In the seemingly endless promotion of weight-loss strategies and diet plans, the ketogenic diet, or "keto" diet, has emerged as a popular option. It's a low-carbohydrate, fat-rich eating plan that has historical roots in treating specific medical conditions. While it's gaining attention as a potential weight-loss strategy, it's essential to understand both its benefits and risks, especially when combined with intermittent fasting. This article delves into the science behind the keto diet, its potential benefits, and the considerations for combining it with intermittent fasting.
The Ketogenic Diet: A Historical Perspective
The ketogenic diet has a rich history, dating back to the 19th century when it was used to manage diabetes. In 1920, it was introduced as an effective treatment for epilepsy in children for whom medication was ineffective. The low-carb diet craze, which started in the 1970s with the Atkins diet, brought the keto diet into the limelight as a potential weight-loss strategy. Today, other low-carb diets, including the Paleo, South Beach, and Dukan diets, are also high in protein but moderate in fat.
How the Keto Diet Works
The premise of the ketogenic diet for weight loss lies in depriving the body of glucose, its primary energy source. Glucose is obtained from carbohydrate foods. When carbohydrate intake is restricted, the body turns to an alternative fuel called ketones, which are produced from stored fat.
The brain requires a steady supply of glucose, about 120 grams daily, as it cannot store it. During fasting or very low carbohydrate intake, the body initially uses stored glucose from the liver and breaks down muscle to release glucose. If this continues for 3-4 days, and stored glucose is depleted, insulin levels decrease, and the body starts using fat as its primary fuel. The liver produces ketone bodies from fat, which can be used in the absence of glucose. This accumulation of ketone bodies in the blood is called ketosis.
Healthy individuals naturally experience mild ketosis during periods of fasting, such as overnight, and during strenuous exercise. Proponents of the ketogenic diet suggest that carefully following the diet can prevent ketone levels from reaching harmful levels (ketoacidosis). The brain will use ketones for fuel, and healthy individuals will typically produce enough insulin to prevent excessive ketone formation.
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The rate at which ketosis occurs and the amount of ketone bodies that accumulate vary from person to person, depending on factors like body fat percentage and resting metabolic rate.
Ketoacidosis: A Dangerous State
Excessive ketone bodies can lead to ketoacidosis, a dangerously toxic level of acid in the blood. During ketoacidosis, the kidneys excrete ketone bodies along with body water in the urine, causing fluid-related weight loss. Ketoacidosis most often occurs in individuals with type 1 diabetes because they do not produce insulin, which prevents the overproduction of ketones. However, in rare cases, ketoacidosis has been reported in non-diabetic individuals following a prolonged very low carbohydrate diet.
Macronutrient Ratios in the Ketogenic Diet
There is no one "standard" ketogenic diet with a specific ratio of macronutrients (carbohydrates, protein, fat). However, the ketogenic diet typically reduces total carbohydrate intake to less than 50 grams a day, sometimes as low as 20 grams. Popular ketogenic resources suggest an average of 70-80% fat from total daily calories, 5-10% carbohydrate, and 10-20% protein. For a 2000-calorie diet, this translates to approximately 165 grams of fat, 40 grams of carbohydrate, and 75 grams of protein.
The protein amount on the ketogenic diet is moderate compared to other low-carb high-protein diets, as excessive protein intake can hinder ketosis.
Food Choices on a Ketogenic Diet
Many versions of ketogenic diets exist, but all restrict carb-rich foods. Some obvious foods to avoid include starches from refined and whole grains like breads, cereals, pasta, rice, and cookies; potatoes, corn, and other starchy vegetables; and fruit juices. Less obvious foods to restrict include beans, legumes, and most fruits.
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Most ketogenic plans allow foods high in saturated fat, such as fatty cuts of meat, processed meats, lard, and butter, as well as sources of unsaturated fats, such as nuts, seeds, avocados, plant oils, and oily fish. A strong emphasis is placed on fats at each meal and snack to meet the high-fat requirement. Some dairy foods may be allowed, but those high in natural lactose sugar, such as cream, ice cream, and full-fat milk, are restricted. Protein intake remains moderate, and certain fruits in small portions, like berries, are permitted.
"Net Carbs" and "Impact Carbs": A Marketing Strategy
"Net carbs" and "impact carbs" are unregulated interchangeable terms invented by food manufacturers as a marketing strategy, appearing on some food labels to claim that the product contains less "usable" carbohydrate than is listed. Net carbs or impact carbs represent the amount of carbohydrate directly absorbed by the body and contributing calories. They are calculated by subtracting the amount of indigestible carbohydrates from the total carbohydrate amount.
Indigestible carbohydrates include insoluble fibers from whole grains, fruits, and vegetables; and sugar alcohols, such as mannitol, sorbitol, and xylitol, commonly used in sugar-free diabetic food products. However, these calculations are not an exact or reliable science because the effect of sugar alcohols on absorption and blood sugar can vary. Some sugar alcohols may still contribute calories and raise blood sugar. The total calorie level also does not change despite the amount of net carbs, which is an important factor with weight loss.
Short-Term Benefits of the Ketogenic Diet
The ketogenic diet has been shown to produce beneficial metabolic changes in the short term. Along with weight loss, health parameters associated with carrying excess weight have improved, such as insulin resistance, high blood pressure, and elevated cholesterol and triglycerides. There is also growing interest in the use of low-carbohydrate diets, including the ketogenic diet, for type 2 diabetes.
Research Findings on the Ketogenic Diet
Research on the ketogenic diet has yielded some promising results:
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- A meta-analysis of 13 randomized controlled trials following overweight and obese participants for 1-2 years on either low-fat diets or very-low-carbohydrate ketogenic diets found that the ketogenic diet produced a small but significantly greater reduction in weight, triglycerides, and blood pressure, and a greater increase in HDL and LDL cholesterol compared with the low-fat diet at one year.
- A systematic review of 26 short-term intervention trials evaluated the appetites of overweight and obese individuals on either a very low calorie or ketogenic diet using a standardized and validated appetite scale. Participants reported less hunger and a reduced desire to eat compared with baseline measures. The authors suggested further studies exploring a threshold of ketone levels needed to suppress appetite, which could allow inclusion of healthful higher carbohydrate foods like whole grains, legumes, and fruit.
- A study of 39 obese adults placed on a ketogenic very low-calorie diet for 8 weeks found a mean loss of 13% of their starting weight and significant reductions in fat mass, insulin levels, blood pressure, and waist and hip circumferences. Their levels of ghrelin did not increase while they were in ketosis, which contributed to a decreased appetite. However, during the 2-week period when they came off the diet, ghrelin levels and urges to eat significantly increased.
- A study of 89 obese adults who were placed on a two-phase diet regimen (6 months of a very-low-carbohydrate ketogenic diet and 6 months of a reintroduction phase on a normal calorie Mediterranean diet) showed a significant mean 10% weight loss with no weight regain at one year.
Potential Risks and Side Effects
Following a very high-fat diet may be challenging to maintain. Some negative side effects of a long-term ketogenic diet have been suggested, including increased risk of kidney stones and osteoporosis, and increased blood levels of uric acid (a risk factor for gout). Possible nutrient deficiencies may arise if a variety of recommended foods on the ketogenic diet are not included. It is important to include a daily variety of the allowed meats, fish, vegetables, fruits, nuts, and seeds to ensure adequate intakes of fiber, B vitamins, and minerals (iron, magnesium, zinc)ânutrients typically found in foods like whole grains that are restricted from the diet.
Limitations of Current Research
Available research on the ketogenic diet for weight loss is still limited. Most of the studies so far have had a small number of participants, were short-term (12 weeks or less), and did not include control groups. A ketogenic diet has been shown to provide short-term benefits in some people including weight loss and improvements in total cholesterol, blood sugar, and blood pressure. However, these effects after one year when compared with the effects of conventional weight loss diets are not significantly different. Eliminating several food groups and the potential for unpleasant symptoms may make compliance difficult. An emphasis on foods high in saturated fat also counters recommendations from the Dietary Guidelines for Americans and the American Heart Association and may have adverse effects on blood LDL cholesterol.
Considerations for Higher Risk Individuals
It's important to consider whether the diet's health benefits extend to higher-risk individuals with multiple health conditions and the elderly. As fat is the primary energy source, there may be a long-term impact on health from consuming different types of fats (saturated vs. unsaturated).
The Ketogenic Diet as an Option
A ketogenic diet may be an option for some people who have had difficulty losing weight with other methods. The exact ratio of fat, carbohydrate, and protein that is needed to achieve health benefits will vary among individuals due to their genetic makeup and body composition. Therefore, if one chooses to start a ketogenic diet, it is recommended to consult with oneâs physician and a dietitian to closely monitor any biochemical changes after starting the regimen, and to create a meal plan that is tailored to oneâs existing health conditions and to prevent nutritional deficiencies or other health complications. A modified carbohydrate diet following the Healthy Eating Plate model may produce adequate health benefits and weight reduction in the general population.
Intermittent Fasting: A Complementary Approach
Intermittent fasting is an eating method that cycles between calorie restriction, or fasting, and normal food consumption during a specific time period. One popular method is the 16/8 method, which involves eating during an eight-hour timeframe before fasting for 16.
Intermittent fasting is mainly used as a weight loss technique, but studies have found that it may benefit health in many other ways. For example, intermittent fasting has been shown to reduce inflammation and improve brain function and blood sugar control.
Combining Keto and Intermittent Fasting: Potential Benefits
Combining the ketogenic diet with intermittent fasting may offer several benefits:
- Smoother Path to Ketosis: Intermittent fasting may help your body reach ketosis quicker than the keto diet alone. During fasting, insulin levels and glycogen stores decrease, leading your body to naturally start burning fat for fuel.
- Increased Fat Loss: Combining the diet and the fast may help you burn more fat than the diet alone. Intermittent fasting boosts metabolism by promoting thermogenesis, or heat production, and may preserve muscle mass during weight loss and improve energy levels.
- Appetite Control: Intermittent fasting can reduce hunger and promote feelings of fullness, which may aid weight loss.
Safety and Considerations
Combining the ketogenic diet with intermittent fasting is likely safe for most people. However, pregnant or breastfeeding women and those with a history of disordered eating should avoid intermittent fasting. People with certain health conditions, such as diabetes or heart disease, should consult with a doctor before trying intermittent fasting on the keto diet.
It's important to note that it may not work for everyone. Some people may find that fasting on the keto diet is too difficult, or they may experience adverse reactions, such as overeating on non-fasting days, irritability, and fatigue.
Is Combining Both Necessary?
Intermittent fasting is not necessary to reach ketosis, even though it can be used as a tool to do so quickly. Simply following a healthy, well-rounded keto diet is enough for anyone looking to improve health by cutting down on carbs.