What is the Ketogenic Diet?

The keto diet, short for ketogenic diet, is a way of eating that is very low in carbohydrates and higher in fat.

Carbohydrates are found in foods such as bread, pasta, rice, potatoes, cereals, fruit, sugary foods, and many drinks. When you eat fewer carbohydrates, your body has less glucose available for energy. It then starts producing ketones from fat, which can be used as another fuel source.

Many people following keto aim to eat around 50g of carbohydrates a day or less. This is much lower than a typical diet and means cutting back on many everyday foods.

It should be noted that keto is different from a general low-carb diet. A low-carb diet may simply reduce carbohydrates, while keto is usually more strict and aims to keep carbs low enough for your body to enter ketosis.

Keto usually focuses on foods that are low in carbohydrates and higher in fat or protein. This can include foods such as:

• Meat, fish, and eggs
• Cheese and full-fat yoghurt
• Tofu and some plant-based proteins
• Nuts and seeds
• Avocado
• Olive oil and other unsaturated oils
• Lower-carb vegetables, such as broccoli, spinach, courgette, mushrooms, peppers, and cauliflower

Although keto is higher in fat, it is still worth thinking about the type of fat you choose. A healthier approach should include unsaturated fats, such as olive oil, avocado, nuts, seeds, and oily fish, rather than relying too heavily on butter, cream, processed meat, fried foods and cheese.

You should also try to include plenty of lower-carb vegetables. These can help provide fibre, vitamins, and minerals, which can be harder to get if you cut out many fruits, wholegrains, beans, and lentils.

Because keto is very low in carbohydrates, it limits many foods that are usually part of a balanced diet. This will include:

• Bread
• Rice
• Pasta
• Potatoes
• Cereals
• Cakes, biscuits, and sweets
• Sugary drinks
• Fruit juice and smoothies
• Most high-carb snacks
• Many fruits
• Beans and lentils
• Some higher-carb vegetables

This is one reason keto can be difficult to follow long term. Some of the foods it limits, such as wholegrains, beans, lentils, fruit, and starchy vegetables, can be nutritious and high in fibre.

If you choose to try keto, it’s important to plan your meals carefully so you are still getting enough fibre, protein, vitamins, and minerals.

Some people find that keto helps them lose weight because it reduces hunger, keeps food choices simple, and cuts out many high-calorie, high-sugar foods.

It may also lead to quick weight loss at the start. However, some early weight loss can be water weight rather than body fat. This happens because your body stores carbohydrates with water, so cutting carbs can reduce stored water in the body.

Keto may also help some people with type 2 diabetes improve blood sugar control in the short term. However, if you have diabetes, you should speak to your GP or pharmacist before making major changes to your carbohydrate intake. This is especially important if you take insulin or medicines that can cause low blood sugar.

Keto is not suitable for everyone, and is not the only way to lose weight. A balanced, reduced-calorie diet may be easier and safer for many people to maintain.

To put it plainly, keto can be restrictive. This means it may be hard to stick to, especially if you enjoy foods such as bread, pasta, potatoes, and similar meals with family and friends.

It may also increase the risk of missing out on important nutrients if it’s not planned well. Cutting out or reducing wholegrains, fruit, beans, lentils, and many vegetables can lower your intake of fibre, vitamins and minerals.

A low-fibre diet can also make constipation more likely. If you try keto, aim to include lower-carb sources of fibre, such as green vegetables, nuts, seeds, and small portions of suitable berries.

You may also notice side effects when you first start. This is sometimes called “keto flu”. Symptoms can include:

• Headache
• Tiredness
• Dizziness
• Feeling irritable
• Nausea
• Constipation
• Trouble sleeping

These symptoms often improve as your body adjusts, but you should get medical advice if they feel severe, do not improve in a few days, or you feel very unwell.

Keto can help some people lose weight, but it’s not the best approach for everyone.

The main reason it may work is that it can reduce appetite and make it easier to eat fewer calories. It also cuts out many foods that are easy to overeat, such as sweets, cakes, biscuits, sugary drinks, and large portions of refined carbohydrates.

However, keto can be hard to maintain. If you stop following it and return to old eating habits, you may regain weight. This is why the best weight loss plan is usually one you can keep up long term.

If keto feels too restrictive, a less strict low-carb diet or a balanced reduced-calorie diet may be easier. You don’t need to completely remove carbs to lose weight.

Keto may be safe for some people in the short term, but is not the right choice for everyone.

Because of its restrictive nature, it can be difficult to follow in a healthy way, and some people may end up eating too much saturated fat. Over time, this may not support heart health or digestive health.

Keto can also affect blood sugar levels. If you have diabetes, very low-carb eating may mean your medication needs reviewing. Don’t change your diabetes medicine without speaking to your healthcare team.

It's also important to know that nutritional ketosis is not the same as diabetic ketoacidosis. Diabetic ketoacidosis is a serious condition that can happen when ketone levels become dangerously high, usually in people with diabetes. If you have diabetes and notice high ketone readings, vomiting, extreme thirst, needing to pee more often, confusion, drowsiness, or fruity-smelling breath, seek urgent medical advice.

You should speak to a GP, pharmacist, or dietitian before starting keto if you:

• Have type 1 or type 2 diabetes
• Take insulin or diabetes medicines
• Are pregnant or breastfeeding
• Have kidney disease
• Have liver, pancreatic, or gallbladder problems
• Have a history of pancreatitis
• Have a history of eating disorders or disordered eating
• Take medicines where food intake affects your dose
• Are underweight or have recently lost weight without trying

If you have any long-term health condition, it’s worth getting advice before making a major change to your diet.