The ketogenic diet, often called the "keto" diet, has surged in popularity recently, evidenced by its position as the most Googled diet in the United States in 2020, with 25.4 million unique searches. This increased 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 popularized the ketogenic diet, sparking interest in its potential benefits and risks.
Historical Context and Evolution of the Keto Diet
The ketogenic diet's roots trace back to 1911, when starvation was first observed to reduce the severity of epileptic seizures. In 1921, Dr. Rollin Woodyatt discovered that acetone and beta-hydroxybutyric acid appeared during starvation and in patients consuming a low-carbohydrate diet, laying the groundwork for using the diet to induce ketosis. In the 1970s, Dr. Robert Atkins popularized nutritional ketosis for weight loss, noting that reducing carbohydrates leads to ketone excretion and reduced hunger. Since then, numerous low-carb diets, such as the South Beach Diet and variations of the Paleo and Mediterranean diets, have emerged as mainstream weight loss options.
Understanding the Ketogenic Diet
The ketogenic diet is characterized by very low carbohydrate intake, with varying levels of protein and fat. The classic ketogenic diet consists of one gram of protein per kilogram of body weight, 10-15 grams of carbohydrates per day, and the remaining calories from fat. The primary goal of the diet is to induce ketosis, a metabolic state where the body relies on fat for energy instead of carbohydrates.
Under normal circumstances, the body utilizes carbohydrates for energy, with insulin facilitating glucose extraction and storage. However, when carbohydrate availability is limited, insulin secretion decreases. Initially, the body uses stored glucose in the form of glycogen, but after three to four days, this supply is depleted. The body then turns to stored fat, breaking it down into free fatty acids that the liver uses to produce ketones. This process is typically observed during starvation, prolonged exercise, and strict adherence to a very-low-carbohydrate diet.
Weight Loss Efficacy
The ketogenic diet has been shown to be an effective weight loss therapy. When carbohydrate intake is decreased, the body must undergo increased gluconeogenesis to provide glucose to the brain. Gluconeogenesis is a metabolically expensive process. Another proposed mechanism of weight loss is direct appetite suppression. During the low-carb, ketogenic diet phase, participants reported significantly decreased hunger, leading the authors to hypothesize that ketosis itself may suppress hunger.
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Numerous studies have evaluated the keto diet’s weight loss efficacy, with many randomized controlled trials demonstrating significant weight loss. A meta-analysis by Mansoor et al. examined 11 randomized controlled trials over six months, involving 1,369 participants, and found that those on low-carbohydrate diets lost 2.17 kg more than those on low-fat diets. However, the weight loss advantage appears less significant in longer-duration studies. A meta-analysis by Bueno et al. analyzed 13 randomized controlled trials with 1,415 subjects over at least 12 months and found that the weight loss was less superior.
Impact on Type 2 Diabetes
Before the discovery of insulin, low-carbohydrate diets were a primary treatment for type 1 diabetes. More recently, there has been renewed interest in using ketogenic diets to manage type 2 diabetes, particularly in conjunction with obesity. The ketogenic diet may improve hyperglycemia through several proposed mechanisms.
One small study of 28 participants found that ketogenic diet counseling, aiming for less than 20 grams of carbohydrates per day, led to improvements in glycemic control after 16 weeks. A two-year study involving 349 participants showed that those following a ketogenic diet had a 0.9% decrease in HbA1c (a marker of long-term blood sugar control) compared to a 0.4% increase in the standard care group. Additionally, the ketogenic diet group reduced their use of diabetic medications by 81%, while medication use increased in the standard care group.
Cardiovascular Considerations
A common concern regarding the ketogenic diet is its potential impact 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 alongside weight loss and found no significant differences in major cardiovascular risk factors between ketogenic and low-fat diet groups.
Another meta-analysis of eight randomized controlled trials with 1,633 participants found no significant difference in LDL-cholesterol levels between groups. However, further analysis suggests that diet composition significantly influences lipid changes. The increase in LDL-cholesterol seen in some studies may be due to increased saturated fat intake when carbohydrates are lowered.
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Keto Diet for Women
Studies have shown that following a keto diet may aid weight loss by increasing fat-burning and decreasing calorie intake and hunger-promoting hormones like insulin - all of which may help encourage fat loss.
For example, one 2018 study of 45 women with ovarian or endometrial cancer found that people who followed a ketogenic diet for 12 weeks had significantly less total body fat and lost 16% more belly fat than participants assigned to a low fat, high fiber diet. A separate 2018 study of adults with obesity that included 12 women demonstrated that following a low calorie ketogenic diet for 14 weeks significantly reduced body fat, decreased food cravings, and improved sexual function.
Risks and Concerns
Despite its potential benefits, the ketogenic diet is not without risks and concerns. There is evidence that women who become pregnant on low-carbohydrate diets have an increased risk of birth defects. A retrospective study found that women with restricted carbohydrate intake were 30% more likely to have infants with neural tube defects and decreased folic acid levels. Therefore, women planning to become pregnant should avoid restrictive low-carbohydrate diets.
The ketogenic diet is also associated with several potential side effects, including:
- High Saturated Fat: The diet's high fat content, particularly saturated fat, may increase the risk of heart disease.
- Kidney Problems: The kidneys help metabolize protein, and the keto diet may overload them.
- Cognitive and Mood Issues: The brain relies on glucose from healthy carbohydrates for optimal function, and restricting carbohydrates may lead to fuzzy thinking and mood swings.
- Nutritional Deficiencies: The diet's restrictions may limit intake of essential nutrients found in fruits, vegetables, and whole grains.
- Kidney Stones: Some studies suggest that the keto diet reduces the amount of citrate released in urine, increasing the risk of kidney stones.
- Digestive Issues: Some dieters report bouts of diarrhea, when on the keto diet. This is likely due to the very high intake of fat, which requires more work for the body to break down.
- Dehydration: Dehydration occurs because people urinate more frequently when shifting into ketosis.
- Low blood pressure: The keto diet can cause your blood pressure to drop in the short term due to a reduction in blood volume and changes in your fluid balance.
Contraindications
The ketogenic diet is not appropriate for everyone and is not recommended for people who are pregnant or nursing or who have certain underlying conditions, including:
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- Liver or kidney failure
- Alcohol or substance use disorders
- Type 1 diabetes
- Pancreatitis
- Disorders that affect fat metabolism
- Certain nutritional deficiencies, including carnitine deficiency
- A blood disorder known as porphyria
Practical Considerations and Recommendations
For patients with type 2 diabetes, any weight loss achieved with the ketogenic diet could lower A1c and help reduce the medication burden. It is important to note that a high-quality diet with adequate intake of fruits and vegetables and low intake of saturated fats would be preferred.
Before starting any significant dietary changes, it’s important to consider the positives and negatives of the diet, as well as its appropriateness based on your current health status. For example, the ketogenic diet may be an appropriate choice for a woman who has obesity or diabetes or is unable to lose weight or manage blood sugar using other dietary modifications. This diet may also be effective for women who have overweight or obesity with polycystic ovarian syndrome (PCOS). Studies show that the keto diet may help people with PCOS lose weight, improve hormonal imbalance, and boost fertility.
Alternative Approaches
Less restrictive diets, including the Mediterranean diet, have been researched for decades and are well known for their safety and beneficial effects on blood sugar control and overall health. Adopting a diet rich in whole, nutritionally dense foods that can be maintained for life is usually best. Intermittent fasting is an approach that allows you to receive the benefits of ketosis while still eating a varied and balanced diet. By cycling between periods of eating and fasting, your body enters “mild ketosis” during the fasting phase.