February 7, 2014, by Duane Mellor
Nutrition in the News – Sugar, Obesity and Diabetes
There has been a lot of attention this year regarding dietary intakes of sugar and risk of diabetes. This was typified by the Action on Sugar press release (http://www.actiononsalt.org.uk/actiononsugar/Press%20Release%20/120017.html ) which linked epidemiological projections on obesity and diabetes to suggest by 2050 the cost to the NHS of obesity to be £50 billion. This was a projection based in turn upon the Foresight report (2007) (http://www.bis.gov.uk/assets/foresight/docs/obesity/17.pdf), which based its data on a time when adult incidence of obesity was rising rapidly. The continued rate of increase levels of obesity do not seem to be occurring and may be plateauing, and although at levels which are impacting significantly upon public health (http://www.noo.org.uk/slide_sets ). The end result of this media interest in health and sugar was a story in the Observer on the 2nd February2014 that cutting sugar intake of the population could save the NHS £50 billion (http://www.theguardian.com/society/2014/feb/02/food-crusaders-challenge-cut-sugar)
The growth of this story appears to raise two questions how dangerous is sugar to health? Then, how sound are these types of projections and extrapolations?
Firstly there is no obligate requirement for sugar in the diet, the human body can synthesise and uses a number of sugars for a range of biological functions. The most abundant one being glucose which is the main sugar in the blood. The sugars which are the focus of this current Action on Sugar campaign are added sugars typically sucrose (a dimer of glucose and fructose) . The argument against added sugar and particularly fructose can be most strongly associated with an American paediatric endocrinologist Dr Robert Lustig (Sugar: The Bitter Truth http://www.youtube.com/watch?v=dBnniua6-oM&feature=player_embedded) and has further been supported by a recent serial cross-sectional study linking rising rates of diabetes within 175 countries to rising sugar intake by Basu et al (2013) (http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0057873). This study attempted to account for alcohol intake and sedentary behaviour along with obesity but did not address fully the issues of nutritional transition and urbanisation. This type of study is widely acknowledged to assess association only and not causality. To do this ideally an interventional or clinical randomised controlled trial design is used, however this would be impractical, expensive and almost impossible to control enough to obtain meaningful data beyond biomarker suggestions of increased risk. In the accepted hierarchy of evidence between the randomised controlled study and the cross-sectional studies are the cohort studies which follow individuals for years after assessing food related behaviour and assess how disease develop. In cohort studies sugar sweetened beverages have been associated with increased risk of obesity and diabetes (Schulze et al 2004, http://jama.jamanetwork.com/article.aspx?articleid=199317 ) and these findings appear to be repeated in other similar studies (Vasanti et al 2010, http://care.diabetesjournals.org/content/33/11/2477.full.pdf). To be clear from a metabolic perspective there is no absolute evidence of sugar or fructose being inherently toxic (Feinman and Fine, 2013 http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3708747/). So, it appears that reducing intake of sugar sweetened beverages is a simple and logical way to reduce risk of developing obesity and diabetes, and could be a potential target for taxation. However, despite not offering any health benefits, moderate (5-10% of total energy intake) from sugar does not appear to increase risk of chronic disease.
So, a reduction in mean sugar intake of the population to 5-10% of energy (25-75g per day depending on target level and gender) may be better for the health of many in the population, but do the proposed cost savings add up. Firstly, to achieve the £50billion saving, it would appear obesity would need to be virtually eliminated as a risk factor to health by 2050. Action on Sugar propose a 20-40% reduction in sugar in foods, has been suggested to reduce intake of the population by 100kcal per day. This reduction, assuming not replaced by other energy sources in the diet would mean a weight loss per adult per year (again based on assumptions for weight loss of 7000kcal being equivalent to 1kg) of 5kg per year, so in theory at least an adult weighing 100kg today with a BMI of 30kgm-2 could reach a BMI of 25kgm-2 and a weight of 70kg in 6 years. However, this projection ignores the reduction in energy requirements and metabolic rate seen with weight loss, which after a 7-10kg weight loss will have reduced by 100kcal. Therefore, although a potentially useful change in the diet, it needs to be part of a wider change in lifestyle to support individuals trying to manage weight, as it is a complicated problem with many precipitating causes and requiring many supportive interventions. The cost savings suggested are further confused as various charities, campaign groups and governments quoting healthcare costs to the NHS and total societal costs. However, with respect to costs it is unlikely that total costs of obesity will be eliminated by any intervention or public health policy, even if that were to be a return to rationing.
In summary, sugar is not toxic, yes the human body has not obligate requirements but in moderation no more than 10% of total energy not acknowledged to increase risk of obesity of diabetes. Care needs to be taken when discussing the future as data can quickly be misinterpreted and over stated. There is a good case to restrict sugar sweetened beverages including possibly be taxation, but this needs to be considered as part of wider public health interventions and as part of the whole dietary pattern of individuals and populations.