The truth about carbs
"Carbs" are a hotly-debated topic, especially in the weight loss world, due in part to diets such as the Atkins, Dukan, South Beach and Ketogenic Diet.
The idea that "carbs are bad" has left many people confused about carbohydrates and their importance for our health, including maintaining a healthy weight.
Dietitian Sian Porter says: "Carbohydrates are such a broad category and people need to know that not all carbs are the same. It's the type, quality and quantity of carbohydrate in our diet that is important.
"While we should reduce the amount of free sugar in our diet, we should base our meals on starchy carbs, particularly the higher fibre varieties.
"There is strong evidence that fibre, found in wholegrain versions of starchy carbs for example, is good for our health."
On this page you can find out all you need to know about carbohydrates, their health benefits, healthier sources of carbohydrates, and how they can help you maintain a healthy weight.
What are carbs?
Carbohydrates are one of 3 macronutrients (nutrients that form a large part of our diet) found in food – the others being fat and protein.
Hardly any foods contain only 1 nutrient, and most are a combination of carbohydrates, fats and proteins in varying amounts.
There are 3 different types of carbohydrates found in food: sugar, starch and fibre.
The type of sugars most adults and children in the UK eat too much of are called free sugars.
These are the sugars added to food or drinks, including sugars in biscuits, chocolate, flavoured yoghurts, breakfast cereals and fizzy drinks.
These sugars may be added at home, or by a chef or another food manufacturer.
Sugars in honey, syrups (such as maple, agave and golden), nectars (such as blossom), and unsweetened fruit juices, vegetable juices and smoothies occur naturally, but still count as free sugars.
Sugar found naturally in milk, fruit and vegetables does not count.
Starch is found in foods that come from plants. Starchy foods, such as bread, rice, potatoes and pasta, provide a slow and steady release of energy throughout the day.
Fibre is the name given to the diverse range of compounds found in the cell walls of foods that come from plants.
Good sources of fibre include vegetables with skins on, wholegrain bread, wholewheat pasta, and pulses (beans and lentils).
Why do we need carbs?
Carbohydrates are important to your health for a number of reasons.
Carbohydrates should be the body's main source of energy in a healthy, balanced diet, providing about 4kcal (17kJ) per gram.
They're broken down into glucose (sugar) before being absorbed into the bloodstream. From there, the glucose enters the body's cells with the help of insulin.
Glucose is used by your body for energy, fuelling all of your activities, whether going for a run or simply breathing.
Unused glucose can be converted to glycogen found in the liver and muscles.
If more glucose is consumed than can be stored as glycogen, it's converted to fat for long-term storage of energy.
Higher fibre starchy carbohydrates release sugar into the blood more slowly than sugary foods and drinks.
Fruit and vegetables, pulses, wholegrain and wholewheat varieties of starchy foods, and potatoes eaten with their skins on, are good sources of fibre.
Fibre is an important part of a healthy, balanced diet. It can promote good bowel health, reduce the risk of constipation, and some forms of fibre have been shown to reduce cholesterol levels.
Research shows diets high in fibre are associated with a lower risk of cardiovascular disease, type 2 diabetes and bowel cancer.
Many people don't get enough fibre. On average, most adults in the UK get about 19g of fibre a day. We're advised to eat an average of 30g a day.
Carbohydrate contains fewer calories gram for gram than fat, and starchy foods can be a good source of fibre, which means they can be a useful part of maintaining a healthy weight.
By replacing fatty, sugary foods and drinks with higher fibre starchy foods, it's more likely you'll reduce the number of calories in your diet.
Also, high-fibre foods add bulk to your meal, helping you feel full. "You still need to watch your portion sizes to avoid overeating," says Sian.
"Also watch the amount of fat you add when cooking and serving them: this increases the calorie content."
Should I cut out carbohydrates?
While we can most certainly survive without sugar, it would be quite difficult to eliminate carbohydrates entirely from your diet.
Carbohydrates are the body's main source of energy. In their absence, your body will use protein and fat for energy.
It may also be hard to get enough fibre, which is important for long-term health.
Healthy sources of carbohydrates, such as higher fibre starchy foods, vegetables, fruits and legumes, are also an important source of nutrients, such as calcium, iron and B vitamins.
Significantly reducing carbohydrates from your diet in the long term could put you at increased risk of insufficient intakes of certain nutrients, potentially leading to health problems.
Cutting out carbohydrates from your diet could put you at increased risk of a deficiency in certain nutrients, leading to health problems, unless you're able to make up for the nutritional shortfall with healthy substitutes.
Replacing carbohydrates with fats and higher fat sources of protein could increase your intake of saturated fat, which can raise the amount of cholesterol in your blood – a risk factor for heart disease.
When you're low on glucose, the body breaks down stored fat to convert it into energy. This process causes a build-up of ketones in the blood, resulting in ketosis.
Ketosis as a result of a low-carbohydrate diet can be linked, at least in the short term, to headaches, weakness, nausea, dehydration, dizziness and irritability.
Try to limit the amount of sugary foods you eat and instead include healthier sources of carbohydrate in your diet, such as wholegrains, potatoes, vegetables, fruits, legumes and lower fat dairy products.
Read the British Dietetic Association's review of low-carb diets, including the Paleo, Dukan, Atkins and South Beach diets.
Don't protein and fat provide energy?
While carbohydrates, fat and protein are all sources of energy in the diet, the amount of energy each one provides varies:
- carbohydrate provides: about 4kcal (17kJ) per gram
- protein provides: 4kcal (17kJ) per gram
- fat provides: 9kcal (37kJ) per gram
In the absence of carbohydrates in the diet, your body will convert protein (or other non-carbohydrate substances) into glucose, so it's not just carbohydrates that can raise your blood sugar and insulin levels.
If you consume more calories than you burn from whatever source, you'll gain weight.
So cutting out carbohydrates or fat doesn't necessarily mean cutting out calories if you're replacing them with other foods containing the same number of calories.
Are carbohydrates more filling than protein?
Carbohydrates and protein contain roughly the same number of calories per gram.
But other factors influence the sensation of feeling full, such as the type, variety and amount of food eaten, as well as eating behaviour and environmental factors, like serving sizes and the availability of food choices.
The sensation of feeling full can also vary from person to person. Among other things, protein-rich foods can help you feel full, and we should have some beans, pulses, fish, eggs, meat and other protein foods as part of a healthy, balanced diet.
But we shouldn't eat too much of these foods. Remember that starchy foods should make up about a third of the food we eat, and we all need to eat more fruit and vegetables.
How much carbohydrate should I eat?
The government's healthy eating advice, illustrated by the Eatwell Guide, recommends that just over a third of your diet should be made up of starchy foods, such as potatoes, bread, rice and pasta, and over another third should be fruit and vegetables.
This means that over half of your daily calorie intake should come from starchy foods, fruit and vegetables.
What carbohydrates should I be eating?
Data from the National Diet and Nutrition Survey, which looks at food consumption in the UK, shows that most of us should also be eating more fibre and starchy foods and fewer sweets, chocolates, biscuits, pastries, cakes and soft drinks with added sugar.
These are usually high in sugar and calories, which can increase the risk of tooth decay and contribute to weight gain if you eat them too often, while providing few other nutrients.
Fruit, vegetables, pulses and starchy foods (especially higher fibre varieties) provide a wider range of nutrients (such as vitamins and minerals), which are beneficial to health.
The fibre in these foods can help keep your bowels healthy and adds bulk to your meal, helping you feel full.
How can I increase my fibre intake?
To increase the amount of fibre in your diet, aim for at least 5 portions of a variety of fruit and veg a day.
Go for higher fibre varieties of starchy foods and eat potatoes with skins on. Try to aim for an average intake of 30g of fibre a day.
Here are some examples of the typical fibre content in some common foods:
- 2 breakfast wheat biscuits (approx. 37.5g) – 3.6g of fibre
- 1 slice of wholemeal bread – 2.5g (1 slice of white bread – 0.9g)
- 80g of cooked wholewheat pasta – 4.2g
- 1 medium (180g) baked potato (with skin) – 4.7g
- 80g (4 heaped tablespoons) of cooked runner beans – 1.6g
- 80g (3 heaped tablespoons) of cooked carrots – 2.2g
- 1 small cob (3 heaped tablespoons) of sweetcorn – 2.2g
- 200g of baked beans – 9.8g
- 1 medium orange – 1.9g
- 1 medium banana – 1.4g
Can eating low glycaemic index (GI) foods help me lose weight?
The glycaemic index (GI) is a rating system for foods containing carbohydrates. It shows how quickly each food affects glucose (sugar) levels in your blood when that food is eaten on its own.
Some low-GI foods, such as wholegrain foods, fruit, vegetables, beans and lentils, are foods we should eat as part of a healthy, balanced diet.
But using GI to decide whether foods, or a combination of foods, are healthy or can help with weight reduction can be misleading.
Although low-GI foods cause blood sugar levels to rise and fall slowly, which may help you to feel fuller for longer, not all low-GI foods are healthy.
For example, watermelon and parsnips are high-GI foods, while chocolate cake has a lower GI value.
And the way a food is cooked and what you eat it with as part of a meal will change the GI rating.
This means GI alone isn't a reliable way of deciding whether foods, or combinations of foods, are healthy or will help you lose weight.
Do carbohydrates make you fat?
Any food can cause weight gain if you overeat. Whether your diet is high in fat or high in carbohydrates, if you frequently consume more energy than your body uses you're likely to put on weight.
In fact, gram for gram, carbohydrate contains fewer than half the calories of fat. Wholegrain varieties of starchy foods are good sources of fibre. Foods high in fibre add bulk to your meal and help you feel full.
But foods high in sugar are often high in calories, and eating these foods too often can contribute to you becoming overweight.
There's some evidence that diets high in sugar are associated with an increased energy content of the diet overall, which over time can lead to weight gain.
Can cutting out wheat help me lose weight?
Some people point to bread and other wheat-based foods as the main culprit for their weight gain.
Wheat is found in a wide range of foods, from bread, pasta and pizza to cereals and many other foods.
But there's not enough evidence that foods that contain wheat are any more likely to cause weight gain than any other food.
Unless you have a diagnosed health condition, such as wheat allergy, wheat sensitivity or coeliac disease, there's little evidence that cutting out wheat and other grains from your diet would benefit your health.
Grains, especially wholegrains, are an important part of a healthy, balanced diet.
Wholegrain, wholemeal and brown breads give us energy and contain B vitamins, vitamin E, fibre and a wide range of minerals.
White bread also contains a range of vitamins and minerals, but it has less fibre than wholegrain, wholemeal or brown breads.
If you prefer white bread, look for higher fibre options. Grains are also naturally low in fat.
Should people with diabetes avoid carbs?
People with diabetes should try to eat a healthy, balanced diet, as shown in the Eatwell Guide.
They should also include higher fibre starchy foods at every meal. Steer clear of cutting out entire food groups.
It's recommended that everyone with diabetes sees a registered dietitian for specific advice on their food choices. Your GP can refer you to a registered dietitian.
There's some evidence that suggests low-carbohydrate diets can lead to weight loss and improvements in blood glucose control in people with type 2 diabetes in the short term.
But it's not clear whether the diet is a safe and effective way to manage type 2 diabetes in the long term.
Weight loss from a low-carbohydrate diet may be because of a reduced intake of calories overall and not specifically as a result of eating less carbohydrate.
There also isn't enough evidence to support the use of low-carbohydrate diets in people with type 1 diabetes.
Douglas Twenefour, Diabetes UK clinical adviser, says: "When considering a low-carbohydrate diet as an option, people with diabetes should be made aware of possible side effects, such as the risk of hypoglycaemia (low blood sugar).
"We also advise that people with diabetes discuss the amount of carbohydrate to be restricted with their healthcare team.
"The best way to manage diabetes is by taking prescribed medications and by maintaining a healthy lifestyle that includes plenty of physical activity, and a balanced diet that is low in saturated fat, salt and sugar and rich in fruit and vegetables, without completely cutting out any particular food groups."
Read Diabetes UK's review of the evidence on low-carb diets and their conclusions.
What's the role of carbohydrates in exercise?
Carbohydrates, fat and protein all provide energy, but exercising muscles rely on carbohydrates as their main source of fuel.
But muscles have limited carbohydrate stores (glycogen) and need to be topped up regularly to keep your energy up.
A diet low in carbohydrates can lead to a lack of energy during exercise, early fatigue and delayed recovery.
When is the best time to eat carbohydrates?
There's little scientific evidence that one time is better than any other.
It's recommended that you base all your meals around starchy carbohydrate foods and you try to choose higher fibre wholegrain varieties when you can.
Page last reviewed: 19 December 2018
Next review due: 19 December 2021