A ketogenic, or keto diet is a high fat diet with an ultra-low amount of carbohydrates, and a moderate amount of protein. A typical ketogenic macronutrient split is 70% fat, 20% protein and 10% carbohydrate. For reference, most Western diets consist of 40-60% carbohydrates.
A keto diet normally allows for around 25-60g of carbs each day (5-12% of total energy intake of a 2,000kcal diet), but you may even see keto diets suggesting as low as 10-15g net carbohydrates a day. Net carbohydrates are those which are digested and absorbed into the body. To get an idea of how few carbohydrates can be eaten, one medium banana contains roughly 25g of carbs.
The maximum amount of carbohydrates a person can eat while still being in nutritional ketosis depends on a variety of factors such as exercise, how long a person has been in ketosis, and body mass index (BMI). Nutritional ketosis is defined as having a blood ketone level above 0.5mmol/L.
Ketones are a group of fatty acid metabolites that our bodies can use as an energy source. They can be taken in the form of a supplement, termed exogenous ketones because they are produced outside of the body, but taking them doesn’t mean the body will enter ketosis.
The body will firstly use glucose as an energy source. However, once all the glucose has been used, including anything that can be converted to glucose such as glycogen, the body will produce ketones. Ketone production can be significantly increased during instances of starvation or with a very low carb intake. Fatty acids from food or stored body fat are combined with an enzyme and a series of chemical reactions occur which eventually form ketones. Breaking this down, this means the body switches from burning glucose to burning fat.
A moderate intake of protein is required for a ketogenic diet because some amino acids, the building blocks that make up protein, can be converted to glucose. Consequently, a high protein intake may take a person out of ketosis. Take a look at our Guide to Protein.
The point at which the body enters ketosis varies from person to person[1, 5]. For some, it can take a couple of days, and for others over a week. Exogenous ketones and ketosis fast do not appear to induce ketosis faster[7, 8], while there is stronger evidence for exercise speeding up the process[9, 10].
This is a more complex question than it first appears. As a keto diet reduces the amount of carbohydrate eaten, this causes a reduction in “empty” carbohydrates (carbohydrates with little nutritional value) and sugar. It also results in less high fat, high sugar, processed foods being eaten.
Many people report that a ketogenic diet increases satiety, in other words, how full they feel. Therefore, the amount of calories that are eaten freely over the day can decrease. The reasons behind this increase in fullness include a higher protein intake compared to a standard Western diet. Protein is the most filling macronutrient, and the body also uses more energy to metabolize protein than carbohydrates and fat so, in theory, energy expenditure increases.
In reality, results are mixed, and it appears a ketogenic diet can cause an increase in energy expenditure of around 50kcal a day; however, this does not translate to an increase in fat loss. Furthermore, ketones may impact hormones related to hunger and satiety[14, 15].
Rapid weight loss is often seen during the initial stages of a ketogenic diet. The body stores a certain amount of carbohydrate as glycogen in muscle and the liver. Glycogen holds onto water and so, during a ketogenic diet, the body dumps extra weight by using up the glycogen. The loss of water, rather than fat, is the main reason why people report initial rapid weight loss.
When compared to other calorie-controlled diets, contrary to popular opinion, ketogenic diets are just as effective for weight loss, not more. This is particularly true over six months or longer[17, 18]. The thought is because if the body is burning fat, then fat loss must be higher. What is often forgotten is that the consumption of fat is also significantly higher, and so fat is only lost in the same way as all diets, in a calorie deficit[19, 20]. Another important point is that over time, the amount of carbohydrate eaten often gradually increases, and there isn’t a decrease in fat or protein, causing weight loss to stall.
If you’re looking to lose weight, we have a handy Guide to Fat Loss.
Since the 1920s, ketogenic diets have been used in the treatment of epilepsy. Epilepsy is a group of related conditions that affect the brain and cause frequent seizures. Seizures occur due to a sudden jolt of electrical activity in the brain which disrupts normal brain function. For people, including children, that have a poor response to medication, a ketogenic diet can help to reduce the frequency and severity of seizures, among other symptoms, which makes epilepsy more manageable. It’s a carefully controlled diet that is conducted under the supervision of a doctor and dietitian. It’s still unclear how the ketogenic diet helps, but one school of thought is it modifies how neurons become excited.
It appears that a ketogenic diet can reduce the symptoms and progression of neurological diseases such as Alzheimer’s and Parkinson’s disease. Although the evidence is growing, it’s currently limited. Again, it’s unclear exactly how this may occur; it’s possible that, as these diseases hinder glucose metabolism, ketosis ensures energy via another source. Alternatively, the ketone bodies themselves may have neuroprotective effects.
As the development of these diseases is still poorly understood, there is no diet that has been shown to have a large impact on prevention. What’s more, the negative effects of the ketogenic diet must be considered. Neurodegenerative disorders put people at a greater risk of malnutrition and a lowered food intake. A ketogenic diet can cause gastrointestinal issues, a reduction in appetite and restricts the consumption of certain foods, thereby leading to worsening symptoms and difficulties in sticking to the diet. Consequently, for high-risk groups such as the elderly, these effects may mean a ketogenic diet is unsuitable[25, 28].
Despite these potential drawbacks, a ketogenic diet has been used successfully for many people with epilepsy, and its uses may widen in the future with continued research.
Keto flu refers to the collection of symptoms that can occur when you first start the diet. As the body adapts to less carbs, you may suffer from headaches, irritability, fatigue, and even muscle cramps. Water and electrolytes are rapidly lost in the initial phase[29, 30], so it’s advisable to increase water, sodium, and potassium intake to account for this loss and reduce any potential symptoms.
The average person will need several dietary changes when starting a ketogenic diet. Commonly, fruit and fibre intake decreases. This is because two portions of fruit can surpass the daily carbohydrate limit, and fibre is typically provided by wholegrains and fruit. The good news is a carefully planned ketogenic diet can still provide sufficient fibre through nuts and vegetables.
“Carefully planned” is the important phrase here. A ketogenic diet must be well thought out to ensure ketosis is maintained and all nutrient needs are met. The diet normally means animal foods become a larger proportion of the diet. The reason for this is that animal proteins tend to be found in foods that are naturally lower in carbohydrates and higher in fat than plant proteins, making them easier to fit into a ketogenic diet. This doesn’t mean the consumption of animal-sourced foods needs to increase but, as previously mentioned, the diet needs to be well planned.
The restrictive nature of a ketogenic diet can make it difficult to stick to in the long-term[31, 32]. If a person is better able to stick to a dietary pattern, then that way of eating is more likely to be successful. Therefore, it makes sense to understand what works for the individual.
On one hand, ketosis could help athletic endurance performance by avoiding glycogen depletion (hitting the wall) because glycogen isn’t being used as a major energy store. Additionally, the body becomes more efficient at using fat for energy. On the other hand, these adaptations may not be big enough to cause a significant change in performance. What’s more, during the final stages of high-intensity exercise glucose becomes more important, so a ketogenic diet may decrease performance[34, 36].
It appears in the general population that a ketogenic diet is likely to have little effect on performance, while in elite athletes there may be a noticeable decline[35, 37]. Further research is required using different types of exercise, duration, and the length of time the diet has been followed for[34-36, 38].
Huel products, on the whole, are not compatible with a ketogenic diet. This is because carbohydrates provide around 35-40% of the total calories of Huel products, except Huel Black Edition. The carbohydrates in Huel products provide an efficient source of energy, mainly from oats and flaxseed. These carbohydrate sources also provide several micronutrients such as vitamin B1 and B6. Moreover, Huel products are high in protein, and most ketogenic diets are moderately low in protein. The current Huel formula is suitable for most of the population who do not follow a ketogenic diet.
The high proportion of fat that is necessary for ketosis creates stability and shelf life issues. Therefore, the fat would have to be separate from the main product and added at the time of consumption, which takes away the convenience of Huel.
However, Huel Black Edition can be tweaked to produce a meal that is suitable for a ketogenic diet. Blending 50g of Huel Black Edition and 50g of desiccated coconut creates a meal where 70% of the calories are provided by fat, 18% by protein and 12% by available carbs. This 555kcal meal contains only 16g of available carbs.
Have a look at Low Carb Huel Hacks for some more ideas.
MCTs (medium-chain triglycerides) are saturated fats that are metabolized differently to the more abundant long-chain triglycerides. They provide a quick source of energy similar to carbohydrates and so can be really useful for people following a ketogenic diet.
MCT oil is commonly sourced from coconut oil. It can also be converted to a powder, making it more convenient. MCT powder is present in Huel Powder and Ready-to-drink to provide an efficient source of saturated fatty acids. You can find out more about MCTs here.
MCT products can help someone sustain ketosis and provide an alternative source of energy. However, adding MCT oil will not cause an individual to enter ketosis without also following a ketogenic diet.
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