Carbohydrates are one of three macronutrients, alongside protein and fats, that are a main source of energy for the body. Carbohydrate quality is more important than quantity, as some sources of carbohydrate are more nutritious than others.

Carbohydrates will not directly cause weight gain. No one food group can cause weight gain on its own, but rather their contribution to overall calorie intake and food quality should be considered.

The difference between refined carbs, whole-food sources of carbs and complex carbs^1,2

Simple carbohydrates, also known as simple sugars, occur naturally in fruit, vegetables, and milk, but this also refers to table sugar (sucrose), which can be added to foods during processing.

Complex carbohydrates are starchy foods and fibres which take longer to break down and digest. These come from vegetables, legumes, wholegrains, nuts, and seeds.

Wholegrains are a type of complex carbohydrate that contains all three parts of the grain: the bran, endosperm, and germ. They are rich in fibre and nutrients, including B vitamins, vitamin E, folic acid, magnesium, iron, zinc, and selenium. Wholegrain foods include wholewheat bread, oats, barley, rye, brown rice, maize, spelt, buckwheat, and quinoa.

Refined carbohydrates are carbohydrates that have been processed to remove the bran and the germ. This means that most of the fibre and nutrients are removed. Foods made of refined carbs include white bread, white pasta, white rice, and prepackaged cakes, biscuits, and pastry products.

What do carbs actually do to our body?

Carbohydrates are the body’s main source of energy ². They are broken down into simple sugars, or glucose, which enter the bloodstream and act as a fuel source for the cells in our body. When sugars enter the bloodstream, it causes a rise in blood glucose levels. Glycaemic index (GI) is a ranking system based on how quickly the body breaks down carbohydrates into glucose ³. Simple sugars are broken down quickly, causing blood glucose levels to rise quickly causing a fast – but short – boost of energy.

Complex carbs have a lower GI because digestion takes longer, the effect on blood glucose is smaller and slower and these carbs provide us with a steady source of energy over a few hours. Refined carbs raise blood glucose levels faster than wholegrains as they contain less fibre ³.

Wholegrains are high in fibre, which can’t be broken down or digested by the body. A higher fibre diet has been linked to the diversity of the gut microbiome, improved digestion, and better bowel health^4,5. There is also strong evidence that diets high in fibre are associated with lower risk of cardiovascular disease, heart disease, stroke, type 2 diabetes, and maintenance of healthy cholesterol levels ^2,6,7. The bulk and fibre content can aid with weight management, as they make you feel fuller and more satisfied after eating ^2,6.

Lady eating a slice of pizza with a happy expression

What happens to our body without enough carbs?

Carbohydrates are the body’s main energy source. Without them, the body starts to rely on proteins and fats for fuel – which may be needed for other essential processes – you might find yourself feeling tired, low on energy or have difficulty concentrating.

Not enough carbohydrates in the diet can also affect the gut ^8,12. Gut bacteria respond to changes in the diet very quickly, and studies have shown changes in bacterial diversity within hours. In the long-term, low-carb diets can reduce the diversity of the gut microbiome and the number of beneficial bacteria. Reduced fibre as a result may also cause changes to the bowel function, for example constipation and/or looser stool.

How many of our total calories should come from carbs?

The Eatwell guide shows that starchy (complex) carbohydrates should make up just over a third of the food we eat, and we should choose wholegrain options wherever possible. Another third should come from fruits and vegetables, which are also a type of carbohydrate^1,13.

The exact calorie contribution of carbohydrates will depend on the individual, but the EFSA suggests that 45% to 60% of total energy intake for adults and children over the age of 1 year should come from carbohydrates, including both simple and complex carbs ¹⁴.

Tips on adding carbs to your diet in a healthy way: ¹

Make simple swaps to wholewheat or brown bread, rice, and pasta.
Beans, peas, and lentils make great additions to evening meals like chilli, shepherd’s pie, curry, and stir fry.
Instead of reaching for the rice, consider other grains, like couscous, quinoa, pearl barley, bulgar wheat, amaranth, or spelt.
Choose oats or a wholegrain cereal for your breakfast.
Aim to eat a wide range of fruit and vegetables, focusing on whole fresh or frozen sources. Leave the skins on for extra fibre. Try and reduce fruit juices and dried fruits as these are sources of concentrated natural sugars.
Snack on nuts and seeds.

Your favourite carbs and the benefits of carbs

It's good to know about the varying benefits of different carbohydrates, and the nutrients they can offer the body.

Lentils are my favourite carb. There are so many different types to choose from, and they are so versatile. They have a low GI so won’t cause the blood sugar to spike and the high fibre and protein will maintain energy levels. They’re also a great source of vitamins and minerals, including iron, magnesium, and B vitamins.

Sources

1. Harvard The Nutrition Source – Carbohydrates: https://www.hsph.harvard.edu/nutritionsource/carbohydrates/

2. SACN Carbohydrates and Health Report (2015): https://www.gov.uk/government/publications/sacn-carbohydrates-and-health-report

3. BDA Glycaemic Index (GI): https://www.bda.uk.com/resource/glycaemic-index.html

4. Dietary fibre from whole grains and their benefits on metabolic health. Nutrients. (2020): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7599874/

5. British Nutrition Foundation – Fibre: https://www.nutrition.org.uk/healthy-sustainable-diets/starchy-foods-sugar-and-fibre/fibre/#:~:text=Fibre%20helps%20to%20keep%20our,different%20effects%20on%20our%20body.

6. Intake of refined carbohydrates and whole grain foods in relation to risk of type 2 diabetes mellitus and coronary heart disease. Journal of the American College of Nutrition. (2002): https://pubmed.ncbi.nlm.nih.gov/12166526/

7. Human postprandial responses to food and potential for precision nutrition. Nature Medicine. (2020): https://www.nature.com/articles/s41591-020-0934-0

8. Prebiotic fiber modulation of the gut microbiota improves risk factors for obesity and the metabolic syndrome. Gut Microbes. (2012): https://www.tandfonline.com/doi/abs/10.4161/gmic.19246

9. The impact of Western diet and nutrients on the microbiota and immune response at mucosal interfaces. Frontiers in Immunology. (2017): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5532387/

10. Diet rapidly and reproducibly alters the human gut microbiome. Nature. (2014): https://pubmed.ncbi.nlm.nih.gov/24336217/

11. Effects of Low-Carbohydrate Diet and Exercise Training on Gut Microbiota. Frontiers in Nutrition. (2022): https://www.frontiersin.org/articles/10.3389/fnut.2022.884550/full#:~:text=Conclusion%3A%20LC%20intervention%20did%20not,induced%20regulation%20of%20cardiometabolic%20health.

12. Short-term impact of a classical ketogenic diet on gut microbiota in GLUT1 Deficiency Syndrome: a 3-month prospective observational study. Clin Nutr. (2017): https://pubmed.ncbi.nlm.nih.gov/28361745/#:~:text=Results%3A%20Compared%20with%20baseline%2C%20there,significant%20increase%20in%20Desulfovibrio%20spp.

13. NHS Starchy foods and carbohydrates: https://www.nhs.uk/live-well/eat-well/food-types/starchy-foods-and-carbohydrates/

14. EFSA – European dietary reference values (DRV) for nutrient intake: https://www.efsa.europa.eu/en/press/news/nda100326#:~:text=The%20intake%20of%20total%20carbohydrates,for%20both%20adults%20and%20children.