KandyWandy: Keto Diet: How It Works, What to Eat, Side Effects and Is It Safe?

Keto Diet: How It Works, What to Eat, Side Effects and Is It Safe?

Middle-aged adult preparing a nutritious lower-carbohydrate meal with fish, eggs, avocado and vegetables.

The ketogenic diet — usually shortened to the keto diet — is one of the most talked-about approaches to weight loss. It dramatically reduces carbohydrate intake while increasing fat, with the aim of shifting the body into a metabolic state called ketosis.

Supporters claim keto can rapidly burn body fat, reduce hunger, improve blood sugar and even transform metabolic health. At the same time, concerns have been raised about constipation, nutrient deficiencies, high cholesterol, sustainability and whether a very high-fat eating pattern is healthy over the long term.

The reality is more complicated than either side of the online debate suggests.

A ketogenic diet can produce weight loss and has legitimate medical uses. But ketosis is not a metabolic shortcut that makes calories irrelevant, and keto is not automatically healthier than other nutritious eating patterns.

Here is what the evidence says about how keto works, what you can eat, weight loss, diabetes, cholesterol, common side effects and who should be particularly cautious.

What Is the Keto Diet?

A ketogenic diet is a very-low-carbohydrate, high-fat eating pattern designed to make the body rely more heavily on fat and ketones for energy.

Normally, carbohydrates from foods such as bread, rice, pasta, potatoes, fruit and sugars are broken down into glucose, which can be used as an important energy source.

When carbohydrate intake becomes very low, insulin levels fall and the body's stored carbohydrate becomes depleted.

The liver then increases the conversion of fatty acids into substances called ketone bodies.

When ketone production rises sufficiently, the body enters nutritional ketosis.

What Is Ketosis?

Ketosis is a metabolic state in which the concentration of ketones in the blood rises because the body is relying more heavily on fat as an energy source.

Ketones can be used by tissues including the brain when glucose availability is reduced.

This is a normal physiological adaptation that can occur during fasting or prolonged carbohydrate restriction.

It is important, however, to distinguish nutritional ketosis from diabetic ketoacidosis.

Ketosis vs Ketoacidosis: They Are Not the Same

Nutritional ketosis from a ketogenic diet is not the same as diabetic ketoacidosis, commonly called DKA.

DKA is a potentially life-threatening medical emergency involving dangerously high ketone levels, metabolic acidosis and usually severe insulin deficiency.

It occurs most commonly in people with type 1 diabetes, although it can occur in other circumstances.

Symptoms can include:

excessive thirst
frequent urination
nausea and vomiting
abdominal pain
rapid or deep breathing
dehydration
fruity-smelling breath
confusion
extreme weakness

Suspected diabetic ketoacidosis requires urgent medical treatment.

How Many Carbohydrates Can You Eat on Keto?

There is no single universally accepted keto diet.

Many ketogenic diets restrict carbohydrate intake to approximately 20–50 grams per day, although the exact amount needed to maintain ketosis varies between individuals.

That is considerably lower than the carbohydrate content of a typical diet.

Someone following keto may therefore severely limit or avoid foods such as:

bread
pasta
rice
cereals
potatoes
cakes and biscuits
sweets
sugary drinks
many high-carbohydrate snacks
large portions of fruit
many starchy vegetables

This degree of restriction is one reason keto can be difficult to maintain over the long term.

What Foods Can You Eat on a Keto Diet?

A ketogenic diet typically focuses on foods that are naturally low in carbohydrates.

Examples include:

eggs
fish
seafood
poultry
meat
cheese
plain unsweetened yoghurt in suitable portions
olive oil
avocado
nuts
seeds
leafy green vegetables
broccoli
cauliflower
courgette
peppers
mushrooms
other non-starchy vegetables

However, simply being low in carbohydrate does not automatically make a food healthy.

The nutritional quality of the fats, proteins and vegetables chosen still matters.

A keto diet based heavily on processed meats, butter and foods rich in saturated fat is nutritionally different from one emphasising fish, olive oil, avocado, nuts, seeds and non-starchy vegetables.

What Foods Are Usually Limited on Keto?

Foods commonly restricted include:

bread
rice
pasta
breakfast cereals
potatoes
sweet potatoes
pastries
cakes
sweets
sugar
sweetened drinks
many fruits
beans and lentils in larger portions
some milk and yoghurt products
high-carbohydrate snack foods

Some of these foods, such as whole grains, fruit, beans and lentils, can be highly nutritious.

Their restriction is one reason careful planning becomes important.

Does Keto Help You Lose Weight?

It can.

People often lose weight after beginning a ketogenic or very-low-carbohydrate diet.

Part of the dramatic early reduction on the scale can result from water loss.

The body stores carbohydrate as glycogen, and glycogen is stored together with water. As glycogen stores decline during carbohydrate restriction, some associated water is lost.

After the initial period, meaningful fat loss still requires an overall energy deficit.

Keto may help some people achieve that deficit because higher intakes of protein and fat can increase fullness and the diet eliminates many calorie-dense refined carbohydrate foods.

But ketosis does not make energy balance irrelevant.

Does Keto Burn More Belly Fat?

You cannot instruct your body to burn fat exclusively from your abdomen by eating a particular diet.

When overall body fat decreases, abdominal fat may decrease as part of that process.

A ketogenic diet may therefore reduce waist circumference when it produces meaningful weight loss, but it should not be marketed as a method that specifically targets belly fat.

Is Keto Better Than Other Diets for Weight Loss?

Not necessarily.

Different dietary approaches can produce weight loss when they create an energy deficit and can be maintained.

The American Diabetes Association's 2026 Standards of Care emphasise that nutrition plans for weight management should be individualised. Its review notes that low-carbohydrate diets have not consistently produced greater long-term benefits than balanced-carbohydrate approaches.

This is an important point because short-term weight loss and long-term weight management are different challenges.

A diet can work extremely well for several months but still be unsuccessful for an individual if the restrictions cannot realistically be maintained.

The best eating pattern is not simply the one that produces the fastest initial change on the scale.

It also needs to support adequate nutrition, health and long-term adherence.

What Is the “Keto Flu”?

Some people experience unpleasant symptoms during the first days of severe carbohydrate restriction.

This collection of symptoms is often informally called the keto flu, although it is not influenza.

Possible symptoms include:

headache
fatigue
dizziness
irritability
difficulty concentrating
nausea
muscle cramps
reduced exercise performance
constipation

Changes in fluid and electrolyte balance may contribute to some early symptoms.

Symptoms are usually temporary, but severe or persistent symptoms should not simply be dismissed as a normal part of keto.

Can Keto Cause Constipation?

Yes.

Constipation can occur, particularly if dramatically reducing carbohydrates also reduces dietary fibre.

Whole grains, beans, lentils and many fruits are important fibre sources in conventional diets.

Someone following keto therefore needs to deliberately include lower-carbohydrate fibre sources such as:

leafy vegetables
broccoli
cauliflower
avocado
nuts
seeds

Adequate fluid intake is also important.

A diet that technically keeps someone in ketosis but contains very little fibre is not well designed.

Can Keto Cause Nutrient Deficiencies?

A poorly planned ketogenic diet can make obtaining certain nutrients more difficult because several major food groups are restricted.

Potential concerns may include inadequate:

fibre
thiamine and other B vitamins
folate
vitamin C
magnesium
potassium
calcium
certain plant-derived nutrients

The exact risk depends on what someone actually eats.

A diet rich in varied non-starchy vegetables, nuts, seeds, fish and other nutrient-dense foods is very different from a diet composed mainly of processed meat, cheese and butter.

Does Keto Cause Bad Breath?

It can.

One ketone called acetone can be released through the breath.

Some people therefore notice an unusual fruity or chemical-like breath odour after entering ketosis.

This can be harmless in nutritional ketosis.

However, fruity breath accompanied by symptoms suggesting diabetic ketoacidosis — particularly in someone with diabetes — should never simply be assumed to be ordinary “keto breath.”

Can Keto Cause Headaches?

Headaches may occur during the early transition to a ketogenic diet.

Possible contributors include:

fluid loss
changes in electrolyte balance
reduced caffeine intake
inadequate food intake
adaptation to severe carbohydrate restriction

Persistent, severe or unusual headaches require appropriate assessment rather than automatically being blamed on keto.

Does Keto Affect Cholesterol?

Responses vary.

Some people experience improvements in triglycerides and HDL cholesterol during carbohydrate restriction and weight loss.

However, LDL cholesterol can rise substantially in some people following a ketogenic diet, particularly when the diet contains large amounts of saturated fat.

This matters because elevated LDL cholesterol is an established cardiovascular risk factor.

Choosing predominantly unsaturated fats from foods such as:

olive oil
nuts
seeds
avocado
fish

may create a more favourable nutritional pattern than relying heavily on:

butter
fatty processed meats
coconut oil
large quantities of high-fat dairy products

Someone following keto — particularly a person with existing cardiovascular risk — may benefit from discussing appropriate cholesterol monitoring with a healthcare professional.

Is Keto Good for Your Heart?

The answer depends heavily on the foods used to construct the diet.

“Keto” describes carbohydrate restriction, not overall nutritional quality.

A ketogenic diet rich in vegetables, nuts, seeds, fish and unsaturated fats cannot automatically be considered nutritionally equivalent to one dominated by bacon, processed meats, butter and cheese.

Long-term cardiovascular evidence for ketogenic diets remains less established than the evidence supporting some other healthy dietary patterns.

Therefore, achieving ketosis should not become more important than overall food quality.

Can Keto Help Type 2 Diabetes?

Reducing carbohydrate intake can lower post-meal glucose levels, and low-carbohydrate eating patterns can be useful for some people with type 2 diabetes.

However, diabetes management needs to be individualised.

A major concern is that changing carbohydrate intake dramatically while continuing the same doses of certain glucose-lowering medicines may increase the risk of hypoglycaemia or other complications.

Medication adjustments should therefore be supervised appropriately.

The American Diabetes Association's 2026 guidance recognises low-carbohydrate eating patterns as one evidence-based option in some settings while emphasising individualised nutrition.

Keto and SGLT2 Inhibitors: An Important Warning

People taking SGLT2 inhibitor medicines need particular caution.

These medicines are used for conditions including type 2 diabetes, heart failure and chronic kidney disease.

They can increase the risk of a potentially dangerous condition called euglycaemic diabetic ketoacidosis, in which ketoacidosis may develop without the extremely high blood glucose traditionally associated with DKA.

The American Diabetes Association's 2026 Standards advise people at risk of ketoacidosis who are treated with SGLT inhibition about this danger and discourage ketogenic eating patterns in this situation.

Do not combine major carbohydrate restriction with diabetes medication changes without appropriate medical guidance.

What About Type 1 Diabetes?

A ketogenic diet can be particularly complicated for someone with type 1 diabetes because insulin deficiency is the central cause of diabetic ketoacidosis.

Anyone with type 1 diabetes considering major carbohydrate restriction should discuss it with their specialist diabetes team rather than attempting to manage insulin changes independently.

Can Keto Help Fatty Liver?

Weight loss itself can improve excess liver fat.

Research continues into whether ketogenic diets have particular effects on metabolic dysfunction-associated steatotic liver disease.

Some short-term studies have reported substantial reductions in liver fat during carbohydrate restriction.

However, promising short-term metabolic findings do not establish that keto is the best long-term treatment for everyone with fatty liver disease.

Sustainable weight management, dietary quality, physical activity and management of related metabolic conditions remain important.

Is Keto Safe for Your Kidneys?

A ketogenic diet is not automatically damaging to healthy kidneys, but people with kidney disease require additional consideration.

Kidney disease can affect how the body handles nutrients, fluids and electrolytes.

Some people with chronic kidney disease may also need individualised guidance concerning protein, potassium, phosphorus or other nutrients.

Anyone with known kidney disease should therefore seek professional advice before beginning a restrictive ketogenic diet.

Does Keto Mean Eating Unlimited Protein?

No.

A traditional ketogenic diet is primarily high in fat, not simply a high-protein diet.

Eating very large amounts of protein may also make maintaining ketosis more difficult for some people.

More importantly, “more protein” is not automatically better.

Protein requirements depend on factors including body size, age, activity, health status and goals.

Can You Exercise on Keto?

Yes, but performance responses vary.

People may initially notice reduced exercise capacity while adapting to carbohydrate restriction.

Carbohydrate is particularly useful during some forms of high-intensity exercise.

Some endurance athletes experiment with low-carbohydrate approaches, but being able to exercise on keto does not mean it improves performance for every athlete or activity.

People exercising for general health do not need to be in ketosis to obtain the benefits of physical activity.

Can Keto Cause Muscle Loss?

Any weight-loss programme can result in loss of some lean tissue as well as body fat.

Strategies that may help preserve muscle during intentional weight loss include:

adequate protein
resistance training
avoiding unnecessarily extreme calorie restriction
maintaining regular physical activity

Rapid weight loss is not automatically superior if a substantial proportion of the weight lost is lean tissue.

Can You Do Keto While Taking a GLP-1 Medicine?

This deserves individual consideration.

GLP-1 medicines can reduce appetite substantially and may cause gastrointestinal symptoms.

Combining a highly restrictive diet with markedly reduced food intake could make it more difficult for some people to consume adequate protein, fibre, fluids and micronutrients.

People using prescription weight-management medicines should focus on nutritional adequacy rather than assuming that stacking multiple restrictive strategies will necessarily accelerate healthy weight loss.

Who Should Be Cautious About the Keto Diet?

Professional advice is particularly important for people who:

have type 1 diabetes
take insulin or certain diabetes medicines
take an SGLT2 inhibitor
have kidney disease
have liver disease
have pancreatic disease
have certain gallbladder problems
are pregnant or breastfeeding
have a history of an eating disorder
take medicines that may be affected by major dietary changes
have a medical condition requiring specialised nutrition

Children should not be placed on a restrictive ketogenic diet for general weight loss without appropriate professional supervision.

Medical ketogenic diets used for epilepsy are specialised treatments and should not be confused with social-media weight-loss versions of keto.

Is Keto Safe During Pregnancy?

Pregnancy is not an appropriate time to experiment casually with highly restrictive diets.

Pregnancy changes nutritional requirements, and adequate intake of essential nutrients is important for both maternal health and fetal development.

Anyone who is pregnant and considering substantial carbohydrate restriction should discuss their diet with an appropriate healthcare professional.

What Is a Healthy Keto Diet?

If someone chooses to follow keto, nutritional quality still matters.

A better-planned version would generally emphasise:

Vegetables:
Leafy greens, broccoli, cauliflower, peppers, mushrooms and other non-starchy vegetables.

Unsaturated fats:
Olive oil, avocado, nuts and seeds.

Protein:
Fish, seafood, eggs, poultry and other suitable protein foods.

Fibre:
Low-carbohydrate vegetables, avocado, nuts and seeds.

Minimally processed foods:
Build most meals around recognisable whole foods rather than packaged products marketed as “keto.”

The word keto on a food package does not automatically make that food nutritious.

Do You Need Keto Products?

No.

Commercial keto bars, powders, drinks, cookies, supplements and ketone products are not required to follow a ketogenic diet.

Some are highly processed and expensive.

Products marketed as “keto” can still contain substantial calories, saturated fat, sweeteners or other ingredients that may not support someone's overall health goals.

Whole foods should generally form the foundation of the diet.

Do Exogenous Ketones Burn Body Fat?

Taking ketones is not the same thing as causing your body to burn its stored fat.

Exogenous ketone supplements can raise blood ketone concentrations, but that does not mean they automatically produce meaningful fat loss.

The presence of ketones in your bloodstream should not be confused with proof that large amounts of body fat are disappearing.

Do You Need to Measure Your Ketones?

Most people trying to improve their diet or lose weight do not need to obsessively monitor ketone levels.

Blood, breath and urine ketone measurements can be useful in specific medical or dietary circumstances.

But chasing the highest possible ketone reading is not the objective of healthy weight management.

Higher ketones do not automatically mean greater fat loss or better health.

Can You Stay on Keto Forever?

Some people can maintain a low-carbohydrate eating pattern for years, while others find strict keto extremely difficult to sustain.

Long-term adherence can be affected by:

food preferences
cultural eating patterns
family meals
social events
cost
food availability
digestive effects
restrictions on fruit, legumes and whole grains

A diet that works only when someone can avoid normal social life may not be a practical long-term solution.

It is reasonable to consider not only whether a diet works, but whether it fits your life.

Frequently Asked Questions

How Fast Can You Lose Weight on Keto?

Early scale weight can fall quickly because carbohydrate depletion causes loss of stored glycogen and associated water.

The rate of longer-term body-fat loss varies according to energy intake, starting weight, physical activity and individual factors.

Can I Eat Fruit on Keto?

Small portions of lower-carbohydrate fruits, particularly berries, may fit some ketogenic diets.

Many fruits contain enough carbohydrate that portion size becomes important when carbohydrate intake is severely restricted.

Fruit is nutritious, so restricting it should not automatically be considered a health benefit.

Are Bananas Keto?

Bananas contain relatively high amounts of carbohydrate compared with many foods typically included on strict ketogenic diets, so a whole banana may use a substantial proportion of someone's daily carbohydrate allowance.

Can You Eat Oats on Keto?

Traditional strict keto diets generally limit oats because they contain significant carbohydrate, although dietary approaches vary.

Can You Eat Beans on Keto?

Beans and lentils provide fibre, protein, minerals and other nutrients but also contain carbohydrate. Larger portions may not fit a strict ketogenic carbohydrate target.

Can Keto Cause Hair Loss?

Rapid weight loss, inadequate energy intake, insufficient protein and nutrient deficiencies can contribute to temporary hair shedding.

Hair loss has many other possible causes, so persistent shedding deserves appropriate assessment.

Does Keto Slow Your Metabolism?

Weight loss itself produces physiological adaptations that can reduce energy expenditure regardless of the diet used.

There is not good evidence that simply entering nutritional ketosis permanently “damages” metabolism.

Do You Need a Cheat Day on Keto?

No specific cheat day is medically required.

A high-carbohydrate meal may temporarily take someone out of ketosis, but the larger question is whether an eating pattern is sustainable enough that repeated cycles of extreme restriction and overeating are unnecessary.

The Bottom Line

The ketogenic diet is a legitimate dietary approach, not a magical fat-burning switch.

Severe carbohydrate restriction can produce nutritional ketosis and may help some people lose weight or manage certain metabolic goals. Keto also has established specialised medical uses, particularly in the treatment of some forms of epilepsy.

But being in ketosis is not synonymous with being healthy.

Food quality, adequate protein, fibre, micronutrients, overall energy intake, cardiovascular risk and whether the diet can realistically be maintained all matter.

Some people may thrive on a carefully planned lower-carbohydrate eating pattern. Others may achieve equally meaningful health improvements with a Mediterranean-style, balanced or other evidence-based approach.

People with diabetes, kidney disease or other significant medical conditions — particularly those taking SGLT2 inhibitors, insulin or other glucose-lowering medicines — should not make major carbohydrate changes without appropriate professional guidance.

The goal should not be to achieve the highest ketone reading.

It should be to find a nutritious, safe and sustainable way of eating that supports your health.

Sources and Further Reading

American Diabetes Association — Standards of Care in Diabetes 2026: Facilitating Positive Health Behaviors and Well-being
https://diabetesjournals.org/care/article/49/Supplement_1/S89/163932

American Diabetes Association — Standards of Care in Diabetes 2026: Obesity and Weight Management
https://diabetesjournals.org/care/article/49/Supplement_1/S166/163915

Mayo Clinic — Low-Carb Diet: Can It Help You Lose Weight?
https://www.mayoclinic.org/healthy-lifestyle/weight-loss/in-depth/low-carb-diet/art-20045831

Harvard Health — Keto Diet and Heart Health
https://www.health.harvard.edu/heart-health/keto-diet-is-not-healthy-and-may-harm-the-heart

Medical Disclaimer

This article is for general educational and informational purposes only and is not a substitute for professional medical advice, diagnosis or treatment. Restrictive diets can affect nutritional intake and may require changes to medicines, particularly medicines used for diabetes. Speak with an appropriate healthcare professional before beginning a ketogenic diet if you have a medical condition, are pregnant or breastfeeding, take prescription medicines or have concerns about your nutritional requirements. Seek urgent medical care if you develop symptoms suggesting diabetic ketoacidosis or another serious medical problem.