What's the ketogenic diet?
Ketogenic diets, also known as 'keto' diets, are very low in carbohydrates, moderate in protein and high in fat.
Ketogenic diets gained popularity as a tool for weight loss in the 1970’s, after Dr Robert Atkins published his now famous dietary programme the ‘Atkins Diet’, which is a modified version of the ketogenic diet. Ketogenic, Atkins and other low-carbohydrate diets continued to become increasingly popular throughout the 1990’s.
Learn more about the history of ketogenic diets in medicine and mental health.
Do you have to cut calories on the ketogenic diet?
Typically, when people talk about going on a diet this means either reducing the amount of food they eat, or swapping high-calorie foods in their diet in favour of low-calorie foods. Both of these methods focus on cutting calorie consumption, which is usually for the purpose of weight loss. However, ketogenic diets don’t focus on calorie restriction. Instead, the main purpose of the ketogenic diet is to reduce the number of carbohydrates (carbs) in favour of eating more fat.
Ketogenic diets typically have a macronutrient ratio of:
- Carbohydrates: a very small amount of carbohydrates (carbs), generally less than 30-50 grams per day.
- Protein: a modest amount.
- Fat: a high amount, generally two-thirds of the daily food intake.
The amount of carbs consumed on a ketogenic diet is much lower compared with other low-carb diets. For example, the Atkins diet is less strict than the ketogenic diet, as you can consume about 50 - 150 grams of carbohydrates.
The ketogenic diet is essentially a reversal of the Western diet, where 50% of calories come from carbohydrates, 15% protein, and 35% fat.
Understanding macronutrient ratios
All the foods we eat contain different amounts of carbohydrates, fat and protein, which are known as macronutrients. Your body and brain require energy to function and these macronutrients provide your body with the energy it needs. This energy can be converted and measured as calories. In contrast, micronutrients are the vitamins and minerals that are vital for us to function in the long term, which don’t contain energy (calories). Humans tend to eat a higher proportion of carbohydrates compared with protein and fat because carbs are the easiest macronutrient for the body to break down and convert into energy.
- Carbohydrates are our main source of energy, as all carbs are eventually broken down into glucose (blood sugar).
- Protein is broken down into amino acids and is essential for muscle growth and to repair tissue.
- Fat is a valuable source of energy that takes longer for the body to break down and convert into fuel.
What are the different types of ketogenic diets?
There are different variations of the ketogenic diet, depending on the proportion of fat, protein and carbs. We’ve ranked them in order of most to least restrictive (meaning how low their carbohydrate content is):
- Classic ketogenic diet (90% fat, 6% protein, 4% carbs)
- Low glycemic index treatment (60% fat, 30% protein, 10% carbs)
- Modified Atkins diet (65% fat, 25% protein, 10% carbs)
- Medium-chain triglycerides (71% fat, 10% protein, 19% carbs)
What is ketosis?
Although carbs are usually our main source of energy, if the body runs out of glucose (carbs) to burn it can convert fat (from food or from fat tissue) into ketones. When the body switches from using glucose to ketones for energy, this is known as ketosis. Under normal conditions, the body won’t convert fat into ketones because it prefers using glucose as the main source of energy. The body will only start converting ketones from fat if consumption of carbs have been drastically reduced (as with ketogenic diets) or when fasting for 16 hours or more.
Ketones can also enter the brain to partially replace glucose as a source of fuel. When the brain switches from using glucose to ketones, this can sometimes have a dramatic effect on changing brain function. Scientists are currently exploring whether ketones can be used to improve the symptoms of some neurological and mental health conditions.
Learn more about the use of ketogenic diets in medicine and mental health.