The Keto diet – Your essential guide
By Martin Ebner,
Updated Sept 2026
By now, you’ll have heard of the ketogenic diet, or keto for short. Bacon became a diet food, blueberries started looking suspicious and people began pouring oil into coffee as though breakfast hadn’t already suffered enough.
But what exactly is keto? Does it work for weight loss, what happens to your training and is removing almost every carbohydrate from your diet remotely sensible?
Here’s the useful version, without pretending ketosis gives you metabolic superpowers.
WHAT IS THE KETO DIET?
Keto is a very-low-carbohydrate, high-fat diet with enough protein to support your body without making protein the main source of energy.
Carbohydrate intake is usually kept below 50 grams per day and sometimes considerably lower. With very little glucose available, the liver produces ketones from fat, which the body and brain can use as an alternative fuel.
This creates nutritional ketosis. It isn’t the same thing as diabetic ketoacidosis, which is a dangerous medical emergency.
A typical keto diet might provide around 5 to 10 per cent of its calories from carbohydrates, 20 to 30 per cent from protein and the remainder from fat. Those numbers aren’t laws, but the carbohydrate restriction needs to be substantial enough for ketosis to occur.
DOES KETO WORK FOR WEIGHT LOSS?
Yes, keto can help people lose weight. It just doesn’t override energy balance.
During the first week or two, weight can fall quickly because reducing carbohydrate also reduces stored glycogen and the water held alongside it. That initial change isn’t all body fat, regardless of what the scales or somebody selling a keto program might suggest.
After that, keto can make a calorie deficit easier for some people. Protein and fat can be filling, food choices become more limited and removing bread, pastries, sweets, alcohol and most snack foods may reduce total calorie intake without deliberate counting.
The strongest broader evidence doesn’t show a dramatic long-term advantage, though. A Cochrane review of 61 randomised trials found little to no difference in weight loss between low-carbohydrate and balanced-carbohydrate weight-loss diets over periods of up to two years.
Keto works when it helps you eat fewer calories consistently. So do other diets.
BURNING MORE FAT ISN’T THE SAME AS LOSING MORE BODY FAT
When you eat considerably more fat and fewer carbohydrates, your body will burn more fat for fuel. That sounds impressive until you remember that you’re also eating considerably more fat.
Using fat for energy during the day doesn’t automatically mean the fat is coming from your waist. Some of it is coming from breakfast.
Body-fat loss depends on the longer-term balance between the energy you consume and use. Ketosis changes the fuel mix. It doesn’t make calories disappear.
That doesn’t make keto pointless. It means the value lies in appetite control, food preference and adherence, not a magical fat-burning state.
WHAT CAN YOU EAT ON KETO?
Most keto diets are based around meat, fish, eggs, full-fat dairy, tofu, olive oil, avocados, nuts, seeds, leafy greens and other lower-carbohydrate vegetables.
Bread, rice, pasta, cereals, potatoes, beans, lentils, most fruit, sweets and sugary drinks are heavily restricted or removed.
You can build a reasonably nutritious keto diet, but it requires more thought than simply adding butter and cheese to everything. Vegetables still matter. So do protein, fibre and the type of fat you eat.
Ideally, most of your fat should come from foods such as olive oil, nuts, seeds, avocado and oily fish rather than treating processed meat, cream and coconut oil as compulsory food groups.
PROTEIN STILL MATTERS
Keto is often described as moderate in protein because very high protein intake may make maintaining ketosis more difficult for some people. That doesn’t mean protein should be kept unnecessarily low.
If you’re dieting and strength training, you still need enough protein to support recovery and retain muscle. Base meals around a useful protein source rather than trying to hit your fat target first and adding protein afterwards.
I’ve covered sensible intake ranges in Protein for fitness goals: how much do you need?.
Losing weight while allowing a large amount of muscle to disappear with it isn’t a particularly impressive trade.
WHAT HAPPENS TO YOUR TRAINING?
Keto doesn’t automatically destroy strength. A 2024 systematic review and meta-analysis found no significant difference in squat or bench-press one-repetition maximum between ketogenic and non-ketogenic groups.
That doesn’t mean every type of performance is unaffected. Repeated hard efforts, higher-volume resistance training, sprinting and intense intervals rely heavily on carbohydrate. Some people adapt reasonably well, while others feel as though somebody has quietly removed the batteries from their legs.
If your priority is maximum high-intensity performance or muscle growth, heavily restricting carbohydrates may create a problem you didn’t need.
If your priority is weight loss and you genuinely prefer eating this way, the trade-off may be acceptable. Watch what happens to your performance rather than assuming keto must either improve or ruin it.
WHAT ARE THE POSSIBLE BENEFITS?
The ketogenic diet has a legitimate medical history. It was developed as a treatment for epilepsy and remains useful in specific clinical settings under professional supervision.
For ordinary weight loss, its greatest advantage may be appetite control. Some people find the combination of protein, fat and fewer highly palatable snack foods makes eating less considerably easier.
It may also improve blood-sugar control for some people with type 2 diabetes. That isn’t a reason to adjust diabetes medication or begin keto without medical support. Substantially reducing carbohydrate can change medication requirements and needs to be handled properly.
Claims about universally sharper thinking, endless energy, reduced inflammation or protection from serious disease are much less certain. Feeling good on a diet isn’t the same as proving it treats everything.
WHAT ARE THE DOWNSIDES?
Keto is restrictive. Eating in restaurants, travelling, sharing meals and maintaining a normal social life can all become more complicated when a small amount of carbohydrate threatens to end the day’s ketosis.
Removing grains, legumes and most fruit can also make fibre and micronutrient intake more difficult. Constipation isn’t a sign that the diet is cleansing you. It’s generally a sign that something needs adjusting.
Blood lipids can respond very differently between people. In one controlled feeding trial, a ketogenic high-fat diet raised LDL cholesterol in every participant. That was a small study in healthy, normal-weight women, so it doesn’t describe everybody, but it’s enough to make monitoring sensible rather than optional.
The quality of the diet still matters. Keto made from fish, eggs, olive oil, nuts and vegetables isn’t nutritionally identical to keto made from bacon, butter and processed cheese.
WHAT IS THE KETO FLU?
Some people report headaches, fatigue, irritability, dizziness or poor training during the first few days of keto. This collection of symptoms is usually called the keto flu, although it isn’t an infection and doesn’t involve an actual flu.
A rapid reduction in carbohydrate can cause changes in stored water and electrolytes. Eating very little overall can make the experience worse.
Stay properly hydrated, make sure you’re still eating enough and don’t assume feeling dreadful proves the diet is working. Anyone with a medical condition or medication affecting blood pressure, glucose or fluid balance should get professional guidance rather than experimenting with electrolyte advice from social media.
WHO SHOULDN’T TRY KETO WITHOUT MEDICAL ADVICE?
Keto isn’t something to begin casually if you’re pregnant, breastfeeding, living with diabetes, taking glucose-lowering medication or have a history of disordered eating.
The same applies if you have a condition affecting your kidneys, liver, pancreas or gallbladder.
Children using ketogenic diets for epilepsy need specialist clinical supervision. That medical treatment shouldn’t be confused with an adult removing toast because they want to lose a few kilos.
If you’re unsure whether a highly restrictive diet is appropriate, ask a qualified doctor or dietitian who understands your medical history.
DO YOU NEED MCT OIL?
MCT oil contains fats that are rapidly absorbed and can increase ketone production. That may be useful if you’re deliberately following a ketogenic diet, but it isn’t required and it doesn’t directly remove body fat.
It also contains calories. One tablespoon of Performance Lab MCT Energy Oil provides 130 calories, so pouring it into coffee without accounting for it can make a calorie deficit smaller rather than larger.
If you want to use MCT oil, start with a small amount and see how your stomach responds. More isn’t better, particularly when more leaves you urgently searching for the nearest toilet.
HOW TO TRY KETO WITHOUT MAKING A MESS OF IT
Decide what you want the diet to achieve. “Being in ketosis” isn’t an outcome by itself. Fat loss, appetite control, blood-glucose management and improved health are outcomes.
Build each meal around sufficient protein and include lower-carbohydrate vegetables. Choose most of your fats from minimally processed sources and don’t treat ketosis as permission to ignore food quality.
Track the things that matter. That could include your weekly weight trend, waist measurement, gym performance, energy, digestion and, where appropriate, blood tests arranged through a medical professional.
Give the approach enough time to judge it, but don’t stay loyal to a diet that makes your training, health or life worse. You’re allowed to change your mind.
KETO IS A TOOL, NOT A PERSONALITY
I don’t recommend keto as the default diet for most people. It’s highly restrictive, it can make training and social eating harder, and it doesn’t offer a substantial long-term weight-loss advantage over a balanced diet you can maintain.
That doesn’t mean it’s useless. Some people enjoy the food, find their appetite easier to manage and get excellent results.
The question isn’t whether keto is good or bad. It’s whether the restrictions solve a problem for you, and whether you can get the same result with considerably less fuss.
If you want help finding an approach that fits your training and actual life, you can read more about my weight-loss coaching.
If you’ve ever found yourself weighing a blueberry because the internet convinced you fruit was the problem, Check It Oot might be for you. It’s where I write about training, nutrition and health without turning food into a religion. One email once or twice a month, written by me and delivered straight to your inbox.
