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expert reaction to study investigating fructose restriction and metabolic measures in obese children

The effect of the limitation of sugar in the diet of a small group of children with obesity is the subject of a paper published in the journal Obesity, with the authors reporting that they observed favourable metabolic outcomes including weight loss.

The SMC also produced a Factsheet on sugar and health.


Prof. Tom Sanders, Professor Emeritus of Nutrition and Dietetics, King’s College London, said:

“In my opinion this paper’s claim of turning sugar into fat needs to be viewed with some caution because this is an uncontrolled trial.

“It was a 9 day study conducted in very fat children (average 93 kg) who lost 0.9kg weight when they were given a diet where starch replaced reported sugar intake.

“As the study lacked a control group who remained on a high sugar diet, the claim that that sugar is more fattening than starch was actually not tested for.

“Instead the comparisons were made with reports of “usual intake”. But it is well known that obese children underestimate and under-report food intake, particularly of soft drinks and snack foods.

“This is a fundamental methodological flaw in the study. It is likely that the changes in metabolic outcomes observed can be explained by the experimental diet providing fewer calories than the children’s usual intake.

“Given the extensive prior knowledge that sugar and starch contain roughly the same number of calories per gram (4 vs 3.75 kcal/g), it is inconceivable that isocaloric substitution of sugar from starch would have such a large effect on metabolism – this would go against the basic laws of thermodynamics.  To achieve this 0.9 kg weight loss would have required a calorie deficit of 630 kcal/d (in terms of soft drink that would be equivalent to the amount energy provide by 5 cans of sugar sweetened beverage a day).

“Some of the metabolic parameters measured such as blood pressure are know to fall with repeat measurement (so called regression to the mean) and as there was not a control, it is not possible to assess the true fall in blood pressure due to the intervention. Restriction in food energy intake would be expected to lower blood pressure and a restriction of carbohydrate intake would have favourable effects on insulin secretion and insulin sensitivity.”


Prof. Naveed Sattar, Professor of Metabolic Medicine, University of Glasgow, said:

“The results are not convincing to me – this is a very small study, and it has not been statistically well controlled. Also, when people are losing weight, even if modest, their metabolic changes can seem larger than they actually are – one needs to see results once folk return to their habitual state after they’ve finished losing weight. Overall, this study is of modest interest but is far from convincing.”


Ms Tracy Parker, Heart Health Dietitian at the British Heart Foundation, said:

“This study is interesting, but we need more research to confirm these findings. Previous studies have suggested that eating too much added sugar increases a person’s risk of development of the various diseases, including cardiovascular disease, type 2 diabetes, hypertension and high cholesterol, because of the link with excess calorie intake leading to obesity. However, this small and short-term study of 43 children found that removing added sugar from the diets of already obese Latino and African American children improved their metabolic health (lower BP, LDL cholesterol, and fasting glucose), without changing weight.

“Both adults and children on average are exceeding their recommended daily sugar intake so it’s important we continue to work as hard as we can to change our behaviour and meet these targets. Cutting down on food and drink with added sugars is a good place to start. Replace sugary drinks with water or sugar-free versions and instead of sweets, biscuits and chocolate, try healthier alternatives like fresh fruit and vegetables, unsalted nuts and seeds and plain popcorn.”


‘Isocaloric Fructose Restriction and Metabolic Improvement in Children with Obesity and Metabolic Syndrome’ by Robert H. Lustig et al. published in Obesity on Tuesday 27 October 2015. 


Declared interests

Prof. Tom Sanders: Prof. Tom Sanders is a Scientific Governor of the charity British Nutrition Foundation, member of the scientific advisory committee of the Natural Hydration Council (which promotes the drinking of water), and honorary Nutritional Director of the charity HEART UK. Prof. Tom Sanders is now emeritus but when he was doing research at King’s College London, the following applied: Tom does not hold any grants or have any consultancies with companies involved in the production or marketing of sugar-sweetened drinks.  In reference to previous funding to Tom’s institution: £4.5 million was donated to King’s College London by Tate & Lyle in 2006; this funding finished in 2011. This money was given to the College and was in recognition of the discovery of the artificial sweetener sucralose by Prof. Hough at the Queen Elizabeth College (QEC), which merged with King’s College London. The Tate & Lyle grant paid for the Clinical Research Centre at St Thomas’ that is run by the Guy’s & St Thomas’ Trust, it was not used to fund research on sugar. Tate & Lyle sold their sugar interests to American Sugar so the brand Tate & Lyle still exists but it is no longer linked to the company Tate & Lyle PLC, which gave the money to King’s College London in 2006. Tom also used to work for Ajinomoto on aspartame about 8 years ago.

Prof. Naveed Sattar: “No COI.”

Ms Tracy Parker: “No conflicts.”

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