New Meta-Analysis on Sugar Sparks Old Debate

January 16, 2013

DUNEDIN, New Zealand — Cutting consumption of sugar produces a small but significant reduction in body weight for adults, a new meta-analysis concludes [1]. The study found less consistent evidence for this effect in children, but this is likely because the kids in the included trials did not tend to comply with advice to reduce intake of sugar-sweetened foods and drinks, say Dr Lisa Te Morenga (University of Otago, Dunedin, New Zealand) and colleagues in their paper published online January 15, 2013 in BMJ.

The review is accompanied by an editorial [2] by Dr Walter C Willett (Harvard School of Public Health, Boston, MA) and Dr David S Ludwig (New Balance Foundation Obesity Prevention Center, Boston Children's Hospital, MA), which concludes that the tide is beginning to turn against sugar, with evidence continuing to accumulate that it is indeed deleterious to health.

Sugar is not the only issue; there is the bigger problem of carbohydrate quality. Large amounts of refined carbohydrates are also a problem.

"It's clear that sugar does have adverse effects, particularly in liquid form as sugar-sweetened drinks," Willett told heartwire . "This study addresses a piece of the picture, the effect on weight gain. There is also a strong body of evidence showing that sugar-sweetened beverages are related to type 2 diabetes. And sugar is not the only issue; there is the bigger problem of carbohydrate quality. Large amounts of refined carbohydrates are also a problem," he added.

This meta-analysis "and other evidence in the broader literature suggest that sugar intake should be limited," say Willett and Ludwig. But the question remains as to what is a desirable limit, they note. Current intake of added sugar in the US and UK is about 15% of total energy, so the 2003 World Health Organization (WHO) aim of limiting intake to 10% "could be viewed as a realistic and practical goal." However, the American Heart Association (AHA) suggests a limit of 5% of energy, "which would be more consistent with a goal for optimal health," they point out.

Refined Carbohydrates Just as Detrimental, Say Editorialists

Willett and Ludwig note that the meta-analysis by Te Morenga et al was commissioned by the WHO, which is in the process of updating its recommendations on intake of dietary sugars. The meta-analysis shows that exchanging dietary sugars with other carbohydrates made no difference to the changes in body weight that they saw, indicating that highly processed carbohydrates are just as detrimental as sugar, say the editorialists.

"Unfortunately, the 2003 WHO report disregarded evidence suggesting that refined grain and potato products have metabolic effects comparable to those of sugar," they note.

Actions are needed at many levels, Willett and Ludwig state. Efforts to reduce sugar intake "are appropriate" but "should form part of a broader effort to improve the quality of carbohydrates." This should include educational programs, improvements in foods and drinks provided in schools and work sites, and supplemental nutrition programs for people with low incomes.

"This is analogous to what we see for fats in that the type of fat you consume is really important. A similar picture is emerging for carbohydrates; quality turns out to be really important," Willett commented. "Another nuance," he says, "is the way we consume things, because that affects the physiologic response." For example, eating a whole fruit is much preferable to drinking fruit juice, he notes. "The sugar in fruits is balanced out by the fiber and other nutrients, and it takes time to be released. When we eat a whole apple or orange, we limit our intake. If you are drinking fruit juice, you might have three or four servings, but you would almost never eat three apples or oranges in a row."

Reducing the amount of sugar consumed in drinks "deserves special attention because of the strength of evidence and the ease with which excessive sugar is consumed in this form," he and Ludwig state. Policy approaches--such as imposing tax on sodas--are "useful," as are restrictions on advertising to children and limits on serving sizes, as have been tried in New York.

This is a global issue, with Coke and Pepsi pushing very hard, and the implications are horrendous.

"Sugar-sweetened beverages are such a big part of the picture," Willett commented to heartwire . "The average consumption among low-income groups in the US is about three servings a day; it's huge. And this is a global issue, with Coke and Pepsi pushing very hard, and the implications are horrendous."

The AHA agrees, showcasing in its top 10 advances of 2012 studies that illustrated the effect of sugar-sweetened beverages on body weight in children.

Willett says physicians and other healthcare providers have an important role to play "by routinely asking about consumption of sugar-sweetened drinks as well as tobacco and alcohol use" and by assuming leadership in public-health efforts to limit sugar as a source of harm.

Advice to Cut Sugar Intake Important for Obesity Reduction Strategies

In their meta-analysis, Te Morenga and colleagues included the results of 30 randomized controlled trials and 38 cohort studies of dietary sugar intake and adiposity. Free sugars were defined as sugars that are added to foods by the manufacturer, cook, or consumer, plus those naturally present in honey, syrups, and fruit juices.

Healthcare providers could play an important role by routinely asking about consumption of sugar-sweetened drinks as well as tobacco and alcohol use.

In trials of adults with at-will--no strict control of food intake--diets, reduced intake of dietary sugars was associated with a small decrease in body weight (0.80 kg; p<0.001). Conversely, increased sugar intake was associated with a comparable weight increase (0.75 kg; p=0.001). Isoenergetic exchange of dietary sugars with other carbohydrates showed no change in body weight.

Trials in children showed no overall change in body weight. But in relation to intake of sodas, after one-year follow-up in prospective studies, the odds ratio for being overweight or obese was 1.55 among the groups with the highest intake compared with those with the lowest intake, they note.

"It seems reasonable to conclude that advice relating to sugars is a relevant component of a strategy to reduce the high risk of overweight and obesity in most countries," the New Zealand group concludes.

Te Morenga et al have no conflicts of interest, nor do Willett and Ludwid.