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.
Carbohydrates a broad category and not all carbs are the same. It's the type, quality and quantity of carbohydrate in our diet that's important.
There is strong evidence that fibre, found in wholegrain versions of starchy carbs, for example, is good for our health.
What are carbs?
Carbohydrates are 1 of 3 macronutrients (nutrients that form a large part of our diet) found in food. The others are 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 that most adults and children in the UK eat too much of are called free sugars.
These are sugars that are added to food or drinks, such as biscuits, chocolate, flavoured yoghurts, breakfast cereals and fizzy drinks.
The sugars in honey, syrups (such as maple, agave and golden syrup), nectars (such as blossom), and unsweetened fruit juices, vegetable juices and smoothies happen naturally, but these still count as free sugars.
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 found in the cell walls of foods that come from plants. Good sources of fibre include fruit and vegetables, wholegrain bread, wholewheat pasta, and pulses (beans and lentils).
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.
Why do we need carbs?
Carbohydrates are important to your health for several reasons.
Carbohydrates should be your body's main source of energy in a healthy, balanced diet.
They're broken down into glucose (sugar) before being absorbed into your blood. The glucose then enters your body's cells with the help of insulin.
Glucose is used by your body for energy, fuelling your activities, whether that's going for a run or simply breathing.
Unused glucose can be converted to glycogen, which is 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.
Starchy carbohydrates that are high in fibre release glucose into the blood slower than sugary foods and drinks.
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 do not get enough fibre. On average, most adults in the UK get about 19g of fibre a day. Adults are advised to eat an average of 30g a day.
The recommended fibre intake for children can vary from 15g to 30g, depending on their age.
Carbohydrate contains fewer calories gram for gram than fat; 4 calories (4kcal) per gram for carbs and 9 calories (9kcal) per gram for fat. Also, 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.
Should I cut out carbohydrates?
While we can survive without sugar, it would be 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, fruit 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 mean you do not get enough nutrients, potentially leading to health problems.
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.
This can cause headaches, weakness, feeling sick, 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, fruit, and legumes.
Diabetes and low-carb diets
There is evidence that low-carb diets are safe and effective in the short-term for most people with type 2 diabetes. They help with weight loss, diabetes control and reducing risk of complications.
It's recommended you talk to a GP or your care team before starting a low-carb diet as it's not suitable for everyone with type 2 diabetes. Your care team should provide advice on how many carbs you should eat. Diabetes UK also provides a 7-day low-carb meal plan on its website.
It's also important to be aware of possible side effects of a low-carb diet, such as low blood sugar (hypoglycaemia).
There is no evidence that a low-carb diet is more effective in the long-term for people with type 2 diabetes than other types of diet such as a reduced-calorie diet.
There is currently no strong evidence that low-carb diets are effective for people with type 1 diabetes.
Low-carb diets are not recommended for children with diabetes as they might affect growth.
Can 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 4 calories (4kcal) per gram
- protein provides 4 calories (4kcal) per gram
- fat provides 9 calories (9kcal) 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, you'll gain weight.
So, cutting out carbohydrates or fat does not necessarily mean cutting out calories if you're replacing them with other foods that contain 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 things make us feel full, such as the type, variety and amount of food we eat, 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 you should have some beans, pulses, fish, eggs, meat and other protein foods as part of a healthy, balanced diet.
But we should not eat too much protein-rich and starchy foods. Starchy foods should make up about a third of the food we eat, and we all need to eat more 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 that contain added sugar.
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 bowel healthy and adds bulk to your meal, helping you to 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 the skin 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 carbohydrate. It shows how quickly each food affects the glucose (sugar) level in your blood when that food is eaten on its own.
Some low-GI foods (foods that are absorbed slower by the body), such as wholegrain cereals, fruit, vegetables, beans and lentils, are foods we should eat as part of a healthy, balanced diet.
But GI alone is not a reliable way of deciding whether foods, or combinations of foods, are healthy or will help you lose weight.
Although low-GI foods cause your blood sugar level 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, yet healthy, 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.
Do carbohydrates make you fat?
Any food can cause weight gain if you eat too much. 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 gain weight.
Gram for gram, carbohydrate contains fewer calories than fat. 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.
But foods high in sugar are often high in calories, and eating these foods too often can contribute to you becoming overweight.
Can cutting out wheat help me lose weight?
Some people point to bread and other wheat-based foods as the main cause of their weight gain.
Wheat is found in a wide range of foods, from bread, pasta and pizza to cereals, biscuits and sauces.
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 will 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.
What's the role of carbohydrates in exercise?
Carbohydrates, fat and protein all provide energy, but your muscles rely on carbohydrates as their main source of fuel when you exercise.
Muscles have limited carbohydrate stores (glycogen) and need to be topped up regularly.
A diet that is 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 choose higher fibre wholegrain varieties when you can.
Page last reviewed: 9 January 2020
Next review due: 9 January 2023