Is the Keto diet worth the hype?
The ketogenic or ‘keto’ diet is becoming increasingly popular. This is often promoted as a way to lose weight, boost health, and even cure diseases. Let’s take a look at the background and mechanisms to this diet, as well as the evidence related to this.
What is the Keto Diet?
This is a high fat, very low-carb diet. This usually contains less than 50g of carbohydrates per day, but some people aim for less than 20g (1; 2); whereas the recommended daily carbohydrate intake for an average woman is about 250g per day (3).
Variations of the Keto Diet Include (4; 5):
- The high-protein ketogenic diet – this is high in fat and protein, while remaining low in carbohydrates
- The cyclical or ketogenic diet – this allows more carbs on certain days, such as a higher carbohydrate intake on 2 days per week or after a workout
- The medium-chain triglyceride (MCT) keto diet – encourages the majority of fat intake from things like MCT oil
Foods Allowed on the Keto Diet:
- Butter and oils
- Cheese 🧀
- Cream 🥛
- Meat and chicken 🍗
- Fish and shellfish 🐟
- Eggs 🥚
- Nuts 🥜
- Avocado 🥑
- Low-carb vegetables like: broccoli, kale, spinach, mushrooms and onions 🥦
- Small amounts of low-carb fruit like: strawberries and blackberries 🍓
- Herbs, spices, salt and pepper 🌱
Foods Discouraged on the Keto Diet:
- Sugary food and drinks 🍩
- Grains and foods like: pasta, rice and couscous 🍚
- Higher-carb vegetables like: potato, squash and carrots 🥔
- Beans, peas, lentils and chickpeas
- Most types of fruit 🍎
- Foods which contain ‘bulk sweeteners’ like sorbitol and xylitol
- Alcohol 🥂
How Does the Keto Diet ‘Work’?
Carbohydrate is the main source of energy for our body, so when we aren’t getting enough carbohydrate our body starts to: use up our energy stores in our liver and muscle; break down fat; create carbohydrate for itself (which is called gluconeogenesis) (6).
But having an extremely low intake of carbohydrate on an ongoing basis causes the body to go into ‘starvation mode’. So to produce another source of energy, the body uses fat and protein to create ‘ketone bodies’ in the liver (7). This process is called ‘ketosis’. Our body can use roughly 80% of the ketone bodies it creates for energy, and the rest are lost through our skin, breath and urine (6).
But following the keto diet doesn’t necessarily mean that you are producing ketone bodies, as it is very difficult to keep the body in ketosis. For example, eating just one sandwich or a large banana would take most people out of ketosis. One sign that the body is creating ketones bodies is strong smelling breath, which is often described as fruity or similar to nail varnish remover.
Established Medical Uses for the Keto Diet
The ketogenic diet first emerged in the 1920s as a treatment for childhood epilepsy. This is still used today for some children with epilepsy, along with guidance from a doctor and dietitian, if they don’t tolerate or don’t respond to their medication (8; 9). However, there is not enough evidence to use this as routine treatment for adults who have epilepsy (9).
This diet can also be used under medical and dietetic supervision as part of the treatment of metabolic disorders such as: glucose transporter type 1 deficiency syndrome (GLUT1DS) and pyruvate dehydrogenase deficiency (PDH) (10).
The Keto Diet & Cancer
There is a theory that keto diets may be useful in the treatment of certain types of brain cancer, based on a metabolic pathway related to cancer called called ‘The Warburg Effect’ (11). There are some animal and lab-based studies which support this, but overall the evidence is very mixed and some studies have found that ketone bodies may actually encourage the growth of cancer cells (11; 12; 13).
Research is ongoing in this area, but at present more evidence is needed (13; 14). Infact following an extremely restrictive diet such as this could be harmful, as cancer already increases the risk of malnutrition, and staying well-nourished is an important part of cancer recovery.
The Keto Diet & Diabetes
Some studies have found that the ketogenic diet may be useful for those with type 2 diabetes, in terms of: promoting weight loss, reducing average blood sugar levels (HbA1c), improving kidney function and heart health (2). But the evidence for a specific benefit of the keto diet in this context isn’t very strong, and much of this is based on small animal studies or confounded by weight loss.
For example, people often lose weight on low-carb diets like this in the short-term, because this causes a reduction in calorie intake. But it is common to regain weight after it has been lost (15), and the recent DIETFITS study highlighted that for those who are trying to lose weight, reducing calories in a realistic way is more important than whether the diet is low-carb or low-fat (16).
Diabetes UK recently highlighted that a low-carb diet can work for some people with type 2 diabetes, but there isn’t enough long-term evidence about this, and there also isn’t enough evidence to recommend low-carb diets for those with type 1 diabetes (17). The keto diet has also been seen to increase the risk of hypoglycemia (dangerously low blood sugar levels) in some people who take medication for type 2 diabetes (1).
The Keto Diet & Heart Disease
Some studies have suggested that the keto diet may have a positive effect on cholesterol levels and heart health (18). But the results of many of these studies may be due to weight loss or a reduced calorie intake, so it is hard to say whether this is related to ketosis itself.
The total amount of carbohydrate consumed is not seen to have a significant effect on the risk of death from heart disease (3). However, a high intake of sugar and refined carbohydrate (white bread, white pasta etc,) is linked with an increase risk of heart disease, and a high intake of wholegrains and fibre is linked with a lower risk of heart disease (3). So the quality of the carbohydrates, and choosing wholegrain versions is important.
How Healthy is the Keto Diet?
A recent large study found that a low-carb diet, where less than 40% of daily energy was coming from carbohydrate, was associated with a higher risk of early death (19). The ketogenic diet is well below this, with usually only 5-10% of daily energy coming from carbohydrate. This study also found the best protection from early death was linked with a moderate intake of carbohydrate (50 – 55% from daily energy), which is in line with the UK government recommendations.
The keto diet is usually very high in saturated fat, and low in fruit, vegetables and wholegrains – which is associated with a higher risk of constipation, bowel cancer, heart disease and early death (3; 20). With a lack of carbohydrate to fuel the body there is a risk that the body will start to burn muscle for energy and some people may feel that they have less energy to exercise. Furthermore, as the keto diet is very restrictive, it runs the risk of creating an obsessive and unhealthy relationship with food.
‘Keto flu’ can occur on this diet, which includes symptoms such as: tiredness, headaches, diarrhoea, cramps, and weakness (21). Some people also find the high fat content of this diet causes nausea or bowel problems. Furthermore, high levels of ketone bodies may weaken the bones, cause kidney problems and physical stress to the body (22; 23; 24).
Take Home Message
The keto diet is very restrictive. Although there are some specific medical cases where the keto diet can be effective, it certainly isn’t an elixir of health as there are numerous risks related to it. There is much more evidence to support the benefits of including plenty of wholegrains, fruit, vegetables, and beans in our diet; rather than following the keto diet which involves cutting out most of these foods.
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(2) Azar et al. (2016) “Benefits of Ketogenic Diet for Management of Type Two Diabetes: A Review
(3) SACN (2015) “Carbohydrates and Health” [accessed September 2018 via: https://www.gov.uk/government/publications/sacn-carbohydrates-and-health-report]
(4) Examine.com (2017) “Does “low-carb” have an official definition?.” [accessed September 2018 via: https://examine.com/nutrition/does-low-carb-have-an-official-definition/]
(5) Neal et al. (20019) “A randomized trial of classical and medium-chain triglyceride ketogenic diets in the treatment of childhood epilepsy” [accessed September 2018 via: https://www.ncbi.nlm.nih.gov/pubmed/19054400]
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