The Complete Guide to Carbohydrates

What carbs are, how your body uses them and how they fit into a healthy diet.

Carbohydrates are one of the three macronutrients your body gets energy from, alongside protein and fat. They're the sugars, starches and fibre found mainly in plant foods and milk, and UK guidance recommends they make up about half of the energy in your diet.

They're also the macronutrient people are most likely to cut when they decide to eat better, and probably the most misunderstood. Carbs get blamed for weight gain, sugar gets compared to a drug, and somehow fruit has ended up on lists of foods to avoid. A proper look at the evidence disproves nearly all of this, although some of it starts from a grain of truth that's been stretched a very long way.

I've spent more than 12 years in and around the gym, and in that time I don't think any nutrient has picked up more misinformation than carbohydrate. In some way, people generally tend to ‘get’ why protein is important. They know they usually need more of it. So, when they’ve realised a calorie deficit is the way to lose weight, carbs tend to be what gets sacrificed to get there. There’s not necessarily anything wrong with that, but when you’re starting a diet on under 1000 calories a day (a separate issue!), eating barely any carbs at all and then wondering why you’ve got no energy and feel awful all the time, clearly something needs to change.

So, in this guide I'll cover what carbohydrates are, the different types and how your body digests and uses them. We'll look at how much you need, where the best sources come from, how to fuel your training and how carbs fit into popular diets such as low carb, keto and carb cycling, before finishing with what the research actually says about the most common carb and sugar myths. I'll give it to you straight throughout and stick to the science, even when it’s perhaps not as interesting as the headlines.

Before we start, there’s one key concept to understand: Whether a carbohydrate helps or hinders you comes down to three things: what it comes packaged with, how much of it you eat, and what you're doing at the time. Let's get into it.

Key takeaways

• Carbohydrates are one of the three macronutrients and your body's preferred fuel, especially for higher-intensity exercise.
• Scientists classify them by size, as monosaccharides, disaccharides, oligosaccharides and polysaccharides. In food, that means sugars, starches and fibre.
• Quality matters more than quantity. Wholegrains, potatoes, pulses, fruit, vegetables and dairy bring fibre, vitamins and minerals along with their carbohydrate.
• UK guidance recommends about half your energy from carbohydrate, at least 30g of fibre a day and no more than 30g of free sugars. Most UK adults struggle to get enough fibre but go over on free sugars.
• If you're active, think in grams per kg of body weight, from 3 to 5g per kg for light activity up to 8 to 12g per kg for very heavy endurance training.
• For lifting, total calories and protein matter more than carbohydrate, although carbs help most with high-volume, fasted or twice-daily training.
• Low-carb and keto diets work for weight loss when they cut calories, and no better than other diets when calories are matched. Keto also holds back endurance performance.
• Carbs don't make you fat on their own, sugar isn't toxic and whole fruit isn't the problem. Energy balance and food quality are what count.
  

What are carbohydrates?

Carbohydrates are compounds made of carbon, hydrogen and oxygen that your body uses mainly for energy. They're one of the three macronutrients, along with protein and fat, and digestible carbohydrates provide 4 kcal per gram.

Most carbohydrates follow the same chemical pattern, fitting the general formula C_x(H₂O)_y: roughly one carbon atom for every molecule of water. That's where the name comes from. Carbo-hydrate means hydrated carbon. Glucose, with the formula C₆H₁₂O₆, is one of the most common examples you’ve probably heard of.

The basic building block is a single sugar unit called a saccharide. Some carbohydrates are just one of these units, while others are chains of thousands. How many units are joined together is how scientists classify carbohydrates, and it explains a great deal about how different foods behave once you've eaten them.

Plants make carbohydrates through photosynthesis, which is why grains, potatoes, pulses, fruit and vegetables supply most of the carbohydrate in our diets. Milk is the main exception from the animal world, thanks to its natural sugar, lactose.

On UK food labels, fibre is counted at 2 kcal per gram rather than 4, because your body can only partly use it. Protein is built in a similar way to carbohydrate, from chains of smaller units called amino acids. The main difference in chemical composition is that proteins also contain nitrogen. We explain this in more detail in our complete guide to amino acids.

What do carbohydrates do in the body?

Carbohydrates supply energy to your cells, fuel your brain and fill the glycogen stores in your muscles and liver. They also spare protein from being burned as fuel, and the fibre they contain feeds the bacteria in your large intestine.

Energy for your cells and your brain

Glucose is the body's most readily used fuel. Almost every cell can burn it, and as exercise gets harder your muscles rely on it more and more, because carbohydrate releases energy faster than fat can.

Your brain is a particularly heavy user. At rest it needs around 120g of glucose a day, which is most of the glucose your whole body uses. It can adapt to run partly on ketones during prolonged fasting or very low-carbohydrate eating, but glucose is its default fuel.

The role of glycogen

Glucose you don't need straight away is stored as glycogen, a branched chain of glucose units packed into your liver and muscles. A typical adult holds around 500g in muscle and around 80g in the liver, and well-trained athletes tend to have higher glycogen stores.

The two stores do different jobs. Liver glycogen keeps your blood glucose steady between meals and overnight. Muscle glycogen stays put and fuels the muscle it's stored in, which is why it matters so much for training.

Each gram of glycogen is stored with at least 3g of water. Understanding this also helps explain the rapid weight change many people see during the first few days of a low-carb diet; that weight is simply the water retained with glycogen in the body being lost.

Sparing protein

When carbohydrate is scarce, your liver makes its own glucose through a process called gluconeogenesis, using amino acids, glycerol from fat and lactate as raw materials. Eating enough carbohydrate means less protein is diverted into making fuel, leaving more available for building and repairing tissue.

Feeding your gut bacteria

Fibre is the carbohydrate your small intestine can't digest. It travels on to the large intestine, where bacteria ferment much of it into short-chain fatty acids, compounds the cells lining your colon use as fuel. Insoluble fibre, which isn't fermented as readily, adds bulk instead.

Are carbohydrates essential?

I'd rather give you the honest answer than the convenient one here: strictly speaking, no. Nutrition scientists call a nutrient essential when your body can't make it, and your liver can produce all the glucose you need from other sources. That's how people follow very low-carbohydrate diets for long periods.

Essential and useful are different things, though. Making glucose from scratch is a fallback rather than the body's preference, high-intensity exercise runs best on carbohydrate, and carbohydrate foods are the only source of fibre. The more useful question is which carbohydrates you eat, and how much.

What are the different types of carbohydrates?

Carbohydrates are classified by size. Monosaccharides are single sugar units and disaccharides are two joined together. Oligosaccharides are short chains of three to nine units, and polysaccharides are long chains of ten or more. In food, these appear as sugars, starches and fibre.

It helps to picture them as beads on a string: one bead, two beads, a short string or a very long one. This is the classification set out by the Food and Agriculture Organization and World Health Organization and confirmed in a later scientific update on carbohydrate terminology, and it's actually very useful to know. A carbohydrate's size, and the way its units are linked, decides how quickly you digest it, or whether you digest it at all.

Monosaccharides

Monosaccharides are the single sugar units that every other carbohydrate is built from. The three that matter in your diet are glucose, fructose and galactose.

Glucose is the one your body runs on, and it's what a blood sugar reading measures. Fructose, found in fruit and honey, is handled mainly by the liver, which converts much of it to glucose. Galactose rarely appears on its own in food. Most of it comes from lactose, the sugar in milk.

Disaccharides

Disaccharides are two monosaccharides joined together. Sucrose, the white sugar in your cupboard, is glucose plus fructose. Lactose is glucose plus galactose. Maltose, made of two glucose units, forms as starch is broken down and is found in malted grains.

Your gut can't absorb disaccharides whole, so enzymes in the lining of the small intestine split them first. When one of those enzymes runs short, problems follow. People with lactose intolerance produce too little lactase, so undigested lactose reaches the large intestine, where bacteria ferment it and cause wind, bloating and discomfort.

Together, monosaccharides and disaccharides are what nutrition scientists mean by sugars. So yes, sugar is a carbohydrate.

UK guidance separates free sugars from the sugars naturally present in whole foods. Free sugars are those added to food and drink by manufacturers, cooks or you, plus the sugars in honey, syrups and fruit juice. The sugars in milk and in whole fruit and vegetables don't count, because they arrive packaged with water, fibre, protein or other nutrients. It's free sugars that the UK's Scientific Advisory Committee on Nutrition recommends limiting.

Oligosaccharides

Oligosaccharides are short chains of three to nine sugar units, and they behave very differently from sugars. Most can't be broken down by human enzymes at all.

Raffinose and stachyose, found in beans, lentils and chickpeas, are the most common. Your small intestine can't digest them, so they reach the large intestine intact, where gut bacteria ferment them and produce gas. This is why beans and lentils in particular are known for causing wind.

Fructo-oligosaccharides, found in onions, garlic, leeks and chicory root, are fermented in the same way, as is inulin, a closely related compound whose chains can run longer than nine units. Because they escape digestion, most oligosaccharides count towards your fibre intake.

Polysaccharides

Polysaccharides are long chains of ten or more sugar units. Sometimes, the chains can even be thousands of units long! In terms of your diet, there are three main ones to be aware of.

Starch is how plants store glucose, and it's the main carbohydrate in grains, potatoes and pulses. It comes in two forms. Amylose is made of long, straight chains that pack tightly together and digest relatively slowly. Amylopectin is heavily branched, which gives digestive enzymes more places to work, so it breaks down faster. The balance between the two is one reason some starchy foods raise blood glucose more quickly than others.

Some starch goes completely undigested. This resistant starch is found in pulses and slightly underripe bananas, and more of it forms when starchy foods such as potatoes, rice and pasta are cooked and then cooled. It behaves much like fibre. If you're cooling rice to eat later, the NHS advises cooling it within an hour, keeping it in the fridge, eating it within 24 hours and reheating it only once, because rice can carry bacteria whose toxins survive cooking.

Glycogen is the animal equivalent of starch: the glucose store in your liver and muscles described earlier. Very little of it reaches you through food, so the glycogen in your body is built from the carbohydrate you eat.

Non-starch polysaccharides include cellulose, hemicellulose, pectin and beta-glucan. They form the cell walls of plants, your enzymes can't break them down, and they make up the bulk of dietary fibre.

Where does fibre fit?

Fibre is an umbrella term for various different carbohydrates rather than a single type. It covers any carbohydrate your small intestine can't digest, which includes non-starch polysaccharides, resistant oligosaccharides and resistant starch. Since SACN's 2015 report, the UK has used this broader definition, counting carbohydrates of three or more units that reach the large intestine undigested.

Fibre is often split into two groups. Soluble fibre, found in oats, barley, pulses and many fruits, dissolves in water to form a gel. Insoluble fibre, found in wholegrains, nuts, seeds and the skins of fruit and vegetables, doesn't dissolve and adds bulk. Most fibre-rich foods contain both.

Fibre is a carbohydrate, even though it provides far less usable energy than starch or sugar.

Simple vs complex carbohydrates

Simple carbohydrates are sugars, meaning monosaccharides and disaccharides. Complex carbohydrates are the larger oligosaccharides and polysaccharides, mainly starch and fibre.

These are broad terms and can be useful shorthand, but they're a poor guide to how a food behaves. An apple is mostly simple sugars, yet it comes with fibre and water that slow down how quickly you eat and absorb it. White bread is mostly complex carbohydrate, yet its finely milled, amylopectin-rich starch is digested almost as fast as sugar. In my honest opinion, how processed a carbohydrate source is tells you far more than what it’s made up of.

Refined vs wholegrain carbohydrates

Refined carbohydrates are grains that have had their bran and germ stripped away, along with sugars extracted from their original plant source. White flour, white rice and table sugar are the obvious examples that have probably just come to your mind. The bran and germ carry most of a grain's fibre and a good share of its vitamins and minerals, so refining trades nutrition for texture and shelf life.

Wholegrains keep all three parts of the grain. That's why wholemeal bread, brown rice, oats and wholewheat pasta are the most sensible choice on paper, and why research on carbohydrates and long-term health points so consistently towards them.

Refined doesn't automatically mean poor, though. White rice is easy to digest both before and after a hard session, and lower-fibre options are often the better choice before a race, when a gut full of fibre is the last thing you want.

Glycaemic index and glycaemic load

The glycaemic index, or GI, ranks carbohydrate foods by how quickly they raise blood glucose compared with pure glucose, which scores 100. Foods scoring 55 or less are low GI, 56 to 69 is medium and 70 or above is high. Glycaemic load, or GL, builds on this by taking the amount of carbohydrate in a typical portion into account.

Low-GI foods are what people usually mean by slow-release carbohydrates. They're digested and absorbed more gradually, so blood glucose rises less sharply after eating them. Fibre, fat, protein, acidity and a higher share of amylose all slow digestion down, while ripeness, processing and longer cooking tend to speed it up. Pasta cooked al dente has a lower GI than the same pasta boiled until soft.

GI is a useful tool, but it's a bit of a blunt one. It's measured on a single food eaten on its own after an overnight fast, which isn't how most people eat, and adding protein, fat or vegetables to a meal changes the response. It also says nothing about nutritional value. Crisps and chocolate can have a lower GI than boiled potatoes, simply because their fat slows digestion.

Glycaemic load is a useful measure because it goes a long way towards fixing this blind spot. For example, watermelon has a high GI, but a typical slice contains so little carbohydrate that its glycaemic load is low.

Used sensibly, GI is a rough guide that points towards minimally processed, fibre-rich carbohydrates most of the time. It shouldn't override the bigger picture of what a whole meal contains, and it's never a reason to fear a single food.

How does your body digest carbohydrates?

Your body breaks digestible carbohydrates down into single sugar units, mainly glucose, which are absorbed through the wall of the small intestine into your bloodstream. Digestion starts in the mouth and finishes in the small intestine, while fibre carries on to the large intestine undigested.

• In the mouth, an enzyme in saliva called salivary amylase starts cutting starch into shorter chains. Chew a piece of bread for long enough and it begins to taste sweet, which is amylase at work. Stomach acid then pauses the process.
• In the small intestine, pancreatic amylase picks up where saliva left off and breaks starch down into maltose and short chains. Enzymes on the intestinal lining, called disaccharidases, then split disaccharides into single units: sucrase handles sucrose, lactase handles lactose and maltase handles maltose.
• Absorption happens only once carbohydrates are single sugar units. Glucose and galactose share one transporter in the gut wall, known as SGLT1, while fructose uses another, GLUT5. Because the two routes are independent of each other, eating glucose and fructose together lets you absorb more carbohydrate per hour than glucose alone. For endurance athletes, this is important to know!
• In the bloodstream, fructose and galactose travel to the liver, which converts most of them into glucose. Rising blood glucose prompts your pancreas to release insulin, which helps move glucose into cells to be used for energy or stored as glycogen.
• In the large intestine, fibre, resistant starch and most oligosaccharides are fermented by gut bacteria, having skipped everything above.

Our complete guide to digestive enzymes covers these enzymes in more detail.

So, this all means that digestible carbohydrates do turn into sugar, in the form of glucose. You might hear that and then worry that carbs are the enemy, given the amount of misinformation about them, but they’re not. That's just the system working as designed, not a problem you need to avoid.

Carbohydrate turning into fat is a different story. Your body can convert carbohydrate into fat through a process called de novo lipogenesis, but in humans it contributes very little unless carbohydrate intake exceeds your total energy needs. What happens far more often is subtler. When you eat more than you need, your body burns the extra carbohydrate first, so more of the fat you eat ends up stored. Weight gain still comes down to total energy intake, just by a less direct route than "carbs turning to fat". Calories in vs calories out will always be the ultimate decider here, regardless of your macronutrient intake.

How many carbohydrates do you need a day?

UK guidance recommends that carbohydrates make up around half of your daily energy intake, mostly from starchy, fibre-rich foods. On food labels, the Reference Intake for an average adult is 260g a day. If you're active, a target based on your body weight is more useful than either.

The Scientific Advisory Committee on Nutrition sets three benchmarks for adults:

• Total carbohydrate should provide around 50% of your energy intake.
• Fibre intake should reach 30g a day.
• Free sugars should make up no more than 5% of your energy intake, which the NHS translates as no more than 30g a day for adults. In real terms, this is roughly seven sugar cubes.

The Eatwell Guide puts this into food terms, with starchy foods making up just over a third of what you eat and fruit and vegetables another third.

Most people in the UK aren't short of carbohydrate overall. The gaps are in their quality. The latest National Diet and Nutrition Survey found that adults aged 19 to 64 ate an average of 16.4g of fibre a day, barely half the 30g target. Free sugars made up 10.4% of their energy intake, around twice the recommended maximum, and only 17% stayed within the 5% limit.

Carbohydrate needs if you're active

For anyone who trains regularly, grams per kilogram of body weight is a more useful measure than percentages. The ranges below come from the joint position stand on nutrition and athletic performance published by the American College of Sports Medicine, the Academy of Nutrition and Dietetics and Dietitians of Canada.

These ranges are built for athletes fuelling heavy training. If you lift weights or train for an hour three or four times a week, the lower bands are the most relevant ones, which is why these numbers probably look quite high.

Low-carbohydrate and ketogenic diets sit well below these ranges, and we cover how they work further down. If you're managing diabetes, your carbohydrate intake is best worked out with your healthcare professional, especially with the potential additional factor of insulin dosages to manage.

The best sources of carbohydrates

The best sources of carbohydrate are minimally processed foods that bring other nutrients along with them: wholegrains, potatoes with their skins, pulses, fruit, vegetables and dairy. Each supplies carbohydrate alongside fibre, protein, vitamins or minerals rather than on its own.

Wholegrains and starchy foods

Oats, wholemeal bread, wholewheat pasta, brown rice, barley, quinoa and buckwheat are all good everyday choices. Oats stand out because they’re a source of beta-glucan, a soluble fibre, which is one reason porridge makes such a reliable breakfast. For an even more complete meal, add some yoghurt and fruit for overnight oats!

Potatoes deserve more credit than they get. They don't count towards your 5 A Day because they're the starchy part of a meal, but leaving the skins on keeps more of their fibre and vitamins.

Pulses

Beans, lentils, chickpeas and peas are unusual because they provide carbohydrate, fibre and a meaningful amount of protein together. They count towards your 5 A Day, although only once however much you eat.

Fruit and vegetables

Whole fruit provides carbohydrate mostly as natural sugars, together with water and fibre. Vegetables vary widely. Starchy ones such as sweetcorn, parsnips and peas contain a fair amount of carbohydrate, while leafy greens contain very little.

Milk and yoghurt

Milk and natural yoghurt supply carbohydrate as lactose, alongside protein and calcium. Cheese contains almost none, because most of the lactose is lost with the whey during cheesemaking.

Is it a carb? A quick reference

Values per 100g from the UK's Composition of Foods Integrated Dataset. CoFID expresses carbohydrate as monosaccharide equivalents, so figures can read slightly higher than on food labels. Fibre is measured using the AOAC method that UK recommendations are based on.

Rice, bread, pasta, porridge oats, potatoes and flour are all carbohydrate foods, as are sugar and fruit. Cheese isn't. It's mostly protein and fat, with barely any carbohydrate at all.

Easy ways to improve your carbohydrate quality

• Swap white bread for wholemeal or seeded, or mix white and brown rice half and half if you're changing gradually.
• Leave the skins on potatoes.
• Add a tin of beans or lentils to a chilli, curry or soup.
• Choose whole fruit over juice, and keep juice to the NHS limit of 150ml a day.
• Start the day with oats. Our overnight oats and creamy chocolate porridge with figs are good places to start.

Carbohydrates for training and performance

Carbohydrate is the main fuel for moderate and high-intensity exercise. How much you need depends on what you're training for: endurance athletes need far more than people lifting weights, and timing matters most when sessions are long, frequent or done on an empty stomach.

Endurance training

In long, hard efforts, muscle glycogen is usually what depletes first. As it drops, the pace you can hold drops with it, which is the feeling endurance athletes call hitting the wall. That's why they need the higher ranges in the table above, and why fuelling during long sessions makes a real difference.

Strength training

This one might surprise you. For people lifting weights, carbohydrate matters less than gym folklore would have you believe. A 2022 systematic review found that carbohydrate intake is unlikely to affect strength training performance in a fed state, in workouts of up to about 10 sets per muscle group. Higher-volume sessions, training fasted and training twice a day were the situations where carbohydrate was more likely to help.

The same picture holds for muscle growth. A 2026 meta-analysis of 11 randomised controlled trials found no significant effect of carbohydrate intake on muscle growth when energy and protein needs were met, though the certainty of the evidence was low. The authors did note that low-carbohydrate diets can blunt appetite, which makes the calorie surplus needed to build muscle harder to sustain.

In practice, that means total energy and protein must be your priority if you're resistance training, and carbohydrate is a matter of preference and practicality as long as both are covered. That said, if your carbs are very low and your sessions feel flat, your lifts stall or your recovery suffers, adding some carbohydrate around training is one of the simplest fixes there is.

This all adds up to one solid piece of advice: you need to find what works for you when it comes to carbs. As the old saying goes, there really is more than one way to skin a cat, and none of the approaches are inherently ‘better’ than the others. One thing I would say from personal experience, however: if you’re doing an especially heavy session then I find it best not to go in completely fasted. For example, if you’re about to attempt a personal best for a heavy compound movement like a deadlift, it’s best to have at least something in your stomach beforehand. That’s almost certainly purely psychological, but I definitely find it better! You may do too, or you may not. The only way to find out is to try for yourself.

Before, during and after training

• Before: for sessions longer than an hour, the position stand recommends 1 to 4g of carbohydrate per kg of body weight in the one to four hours beforehand, with larger amounts further out from the session.
• During: for sessions lasting more than about an hour, 30 to 60g of carbohydrate an hour helps maintain performance. For events beyond two and a half hours, up to 90g an hour can be used, as long as it comes from a mix of glucose and fructose. That's the two-transporter system from the digestion section at work, and it's why many sports drinks and gels combine the two.
• After: if your next session is less than eight hours away, aim for 1.0 to 1.2g per kg of body weight per hour for the first four hours to refill glycogen quickly. With a day or more to recover, timing matters much less and your total daily intake will refill your stores. Either way, pairing carbohydrate with protein covers refuelling and repair together. Our guide to the best supplements for muscle recovery goes into more detail on this.
  

Hydration matters too, especially in long or hot sessions. The Hydrate Blend provides electrolytes with zero sugar and no carbohydrate, so for long sessions your carbohydrate needs to come from food, a gel or a sports drink alongside it.

How carbohydrates fit into different diets

Most popular diets differ mainly in how they handle carbohydrate: how much you eat, which kinds and when. Strip away the branding and you'll find most of them come back to the same principles. Here's how four common approaches work, what the evidence says about each, and who they tend to suit.

High-carbohydrate diets

A high-carbohydrate diet gets more than half of its energy from carbohydrate. The UK's recommended intake of around 50% already sits close to that line, so in practice "high carb" usually describes athletes eating well above it to fuel heavy training.

This is where the case for carbohydrate is strongest. Endurance athletes training for several hours a day need the 6 to 12g per kg covered earlier to keep their glycogen stores topped up. Before endurance events lasting longer than about 90 minutes, many also use carbohydrate loading, eating 10 to 12g per kg a day for the 36 to 48 hours beforehand, as set out in the joint position stand.

The catch is volume and quality. Eating 500g or more of carbohydrate a day takes a lot of food, and lower-fibre choices often become a practical necessity around training. Outside of heavy training, a very high intake built on refined foods isn't the goal: the large mortality study covered in the myths section of this article found that risk rose at the very highest carbohydrate intakes as well as the lowest.

Low-carbohydrate diets

There's no single agreed definition, but low-carbohydrate diets are usually taken to mean less than 130g of carbohydrate a day, or roughly a quarter of your total calories. In practice that means cutting back on bread, rice, pasta, potatoes and sugar, and eating more protein, fat and non-starchy vegetables.

The first thing most people notice is how quickly the scales move, at least at first. That’s a big clue; with less carbohydrate coming in, glycogen stores fall and the water stored alongside them goes too. Much of that early drop is glycogen and water rather than fat, which is why it comes back when you increase your carbohydrate intake again.

This is genuinely one of the most common issues I see with people dieting. They see the drop, immediately think the fat is falling off them (and less water retention often makes them feel that way too) so the diet must be working. Then progress inevitably stalls and they panic, leading to the snap reaction of dropping their calories. What follows is a severe energy deficit that leaves them feeling awful, demotivated and puts them at a much higher risk of lean tissue loss. Arguably the best thing you can do is arm yourself with the knowledge of what to expect ahead of time. That way, when the initial loss and subsequent slowing down happen, you know exactly what’s really going on.

Over the longer term, low-carb diets work about as well as other approaches. In the DIETFITS trial, 609 adults followed either a healthy low-fat or a healthy low-carbohydrate diet for a year. Both groups lost similar amounts, an average of 5.3kg on the low-fat diet and 6.0kg on the low-carbohydrate diet, and the difference between them wasn't statistically significant. Studies that control exactly what participants eat have found no fat-loss advantage for low-carbohydrate diets when calories are matched. Where low carb helps, it's usually because some people find it easier to eat less this way.

The trade-offs with low carb are worth knowing before you do it. Hard training on low glycogen feels harder, proper fibre intake is harder to hit which can cause digestion issues, and the quality of whatever replaces the missing carbohydrate is crucial, as the myths section covers. If you take medication for diabetes, speak to your diabetes team before cutting carbohydrate significantly, because some medicines can cause low blood sugar when intake drops.

Ketogenic diets

A ketogenic, or keto, diet cuts carbohydrate low enough, usually below about 10% of your total intake per day, that the liver starts turning fat into ketones, which the brain and muscles can use as fuel. Fat supplies most of the day's energy, with moderate protein.

Keto is a recognised medical therapy, still used under specialist supervision for drug-resistant epilepsy. As a weight-loss diet, it shares the strengths and limits of other low-carb approaches. It can curb appetite for some people, but it hasn't been shown to burn more body fat when calories are matched.

For endurance performance, the evidence is clearer. In a study of elite race walkers, three weeks on a low-carbohydrate, high-fat diet sharply increased how much fat they burned during exercise but made them less economical at race pace. Walkers on high-carbohydrate and periodised-carbohydrate diets improved their 10km race times by around 5 to 7%, while the low-carb group didn't improve at all. For lifting, muscle can still be built on keto if protein and calories are high enough, although the appetite effect can make that harder.

The first week or two can be rough. In an analysis of online reports of so-called keto flu, the most common symptoms were flu-like feelings, headaches, fatigue, nausea and dizziness, mostly reported in the first week and usually fading within a month.

Zero-carb or carnivore diets go further still, cutting out plant foods entirely. There's very little research on them, and they remove every source of fibre.

Carb cycling

Carb cycling means varying your carbohydrate intake from day to day to match your training: more on hard or long training days, less on rest or light days, with protein staying roughly constant. It's popular for fat loss and body composition, and it often works because it lowers your average intake while keeping enough fuel for the sessions that need it.

Sports scientists use the same idea under a different name. Carbohydrate periodisation, or fuel for the work required, plans carbohydrate intake around the intensity and length of each session. Some endurance athletes go further with "train low" sessions, deliberately training with reduced glycogen to amplify the muscle's response to training. Those changes can be seen quite clearly in controlled testing environments but don't always translate into better performance, so train-low sessions are best kept away from the sessions where quality matters most.

Done well, carb cycling is simply a practical way to put carbohydrate where it does the most good. There's little research on it as a named diet, and it’s not a magic trick. Like every other diet, its success in terms of your weight still comes down to your weekly energy intake.

The above being said, carb cycling is one of my personal favourite approaches to dieting and one I’ve seen the most success with, both for clients and myself. One of the great things about it is it’s not anywhere near as restrictive as it might sound and there are a few ways to go about it. You could simply do a high day and a low day for training and non-training days respectively or high, medium and low days for more variance. Total calories can also be adjusted on these days for even more control if you need it. By slightly increasing your calories along with your carbohydrate intake on your heavier or more intense training days, you not only supply yourself with a bit more energy, you may also help suppress some of the body’s responses to a calorie deficit which helps with how you might be feeling during a dieting phase.

Which approach is right for you?

Like so much in fitness, the honest answer is that it depends. The best approach is the one that covers your energy and protein needs, fuels the training you do, and that you can keep up for months rather than weeks. I can't stress that last part enough. A perfect plan you follow for three weeks will lose out to a sensible one you follow for a year. If you're training for endurance events, carbohydrate is hard to do without. If you lift weights a few times a week and find a lower-carb diet easier to stick to, the evidence suggests you'll do fine, as long as your protein and fibre intake don't suffer. If you're pregnant, managing a medical condition or taking regular medication, speak to your GP before making big changes to how you eat.

Carbohydrate and sugar myths: what the evidence says

Now for the part I've been looking forward to. Here's what the research actually shows on six of the most common carbohydrate and sugar myths.

Myth: carbs make you gain weight

Weight change follows energy balance. Eat more energy than you use over time and you gain weight, whether that energy comes from carbohydrate, fat or protein.

As the trials in the low-carbohydrate section above show, cutting carbs leads to weight loss when it cuts calories, and does no better than other diets when calories are matched. The quick drop in the first week is glycogen and water, not a sign that carbohydrate was the problem.

You may also come across the carbohydrate–insulin model, the idea that carbs drive weight gain by raising insulin and pushing the body to store fat. Its supporters and its critics still debate it, but controlled feeding studies haven't found the fat-loss advantage it predicts when calories are equal.

Myth: cutting carbs is the healthiest way to eat

Generally, severely restricting or eliminating a food group is rarely ever healthy. In the case of carbs, the research points to quality mattering far more than quantity. A large study published in The Lancet Public Health linked both very low and very high carbohydrate intakes with higher mortality, with the lowest risk at moderate intakes of around 50 to 55% of your total intake. Replacing carbohydrate with animal fat and protein was linked to higher risk, while plant sources were linked to lower risk.

A series of meta-analyses commissioned by the World Health Organization found that people eating the most fibre and wholegrains had consistently lower rates of heart disease, stroke, type 2 diabetes and bowel cancer than those eating the least, with the greatest benefit at around 25 to 29g of fibre a day. More recently, a 2025 study of more than 47,000 women linked a higher intake of good-quality carbohydrate, from wholegrains, fruit, vegetables and pulses, with better odds of ageing without major chronic disease.

These are observational studies, which show associations rather than proving cause and effect. Taken together, though, they give no support to the idea that the less carbohydrate you eat, the healthier you'll be.

Myth: eating carbs at night makes you store fat

Your body doesn't switch into fat-storing mode after a certain hour. Over a day or a week, total energy intake decides whether you gain or lose weight. In one six-month trial, people who ate most of their carbohydrate at dinner lost more weight than those who spread it through the day, although it was a small study of 78 people.

I’d advise you to structure your carbohydrate intake around your training times, especially if you’re doing a particularly intense session. For those training in the evening, that naturally means you’ll be eating more carbs later. For weight, and particularly fat loss, this has no meaningful impact whatsoever. If anything, it might even have a slight positive effect if you can exert yourself more, as that means more calories burned and therefore a bigger deficit. Remember, the clock doesn’t reset itself at midnight, so you’re better off looking at your carbs, and calories overall, weekly rather than daily.

Myth: sugar is toxic and addictive

Sugar isn't a poison, and the evidence that it's addictive in the same way drugs are is weak. A review of the research found little evidence to support sugar addiction in humans. Addiction-like behaviour in animal studies tends to appear only when access to sugar is restricted to short bursts, which isn't how people eat.

That doesn't make sugar harmless in any amount. Free sugars are easy to eat in large quantities, particularly in drinks, they bring little else nutritionally, and they're a major cause of tooth decay. The UK advice to keep free sugars under 30g a day for adults is valid and something you should consider tracking alongside your overall calories and macros.

Myth: fruit has too much sugar

The sugar in whole fruit isn't a free sugar under the UK definition, because it comes with fibre and water inside intact plant cells. Eating whole fruit is linked with a lower risk of type 2 diabetes, while drinking fruit juice is linked with a higher one.

Juice and smoothies are where the free sugar limit applies. Juicing and blending break down the fruit's structure and release its sugars, which is why the NHS counts juice as only one of your 5 A Day and caps it at 150ml.

Myth: white carbs are always the worst choice

Colour is a blunt way to judge a food. Potatoes are a nutritious staple, especially with the skins left on. White rice and other lower-fibre carbohydrates have a real place before and around training, when you want fuel that digests easily. Wholegrains are still the better everyday default for fibre, but a meal of white rice, vegetables and a good source of protein is a perfectly healthy one. Our sweet chilli chicken rice is a good example.

How to read carbohydrates on a UK food label

On UK food labels, the carbohydrate figure covers sugars, starch and polyols but not fibre, which is listed separately. The "of which sugars" line shows all the sugars in the product, whether added or naturally present.

Why "net carbs" don't apply in the UK

On American labels, total carbohydrate includes fibre, which is why "net carbs", total carbohydrate minus fibre, became popular online. On UK and European labels, fibre has already been taken out of the carbohydrate figure, so subtracting it again when tracking your food would mean underestimating the total amount of carbohydrate you're eating.

What "of which sugars" means on UK food labels

"Of which sugars" counts every sugar in the product, including lactose in milk and the natural sugars in fruit, not only added sugar. A plain yoghurt can carry a few grams of sugar per 100g with none added at all. To find added sugars, check the ingredients list for sugar, glucose syrup, honey, dextrose, invert sugar syrup and fruit juice concentrate.

As a rough guide, front-of-pack labels class more than 22.5g of total sugars per 100g as high and 5g or less as low. The Reference Intakes printed on labels are 260g of carbohydrate and 90g of total sugars a day for an average adult.

Polyols

Polyols, also called sugar alcohols, are sweeteners such as erythritol, xylitol and sorbitol. They're counted within the carbohydrate figure at 2.4 kcal per gram and may be listed on a line of their own. You'll find them in protein bars and "no added sugar" products, and foods containing more than 10% added polyols must carry a warning that excessive consumption may have a laxative effect.

The same habits apply to supplements. A 40g serving of The Lean Protein, for example, contains 2.0g of carbohydrate, of which 1.1g is sugar. Our guide to what makes a healthy protein powder covers what else to look for on the label.

Building carbohydrates into a healthy diet

Build most meals around a minimally processed carbohydrate, pair it with a source of protein and plenty of vegetables, and adjust the portion to how active you are that day. Making this a habit covers quality, quantity and context, and you don't need to overhaul everything at once to start. Small changes you can repeat every day will carry you a lot further than a dramatic plan you start on a Monday (we all do!) and abandon by Friday.

In practice, that might mean a fist-sized portion of wholegrains or potatoes at most meals, with a little more on training days and a little less on rest days. Pulses can fill both the carbohydrate and the protein slot. Whole fruit makes an easy snack, and any especially high sugar foods should be eaten in moderation rather than as staples of your diet.

Breakfast is an easy place to start. Porridge and overnight oats give you wholegrain carbohydrate and soluble fibre, and stirring in a scoop of protein turns them into a more complete meal. Innermost's two proteins are built around different goals: The Strong Protein if you're focused on building strength and muscle, and The Lean Protein if you're eating in a calorie deficit to lose fat. Either works well in both.

If you're taking a GLP-1 medication and your appetite is smaller than usual, our complete guide to diet, training and lifestyle on a GLP-1 covers how to build meals around that.

Frequently asked questions about carbohydrates

What are carbohydrates?

Carbohydrates are one of the three macronutrients, alongside protein and fat. They're made of carbon, hydrogen and oxygen and include sugars, starches and fibre. Your body digests most of them into glucose, its main source of energy, and they provide 4 kcal per gram. UK guidance recommends they make up about half of your daily energy intake.

Is rice a carbohydrate?

Yes. Rice is a starchy carbohydrate food, with around 31g of carbohydrate in 100g of boiled white long-grain rice. Brown rice contains more fibre than white because it keeps the bran layer, but both are good sources of carbohydrate. White rice digests more easily, which makes it a practical choice before training.

Is sugar a carbohydrate?

Yes. Sugars are the simplest carbohydrates, made of one or two sugar units. Glucose, fructose and galactose are single units, while sucrose, lactose and maltose are pairs. UK guidance advises limiting free sugars, the sugars added to food plus those in honey, syrups and fruit juice, to no more than 30g a day for adults.

What's the difference between simple and complex carbohydrates?

Simple carbohydrates are sugars, made of one or two sugar units. Complex carbohydrates, such as starch and fibre, are longer chains. The labels are a rough guide only. White bread is complex but digests quickly, while fruit is simple but comes with fibre. Whether a food is wholegrain or refined tells you more.

How many grams of carbohydrates should I eat a day?

UK guidance suggests about half your energy should come from carbohydrate, and the Reference Intake on food labels is 260g a day for an average adult. Active people need more. Sports nutrition guidelines range from 3 to 5g per kg of body weight for light activity up to 8 to 12g per kg for very heavy endurance training.

Do carbohydrates make you fat?

Not on their own. Weight gain comes from eating more energy than you use, whatever its source. Trials comparing healthy low-carbohydrate and low-fat diets find similar weight loss over a year. The fast early drop on a low-carb diet is mostly glycogen and water, which returns when carbohydrate is reintroduced.

Is a low-carb diet better for weight loss?

Not on its own. In a year-long trial of 609 adults, people on a healthy low-carbohydrate diet lost a similar amount of weight to those on a healthy low-fat diet. Low-carb diets help some people because they find it easier to eat less, but when calories are matched, they don't lead to more fat loss.

What is carb cycling?

Carb cycling means eating more carbohydrate on hard or long training days and less on rest or light days, while keeping protein roughly the same. It's a practical way to match fuel to training. There's little research on it as a named diet, and weekly calorie intake still determines whether your weight changes.

How many calories are in a gram of carbohydrate?

A gram of digestible carbohydrate provides 4 kcal, compared with 4 kcal for protein and 9 kcal for fat. On UK food labels, fibre is counted at 2 kcal per gram and polyols, or sugar alcohols, at 2.4 kcal per gram, because your body can only partly use them.

Is fibre a carbohydrate?

Yes. Fibre is the carbohydrate your small intestine can't digest, including non-starch polysaccharides such as cellulose, resistant starch and many oligosaccharides. It reaches your large intestine intact, where gut bacteria ferment some of it. UK guidance recommends adults eat 30g a day, and fewer than one in twenty UK adults manages it.

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