Carbohydrates: how to assess their quality in the diet?
Editorial
Dietary carbohydrates are the main source of energy, accounting for 55 to 80% of our daily energy (Tan et al., 2023). There is a wide variety of carbohydrates, which are metabolised by different metabolic pathways and, therefore, have different effects on the body. Simple carbohydrates contain one or two sugars molecules such as glucose, sucrose, fructose and lactose. Despite their varying metabolic pathways, high consumption of foods enriched with simple carbohydrates, particularly sucrose, glucose and fructose, is associated with an increased risk of chronic diseases (Campos et al., 2022). Complex carbohydrates, including starches and glycogen, consist of long chains of sugar molecules. High consumption of complex carbohydrates is also associated with increased risk of chronic diseases, but this is affected by other factors.
Besides biochemical properties, quality and digestibility of dietary carbohydrates is also central. Usually, the assessment of carbohydrate quality is based on the determination of the glycemic index, a metric that determines how carbohydrates-containing foods affect blood glucose levels relative to a glucose standard. Nevertheless, dietary carbohydrates are more than just “sugars” and traditional indicators have recently become controversial.
Many foods containing carbohydrates provide other valuable macro and micronutrients, which need to be considered when assessing carbohydrate quality. For instance, fruit and vegetables contain both simple and complex sugars, and can be rapidly digested and metabolized, but they are considered high quality carbohydrates because they are rich in vitamins, minerals, dietary fibre while being relatively low in energy.
To address this issue, new indicators based on the content of fibres and whole grains have been recently designed to identify foods rich in carbohydrates and distinguish their effects on health. This month, the Global Fruit and Vegetables Newsletter will focus on the characteristics and relevance of different carbohydrates quality indicators.
The first article (Campos et al., 2022) synthesizes data presented at the American Society of Nutrition symposium on carbohydrate quality and highlights the use of fiber to elaborate indicator ratios of carbohydrate quality.
The second article (Olmedo et al., 2024) assesses the association between carbohydrate quality index (CQI) and obesity-related cancers in Spanish adults from the SUN (Seguimiento Universidad de Navarra) prospective cohort. The results show that a higher CQI, and in particular a higher intake of dietary fibre, is inversely associated with the risk of obesity-related cancers.
The third article (Cui et al., 2023) is a prospective cohort study investigating the association between three indicators of carbohydrate quality and the occurrence of type 2 diabetes (T2D) in Chinese adults. Results show U-shaped association between glycemic index and carbohydrate-fibre ratio and T2D risk, while an inverse relationship between carbohydrate quality index and T2D risk was observed, particularly in participants aged <60 years.
Together, these three articles highlight new indicators for assessing carbohydrate quality, with a multi-modal method to approach the nutritional quality of foods and products, and their impact on health. Fruit especially can be positively targeted with these news indicators, highlighting their nutritional quality, whether for prevention or for consumption in the context of specific pathologies.
Lisa Te Morenga is Professor and research scientist at the Centre for Public Health Research (Massey University). Her research involves the role of diet, (particularly dietary carbohydrates including dietary fiber, wholegrains and sugars) in the aetiology, treatment and prevention of obesity, the metabolic syndrome, diabetes and cardiovascular disease. She is particularly interested in the relationship between nutrition and hauora (Māori health) and achieving health equity.