Carbohydrates should be the body’s main source of energy in a healthy balanced diet, but not all carbohydrates are the same (more on this below). There are three different types of carbohydrates found in food – sugar, starch and fibre. The government published new guidelines in July 2015 recommending that adults should aim for a fibre intake of 30 grams a day.
On average, we consume much less fibre than the recommended amount. In 2018, the UK National Diet and Nutrition Survey found that the average intake in adults is 19 grams per day, well below the recommended 30 grams per day.
Carbohydrates are essential for good health as they provide us with glucose, which is the main source of energy for the human body and all its cells. They are present in food in the form of sugar (simple carbohydrates), starch and fibre (complex carbohydrates). Fibre is the only type of carbohydrate that cannot be converted to glucose and used as an energy source but it has other important functions.
When people talk about blood sugar levels, it always means the amount of glucose in the blood. As carbohydrates get digested, they release glucose into the bloodstream. Some foods release it faster and some slower. Based on this, a measurement of glucose-release speed has been devised called the ‘glycaemic index’ (GI). Foods that release glucose quickly have a high GI, foods that release it slowly have a low GI and there’s a whole range of foods with a medium GI.
A carbohydrate is a molecule containing carbon, oxygen and hydrogen. Depending on how many of these molecules are bound together, their different types and number, carbohydrates can be either simple or complex. Both simple and complex carbohydrates can be a part of a healthy diet.
Simple carbohydrates (sugars):
- single sugar molecules (monosaccharides) – eg glucose and fructose
- two sugar molecules linked together (disaccharides) – eg table sugar (sucrose, consisting of glucose and fructose) and milk sugar (lactose, consisting of glucose and galactose)
These carbohydrates are digested quickly and we should watch our intake – with the exception of fruit and vegetables. Fruit and vegetables naturally contain fructose, a simple sugar. But if fruit and vegetables are eaten fresh and whole they also supply a wealth of complex carbohydrates along with many other nutrients which slow down the speed of sugar absorption. Fruit and vegetables are among the healthiest foods so there’s no need to limit their intake. They are best eaten raw, lightly cooked or blended in a smoothie (avoid canned). See our wallchart comparing smoothies and fresh juice here.
Beware of fruit juices – unless they are freshly made, they undergo a pasteurisation process which destroys most of the goodness of the fruit and the result can be little more than just sweet water.
Complex carbohydrates (polysaccharides) consist of many sugar molecules linked together in complex structures. Complex carbohydrates usually mean starch and fibre. The difference is that we can digest starch very well – your body breaks it down to single glucose molecules – whilst we cannot digest fibre.
In terms of starch, it’s naturally a part of many foods (wholegrains, pulses, root vegetables, pumpkins, courgettes etc) which belong in a healthy diet. These foods contain starch along with many other nutrients and your body digests them slower. On the other hand, refined starches used as a binding ingredient in foods such as biscuits, processed snack foods and sweets are extracted from their natural source – a process that strips off all the other nutrients – and are not very healthy because your body can digest them faster which may result in high blood sugar levels.
If you have too much sugar in your blood at any given moment (more than your body’s cells can take up), your body will immediately try to restore the balance by removing some of the sugar and storing it as fat.
The healthiest sources of carbohydrates:
Unprocessed or minimally processed foods such as wholegrains, fruit and vegetables, pulses (lentils, beans, peas) – these release their energy gradually, promote good health by providing vitamins, minerals, fibre, antioxidants and many important phytonutrients.
Unhealthy sources of carbohydrates
Processed or refined foods such as white bread, pastry, sugary and savoury processed snacks, cakes, sweets, fizzy and sugary drinks (including hot drinks with flavoured syrups) and other processed commercial foods – these contain easily digested carbohydrates that turn to sugar fast and may contribute to weight gain, heart disease, diabetes and some types of cancer. See additional information at the end of this section for more on sugars and sweeteners.
Dietary fibre is the name for a large group of complex carbohydrates that we cannot digest. Fibre is naturally found in unrefined plant foods (fruit and vegetables, wholegrains, pulses, nuts and seeds) but never in animal foods. . See additional information at the end of this section for more on soluble and insoluble fibre.
Even though we cannot digest it, fibre is a very important and beneficial part of any diet. It keeps our digestive system healthy, improves our energy metabolism (slows down sugar absorption), helps in healthy weight management, can reduce blood cholesterol and the risk of heart disease, some cancers (particularly colon cancer) and diabetes and encourages the 'good' bacteria in the gut.
It’s easy to get plenty of fibre (without the need for counting) from fruit and vegetables, wholegrains (cereal, oats, wholemeal bread and pasta, brown rice, grains), pulses (lentils, beans, chickpeas, peas, soya) and nuts and seeds.
No, a healthy, varied, vegan diet will provide all you need.
To boost your fibre intake try to include the following in your diet:
- Porridge oats – a great source of fibre
- Dried fruit is packed with fibre and can boost your intake significantly
- Wholegrain and wholemeal foods – avoid white bread and pasta, choose wholegrain and wholemeal varieties
- Jacket potato – the skin is the important bit
- Beans – all beans are good, whether baked beans or kidney beans in a chilli or a bean salad
- Brown rice – white rice doesn't provide as much fibre
- Nuts and seeds – almonds, pecans and walnuts provide plenty as do sesame and sunflower seeds
- Fruit and veg – aim for at least 5-a-day portions
Low-carb, ketogenic or paleo diets usually focus on high protein and fatty foods and severely restrict the intake of carbohydrates. This forces your metabolism to change and draw the energy mostly from fat and protein, which makes you less hungry and leads to weight loss. But – and there’s a big but! – these diets are effective only for short term weight loss and have a whole range of unpleasant adverse effects such as constipation, headaches, kidney fatigue, bad breath, decreased insulin sensitivity, increased cholesterol levels and more. In the long term, they are not any more effective for weight loss and maintenance than low-fat diets which don’t have these nasty side effects and allow your body to function naturally.
Our bodies run on carbs so don’t avoid them. Choose the good ones and you’ll be the best you can be. A steady energy supply from good carbs also makes you feel good, physically and mentally.