What is the Keto diet and what can you eat on it?

With so many diets to choose from it can be an exhausting task trying to figure out which one will work best for you.

a collage showing the keto diet foods

The keto diet is a favourite with Halle Berry, the Kardashians and basketball player Lebron James. But what exactly does it entail? We've asked the experts.

It's the famous low-carb high-fat diet (opens in new tab) that has garnered an army of fans worldwide. They claim that unlike quick-fix extreme diets (opens in new tab), the ketogenic plan is one that changes eating habits and develops a healthier way of eating long term. And it's this and the different variations of this diet - including the Lazy keto (opens in new tab) plan - that enables dieters to easily factor it into their lifestyle.

Though there's plenty of praise, some skeptics suggest it’s outdated for painting carbohydrates as a non-essential. And even representatives of Harvard Medical School have warned (opens in new tab) of its risks. "The Keto diet, when done right and for the appropriate reasons, can be a safe and effective option for many," Nutritionist and PT Florence Seabright (opens in new tab) tells us. "If, however, it’s being undertaken for the wrong reasons, such as weight loss, it can be potentially damaging and demotivating long term."

What is a keto diet?

Essentially the keto diet is a low-carb, moderate-protein and very high-fat eating plan. "The goal of this kind of diet is to reduce carbohydrates enough (less than 20-50g per day) that you put the body into a state of ketosis, in which it prioritises burning fat (opens in new tab) for fuel," explains nutritionist Flo, founder of FBF Collective (opens in new tab).

The keto diet dates back to the 1920s when it was originally used as a treatment option for children with epilepsy. Though over time, it has became more popular as a weight loss diet. Whilst different variations of the keto diet exist, the plan usually focuses on the food groups - carbohydrates, protein and fat - in varying consumptions.

Person preparing avocado, part of the keto diet

Credit: Getty

An Indian review into keto diets (opens in new tab) established four different kinds:

  • Standard ketogenic diet: A typical day on the original keto diet would see a dieter consume 70% fat, 20% protein, and only 10% carbs.
  • High protein ketogenic diet: As the title suggests, this version of keto is more of a high-protein diet (opens in new tab). This increases the protein allowance to 35% a day. Whilst decreasing the daily fat allowance to 60%. Plus only 5% carbs.
  • Cyclical ketogenic diet: The cyclical keto diet involves five days on the original keto plan and 2 high carb days.
  • Targeted ketogenic diet: This alternative keto plan is similar to the standard plan, but allows carbs to be eaten before workouts.

How do keto diets work?

Keto diets work by putting the body into a metabolic state known as ketosis. This ‘state’ forces the body to burn fat rather than carbs for energy. And this is what helps dieters to lose weight. 

"Due to the significantly reduced intake of carbohydrates, your body starts producing high levels of “ketone bodies” from fat," Flo explains. "These are prioritised to help fuel the body, rather than using glucose."

Glucose (or sugar) is usually the body's main source of energy, so when this is deprived it needs to get this from elsewhere - in this case the high-fat you are consuming on keto. This in turn is what turns your body into a fat-burning machine.

One Australian study (opens in new tab) indicates your body is in ketosis when you experience symptoms like dry mouth, plus increased thirst and urination. Whilst another study (opens in new tab) warns that protein consumption can affect your ability to enter ketosis, because this can be converted into glucose if eaten in high quantities. It's for this reason that on a standard keto diet - your protein allowance is restricted to 20% a day.

A loss of water weight is another way keto diets works to aid weight loss. One Spanish study (opens in new tab) highlighted that the restriction of carbohydrates on keto leads to a reduction in water weight. This is because when carbohydrates are stored in the body, they hold water. So when you reduce the amount of carbs going into the body, these stored carbohydrates are released with the water, resulting in weight loss in some circumstances.

Keto diet food list

  • Meats – fish, beef, lamb, poultry, eggs, etc.
  • Leafy greens – spinach, kale, etc.
  • Above ground vegetables – broccoli, cauliflower, etc.
  • High fat dairy products – hard cheeses, high fat cream, butter, etc.
  • Nuts and seeds – macadamias, walnuts, sunflower seeds, etc.
  • Avocado and berries – raspberries, blackberries, and other low glycemic impact berries.
  • Sweeteners – stevia, erythritol, monk fruit, and other low-carb sweeteners.
  • Other fats – coconut oil, high-fat salad dressing, saturated fats, etc.

A post shared by Suzanne Ryan (@ketokarma) (opens in new tab)

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Foods to avoid on the keto diet

  • Grains – wheat, corn, rice, cereal, etc.
  • Sugar – honey, agave, maple syrup, etc.
  • Fruit – apples, bananas, oranges, etc.
  • Tubers – potato, yams, etc.
  • Legumes - kidney beans, lentils, chickpeas, etc.
  • Sauces - mayonnaise, tomato ketchup, BBQ sauce, salad dressings, etc.
  • Alcohol - beer, wine, spirits, etc.

Just like the Atkins diet (opens in new tab), when following keto you'll want to stick to low carb recipes (opens in new tab) or have meals that skip them entirely. It's also important to stop drinking alcohol (opens in new tab) whilst on the plan.

A lot of the foods you're told to avoid are also ones that contain too much sugar (opens in new tab) or hidden sugar (opens in new tab). Indeed a 2020 review (opens in new tab) into sugar and obesity deemed that the two had a hand-in-hand relationship.

Recommended books:

Complete Keto Diet Book - £9.99 | Amazon 
A total guide for beginners and long-term followers, this bookazine is essential for anyone who wants to learn more about living a keto lifestyle. Find recipes for easy meals, delicious desserts and healthy snack ideas aong with tips for sticking to your plan.  (opens in new tab)

Complete Keto Diet Book - £9.99 | Amazon 

A total guide for beginners and long-term followers, this bookazine is essential for anyone who wants to learn more about living a keto lifestyle. Find recipes for easy meals, delicious desserts and healthy snack ideas aong with tips for sticking to your plan. 

Keto Baking -  £9.99 | Amazon
Following a keto diet doesn't mean you have to miss out on cakes, cupcakes, biscuits and even doughnuts - as this recipe bookazine shows! Find 50+ low carb and sugar free recipes, with under 10g net carbs. This in-depth guide also looks at the science and benefits of the diet plan.  (opens in new tab)

Keto Baking -  £9.99 | Amazon

Following a keto diet doesn't mean you have to miss out on cakes, cupcakes, biscuits and even doughnuts - as this recipe bookazine shows! Find 50+ low carb and sugar free recipes, with under 10g net carbs. This in-depth guide also looks at the science and benefits of the diet plan. 

What are the benefits of the keto diet?

1. Weight loss

Dr Sohere Roked from OMNIYA MediClinic says that because you are removing carbs and sugars largely from your diet, the body has no other option but to burn fat for energy. And this inevitably is what causes weight loss on the Keto plan. What's more, there are over 30 scientific studies showing that, compared to other diets, low-carb and keto diets result in more effective weight loss. Take for example this Brazilian study, which found that weight loss results were greater on the keto diet compared to a low fat diet.

2. Controlled blood sugars

Dr Roked confirms that keto naturally lowers blood sugar levels. This is because you’re not eating as many carbs, so your body can’t produce glucose. As such, researchers at the South Asian University even "recommend it (keto) as an adjunctive treatment for type 2 diabetes". With their 2020 study also finding the plan helps to control glucose levels.

3. Increased energy

Because a keto diet helps your body turn fat into an energy source, it is also helping to increase your energy levels as it is giving your body a more reliable energy source. This allows you to feel more energised throughout the day.

woman running with headphones on path

(Image credit: Getty)

4. Good for the brain

A 2019 study found that the ketogenic diet "improved cognitive performance in elderly adults with Alzheimer's disease". There's further good news too, with an American study reporting that those who follow a low-carb plan had improved verbal memory.

5. Better appetite control

Fat is naturally more satisfying and ends up leaving us in a satiated (‘full’) state for longer. This means less cravings for less junk food and snacking in-between meals. In fact, one Aberdeen based study deemed keto as significantly reducing hunger and food intake compared to non-ketogenic diets.

What are the side effects of the ketogenic diet?

The most common side effects for people undergoing the keto diet are headaches, tiredness, muscle fatigue, cramping, constipation and heart palpitations.

Often these symptoms are mild and short-lived for most people. As they're just your body adjusting to burning a new energy source: fat. Nevertheless, there are things you can do to help deal with said side effects.

How to reduce the side effects:

  • Cramps: specifically leg cramps, are a result of keto being a diuretic (promoting water and salt loss). Therefore it's essential to make sure you drink plenty of water (opens in new tab) and up your sodium intake – sprinkle a little salt on everything!
  • Constipation: Seek out natural constipation remedies (opens in new tab) like drinking waters and ensuring you eat vegetables which contain good quality fibre.
  • Breath: "Some people may also experience bad breath," nutritionist Flo tells us. So be sure you're brushing frequently and have mints to hand after meals.

Nutritionist and PT Flo puts some of these side effects down to the change in carboydrate consumption too:

"A sudden and drastic reduction in carbohydrates can initially cause some side effects; from nausea and vomiting to flu like symptoms in the first few weeks," she tells us. "These generally improve after the initial period and one way of minimising these side effects would be to reduce carbohydrate intake over time rather than all at once."

If you experience side effects like heart palpitations, stop your diet immediately and seek medical help. No diet is ever worth risking your life for.

Is the keto diet safe?

Yes, the keto diet is generally very safe. Though health professionals have suggested that people with certain conditions may need to take extra precautions when on the plan.

People who suffer from diabetes may have to dramatically lower any insulin doses they take immediately.

"As the keto diet restricts the carbohydrates that raise your blood sugar, you may no longer need medication to lower it," GP Dr Shan Hussain (opens in new tab) tells GoodtoKnow. "Taking the same dose of insulin as you did prior to adopting a low-carb diet might result in hypoglycemia (low blood sugar)."

a close up of a diabetes test - diabetics should be careful when following the keto diet

Credit: Getty

If you are on blood pressure medication and start a low-carb diet, there’s also a risk of getting low blood pressure. Which means you may very quickly become too healthy for your medication. If you feel weak, tired, dizzy or generally unwell you should check your blood pressure. If it’s low (e.g. below 120/80) you should contact your doctor to discuss lowering or stopping your medication.

Dr Shan advises anyone who is "on medication for diabetes or hypertension should proceed with caution and seek medical advice prior to undertaking the Keto diet".

Women who are breastfeeding (opens in new tab) should also be cautious and choose a more moderate low-carb version of the keto diet. As in extremely rare cases a strict low-carb diet could be potentially dangerous.

Breastfeeding can cause you to lose sugar via the milk, possibly around 30 grams per day or more. So not eating carbohydrates could lead to a dangerous condition called ketoacidosis, in rare cases. Aim for around 50 grams of carbs a day and always consult your health advisor or breastfeeding specialist for advice before embarking on a diet while breastfeeding.

The restrictive nature of Keto furthermore means that it can incur some dietary problems whilst following. And because of this, Flo asks to seek medical advice first. Especially if worried:

"Undertaking a very restrictive dietary intervention such as this can have implications on your vitamin and mineral intake, fibre intake, food choices and habits," she says. "Even your relationship with food.

"Therefore, if the ketogenic diet is something you are keen to try, I would always advise getting some professional support from a fully qualified Nutritionist or Dietitian to help you understand if this is the best way to reach your specific goal. And, if so, to support you along the way."

Keto diet - a nutritionist's verdict

Nutritionist and personal trainer Flo Seabright doesn't see the keto diet as a sustainable long-term diet. "Although there is some discussion about the potential health benefits of following a ketogenic diet, it is often wrongly hailed as a 'magic pill' for weight loss and can be difficult to do safely and effectively alone."

"We already know that carbohydrates are not the enemy and, although the sheer amount of restriction needed to achieve such a low intake of carbohydrate might, initially, contribute to reducing overall calorie intake (the primary driver of fat loss), the purpose of the keto diet and achieving ketosis is not to help facilitate weight loss."

She asks that those who are thinking about taking it up consult a medical professional first. As it's important to receive the right information to "maximise the chances of a positive outcome".

"Just like any other dietary intervention, Keto has its place," she adds. "It’s just about making sure we are using the right tool, at the right time, for the right reason."