The truth about carbs

"Carbs" are a hotly-debated topic, especially in the weight loss world, due in no small part to the popularity of low-carb diets such as the Atkins, Dukan and South Beach.

The "carbs are bad" mantra from Dr Atkins and co. 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 and it is the type, quality and quantity of carbohydrate in our diet that is important.

"While we should reduce the amount of sugar in our diet, particularly added sugars, we should base our meals on starchy carbs, particularly the less processed wholegrain 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 lose weight.

Many people don't get enough fibre.

 

We are advised to eat about 18g a day.

What are carbs?

Carbohydrates are one of three macronutrients (nutrients that form a large part of our diet) found in food – the others being fat and protein. Hardly any foods contain only one nutrient and most are a combination of carbohydrates, fats and proteins in varying amounts. There are three different types of carbohydrates found in food: sugar, starch and fibre.

  • Sugar is found naturally in some foods, including fruit, honey, fruit juices, milk (lactose) and vegetables. Other forms of sugar (for example table sugar) can be added to food and drink such as sweets, chocolates, biscuits and soft drinks during manufacture, or added when cooking or baking at home. Remember: sugar is a carbohydrate but not all carbohydrate are sugars. Find out more about sugar.
  • Starch, made up of many sugar units bonded together, 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. Find out more about starchy foods.
  • 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). Find out more about fibre.    

Why do we need carbs?

Carbohydrates are important to your health for a number of reasons.

Energy
Carbohydrates should be the body's main source of energy in a healthy balanced diet, providing about 4kcal (17kJ) per gram. They are 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 is converted to fat, for long-term storage of energy. High fibre, starchy carbohydrates release sugar into the blood more slowly than sugary foods and drinks.

Disease risk
Vegetables, pulses, wholegrain 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 people in the UK get about 18g of fibre a day. We are advised to eat an average of 30g a day.

Calorie intake
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 a weight loss plan. By replacing fatty, sugary foods and drinks with high-fibre starchy foods, it is more likely you will 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 is what 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 a healthy digestive system and to prevent constipation. Healthy sources of carbohydrates such as starchy foods, vegetables, fruits, legumes and lower fat dairy products are also an important source of nutrients such as calcium, iron and B vitamins.

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 are 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 that 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 will gain weight. So cutting out carbohydrates or fat does not necessarily mean cutting out calories if you are replacing them with other foods containing the same amount 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 and variety of food eaten, eating behaviour and environmental factors, such as portion size and 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 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 wholegrain varieties) provide a wider range of nutrients (such as vitamins and minerals) which can benefit our health. The fibre in these foods can help to keep your bowels healthy and adds bulk to your meal, helping you to feel full.

Sian says: "Cutting out a whole food group (such as starchy foods) as some diets recommend could put your health at risk because as well as cutting out the body's main source of energy you'd be cutting back essential nutrients like B vitamins, zinc and iron from your diet." 

How can I increase my fibre intake?

To increase the amount of fibre in your diet, aim for at least five portions of a variety of fruit and veg a day, go for wholegrain 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:

  • two breakfast wheat biscuits (approx. 37.5g) – 3.6g of fibre
  • one slice of wholemeal bread – 2.5g (one slice of white bread – 0.9g)
  • 80g of uncooked wholewheat pasta – 7.6g  
  • one 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 GI (glycaemic index) 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. However, 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, and 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. Also, the cooking method and eating foods in combination as part of a meal, will change the GI rating. Therefore, GI alone is not a reliable way of deciding whether foods or combinations of foods are healthy or will help you to lose weight.

Find out more about the glycaemic index (GI).  

Do carbohydrates make you fat?

Any food can be fattening 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 are likely to put on weight. In fact, gram for gram, carbohydrate contains fewer than half the calories of fat and wholegrain varieties of starchy foods are good sources of fibre. Foods high in fibre add bulk to your meal and help you to feel full.

However, foods high in sugar are often high in calories and eating these foods too often can contribute to you becoming overweight. There is 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.

"When people cut out carbs and lose weight, it's not just carbs they're cutting out, they're cutting out the high-calorie ingredients mixed in or eaten with it, such as butter, cheese, cream, sugar and oil," says Sian. "Eating too many calories – whether they are carbs, protein or fat – will contribute 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. However, there is no evidence that wheat is 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 is 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. 

Find out if cutting out bread could help ease bloating or other digestive symptoms.  

Should people with diabetes avoid carbs?

Diabetes UK recommends that people with diabetes should try to eat a healthy balanced diet, as depicted in the Eatwell Guide, and to include starchy foods at every meal. Steer clear of cutting out entire food groups. It is 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.

Diabetes UK says there is some evidence which suggests that low-carb diets can lead to weight loss and improvements in blood glucose control in people with type 2 diabetes in the short term. However, it is unclear whether the diet is a safe and effective way to manage type 2 diabetes in the long term.

Weight loss from a low-carb diet may be because of a reduced intake of calories overall and not specifically as a result of eating less carbohydrate. There is also not enough evidence to support the use of low-carb 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. However, muscles have limited carbohydrates stores (glycogen) and they 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?

When you should eat carbohydrates particularly for weight loss is the subject of much debate, but there's little scientific evidence that one time is better than any other. It is recommended that you base all your meals around starchy carbohydrate foods, try and choose higher-fibre, wholegrain varieties when you can.

Page last reviewed: 24/10/2016

Next review due: 24/10/2018

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