Carbohydrates: An overview

 Although the "low-carb" diet has been fashionable since the 1970s, the amount of sugar we consume and the consequences of excess intake have only been hot topics in nutrition for the past few years. 

Free sugars

Free sugars are classified as any sugars added to a product or food item and the sugar naturally present in syrups, honey and fruit juices. 

The world health organization published new guidelines on sugar intake in 2015, which urged governments to commit to reducing the intake of "free sugars" in adults and children. "Free sugars" include any sugar that's added to a product by manufacturers, cooks or consumers, or the sugar naturally present in syrups, honey and fruit juices. It doesn't include sugars in dairy products, nor in fresh or dried fruit as the sugar is held within the cell structure of the food. 

In the US, the 2015-2020 Dietary guidelines for Americans recommend restricting added sugars to no more than 10% of daily calories. Sugar consumption likewise rose up the UK public-health agenda in 2015, when the Scientific Advisory Committee on Nutrition (SACN) published its report "Carbohydrates and Health", which concluded that there is sufficient evidence of a direct link between sugar intake and obesity risk. In the report, SACN advised the government to reconsider its recommended daily intake of free sugars and to halve it to no more than 5% of daily energy intake. In more everyday terms, SACN said that adults (and children over 11) should be consuming no more than 30g (1oz, seven cubes) of sugar each day, children from 7 to 10 years should consume no more than 24g (0.9oz, six cubes) and children aged 4 to 6 years no more than 19g of free sugars (0.7oz, five cubes). 

So how much are sugars, and more widely carbohydrates, responsible for our current obesity epidemic? Are all carbohydrates bad for our health or are there some types out there that we should be eating more of?

Should you cut ALL carbs?

Carbohydrates include starches and sugars, as well as the fibre found in fruit, vegetables, pulses and grains. As one of the three macro-nutrients (the others being protein and fat), they are one of the three main ways in which the body obtains energy or calories. 

In fact, carbohydrate is the body's main source of energy for physical activity and is also needed by the brain. Starchy foods, particularly wholegrain foods, are also good sources of a number of important vitamins and minerals, as well as fibre. 

In the UK, SACN extensively reviewed the evidence linking consumption of carbohydrate with health outcomes (looking at more than 600 peer-reviewed research papers). Although a high sugar intake was linked with increased risk of dental caries and weight gain, a high fibre intake was crucially found to help reduce the risk of heart disease, strokes, type 2 diabetes and colorectal cancer. Based on this evidence, the UK has new fibre recommendations: at least 30g (1oz) per day for adults; and for children, ages 2-5, 15g (0.5oz)/day; ages 5-11, 20g (0.7oz)/day; ages 11-16, 25g (0.9oz)/day; and ages 16-18, 30g/day. 

Meanwhile, the European Food Safety Authority (EFSA) recommends 25g fibre per day for adults. Although fibre is often overlooked in much of the media coverage about carbohydrates, it is just as challenging to achieve, in the context of the dietary changes that most of us will need to make, as the new sugar recommendation. 

So carbohydrates are still an important part of our diet - overall around 50% of our energy should come from carbohydrates. This means basing most of our meals on starchy foods. However, just as we have recognized that we need to think about the type as well as the amount of fat in our diets, the same is true for carbohydrates. 

Does sugar make you fat?

There is good evidence that eating too much sugar can lead to weight gain. Humans have an innate desire for sweetness from birth, and sugar-containing foods, snacks and drinks are highly palatable and easy to consume in excess. However, it is important to remember that the underlying cause of obesity is energy imbalance - in other words, any source of excess calories can result in weight gain. Surveys reveal that our sugar consumption has been falling since around 2000, whilst obesity rates have continued to increase, suggesting that focusing on sugar alone isn't going to stop the epidemic. 

The bottom line: There is widespread agreement that, on average, we eat too much sugar, and world health advice emphasizes that intake should be reduced. Foods high in free sugars can be high in energy and are often considered more palatable, therefore increasing the risk of excessive consumption, which in turn can lead to weight gain and obesity. But sugars are also naturally present in fruit, vegetables, milk and grains, and these are all foods that are important nutrient providers. So we should try to cut down on added sugars, for example in biscuits, cakes, confectionery, sugary drinks and breakfast cereals, but still eat plenty of fruit and vegetables and some lower-fat dairy products (preferably those without added sugars).