Conducted by researchers from the University of Auckland, the study was done based on a comprehensive review of PubMed scientific literature pertaining to sugar and sucrose.
The researchers identified studies using the keywords ‘liquid sugar and solid sugar’ and ‘liquid sucrose and solid sucrose, in addition to a nonexhaustive review using the keywords ‘fruits and fruit juices’. Over 200 articles from across the globe resulted, which were included in the review.
All in all, they found that liquid added sugars in the diet carry greater risk than solid added sugars, in terms of the ability to induce features of metabolic syndrome such as weight gain and insulin resistance.
“We believe this is related to the rapid absorption of fructose in liquid form resulting in greater concentration of fructose in the portal vein, which transports nutrients from the gut to the liver,” study co-researcher Dr Simon Thornley told FoodNavigator-Asia.
“Liquids are easier to digest than solids as the food is readily broken down into small particles and is able to be transported easily through the gut wall. Solid food is delayed by the stomach emptying and requires enzyme action to break down complex particles into their constituent chemicals for absorption,” he explained.
“There is also some evidence that glucose accelerates the absorption of fructose across the gut mucous membrane.”
In the study, especial focus was placed on explaining the effects of fructose on human health and its possible pathways.
“Fructose, we believe, is especially harmful to human metabolic health, raising triglyceride levels, leading to insulin resistance, fat deposition and weight gain,” said Dr Thornley.
“Almost all fructose is accompanied by glucose in food, whether the fructose is in sucrose form (table sugar) or there is starch (chains of glucose) or simple glucose in the food.”
The fruit effect
When it came to fruits and fruit juices though, the study said that the link with metabolic disease risk was less straightforward, though fruit juice ‘appeared to carry less risk than soft drinks’.
“The paper shows that there is some epidemiological evidence linking fruit juice intake with adverse metabolic health effects, but the evidence is not as consistent as for sugar sweetened soft drinks,” said Dr Thornley.
“The issue of added vs. intrinsic sugar is [complicated], but I think added sugar tends to be more concentrated than intrinsic forms. It becomes even more complicated when fruit juice is considered, since this is intrinsic sugar that is concentrated.”
“[That said], we believe both [fruit juice and soft drinks] carry concentrated fructose, which is likely to be harmful, but the evidence for harm is more consistent for sodas than juices.”
Overall, when it came to fruit juices, the study’s recommendation was to accede to the American Academy of Pediatrics’s recommendation that the daily consumption of fruit juice for children be restricted to 4 to 6 oz (1 to 6 years old) or 8 to 12 oz (7 to 18 years old).
Soft drink consumption in New Zealand
The study also found that in the 14 years from 2002 to 2016, the consumption of overall sugar-sweetened drinks in New Zealand showed an increasing pattern, as opposed to countries like the United Kingdom and United States which showed a decrease.
“[Although the intake of soft drinks in New Zealand overall was reduced], this was compensated for by the increase in consumption of juices and sports and energy drinks,” said the study.
In 2016, the average daily intake of sugary beverages per capita in New Zealand was found to be 175ml. New Zealand has the third highest obesity rate in the world.
“Using the sugar content of Coca-Cola (0.108 g/mL) as a measure, this would lead to an average intake of 19g of liquid sugars per person per day in New Zealand,” said the researchers.
This is not good news, and steps need to be taken to prevent this ‘dangerous’ practice going further, they added.
In a statement, lead researcher Dr Gerhard Sundborn that: “It is clear that sugar in drinks is more dangerous than sugar in foods, which means we should focus our [sugar-reduction] efforts on sugary drinks initially.”
“We have one of the highest rates of child obesity and adult obesity in the world, and our Government and Minister of Health, Hon. Dr David Clark, need to implement a tax on sugary drinks to address this issue,” added Dr Thornley.
Study: Are Liquid Sugars Different from Solid Sugar in Their Ability to Cause Metabolic Syndrome?
Authors: Sundborne, G. et. al.