Carbohydrates are the primary source of energy in the diet with a recommendation that they make up 50% of our total dietary energy intake, that’s around 1,000 calories for women and 1,250 for men per day.
They are classified into different groups by their structure, principally by chain length, made up of different numbers of single units. They differ further within each of these groups with how the units are joined together. Humans are unable to digest some carbohydrates as we lack the enzymes to break them down. These don’t provide energy but have other functional roles in the body.
Simple carbohydrates include added sugars and natural sugars and are often listed on food labels as ‘carbohydrates (of which sugars)’. They consist of one (mono) or two (di) single units called monosaccharides and disaccharides. An example of a monosaccharide is glucose which the body breaks all carbohydrates down to, where it can then be used as energy. Lactose, found in dairy foods, is a disaccharide formed of one glucose and one galactose unit.
Complex carbohydrates are longer chains of sugars called oligosaccharides and polysaccharides such as starch and polyols (e.g. sorbitol and xylitol which are often used as sweeteners). They are found in starchy foods like bread, cereals, rice, pasta and potatoes. Try wholegrain varieties whenever you can. You should get most of your energy from complex carbohydrates (starchy foods) rather than from simple carbohydrates (sugars), because starchy foods are typically more nutrient dense and can provide fibre, B vitamins, calcium and iron. Refined (white) carbohydrates can contribute to weight gain and increase risk of heart disease and diabetes if eaten in large quantities, they are typically lower in fibre than wholegrain alternatives therefore are processed quicker by the body and will not keep us as satiated.
Why wholegrains are better sources of carbohydrates.
Wholegrains provide a great source of fibre which is essential for good digestive health and there is evidence that high intakes are associated with lower risk of developing coronary heart disease, type 2 diabetes and colorectal cancer. Eating plenty of wholegrains, fruit and vegetables can help you maintain a healthy weight – their fibre and bulk makes us feel fuller on fewer calories.
A 2018 study 'Does high-carbohydrate intake lead to increased risk of obesity? A systematic review and meta-analysis', has looked into two areas of carbohydrate consumption, the first objective of this systematic review (a type of literature review, so no new research is conducted but existing research is examined and compared) was to test for any association between high and low carbohydrate diets and obesity and the second objective was to test for any association between total carbohydrate intake and obesity. For the former objective there was a weak increase in obesity risk with a high carbohydrate diet, 8 of the studies examined showed an increased risk of obesity, whilst 5 showed a reduced risk, however on statistical analysis the results were not found to be statistically significant, therefore no association could be determined.
As for the studies second objective, testing total carbohydrate intake and obesity risk, 6 studies found a reduced risk of obesity and 5 studies found an increased risk, again with non-significant associations.
This study did not distinguish between the various types of carbohydrate, and refined and unrefined carbohydrates could have varying effects on obesity, although evidence on this is yet to be conclusive. However the conclusion was that a high carbohydrate diet or an increased proportion of energy from carbohydrate sources (as opposed to from protein or fat) does not significantly increase obesity risk.
Reference: Sartorius K, Sartorius B, Madiba TE, et al. Does high carbohydrate intake lead to increased risk of obesity? A systematic review and meta-analysis. BMJ Open 2018;8:e018449. doi:10.1136/bmjopen-2017-018449