From the simple to the complex, not all carbohydrates are created equal.

Nutrient type Macronutrient

Overview Dietary carbohydrates include simple carbohydrates - single sugars and small sugar molecules, including glucose, fructose, lactose and sucrose - and complex carbohydrates such as starches and fibre, which are formed from larger molecules [1]. Sugars and starches - known as available carbohydrates - provide a readily-available energy source for cellular metabolism; meanwhile, resistant starch and dietary fibre - critically important for gastrointestinal health and healthy blood glucose and cholesterol levels - are known as unavailable carbohydrates [2].

Rich food sources Complex carbohydrates include whole grains (rice, wheat, rye, barley, oats), legumes (chickpeas, lentils, beans, peas), potatoes, sweet potatoes and other root vegetables [1]. Dietary fibre - in both soluble and insoluble forms - is found in all plant foods, and is much higher in wholegrain cereals compared to refined ‘white’ alternatives [3]. Simple carbohydrates are naturally found in fruits, vegetables, juices, maple syrup and honey [2].

Functions and benefits

• Available carbohydrates (sugars and starches) are an essential source of glucose - for energy - to power cellular metabolism throughout the entire body [1]. Moreover, the brain, nervous system and red blood cells all rely upon glucose as their primary energy source [2].

• Meanwhile, unavailable carbohydrates (dietary fibre and resistant starch) support bowel function, facilitating elimination, alleviating constipation and protecting the bowel lining. Dietary fibre also supports cholesterol excretion, anti-inflammatory activity, and slows down nutrient digestion and absorption for improved glycaemic control and greater satiety (satisfaction) after eating, thereby reducing the risks of obesity, bowel cancer, cardiovascular disease and type II diabetes [1; 2].

• Soluble fibre in particular also supports prebiotic activity, providing fermentable food for beneficial probiotic bacteria in the colon [2].

Storage in the body Excess glucose is stored as glycogen in the liver and muscles. Once the body’s limited glycogen stores are full, any further glucose in excess of the body’s energy requirements is stored as fat in adipose tissue [1].

Signs and symptoms of inadequate carbohydrate intake

When carbohydrate intake is insufficient for the body’s energy requirements and glycogen stores are depleted, ketosis - involving the production of ketone bodies from the (incomplete) breakdown of fat - occurs, to meet some of the energy needs of the brain and nervous system, in particular. Adverse effects of ketosis include dehydration, weakness, fatigue, headaches and irritability. Nausea and loss of appetite may also be experienced [1; 2].

Furthermore, constipation - indicated by way of small, dry, uncomfortable and/or infrequent bowel movements - and other gastrointestinal disorders signal low dietary fibre intake [2].

Recommended carbohydrate intake

• Dietary guidelines suggest that 45-65 per cent of an individual’s daily energy requirements are met by carbohydrates [1].

Adequate intake (AI) | Dietary fibre

• Women (19-70+ years): 25 g/day

• Men (19-70+ years): 30 g / day

• Children:

  • Girls: 14 g/day (1-3 years); 18 g/day (4-8 years); 20 g/day (9-13 years); 22 g/day (14-18 years)

  • Boys: 14 g/day (1-3 years); 18 g/day (4-8 years); 24 g/day (9-13 years); 28 g/day (14-18 years) [4].

Note. Adequate intake (AI) is used where a RDI cannot be determined; AI refers to the minimum level of intake of a particular dietary nutrient that is considered unlikely to be inadequate. It is based on the approximated / estimated average intake of the nutrient for particular groups of apparently healthy people [4]. As such, individual requirements may differ.

Indicative (approximate) serving sizes - examples only

• 1 cup of cooked lentils or chickpeas provides ~8-11 g dietary fibre

• Two pieces of wholegrain bread with seeds offer ~6g dietary fibre (compared to ~2g in two pieces of white sourdough)

• 1 serving of fruit (e.g. apple, orange, two kiwifruit) provides ~4-5g dietary fibre

• Half a cup of cooked sweet potato or quinoa offers ~3g dietary fibre

• Half a cup of brown rice provides ~2g dietary fibre (compared to <1g in half a cup of white rice) [5].

Recipes to try | Fibre-rich sides

• Roast cauliflower + quinoa salad, by Jessica Cox (@jescoxnutritionist)

• Sesame seed + turmeric sweet potato wedges, by Jessica Cox (@jescoxnutritionist)

Other notes

• When increasing dietary fibre intake, introduce a variety of additional fibre-rich foods gradually - over several weeks - and concurrently increase fluid intake. This will support the movement and excretion of greater amounts of fibre and provide adequate time for the gastrointestinal tract to adapt, thereby helping to prevent any abdominal discomfort, bloating, gas and/or diarrhoea [1].

• Minimally-processed forms of sugar (such as those found naturally in fruits and vegetables, along with - to a lesser extent - quality honey and maple syrup) offer greater health benefits than their highly-processed counterparts. This is due to the presence of other essential nutrients including vitamins and minerals, as well as - for fruits and vegetables - water and dietary fibre, which helps to slow glucose absorption, thereby delivering a modest rise in blood glucose and smoother return to normal [1].

• The AI for dietary fibre increases with increased energy requirements, including those associated with pregnancy and breastfeeding [4].

References.

[1] Whitney, E., Rolfes, S., Crowe, T., & Walsh, A. (2019). Understanding nutrition (4th ed.). Cengage Learning Australia Pty Limited. 

[2] Paxton, F. (2015). Foundations of naturopathic nutrition: A comprehensive guide to essential nutrients and nutritional bioactives. Routledge.

[3] Prasadi, V., & Joye, I. (2020). Dietary fibre from whole grains and their benefits on metabolic health. Nutrients, 12(10), 3045. https://doi.org/10.3390/nu12103045

[4] Australian National Health and Medical Research Council and New Zealand Ministry of Health. (2019). Dietary fibre. Nutrient Reference Values for Australia and New Zealand. Retrieved February 28, 2022, from https://www.nrv.gov.au/nutrients/dietary-fibre

[5] Food Standards Australia and New Zealand. (2021). Australian Food Composition Database. https://www.foodstandards.gov.au/science/monitoringnutrients/afcd/Pages/default.aspx