What are carbohydrates? How much – and what types – to eat for good health

“There are different types of carbohydrates, which is where much of the confusion stems from,” says registered dietitian Catherine Culbert. “Some carbs can be high in sugar with low levels of other essential nutrients, while others are higher in fibre and nutrients.” According to the British Dietetic Association, carbohydrates can be divided into the following categories.

These are usually digested and turned into glucose quickly and easily by our bodies.

Examples are foods containing free sugars – any sugars added to a food or drink, which are not already inside the cells of the food. These include sweets or biscuits, or sugars naturally present in honey, syrups and fruit juices (when fruit is turned into juice, the cell walls are broken down so the sugar is no longer contained inside the cells, turning it into free sugars).

Free sugars are linked to poor dental health as well as heart disease and stroke. Natural sugars, such as those found in milk, plain yogurt and fruit, are also classed as simple carbohydrates.  

Complex carbohydrates take longer to break down than simple types, according to Dr Denise Robertson, reader in nutritional physiology at the University of Surrey and lead researcher into carbohydrate in the diet. This results in “a slow, sustained energy release,” she says.

Foods that contain complex carbs include bread, pasta and rice, as well as pulses and many vegetables.

These don’t have the same health risks associated with them as simple carbohydrates, according to Robertson. It’s best to opt for wholegrain varieties, such as wholemeal bread, wholegrain rice and wholewheat pasta. These have links to heart health, as well as the gut health benefits of fibre. 

Some types of starches, called resistant starches, cannot be broken down into glucose and pass through the body undigested; this is known as fibre. Foods containing fibre are often those that also contain complex carbohydrates, including vegetables, nuts, seeds, bread and rice as well as fruits.

We should opt for fibre-rich starchy carbohydrates, such as wholegrain foods, pulses and leafy greens, where possible. Robertson explains that fibre helps us to have a symbiotic relationship with our gut bacteria; we eat fibre, which feeds our beneficial bacteria and, in return, they help us with everything from aiding digestion to supporting our immune system.  

Some foods are higher in carbohydrates than others, but it’s worth noting that the type of carbohydrate you’re eating is more important than the amount you’re adding to your diet.

Foods are considered high in carbohydrates if they have more than 23g (four fifths of an ounce) total carbs per 100g (three and a half ounces). However, just because they are high, doesn’t mean they are unhealthy.  

The list below, detailing the amount of carbs in different foods per 100g, separates starches and sugars for this reason. 

• White bread: 56g total carbs; 48g starches; 6g sugars
• Wholegrain bread: 42g total carbs; 40g starches; 3g sugars
• Long-grain boiled white rice: 31g total carbs; 31g starches; trace amounts of sugars
• Quinoa: 56g total carbs; 48g starches; 6g sugars
• Dried white pasta, boiled in unsalted water: 38g total carbs; 36g starches; 1g sugars. 

The carbohydrates found in wholegrains, high–fibre foods, and fruit and vegetables provide benefits related to “energy, digestion, sleep and brain function”, says Culbert.  

Primarily, carbohydrates act as a source of fuel. Culbert says: “They are the body’s greatest source of energy, which aids us in other ways, from completing physical activities to [carrying out] biological processes such as digestion and concentration, as well as [sustaining] mental wellbeing.”  

“Carbohydrates provide around 50% of our daily energy,” adds Robertson.  

It’s not only protein that is important for promoting muscle growth. Culbert says: “In order to build muscle we need to be doing regular strength training. Carbs provide the source of fuel for these training sessions, allowing us to push our bodies and lift heavier weights.”  

Robertson adds: “If you’re fairly active as you get older, consuming carbohydrates for fuel becomes even more important, as our muscle mass decreases, causing our energy levels to also.” Age-related loss of muscle mass and strength (known as sarcopenia) happens at a rate of 3-8% per decade after the age of 30, which accelerates after the age of 60.  

If you’re a woman going through the menopause, this can also affect your muscle mass due to lower oestrogen levels.  

A particular type of carbohydrate is best known for this; fibre helps “the digestive system to function healthily”, says Culbert. The two types of fibre – soluble and insoluble – play a part in this. Insoluble fibre adds bulk to your stools and makes them easier to pass, which can help to prevent constipation. Meanwhile, soluble fibre helps to slow down digestion and relieve symptoms such as diarrhoea. Together, they help you to have regular bowel movements. 

As mentioned, fibre also nourishes our good gut bacteria. This then helps to increase the diversity of microbes in our gut. Greater diversity of gut bacteria is considered healthier. This is even more important as we age, as our microbe diversity tends to decrease. 

“[Certain] carbohydrates also provide us with essential nutrients, including calcium, iron, B vitamins and vitamin C, as well as [contributing to] a lower risk of cardiovascular disease,” says Culbert. It probably comes as no surprise that we have starchy carbs and fibre to thank for this. 

Research shows eating more fibre, in particular, has protective effects against disease. This is especially important as we get older because Robertson says our risk factors for various chronic conditions and illnesses increase. The same research showed those who ate foods high in fibre reduced their risk of coronary heart disease, stroke, type 2 diabetes and/or colon (bowel) cancer by 16-24%. What’s more, for every 8g (a third of an ounce) of fibre eaten, total deaths and incidences of coronary heart disease, type 2 diabetes and colorectal cancer dropped by 5-27%.   

Other study findings have suggested that fibre may play a role in supporting brain health and preventing dementia.

This is where many experience confusion, as the “right” amount of carbohydrates is different for everyone. 

And Culbert says your carbohydrate intake “should match your physical activity levels. For example, if you do limited exercise, you will need less carbs than someone who is very active”, a rule of thumb is that a portion about the size of your fist is a suitable amount to have with each meal. 

However, according to the British Dietetic Association, our portion sizes have increased over the past 40 years. The association says that we need to be “carbohydrate aware” by limiting our intake of free sugars and processed foods, and instead opting for starchy carbohydrates and wholegrain varieties. Current recommendations are that we should consume no more than 30g (1oz or around seven teaspoons) of free sugar per day. 

Choosing the right kind of carbohydrate also helps us get enough fibre – something many of us don’t manage. Most of us are only eating around 20g (three quarters of an ounce) per day and government guidelines say we should aim to increase this to 30g (1oz).  

People with type 2 diabetes can’t produce enough of, or effectively use, the hormone insulin, which is needed to use glucose as energy and regulate our blood sugar levels. This means their blood sugar levels can become too high, which can lead to further complications such as nerve damage in your hands and feet, or sight issues. As carbohydrates are the only nutrient that directly increases your blood glucose levels, being carbohydrate aware is even more important if you’re type 2 diabetic.  

Also, those with diabetes will need to consider whether a food is low or high on the glycaemic index (GI), as different foods raise blood glucose levels at different speeds. Even so, the same portion guidelines apply. A low-carb diet or reducing your carbohydrate intake can be beneficial for some, but you still need to make sure you’re getting essential nutrients and enough fibre.  

“If you’re diabetic, fibre is your friend,” says Robertson. “When you eat fibre, it doesn’t raise your blood sugar levels.”