The popularity of low-carb diets such as The Atkins Diet has resulted in a lot of confusion around the importance of carbohydrates. Popular mantras such as ‘carbs are bad’ has led many people to believe that all carbohydrates are the same and make you put on weight. However, carbohydrates is the umbrella term for such a broad category and I’m going to help you understand why you need them in your diet and which ones you should be eating more of.
What are carbohydrates?
Carbohydrates are one of three macronutrients (the others being protein and fat) that are required in large amounts to meet the nutritional needs of the body.
There are three different types of carbohydrates; sugar, starch and fibre. They are categorised according to their chemical structure and how quickly they are digested and absorbed.
Sugars are generally categorised as simple carbohydrates as they are broken down easily by the body. They are divided into single sugars (monosaccharides) which include glucose, fructose and galactose, or double sugars (disaccharides) which include sucrose, lactose and maltose.
Starch and fibre are longer chains of sugars and are referred to as complex carbohydrates as they take longer to be broken down by the body.
What foods are they in?
Sugar is found naturally in foods such as fruit, veg, milk and honey. However, the main source of sugar in our diet is in the form of table sugar (extracted from sugar cane or sugar beet) which is added to lots of food and drink such as cakes, sweets, chocolate and fizzy drinks.
Starch is found mainly in vegetables like potatoes, and foods that come from plants such as rice, bread, pasta and couscous. You can buy them wholegrain or refined to remove the germ and bran.
Fibre is found in the cell walls of unrefined plant foods. Most foods contain a mixture of two types of fibre; soluble and insoluble. Foods that are high in soluble fibre include grains (oats, barley and rye), pulses (lentils and soya beans), fruits (bananas and apples) and root vegetables (carrots and sweet potatoes), whereas foods high in insoluble fibre include wholegrains (bread, pasta and rice), nuts, seeds and some fruit and veg, specifically in the stalks, skin and seeds.
What is their role within the body?
Carbohydrates are converted in the body to glucose to be used as a source of energy, providing 4 calories per gram. They provide the body with a variety of nutrients including zinc, iron and B vitamins.
Fibre is metabolised differently to starch and sugar. Its primary role is to keep our digestive system healthy and to make us feel full. Soluble fibre absorbs water to form a gel-like substance which helps to slow digestion and regulate blood sugar levels. It also helps to improve heart health by trapping cholesterol so less is absorbed into the blood and instead is removed as waste. Whereas insoluble fibres pass through the gut without being broken down and add bulk to the stools, which helps food move more quickly through the digestive system. Fermentable fibres such as oats also help to feed the good bacteria in your gut which influences the immune system, hormones and extracts key nutrients from foods. To learn more about fibre, read our article on fibre here.
How much should you eat?
The National Diet and Nutrition Survey found that we’re eating too many simple sugars found in biscuits, cakes, pastries, chocolate and sweets, and not enough fibre and starchy carbohydrates. Refined carbohydrates have had most of their nutritional value removed, for example white bread is processed to remove the germ and bran which contains most of the fibre, B vitamins, calcium and iron.
The governments Eatwell Guide shows you how much of each food group you should eat to achieve a healthy, balanced diet. It recommends that starchy carbohydrates should make up just over a third of the food you eat and you should choose less processed, wholegrains carbohydrates where possible to increase your fibre intake. Most people in the UK are not eating enough fibre at only 18g a day, which is less than two thirds of the recommendation. It also recommends that foods high in sugar are not needed in the diet and should be eaten less often and in smaller amounts.
The recommended daily intake of carbohydrates for an average adult (70kg) is 260g including 90g of sugars and 30g of fibre. We’re also recommended to limit our intake of free sugars to 5% of our energy intake (calories), which is roughly 30g or 7 teaspoons a day. Free sugars are sugars added to foods by the manufacturer, cook or consumer, plus sugars present naturally in honey, syrups and unsweetened fruit juices. Sugars found in milk, fruit and vegetables don’t count as free sugars but they are included in the ‘total sugar’ figure found on food labels.
What is the glycaemic index?
The glycaemic index (GI) indicates how quickly a carbohydrate containing food raises blood sugar levels. Foods that are broken down quickly by the body and cause a spike in blood glucose levels have a high GI, such as fizzy drinks and white bread. Whereas foods that have a low or medium GI are broken down more slowly and cause a gradual rise in blood sugar levels, such as wholegrains, pulses and some fruit and veg.
The GI of a food does not necessarily indicate how healthy a food is. Often low GI foods are less processed and contain more fibre but this isn’t always the case. For example a watermelon has a high GI because it’s mostly made up of water however it only contains a small amount of carbohydrate (this is when glycaemic load may be more appropriate). There are also many things that can affect the GI of a food such as the way it’s been prepared, whether it’s been cooked, how ripe it is and the presence of fat and protein (which slows down absorption).
What happens if we eat too much sugar?
Our desire for sweet foods is thought to be due to our primal ancestors and how they evolved craving sweet fruits as they were high in nutrients and vital to our survival. Our intake of sugar has gradually risen since the 1970s when the government recommended we reduce our intake of fat. Our bodies work efficiently at breaking down carbohydrates into sugar but if we consume too much we increase our risk of obesity, insulin resistance, type 2 diabetes, cardiovascular disease, liver disease and tooth decay.
Insulin is a hormone that helps control blood glucose levels by signalling the liver and muscles to take in glucose from the blood and use it as energy or store it as glycogen. If we consume too much sugar, the sugar is converted into fat by a process known as lipogenesis.
One sugar to be aware of is fructose which is found naturally in fruit, root vegetables and honey but also in sugar alternatives such as agave. It is metabolised differently to glucose and many people believe it to be healthier as it does not raise blood glucose levels and therefore has a lower GI. However, the liver is the only organ that can metabolise fructose in large amounts and consuming too much causes it to be converted into fat and increases your risk of a condition known as Non-Alcoholic Fatty Liver Disease (NAFLD). We do not need to limit our intake of fruit however we should be cautious of drinking too many juices and smoothies, and eating dried fruits and sugar alternatives such as agave.
What’s the difference between natural and refined sugar?
‘Natural sugars’ are sugars found in foods such as fruit and milk, whereas ‘refined’ or ‘processed’ sugars are commonly made from sugar cane or sugar beet that has been processed to form crystallised sugar such as table sugar. Whilst it seems that natural sugars should be healthier, this is not always the case.
Our bodies respond in a similar way to any type of sugar whether its table sugar, golden syrup, maple syrup or honey. Some sugars may contain slightly more nutrients than others but this difference is only small. The main difference between natural and refined sugar is the way in which the sugars are delivered. For example, a piece of fruit such as an orange not only contains sugar but also fibre and vitamin C. This fibre helps slow down the release of sugar into the bloodstream and causes a gradual rise in blood sugar. Orange juice is a good source of vitamin C but it’s had the fibre removed and therefore the sugar increases blood sugar levels at a much quicker rate than a whole piece of fruit.
Refined sugar is often referred to as ‘empty calories’ as it has very little nutritional value.
• Eat more fibre rich foods such as oats, beans and lentils
• Choose wholegrain bread, pasta and rice
• Eat less simple sugars found in refined carbohydrates like white bagels, biscuits, cakes, pastries and sweets
• Limit your intake of free sugars to 30g or 7 teaspoons a day
• Use a third of your plate or the size of your fist as a portion guide for carbohydrates
• Combine high GI foods with protein and fat to slow down the release of sugars into the blood
Speak again soon,
Gemma, The Food Doctor nutritionist