The ketogenic, or keto, diet is a popular and effective way to lose weight and improve your health. This low-carb, high-fat diet shifts the body's metabolic state, leading to elevated ketone levels, a condition called ketosis. When followed correctly, this diet raises blood levels of ketones, which are chemical byproducts that provide a new fuel source for your cells and are responsible for most of the unique health impacts of the keto diet.
Introduction to Ketosis and the Keto Diet
On a keto diet, your body undergoes many biological adaptations, including a reduction in insulin levels and the increased breakdown of fat. When this happens, your liver starts producing high numbers of ketones to supply energy for your brain. Understanding ketosis and its effects on the body is crucial for anyone considering or currently following a ketogenic diet.
Ketosis vs. Ketoacidosis
It is important to understand the difference between ketosis and ketoacidosis. During very low carbohydrate intake, the regulated and controlled production of ketone bodies causes a harmless physiological state known as dietary ketosis. In ketosis, the blood pH remains buffered within normal limits. The latter is a very serious condition that can affect people with diabetes. Diabetic patients know that the detection in their urine of the ketone bodies is a danger signal that their diabetes is poorly controlled. Indeed, in severely uncontrolled diabetes, if the ketone bodies are produced in massive supranormal quantities, they are associated with ketoacidosis. In this life-threatening complication of diabetes mellitus, the acids 3-hydroxybutyric acid and acetoacetic acid are produced rapidly, causing high concentrations of protons, which overwhelm the body's acid-base buffering system.
How Ketosis Works
Ketosis is a metabolic state in which your body uses fat for fuel instead of carbs. It occurs when you significantly reduce your consumption of carbohydrates, limiting your body’s supply of glucose (sugar), which is the main source of energy for the cells.
Following a ketogenic diet is the most effective way to enter ketosis. Generally, this involves limiting carb consumption to around 20 to 50 grams per day and filling up on fats, such as meat, fish, eggs, nuts, and healthy oils. It’s also important to moderate your protein consumption because protein can be converted into glucose if consumed in high amounts, which may slow your transition into ketosis.
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Types of Ketogenic Diets
There are several versions of the ketogenic diet, and what you eat depends on the type. They include:
- Standard Ketogenic Diet (SKD): This is a very low carb, moderate protein, and high-fat diet. It typically contains 70% fat, 20% protein, and only 10% carbs.
- Cyclical Ketogenic Diet (CKD): This diet involves periods of higher carb refeeds, such as 5 ketogenic days followed by 2 high carb days.
- Targeted Ketogenic Diet (TKD): This diet allows you to add carbs around workouts.
- High Protein Ketogenic Diet: This is similar to a standard ketogenic diet but includes more protein. The ratio is often 60% fat, 35% protein, and 5% carbs.
However, only the standard and high-protein ketogenic diets have been studied extensively. Cyclical or targeted ketogenic diets are more advanced methods and primarily used by bodybuilders or athletes. The information in this article mostly applies to the standard ketogenic diet (SKD), although many of the same principles also apply to the other versions.
Benefits of Ketosis
Research has shown that ketosis may have several health benefits. One of the biggest benefits of ketosis may be weight loss. The process can help you feel less hungry, which may lead to eating less food. It can help you lose belly fat (visceral fat) while maintaining a lean mass. Other possible benefits of ketosis include treating and managing diseases such as:
- Epilepsy: Healthcare providers often put children with epilepsy on the keto diet to reduce or even prevent seizures by altering the “excitability” part of their brain.
- Other Neurologic Conditions: Research has shown the keto diet may help improve neurological conditions such as Alzheimer’s disease, autism, and brain cancers such as glioblastoma.
- Type 2 Diabetes: The keto diet can help people with Type 2 diabetes lose weight and manage their blood sugar levels.
- Heart Disease: The keto diet may lower your risk of developing cardiovascular disease by lowering your blood pressure, improving your HDL (“good”) cholesterol levels, and lowering your triglycerides.
- Metabolic Syndrome: The keto diet may reduce your risk of developing metabolic syndrome, which is associated with your risk of heart disease.
Ketosis has also been shown to increase your focus and energy. The keto diet delivers your body’s energy needs in a way that reduces inflammation. Research suggests your brain works more efficiently on ketones than on glucose.
10 Common Signs and Symptoms of Ketosis
Here are 10 common signs and symptoms of ketosis, both positive and negative:
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- Bad Breath: Many people on keto and similar diets, like the Atkins diet, report that their breath takes on an unusual, fruity smell. Elevated ketone levels cause the bad breath. The specific culprit is acetone, a ketone that exits the body in your urine and breath. While this breath may be less than ideal for your social life, it can be a positive sign for your diet. Brushing your teeth several times per day or using sugar-free gum can resolve the issue. Staying hydrated by drinking a lot of water may also help. Check the nutrition label for carbs if you’re using gum or other alternatives like sugar-free drinks. These products may raise your blood sugar levels and reduce your ketone levels.
- Weight Loss: Keto diets, along with other low-carb diets, are highly effective for weight loss, though it should be noted that in one study, 8 participants dropped out because of safety concerns such as increased LDL cholesterol or increased creatinine. As many weight loss studies have shown, you may experience both short- and long-term weight loss when switching to a keto diet. Fast weight loss can occur during the first week. While some people believe this to be fat loss, it’s primarily water weight. After the initial rapid drop in water weight, you should continue to lose body fat consistently as long as you stick to the diet and remain in a calorie deficit.
- Increased Ketones in the Blood: One of the hallmarks of a keto diet is a reduction in blood sugar levels and an increase in ketones. As you progress into a keto diet, you’ll start to burn fat and ketones as your main fuel sources. The most reliable and accurate method of measuring ketosis is to measure your blood ketone levels using a specialized meter. This is the method used in most research studies. The meter measures your ketone levels by calculating the amount of beta-hydroxybutyrate (BHB) in your blood. This is one of the primary ketones present in the bloodstream. According to some experts on the keto diet, nutritional ketosis is defined as blood ketones equal to or above 0.5 millimolar (mM). The main downside of this test method is that it requires pricking your finger to draw blood. What’s more, test kits can be expensive. For this reason, most people will just perform one test per week or every other week.
- Increased Ketones in the Breath: Another way to measure blood ketone levels is a breath analyzer. It monitors acetone, one of the three main ketones in your blood during ketosis. This gives you an idea of your body’s ketone levels since more acetone leaves the body when you’re in nutritional ketosis. The use of acetone breath analyzers has been shown to be fairly accurate, though less accurate than the blood monitor method.
- Appetite Suppression: Many people report decreased hunger while following a keto diet. The reasons why this happens are still being investigated. However, it’s been suggested that this hunger reduction may be due to alterations to your body’s hunger hormones, along with an increased intake of proteins. The ketones themselves may also affect your brain, helping to reduce appetite.
- Increased Focus and Energy: People often report brain fog, tiredness, and feeling sick when starting a very low carb diet. This is termed the “low carb flu” or “keto flu”. However, long-term keto dieters often report increased focus and energy. When you start a low carb diet, your body must adapt to burning more fat for fuel instead of carbs. When you get into ketosis, a large part of the brain starts burning ketones instead of glucose. It can take a few days or weeks for this to start working properly. Ketones are an extremely potent fuel source for your brain. They have even been tested in a medical setting to treat brain diseases and conditions such as concussion and memory loss. Eliminating carbs can also help control and stabilize blood sugar levels. This may further increase focus and improve brain function.
- Short-Term Fatigue: The initial switch to a keto diet can be one of the biggest issues for new dieters. Well-known side effects can include weakness and fatigue. These often cause people to quit the diet before they get into full ketosis and reap many of the long-term benefits. These side effects are natural. After several decades of running on a carb-heavy fuel system, your body is forced to adapt to a different system. To reduce fatigue during this switch, you may want to take electrolyte supplements. If you do, be sure to read the labels on any electrolyte supplements since they may contain added carb content. Electrolytes are often lost because of the rapid reduction in your body’s water content. When adding these supplements, make sure to include sodium, potassium, and magnesium.
- Short-Term Decreases in Performance: As discussed above, removing carbs can lead to general tiredness at first. This includes an initial decrease in exercise performance. It’s primarily caused by the reduction in your muscles’ glycogen stores. They provide the main and most efficient fuel source for all forms of high-intensity exercise. After several weeks, many keto dieters report that their performance returns to normal. In certain types of ultra-endurance sports and events, a keto diet could even be beneficial. What’s more, there are further benefits - primarily an increased ability to burn more fat during exercise. One small yet famous study found that athletes who had switched to a keto diet burned as much as 230% more fat when they exercised compared to athletes who weren’t following this diet. While it’s unlikely that a keto diet can maximize performance for elite athletes, once you become fat-adapted, it should be sufficient for general exercise and recreational sports.
- Digestive Issues: Digestive issues such as constipation and diarrhea are common side effects in the beginning. Some of these issues should subside after the transition period, but it may be important to be mindful of different foods that may be causing digestive issues. Also, make sure to eat plenty of healthy low carb veggies, which still contain plenty of fiber. Most importantly, don’t make the mistake of eating a diet that lacks diversity. Doing so may increase your risk of digestive issues and nutrient deficiencies.
- Insomnia: One big issue for many keto dieters is sleep, especially when they first change their diet. A lot of people report insomnia or waking up at night when they first reduce their carbs drastically. However, this usually improves in a matter of weeks. Many long-term keto dieters claim that they sleep better than before after adapting to the diet.
Potential Risks and Side Effects
While the keto diet has its benefits, staying on it in the long term may have some negative effects, including risks of the following:
- Low protein in the blood
- Extra fat in the liver
- Kidney stones
- Micronutrient deficiencies
A type of medication called sodium-glucose cotransporter 2 (SGLT2) inhibitors for type 2 diabetes can increase the risk for diabetic ketoacidosis, a dangerous condition that increases blood acidity. Anyone taking this medication should avoid the keto diet. More research is being done to determine the safety of the keto diet in the long term. Keep your doctor informed of your eating plan to guide your choices.
Foods to Eat and Avoid
Here’s a list of foods that need to be reduced or eliminated on a ketogenic diet:
- Sugary Foods: Soda, fruit juice, smoothies, cake, ice cream, candy, etc.
- Grains or Starches: Wheat-based products, rice, pasta, cereal, etc.
- Fruit: All fruit, except small portions of berries or strawberries
- Beans or Legumes: Peas, kidney beans, lentils, chickpeas, etc.
- Root Vegetables and Tubers: Potatoes, sweet potatoes, carrots, parsnips, etc.
- Low Fat or Diet Products: Low fat mayonnaise, salad dressings, and condiments
- Some Condiments or Sauces: Barbecue sauce, honey mustard, teriyaki sauce, ketchup, etc.
- Unhealthy Fats: Processed vegetable oils, mayonnaise, etc.
- Alcohol: Beer, wine, liquor, mixed drinks
- Sugar-Free Diet Foods: Sugar-free candies, syrups, puddings, sweeteners, desserts, etc.
You should base the majority of your meals around these foods:
- Meat: Red meat, steak, ham, sausage, bacon, chicken, and turkey
- Fatty Fish: Salmon, trout, tuna, and mackerel
- Eggs: Pastured or omega-3 whole eggs
- Butter and Cream: Grass-fed butter and heavy cream
- Cheese: Unprocessed cheeses like cheddar, goat, cream, blue, or mozzarella
- Nuts and Seeds: Almonds, walnuts, flaxseeds, pumpkin seeds, chia seeds, etc.
- Healthy Oils: Extra virgin olive oil, and avocado oil
- Avocados: Whole avocados or freshly made guacamole
- Low Carb Veggies: Green veggies, tomatoes, onions, peppers, etc.
- Condiments: Salt, pepper, herbs, and spices
It’s best to base your diet mostly on whole, single-ingredient foods.
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Sample Keto Meal Plan
Here’s a sample ketogenic diet meal plan for one week:
- Monday
- Breakfast: Veggie and egg muffins with tomatoes
- Lunch: Chicken salad with olive oil, feta cheese, olives, and a side salad
- Dinner: Salmon with asparagus cooked in butter
- Tuesday
- Breakfast: Egg, tomato, basil, and spinach omelet
- Lunch: Almond milk, peanut butter, spinach, cocoa powder, and stevia milkshake with a side of sliced strawberries
- Dinner: Cheese-shell tacos with salsa
- Wednesday
- Breakfast: Nut milk chia pudding topped with coconut and blackberries
- Lunch: Avocado shrimp salad
- Dinner: Pork chops with Parmesan cheese, broccoli, and salad
- Thursday
- Breakfast: Omelet with avocado, salsa, peppers, onion, and spices
- Lunch: A handful of nuts and celery sticks with guacamole and salsa
- Dinner: Chicken stuffed with pesto and cream cheese, and a side of grilled zucchini
- Friday
- Breakfast: Sugar-free Greek, whole milk yogurt with peanut butter, cocoa powder, and berries
- Lunch: Ground beef lettuce wrap tacos with sliced bell peppers
- Dinner: Loaded cauliflower and mixed veggies
- Saturday
- Breakfast: Cream cheese pancakes with blueberries and a side of grilled mushrooms
- Lunch: Zucchini and beet “noodle” salad
- Dinner: White fish cooked in olive oil with kale and toasted pine nuts
- Sunday
- Breakfast: Fried eggs with and mushroomslunch: low carb sesame chicken and broccoli
- Dinner: Spaghetti squash Bolognese
Always try to rotate the vegetables and meat over the long term, as each type provides different nutrients and health benefits.
Tips for Eating Out on Keto
When eating out, select a meat-, fish-, or egg-based dish. Order extra veggies instead of carbs or starches, and have cheese for dessert.
Managing the Keto Flu
Many of the side effects of starting a ketogenic diet can be limited. Easing into the diet and taking mineral supplements can help.
Supplements for Keto
Although no supplements are required, some can be useful.
- MCT Oil: Added to drinks or yogurt, MCT oil provides energy and helps increase ketone levels.
- Minerals: Added salt and other minerals can be important when starting out due to shifts in water and mineral balance.
- Caffeine: Caffeine can have benefits for energy, fat loss, and performance.
- Exogenous Ketones: This supplement may help raise the body’s ketone levels.
- Creatine: Creatine provides numerous benefits for health and performance. This can help if you are combining a ketogenic diet with exercise.
- Whey: Use half a scoop of whey protein in shakes or yogurt to increase your daily protein intake.
Additional Considerations
During very low carbohydrate intake, the regulated and controlled production of ketone bodies causes a harmless physiological state known as dietary ketosis. Ketone bodies flow from the liver to extra-hepatic tissues (e.g., brain) for use as a fuel; this spares glucose metabolism via a mechanism similar to the sparing of glucose by oxidation of fatty acids as an alternative fuel. In comparison with glucose, the ketone bodies are actually a very good respiratory fuel. Indeed, there is no clear requirement for dietary carbohydrates for human adults. Interestingly, the effects of ketone body metabolism suggest that mild ketosis may offer therapeutic potential in a variety of different common and rare disease states. Also, the recent landmark study showed that a very-low-carbohydrate diet resulted in a significant reduction in fat mass and a concomitant increase in lean body mass in normal-weight men.
Contrary to popular belief, insulin is not needed for glucose uptake and utilization in man. According to the American Heart Association (AHA) Nutrition Committee, "Some popular high-protein/low-carbohydrate diets limit carbohydrates to 10 to 20 g/d, which is one fifth of the minimum 100 g/day that is necessary to prevent loss of lean muscle tissue [1]." Clearly, this is an incorrect statement since catabolism of lean body mass is reduced by ketone bodies (possibly through suppression of the activity of the branched-chain 2-oxo acid dehydrogenase), which and probably explains the preservation of lean tissue observed during very-low-carbohydrate diets.
The hormonal changes associated with a low carbohydrate diet include a reduction in the circulating levels of insulin along with increased levels of glucagon. This activates phosphoenolpyruvate carboxykinase, fructose 1,6-biphosphatase, and glucose 6-phosphatase and also inhibits pyruvate kinase, 6-phosphofructo-1-kinase, and glucokinase. However, the body limits glucose utilization to reduce the need for gluconeogenesis.
In the liver in the well-fed state, acetyl CoA formed during the β-oxidation of fatty acids is oxidized to CO2 and H2O in the citric acid cycle. However, when the rate of mobilization of fatty acids from adipose tissue is accelerated, as, for example, during very low carbohydrate intake, the liver converts acetyl CoA into ketone bodies: Acetoacetate and 3-hydroxybutyrate. The liver cannot utilize ketone bodies because it lacks the mitochondrial enzyme succinyl CoA:3-ketoacid CoA transferase required for activation of acetoacetate to acetoacetyl CoA [3]. Therefore, ketone bodies flow from the liver to extra-hepatic tissues (e.g., brain) for use as a fuel; this spares glucose metabolism via a mechanism similar to the sparing of glucose by oxidation of fatty acids as an alternative fuel. Indeed, the use of ketone bodies replaces most of the glucose required by the brain.
Not all amino acid carbon will yield glucose; on average, 1.6 g of amino acids is required to synthesize 1 g of glucose [4]. Thus, to keep the brain supplied with glucose at rate of 110 to 120 g/day, the breakdown of 160 to 200 g of protein (close to 1 kg of muscle tissue) would be required. This is clearly undesirable, and the body limits glucose utilization to reduce the need for gluconeogenesis and so spare muscle tissue.
In comparison with glucose, the ketone bodies are a very good respiratory fuel. Whereas 100 g of glucose generates 8.7 kg of ATP, 100 g of 3-hydroxybutyrate can yield 10.5 kg of ATP, and 100 g of acetoacetate 9.4 kg of ATP [5]. The brain will use ketone bodies whenever provided with them (i.e., whenever blood ketone body levels rise). The blood-brain barrier transporter for ketone bodies is induced during starvation or very low carbohydrate intake, further promoting the flow of ketone bodies [6]. This transporter has a Km that exceeds the concentrations of circulating ketone bodies that occur during starvation or very low carbohydrate intake, and a Vmax well in excess of energy demands [6]. Therefore, ketone body delivery to the brain will never be limited by this transporter. However, continued use of some glucose appears obligatory [6] and is supplied by way of hepatic gluconeogenesis. Finally, because of the inactivation of pyruvate dehydrogenase (by the low insulin concentration), the glucose that is used by tissues outside the brain is largely only partially broken down to pyruvate and lactate, which can then be recycled in the liver trough gluconeogensis [7]. Therefore, red blood cells, for instance, which have an obligatory requirement for glucose, are not depleting the body of glucose.
Interestingly, Volek et al. recently reported that a very-low-carbohydrate diet resulted in a significant reduction in fat mass and a concomitant increase in lean body mass in normal-weight men [8]. They hypothesized that elevated β-hydroxybutyrate concentrations may have played a minor role in preventing catabolism of lean tissue but other anabolic hormones were likely involved (e.g., growth hormone).