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What is the evidence for sugar intake limits?

Jimmy Louie is an Associate Professor of Dietetics at the Department of Nursing and Allied Health of the Swinburne University of Technology. Associate Professor Louie has a strong track record in nutritional epidemiology and is best known for his research on the association between carbohydrate nutrition (specifically glycaemic index and added sugar consumption) and health outcomes.

How would you sum up where we are at in the sugar debate?

The debate surrounding the negative impact of high consumption of 'free' sugars on health outcomes has persisted, with anti-sugar advocates arguing for strict limitations on the intake of 'free' sugars from all foods, while some researchers argue that 'free' sugars are no different from other caloric nutrients like fat and protein. Despite this ongoing debate, numerous public health agencies worldwide, including the World Health Organization (WHO) [1], the U.S. Department of Agriculture (USDA) [2], and the Scientific Advisory Committee on Nutrition (SACN) [3], have issued quantitative guidelines recommending a reduction in free sugars intake to below 10% of daily energy intake for improved health, and a conditional target of 5% for additional health benefits. However, much of the evidence informing these guidelines is derived from studies on sugar-sweetened beverages (SSBs) and extrapolating these findings to villainise 'free' sugars from other food sources lacks sufficient evidence.

How well is the WHO 5-10% energy from free sugars guideline supported by the available evidence? 

A substantial body of evidence consistently links sugars from SSBs to negative health outcomes [4,5]. However, it is important to note that most governments and public health agencies have extended these findings beyond their scope and issued guidelines advocating for a reduction in free sugars intake from all food sources [1-3]. Studies investigating the effects of sugars from solid foods on metabolic and endocrine health have generally yielded inconclusive results [6-9]. For example, while a high intake of liquid sugars has been associated with higher body mass index (BMI) and waist circumference, no such associations have been found for solid sugars in prospective cohort studies involving children [9,10].

What are the differences between solid and liquid sugars?

Our research group has previously published on the physiological differences between sugars derived from solid and liquid sources [11]. In brief, intake of sugars from solid sources is less likely to result in overconsumption of dietary energy, a key contributor to weight gain. Whereas, energy compensation from liquid sugars is incomplete and leads to higher overall energy intake. This disparity may be due to the faster gastric emptying time of liquid sugar sources, leading to a higher absorption rate of fructose and increased exposure of the liver to dietary fructose [12,13]. Animal studies have also shown that administration of sugar in drinking water leads to obesity and metabolic disturbances, while a solid high-sugar diet does not have the same effect [14]. Additionally, some studies have suggested that high intake of SSBs may contribute to overeating and weight gain by disrupting the production of appetite control hormones [15]. However, no such effect has been observed with high consumption of solid sugar-containing foods, although the precise mechanisms remain unclear [16].

What is your view on the term ‘free sugars’ and its definition? What issues has it raised in research?

One of the challenges is defining 'free sugars' accurately. The concept of 'free sugars' encompasses all monosaccharides and disaccharides added to foods by manufacturers, cooks, or consumers, as well as sugars naturally present in honey, syrups, and fruit juices [1]. While the concept of 'free sugars' improves upon the use of ‘total sugars’ in health risk assessments, accurately measuring and quantifying free sugars poses significant challenges [17]. Differentiating between naturally occurring sugars and those added during processing can be complex, especially in products where sugars are present in both forms. With the absence of chemical structural differences, it is impossible to quantify the amount of free sugars in food products using laboratory analysis, leaving the only option as labelling of free sugar content in packaged foods by food manufacturers who know the formulation of their products. Unfortunately, this requirement is not mandatory in most parts of the world except the U.S (where the content of added sugars, defined similarly to free sugars, must be displayed on food label) [18].

Is there anything else you’d like to say to Australasian health professionals about sugar intake recommendations?

Maintaining a balanced perspective on sugar consumption is important. While excessive free sugar intake can contribute to health issues, it is crucial to note that most of the studies underpinning the evidence base have examined free sugars intake from SSBs. Health professionals should avoid an overly simplistic view that villainises free sugars entirely, but instead focus on promoting informed choices based on individual circumstances and dietary patterns. Currently, consumers and health professionals in most parts of the world lack the necessary knowledge and information to effectively apply the quantitative sugar guidelines. Guidelines regarding sugars and health for the public should therefore consist of clear and practical messages that are easily understood and implemented, which focuses on limiting the consumption of SSBs and other high-sugar discretionary foods, as these recommendations are supported by robust scientific evidence. 

Further reading

Yan R, Chan CB, Louie JCY. Evidence does not support the reduction of added sugar intake from all food sources. Nat Rev Cardiol. 2022 Dec;19(12):845

Yan RR, Chan CB, Louie JCY. Current WHO recommendation to reduce free sugar intake from all sources to below 10% of daily energy intake for supporting overall health is not well supported by available evidence. Am J Clin Nutr. 2022 Jul 6;116(1):15-39


  1. World Health Organization, Guideline: Sugar intake for adults and children, WHO Department of Nutrition for Health and Development (NHD), Geneva, Switzerland, 2015, pp. 50.
  2. U.S. Department of Agriculture, Dietary Guidelines for Americans 2020 - 2025, USDA, Washington D.C., USA, 2020.
  3. Scientific Advisory Committee on Nutrition, Why 5%? An explanation of the Scientific Advisory Committee on Nutrition’s recommendations about sugars and health, in the context of current intakes of free sugars, other dietary recommendations and the changes in dietary habits needed to reduce consumption of free sugars to 5% of dietary energy, Public Health England, London, UK, 2015.
  4. Y. Wang, R. Zhao, B. Wang, C. Zhao, B. Zhu, and X. Tian, The Dose-Response Associations of Sugar-Sweetened Beverage Intake with the Risk of Stroke, Depression, Cancer, and Cause-Specific Mortality: A Systematic Review and Meta-Analysis of Prospective Studies. Nutrients 14 (2022) 777.
  5. N. Neelakantan, S.H. Park, G.-C. Chen, and R.M. van Dam, Sugar-sweetened beverage consumption, weight gain, and risk of type 2 diabetes and cardiovascular diseases in Asia: a systematic review. Nutr. Rev. 80 (2021) 50-67.
  6. J.C. Laguna, M. Alegret, M. Cofán, A. Sánchez-Tainta, A. Díaz-López, M.A. Martínez-González, J.V. Sorlí, J. Salas-Salvadó, M. Fitó, M. Alonso-Gómez Á, L. Serra-Majem, J. Lapetra, M. Fiol, E. Gómez-Gracia, X. Pintó, M.A. Muñoz, O. Castañer, J.B. Ramírez-Sabio, J.J. Portu, R. Estruch, and E. Ros, Simple sugar intake and cancer incidence, cancer mortality and all-cause mortality: a cohort study from the PREDIMED trial. Clin. Nutr. 40 (2021) 5269-5277.
  7. S. Janzi, S. Ramne, E. González-Padilla, L. Johnson, and E. Sonestedt, Associations between added sugar intake and risk of four different cardiovascular diseases in a Swedish population-based prospective cohort study. Front Nutr 7 (2020) 603653.
  8. A. Bergeron, M. Labonté, D. Brassard, C. Laramée, J. Robitaille, S. Desroches, V. Provencher, C. Couillard, M.C. Vohl, M. Bélanger, B. Lamarche, and S. Lemieux, Associations of intake of free and naturally occurring sugars from solid foods and drinks with cardiometabolic risk factors in a Quebec adult population: the PREDISE (PRÉDicteurs Individuels, Sociaux et Environnementaux) Study. J. Nutr. 151 (2021) 1561-1571.
  9. M. Zheng, M. Allman-Farinelli, B.L. Heitmann, B. Toelle, G. Marks, C. Cowell, and A. Rangan, Liquid versus solid energy intake in relation to body composition among Australian children. J. Hum. Nutr. Diet. 28 Suppl 2 (2015) 70-9.
  10. J.A. Welsh, Y. Wang, J. Figueroa, and C. Brumme, Sugar intake by type (added vs. naturally occurring) and physical form (liquid vs. solid) and its varying association with children's body weight, NHANES 2009-2014. Pediatr. Obes. 13 (2018) 213-221.
  11. R.R. Yan, C.B. Chan, and J.C.Y. Louie, Current WHO recommendation to reduce free sugar intake from all sources to below 10% of daily energy intake for supporting overall health is not well supported by available evidence. The American Journal of Clinical Nutrition 116 (2022) 15-39
  12. G. Sundborn, S. Thornley, T.R. Merriman, B. Lang, C. King, M.A. Lanaspa, and R.J. Johnson, Are liquid sugars different from solid sugar in their ability to cause metabolic syndrome? Obesity (Silver Spring) 27 (2019) 879-887.
  13. M.L. López-Portillo, A. Huidobro, E. Tobar-Calfucoy, C. Yáñez, R. Retamales-Ortega, M. Garrido-Tapia, J. Acevedo, F. Paredes, V. Cid-Ossandon, C. Ferreccio, and R.A. Verdugo, The association between fasting glucose and sugar sweetened beverages intake is greater in Latin Americans with a high polygenic risk score for type 2 diabetes mellitus. Nutrients 14 (2021).
  14. J. Togo, S. Hu, M. Li, C. Niu, and J.R. Speakman, Impact of dietary sucrose on adiposity and glucose homeostasis in C57BL/6J mice depends on mode of ingestion: liquid or solid. Mol Metab 27 (2019) 22-32.
  15. D.M. Sigala, A.M. Widaman, B. Hieronimus, M.V. Nunez, V. Lee, Y. Benyam, A.A. Bremer, V. Medici, P.J. Havel, K.L. Stanhope, and N.L. Keim, Effects of consuming sugar-sweetened beverages for 2 weeks on 24-h circulating leptin profiles, ad libitum food intake and body weight in young adults. Nutrients 12 (2020)
  16. D.M. Sigala, and K.L. Stanhope, An exploration of the role of sugar-sweetened beverage in promoting obesity and health disparities. Curr Obes Rep 10 (2021) 39-52.
  17. C.H.C Yeung, and J.C.Y. Louie, Methodology for the assessment of added/free sugar intake in epidemiological studies. Curr Opin Clin Nutr Metab Care 22 (2019) 271-277. doi: 10.1097/MCO.0000000000000567.
  18. E.A. Magnuson, and P.S. Chan, Added Sugar Labeling. Circulation 139 (2019) 2625-2627

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