Are you confused by all the endless marketing of diets and weight-loss strategies? This series will look at popular diets and review the research behind them.
What is it?
The ketogenic, or “keto”, diet is a low-carbohydrate and fat-rich eating plan that has been used for many centuries to treat certain medical conditions. The ketogenic diet was popularly used in the 19th century to control diabetes. It was first introduced in 1920 as a treatment for epilepsy in children who were unable to receive medication. It has been used in closely controlled settings to treat cancer, diabetes and polycystic Ovarian Syndrome, as well as Alzheimer’s disease.
This diet is becoming increasingly popular as a weight-loss strategy because of the low-carb diet craze. It all started in 1970s with Atkins, a low-carbohydrate and high-protein diet that was a huge commercial success. Other low-carb diets, such as the Paleo and South Beach diets, are high in protein, but low in fat. The ketogenic diet, on the other hand, is distinguished by its high-fat content (often 70% to 80%), but with only moderate amounts of protein.
How it works
The ketogenic diet is based on the idea that the body will lose glucose, the main source of energy, if it is depleted of carbohydrate foods, then a secondary fuel called ketones, is made from stored fat. (Hence, the name “keto-genic). Because it can’t store glucose, the brain needs 120g of glucose daily. Fasting is when there are very few carbohydrate intakes. The body pulls glucose from the liver first and then temporarily breaks down muscle to release glucose. After this process continues for three to four days, the blood levels of insulin, a hormone known as, decreases and the body starts using fat as its primary fuel. The liver makes ketone bodies out of fat. These ketone bodies can be used even when glucose is not present. 
This is when ketone bodies build up in the blood. Normal ketosis is experienced by healthy people when they fast (e.g., while sleeping over) or engage in strenuous exercise. The ketogenic diet advocates that blood ketones levels should not exceed a safe level. This is known as ketoacidosis. Because the brain uses ketones as fuel, healthy people will usually produce enough insulin to stop excess ketones from developing. The time taken to reach ketosis and the amount of ketone bodies in the blood will vary from person-to-person. This is dependent on factors like body fat percentage and resting metabolism rate. 
What is ketoacidosis?
Ketoacidosis is a condition where excessive ketone body levels can cause dangerously high blood acidity. Ketoacidosis is when the kidneys start to produce ketone bodies and body water in urine. This causes some fluid-related weight loss. Ketoacidosis is most common in people with type 1 diabetes. This is because insulin, a hormone that stops the overproduction ketones, is not produced. In rare cases ketoacidosis can also occur in individuals who have not been diagnosed with diabetes. [4,5]
There is no “standard” ketogenic diet that has a certain ratio of macronutrients (carbohydrates and protein) The ketogenic diet reduces total carbohydrate intake by less than 50g per day, which is less than a medium plain bagel. It can also be as low at 20 grams per day. Most ketogenic resources recommend an average of 70-80% fat, 5-10% carbohydrates, 10-20% protein, and 5-7% fat from total daily calories. This means that a 2000-calorie diet would have 165g fat, 40g carbohydrate, 75g protein, and 45g sugar. Because too much protein can cause ketosis, the ketogenic diet has a lower protein intake than other low-carb diets. A ketogenic diet provides enough protein to maintain lean body mass, including muscle, while still causing ketosis.
There are many ketogenic diets, but none ban carb-rich food. You may recognize some of these foods: starches made from whole and refined grains, such as breads, cookies, pasta, rice and pasta; potatoes, corn and other starchy veggies; and juices. Beans, legumes, most fruits, and some vegetables may not be obvious. Many ketogenic diets allow foods high in saturated fat such as fatty cuts of meat, processed meats and butter. However, they also allow food rich in unsaturated fats such as nuts and seeds, avocados and plant oils. The ketogenic food list may differ depending on where you get your information.
Here is a list of foods that are generally allowed on the diet
* High emphasis on fats in every meal and snack to satisfy the high-fat requirement. Lard, cocoa butter, poultry fat, most plant fats (olive oil, palm oil, coconut fat), certain nuts (macadamias, walnuts almonds, pecans), as well as seeds (sunflowers, pumpkins, sesame seed, hemp, flax) are all allowed.
* Some dairy foods might be allowed. Dairy can be a good source of fat but some dairy foods are high in natural sugars like cream and full-fat milk. These dairy foods are therefore restricted. Butter and hard cheeses might be permitted due to their lower lactose levels.
* Protein stays moderate. Many programs recommend grass-fed beef (not grains-fed) and free range poultry, which offer slightly higher levels of omega-3 fats, as well as pork, bacon, wild-caught seafood, organ meats and eggs, and certain nuts and seeds.
* All non-starchy vegetables are allowed: Most leafy greens (kale and Swiss chard), collards, spinachs, bok choys, lettuces), broccoli, Brussels sproutss, cauliflower, bell peppers. Onions, garlic, mushrooms. cucumbers. Celery. Summer squashes.
* Some fruits are small in size, such as berries. They are higher in net carbs* than other fruits, despite being carbohydrate rich.
* Other: Dark chocolate (at least 90% cocoa solids), dark chocolate, cocoa powder, unsweetened tea and coffee, as well as unsweetened mustards, vinegars, and mustards.
* Whole and refined grains, flour products, added sugars in food or beverages, starchy vegetables such as potatoes, corn, winter squash, and other whole and refined grain products.
* Other than the permitted list of fruits, except when they are included in a designated carbohydrate restriction. All fruit juices.
* Lentils, beans, and peanuts are all included.
* Some programs allow small amounts or low-carbohydrate beers and wines, but most prohibit full-carbohydrate wine and beer.
*What are Net Carbs?
Both “net carbs” or “impact carbs”, are terms that are used in both ketogenic and diabetic diets. These terms are interchangeable and unregulated. They appear on food labels to say that the product has less “usable” carbohydrates than what is listed.  The amount of carbohydrate directly absorbed by the human body and that contribute calories are called net carbs. These are calculated by subtracting the indigestible carbohydrate amounts from the total carbohydrate. Indigestible (or unabsorbed) carbohydrates are insoluble fibers found in whole grains, fruits, vegetables, and sugar alcohols such as mannitol and sorbitol. These sugar alcohols are commonly used in sugar-free diabetic foods products. These calculations are not exact and reliable because of the variability in sugar alcohols’ effects on blood sugar absorption. Sugar alcohols can still add calories and increase blood sugar. The net carbs do not affect the total calorie count, which is important for weight loss. Even within the ketogenic community, there is much debate about net carbs.
The ketogenic diet is a way to lose weight. Once this is achieved, one can follow the ketogenic diet for a few days each week or several weeks per month to prevent weight gain. The days can be interchanged with days that allow for higher carbohydrate intake.
The Research So Far
In the short-term, the ketogenic diet is known to have beneficial metabolic effects. In addition to weight loss, other health parameters that are associated with excess weight such as insulin resistance, high bloodpressure, elevated cholesterol, and triglycerides have been improved. [2,7] Type 2 diabetes is becoming a growing concern. Although there are many theories about why the ketogenic diet promotes weight-loss, they have not been proven in consistent research. [2,8,9]
* Satisfying effect due to high-fat diet.
When eating a restricted amount of carbohydrate, there is a decrease in appetite-stimulating hormones such as insulin or ghrelin.
* Ketone bodies play a direct role in reducing hunger. They are the body’s primary fuel source.
* Increased calorie consumption due to metabolic effects of converting protein and fat to glucose.
* Increased fat loss and lean body mass partly due to lower insulin levels.
Below is a summary of research findings. The research listed below has been restricted to ketogenic diet research: They contain approximately 70-80% fat, 10-15% protein, and 5–10% carbohydrates. These ratios may not be applicable to diets that are otherwise called “low carbohydrate”, which allows for higher amounts of carbohydrate or protein. This list only includes diets that use the terms “ketogenic” and “keto” or follow the macronutrient ratios mentioned above. This list does not include studies that have examined ketogenic diets for obesity and overweight, even though there is extensive research. This paragraph was added to clarify 5.7.18.
* 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. The authors acknowledge that there was a slight weight difference of approximately 2 pounds between the diets. However, compliance with the ketogenic diet decreased over time which could have explained the larger difference at one and two years. (The authors didn’t provide any additional data).
* A systematic review of 26 short term intervention trials (ranging from 4-12 weeks), evaluated the appetites and weights of obese and overweight individuals on either a low-calorie diet (800 calories per day) or a ketogenic diet (no calorie restriction, but =50gm carbohydrate/day) using a validated and standardised appetite scale. The studies did not compare the two diets. Instead, participants’ appetites were measured at baseline and after the diet ended. Participants reported feeling less hungry and more satisfied after losing significant weight. The authors observed that participants did not feel more hungry despite strict diets. They speculated that this was due to changes in appetite hormones like ghrelin, leptin, and ketone bodies as well as increased fat and protein intakes. Further research is needed to determine if a lower level of ketone can suppress appetite. In other words, could a higher carbohydrate intake be combined with a milder ketosis to still have a satisfying effect. This could be used to allow the inclusion of healthier higher carbohydrate foods such as whole grains, legumes and fruit. 
A study of 39 obese people who were on a ketogenic diet very low in calories for eight weeks showed a loss of 13% and significant reductions of fat mass, insulin levels and blood pressure. They had a decreased appetite because their levels of ghrelin didn’t increase when they were in ketosis. However, their ghrelin levels and cravings for food significantly increased during the 2-week period after they were released from ketosis. 
* 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. The ketogenic diet offered 980 calories, 12% carbohydrate and 36% protein. 52% of the weight loss was due to Mediterranean diet. This diet provides about 1800 calories, 58% carbohydrate and 15% protein. 27% of the Mediterranean diet’s calories are from fat. Eighty-eight% of participants followed the whole regimen.  The ketogenic diet in this study was slightly lower in fat, carbohydrate, and protein than the typical ketogenic diet which provides 70% or more calories from fat and less protein.
It can be difficult to follow a high-fat diet. Extreme carbohydrate restriction can cause hunger, fatigue, mood swings, constipation, headaches, brain fog, and irritability.
A long-term ketogenic diet can have some negative side effects, such as increased risk of osteoporosis and kidney stones, as well increased levels of uric acids (a risk factor for developing gout). If a wide variety of foods that are recommended for ketogenic diet aren’t included, there may be nutritional deficiencies. You should not eat only high-fat foods. It is also important to include a variety of foods other than meat, fish, vegetables, nuts, seeds, and fruits. This will ensure that you get adequate amounts of fiber, vitamins, minerals (iron and magnesium), and other nutrients such as whole grains, which are often missing from the ketogenic diet. A registered dietitian can help you create a ketogenic diet that reduces nutritional deficiencies, as whole food groups are not allowed.
* What are the long-term effects (over a year) of the ketogenic diet, and what safety concerns are associated with it?
* Does the diet have health benefits that extend to high-risk individuals who are older or have multiple health conditions? What diseases are the potential benefits of the diet?
* Since fat is the primary source of energy, will there be a long-term effect on your health if you consume different types (saturated or unsaturated) of fats in ketogenic diets?
* Can a high-fat, moderately protein ketogenic diet be used safely for diseases that affect normal protein and fat metabolism (e.g. kidney or liver disease)?
* Are there times when a ketogenic diet is too restrictive?
The research available on the ketogenic diet to lose weight is limited. The majority of studies have been limited in number, had short durations (12 weeks or less), and did NOT include control groups. Some people have experienced short-term weight loss, improvements in blood sugar and total cholesterol as well as improved blood pressure. These effects are not as dramatic after a year when compared to conventional weight loss methods. 
Compliance may be difficult if you eliminate several food groups. The American Heart Association’s Dietary Guidelines for Americans recommends against focusing on foods high in saturated fat. This can have negative effects on blood LDL cholesterol. It is possible to alter the diet to include foods rich in saturated fat, such as avocado, olive oil, nuts, seeds and fatty fish.
For those who have struggled to lose weight using other methods, a ketogenic diet might be an option. Due to individual differences in genetic makeup and body composition, the exact amount of fat, carbohydrate and protein required to achieve health benefits will differ. It is important to consult your physician and a dietitian before starting a ketogenic diet. This will allow you to monitor any changes in your biochemistry and create a meal plan tailored to your current health condition. The guidance of a dietitian can also be provided regarding reintroducing carbohydrates after weight loss.
Modified carbohydrate diets following the Healthy Eating Plate model can provide adequate weight loss and health benefits. 
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