where significant weight loss is achieved. For example, a meta-analysis by Mansoor et al. looked at mean weight loss in 11 randomized controlled trials for six months with a total of 1,369 participants. In the trials analyzed, participants were randomized into low carbohydrate versus low-fat diet plans. This study found that compared to low-fat diets, low-carbohydrate diets participants lost 2.17 kg more than the low-fat diets (95% CI −3.36, −0.99).
The keto diet helps reduce seizures in children with epilepsy. Endurance athletes and body builders also use it to scrap fat in short timeframes. The keto diet is being studied for reducing symptoms for patients with progressive neurological disorders like Parkinson’s disease.
For patients with type 2 diabetes, it is likely that any weight loss achieved with the ketogenic diet could lower A1c and help reduce the medication burden.
Managing Type 2 Diabetes with Ketogenic Diets
More recently, there has been significant interest in the use of ketogenic diets to treat type 2 diabetes in conjunction with obesity. There are several proposed mechanisms that support the use of ketogenic diets to improve hyperglycemia. Testing this hypothesis, investigators have looked to see if the ketogenic diet can help improve hyperglycemia. One small, shorter study recruited 28 participants to follow for 16 weeks. In this study all 28 subjects that were enrolled received ketogenic diet counseling with a goal of less than 20 grams of carbohydrates per day. At the end of the 16 weeks, 21 participants had completed the trial.
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In a two-year, open label, non-randomized, controlled study, 349 participants received either standard care or were educated to follow a ketogenic diet. At the end of two years, those who had followed diets to stimulate ketosis had a 0.9% decrease in HbA1c versus a 0.4% increase in the standard of care arm. In addition, those following the ketogenic diet decreased their use of diabetic medications by 81%, while medication use increased in standard of care patients. Another similar trial looking at glycemic control outcomes after two years showed no significant difference in HbA1c levels between the low-fat and low-carbohydrate groups. These studies show than in the shorter term, there seem to be clinically significant improvements in glycemia control outcomes. A very recent meta-analysis by Goldenberg et al.
Considerations for Type 1 Diabetes
It is important to understand the impact of the ketogenic diet in patients with type 1 diabetes. Although it has not been studied extensively, there have been trials showing positive outcomes. One small trial with ten participants were randomized into a carbohydrate restricting arm versus a standard carbohydrate counting arm. They were followed for 12 weeks. A critical point to mention is the hypoglycemic risk of the ketogenic diet in the type 1 diabetes population. In an observational study with 11 participants, subjects were followed on a ketogenic diet for three years.
Risks and Concerns
A ketogenic diet has numerous risks. Top of the list: it's high in saturated fat. McManus recommends that you keep saturated fats to no more than 7% of your daily calories because of the link to heart disease. Kidney problems. The kidneys help metabolize protein, and McManus says the keto diet may overload them. Fuzzy thinking and mood swings. The brain works best when the energy source is sugar from healthy carbohydrates to function.
While these mechanisms provide insight into how the ketogenic diet promotes decreased appetite and fat loss, it is important to note that evidence shows weight loss from the ketogenic diet can be partially attributed to water loss. In another study, 20 obese subjects were followed for four months on a ketogenic diet.
Cardiovascular Risks
A common concern physicians have with the ketogenic diet is its effect on blood lipids and lipoproteins, and more broadly, its effect on cardiovascular disease risk factors. The meta-analysis by Mansoor et al. evaluated cardiovascular risk factors in addition to weight loss as noted above. They evaluated 11 randomized controlled trials with 1,369 participants placed into ketogenic versus low-fat diet arms.
In another meta-analysis, the authors reviewed eight randomized controlled trials lasting six months with 1,633 participants in a ketogenic versus low-fat randomization. In this analysis, they found no significant difference in LDL-cholesterol levels between groups (0.07 mmol/L; 95% confidence interval [CI], 0.02-0.13; P <0.009] 26. Further analysis suggests that the variation in diet composition may have a significant effect on the lipid changes seen. The increase in LDL-cholesterol seen in some of the randomized controlled studies may be due to the increased intake of saturated fats when carbohydrates are lowered.
One meta-analysis centered on randomized controlled trials analyzed long-term effects of low-fat versus high-fat diets. The meta-analysis included 32 studies with 8,862 participants that were followed for a minimum of 12 months.
Studies generally show improvement in HDL and triglycerides, but LDL response is variable. This may be due to significant variability in the content of the diet of each specific person.
Potential for Nutrient Deficiencies
“Because the keto diet is so restricted, you’re not receiving the nutrients - vitamins, minerals, fibers - that you get from fresh fruits, legumes, vegetables and whole grains,” says Dr. Ring. People report feeling foggy, irritable, nauseous and tired. “In particular, low fiber intake can disrupt gut microbiota and lead to chronic constipation, while inadequate magnesium, vitamin C and potassium can contribute to muscle cramps, fatigue and weakened immune function,” explains Dr.
Kidney Disease
The keto diet may not be appropriate for everyone, specifically people with kidney disease. “Although more research is needed in that area, there is some suggestion that it can make kidney disease worse over time,” says Dr.
Dehydration and Low Blood Pressure
Some people also experience dehydration on the keto diet because they’re eliminating glycogen, which holds water, from the bloodstream. Following a keto diet can also cause your blood pressure to drop in the short term due to a reduction in blood volume and changes in your fluid balance. Symptoms of low blood pressure include dizziness, lightheadedness or fainting, especially when standing up quickly.
Low Blood Sugar
Following a keto diet can also cause your blood sugar to drop, which can be dangerous for people living with diabetes. Common symptoms of low blood sugar include weakness or shaking, sweating, a fast heartbeat and dizziness.
Psychological Distress
When you micromanage your food intake by tracking how much you eat, it disconnects you from what your body is asking for. You start using outside numbers to determine what to eat instead of listening to your body. Monitoring food so closely can lead to psychological distress, such as shame and binge eating.
Risks During Pregnancy
There is evidence that women who become pregnant on low-carbohydrate diets have increased risk of birth defects. The National Birth Defects Prevention Study retrospectively looked at mothers with infants with stillbirths, anencephaly, or spina bifida (1,740) versus mothers with infants without defects (9,545). They found that women with restricted carbohydrate intake, defined as less than the fifth percentile among the control group were 30% more likely to have infants with neural tube defects (Odds ratio of 1.30, 95% (1.02, 1.67) p<.01) as well as decreased folic acid levels. Women who plan to become pregnant should be advised to avoid restrictive low-carbohydrate diets.
Variations of the Ketogenic Diet
The popular low-carb diets (such as Atkins or Paleo) modify a true keto diet. So why do people follow the diets? They're everywhere, and people hear anecdotally that they work. Theories about short-term low-carb diet success include lower appetite because fat burns slower than carbs. But concerns remain about staying on a keto diet long term. And eating a restrictive diet, no matter what the plan, is difficult to sustain.
Strict Keto Diet
When people say they’re on the strict version of keto, they’re likely referring to the diet that’s been shown to help treat epilepsy. Sometimes called the therapeutic keto diet, this way of eating is the original version of keto, which was created in the 1920s to help treat seizures. This version of the diet allows the lowest amount of carbohydrates, hence being the strictest. It permits 4 grams of fat for every 1 gram of combined protein and carbohydrates, so 80 to 90 percent of daily calories come from fat, 6 to 8 percent from protein, and just 2 to 4 percent from carbohydrates.
Standard Keto Diet
The most common approach to keto but not precisely defined by dietary experts, the “standard” keto diet involves getting 70 to 80 percent of your calories from fat, 10 to 20 percent from protein, and 5 to 10 percent from carbohydrates. Most on the standard keto diet need to limit their carbohydrate intake to about 20 to 30 grams per day, says Shapiro. While this is the keto diet that most people follow, it’s not the original, or therapeutic, version of keto that can help children with epilepsy.
Targeted Keto Diet
The target keto diet involves following the keto diet as usual until 30 to 45 minutes before exercising, at which point you eat about 25 grams of carbohydrates, says Daniela Torchia, PhD, a registered dietitian based in Lakewood Ranch, Florida. The idea is that you’ll have just enough carbs to fuel your workout effectively and still be able to return to ketosis easily after you cool down. Choose carbohydrates that are easy to digest (white bread or white rice, for example) and be sure not to add calories to your daily total, simply redistributing them instead, says Torchia.
High-Protein Keto Diet
This version of keto calls for upping the protein intake just a bit. With this type, protein should make up about 30 percent of your daily calories, with an additional 65 percent coming from fat and 5 percent from carbohydrates, says Spritzler. Aim to source your protein from both animals (meat, fish, and dairy) and plants (nuts and seeds), she suggests.
Cyclical Keto Diet
On the cyclical keto diet, also called keto cycling, you cycle in and out of keto, usually staying on the diet for five days, followed by one or two days that allow for more carbs. The point of keto cycling is to make it easier for someone to follow [the diet],” says Kizer. “Every five to six days, they can have the carbohydrates they’ve been entirely restricting.” There’s no set protocol in terms of what your carb days should look like, but Kizer warns not to go overboard, because that will make it more difficult for the body to return to ketosis.
Lazy Keto Diet
The purpose of the so-called “lazy keto” diet is to make keto easier to follow. For some people, counting calories, fat, and protein intake is too complicated. “All you track is carbs in lazy keto,” says Kizer. You should still see results that are similar to regular keto as long as you keep your carb intake low enough and don’t go overboard in the protein department, says Kizer. “As long as carbs stay low enough, which vary by person but are usually below 50 grams a day, one will stay in ketosis,” she says. As a result, you may see the effects associated with being in that metabolic state.
Mediterranean Keto Diet
Think of Mediterranean keto as a combination of two popular approaches to eating: sticking to standard keto macronutrient amounts while emphasizing Mediterranean diet elements like fatty fish and olive oil. The emphasis is on the quality of fats you eat, says Madeline McDonough, RDN, who is based in Boston. “Unlike the standard keto diet, which doesn’t specify which fats to prioritize, Mediterranean keto diets emphasize options like monounsaturated fatty acids, which may help lower LDL cholesterol, and omega-3 fatty acids that are anti-inflammatory,” she says.
Keto 2.0
The latest revamp of the keto diet is called keto 2.0, and it’s gaining traction with those who feel that the standard keto diet is too restrictive and difficult to sustain in the long run, says Penny Scholl, RD, in Avon, Massachusetts, who covers keto approaches on her blog, Remake My Plate.
Keto-Friendly Sweeteners
To maintain ketosis, people also need to reduce their sugar consumption. This can make it challenging if they wish to use sweeteners in baked goods, sauces, and beverages. Traditional sweeteners, such as white sugar, are high in carbs, so they are not suitable for people wanting to stick to a keto diet.
To stay in ketosis, people can choose low carb sweeteners, such as:
- Monk fruit: A natural sweetener with no calories or carbs.
- Stevia: Another natural sweetener with little to no carbs or calories.
- Yacon syrup: Contains fewer calories than table sugar, but high temperatures will break down the FOSs.
- Sucralose: A non-nutritive sweetener with little to no calories.
- Xylitol: A sugar alcohol that tastes similar to table sugar but can cause digestive issues.
- Erythritol: Another sugar alcohol with fewer calories than table sugar and may not cause digestive issues.
Sweeteners to Avoid on a Keto Diet
There are some sweeteners people should avoid while on a low carb diet, including the below.
- Maltodextrin: Contains the same number of carbs as table sugar.
- Honey: Contains a high amount of sugar and carbs.
- Coconut sugar: Contains just as many carbs as table sugar.
- Maple syrup: Contains large amounts of sugar and carbs.
- Agave nectar: Almost 85% fructose.
- Dates: Contain 75 g of carbs per 100 g.