The Ketogenic Diet: Does it Work?

The ketogenic diet was originally developed in the 1920s to help children with epilepsy to control seizures. However, more recently it has become a trendy way to lose weight, improve health and even treat disease.

Characteristics of the ketogenic Diet

The ketogenic diet is characterised by a high fat content, with controlled amounts of protein and limited carbohydrate intake. There are different forms of the ketogenic diet, however for the purposes of this article, we will be referring to the classical ketogenic diet.

The classical ketogenic diet is based on a ratio system of fat to protein and carbohydrate. The most commonly used ratios are 4:1 and 3:1. This means that for every 4 or 3g of fat eaten, there is 1g of protein and carbohydrate. This is the minimal amount of protein required for normal growth and development.

The diet usually contains 20-50g carbohydrate/day whereas the government’s recommended daily amount in the UK is at least 260g/day. Fat provides between 80 and 90% of the total energy, with common sources including butter, cream, oil. Small amounts of protein foods such as poultry and fish are allowed, and low carbohydrate foods such as certain fruits and vegetables provide the remaining energy. High carbohydrate foods such as bread, pasta and rice are not usually permitted on this diet.

Acceptable Foods

  • Dairy: butter, cheese, cream

  • Fats: mayonnaise, oils, nuts, avocado

  • Protein: meat and chicken, fish and shellfish, eggs

  • Carbohydrates: low-carb vegetables like broccoli, mushrooms and onions, small amounts of low-carb fruit (i.e. berries)

  • Other: Herbs, spices, salt and pepper

How Does the Ketogenic Diet lead to Weight Loss?

The body’s main source of energy is in the form of carbohydrate. When we don’t eat enough carbohydrate, our body starts to utilise other sources of energy. For example, the body can adapt to use the energy stored in our liver and muscles, it can breakdown body fat, and it can even create carbohydrate itself in the liver.

When we consume too little carbohydrate, the body enters a fasting state. It uses body fat and protein to produce ketones in the liver, which provide energy for the body. Ketogenesis is a metabolic pathway that produces ketone bodies, which provide an alternative form of energy for the body. The aim of the ketogenic diet is to drive the process of ketogenesis and keep the body in a state of ‘ketosis’.

Research has shown that very low carbohydrate diets result in superior weight loss (marginally) compared to a low-fat diet. However, like the majority of diets, that difference in weight loss seems to disappear over time.

Other Health Benefits of the Ketogenic Diet

A recent review looking at the health benefits of the ketogenic diet in patients with type 2 diabetes found that the diet can have impressive results. Some of the benefits included weight loss, improvements in longer-term blood sugar levels (Hba1c) and blood lipid profiles, and even reversal of diabetic complications such as retinopathy. However, a lot of these studies have been conducted in animals, meaning that the results don’t necessarily apply to humans.

Similarly, another review looking at the effects of the ketogenic diet on cardiovascular risk found that the ketogenic diet may be associated with some improvements in cholesterol (HDL), however these effects are usually limited in time. The authors mentioned that some studies showed that high-fat diets have been associated with increased insulin resistance and non-alcoholic fatty liver disease in rodents, both of which are potential negative effects of the ketogenic diet.

The authors of both reviews concluded that further studies are required in larger groups of patients. They also mentioned that scientists don’t yet know the long-term effects of following a ketogenic diet in diabetic and heart disease patients.

The ketogenic Diet and Chronic Fatigue Syndrome (CFS)

There have not been any scientific studies looking at the effects of a ketogenic diet on chronic fatigue syndrome. No evidence means that we don’t know whether the intervention (i.e. the ketogenic diet) would be beneficial or harmful to the patient.

Although there are online bloggers and even doctors promoting ketogenic diets as cures for chronic fatigue syndrome, their arguments are highly flawed. For example, most studies were conducted in animals, which means the findings don’t necessarily translate to humans.

In fact, a large and recent systematic review found that there is insufficient evidence to support elimination or modified diets to treat the symptoms of chronic fatigue syndrome.

Interestingly, a Dutch study found that CFS patients tended to lead a healthier lifestyle (including adequate fruit, vegetable and fibre intake) compared with the general population and that there was no link between lifestyle factors and fatigue severity or functional impairments in CFS.

Cons of the Ketogenic Diet

The ketogenic diet is highly restrictive, meaning that it is very difficult to follow. As with any diet, following a highly restrictive regimen can lead to an obsessive and unhealthy relationship towards food. For this reason, the diet does not work for everyone.

It is also worth noting that following a ketogenic diet does not mean that you are in a state of ketosis. It is very difficult to maintain a state of ketosis, and the gold standard method to determine if your body is in ketosis is to test the pH of your urine, which may not be realistic in day-to-day life. Strong smelling breath (similar to nail polish remover) is another indicator of being in a state of ketosis.

The diet has also been associated with some unpleasant side effects, often referred to as ‘keto flu’. These include bad breath, constipation, tiredness, headaches and fatigue. It is also worth noting that this is not a balanced diet, and therefore it requires careful planning and supervision.

Finally, people often lose weight on a low carbohydrate diet due to reduced calorie intake, however research has shown that in the longer term, weight regain is common amongst dieters.

Take away message

A ketogenic diet has been shown to be an effective treatment for certain conditions such as epilepsy, and has been shown to marginally accelerate weight loss when compared with other diets. More research is required in humans to better understand the long-term effects of the ketogenic diet on our health.

However, it is hard to follow due to its restrictive nature, and has the potential to be heavy on red meats and processed foods, which can increase our risk of diseases like colorectal cancer. A ketogenic diet requires careful planning and ideally supervision from a Registered Dietitian to ensure sufficient nutritional adequacy.

There remains strong evidence to support the health benefits of a balanced and unprocessed diet which is rich in wholegrains, fruits, vegetables, lean meat and fish and legumes. As with any diet, the choice is yours.


Additional References:

Gandy, J. (2016). Manual of dietetic practice. 5th ed. Chichester: Wiley, pp.198-199.