Sugar intake must come down, says WHO

British government's advisory committee, some of whom receive funding from food industry, sceptical about link with obesity by Sarah Boseley

The World Health Organisation is set to recommend a cut in the amount of sugar in our diets in the coming months, following reviews of the scientific evidence of the link with obesity – but any proposed lower limit for sugar will have to overcome scepticism among scientific advisers to the British government.

Next year, the government's scientific advisory committee on nutrition (SACN) will report on carbohydrates, including sugar, in people's diet. Its members, some of whom receive funding from industry, are thought to be sceptical that the sugar is a cause of obesity.

The chairman of the SACN working group on carbohydrates, Professor Ian Macdonald, from Nottingham University, has been on the Mars and Coca-Cola European advisory boards, although he has stepped down from both for the duration of the inquiry.

The professor is the academic lead for his university's "strategic relationship" with Unilever, which owns ice-cream brands as well as margarine and weight-loss products. Unilever's Dr David Mela sits with him on the SACN carbohydrate group and the two are also on the government's calorie reduction expert group, which advises food companies and health groups involved in the Department of Health's Responsibility Deal, aimed at improving public health in England.

Macdonald does not believe his links to Mars and Coca-Cola are a problem. "I have explained my associations with industry to the Department of Health and they are quite happy with the relationships," he said. "I think it's a more balanced view than some of the views of my nutritional colleagues and also than some of the industrial views. Some of the industrial people can't see what they're doing wrong. That's not right – they do need to start helping people to consume sensible amounts of food and be less sedentary than they are at the moment."

However, Macdonald voiced scepticism about some of the claims of the anti-sugar lobby. "But as far as sugar goes, it's difficult to know where to start because there are people who believe it is the cause of all of our problems. [Professor] John Yudkin started this in the 1960s with [his book] Pure, White and Deadly and other people have picked it up at intervals beyond. The consumption rates are a bit higher than they were in the 1960s, but not excessively so. Consumption hasn't trebled."

The belief that the industry should be at the table is common to many of those in the field of nutrition in the UK. The British Nutrition Foundation's director, Professor Judy Buttriss, is also on the calorie reduction group. The foundation takes funding from British Sugar and Tate & Lyle among others, arguing, as some doctors do over drug company funds, that the money has no influence on their scientific independence.

In other quarters concern over sugar in the diet and particularly in sweetened soft drinks has been growing. Health campaigners, worried about rising rates of obesity-related disease such as diabetes and heart problems, have targeted the so-called empty calories in sugar and say that sweetened soft drinks deliver calories without filling people up. The industry says the problem is caused by all of us eating too much of every type of food – not just sugar – and doing too little exercise. It frequently cites studies by industry-funded scientists to make the point.

The WHO's nutrition guidance expert advisory group (NUGAG) is updating its recommendation that sugar should not account for more than 10% of the calories in our diet. That was passed in 2003 only after a fight with the sugar industry. As the Guardian revealed at the time, the US sugar industry threatened to put pressure on the US government to withdraw American funding from the WHO if the restrictions went ahead.

A number of experts think 10% is now too high in the context of rising obesity. The WHO commissioned a review of the scientific evidence on sugar and weight gain to inform NUGAG's discussions from Professor Jim Mann's team at the department of human nutrition and medicine at the University of Otago in New Zealand. It was published in January in the British Medical Journal.

The BMJ paper says that people get fat from eating sugar because they take in too many calories, rather than any intrinsic effect on the metabolism of the sugar itself. But, it says, "when considering the rapid weight gain that occurs after an increased intake of sugars, it seems reasonable to conclude that advice relating to sugars intake is a relevant component of a strategy to reduce the high risk of overweight and obesity in most countries".

Speaking to the Guardian, Mann said that sugar "unquestionably contributes to obesity", although he thinks some anti-sugar campaigners have gone too far. "We've got to try to find the happy medium. I don't think sugar is the cause of all evil. It's an important factor and if we're eating more sugar and less fat then we need to take note of it."

Sugar is energy-dense. People who gave up sugar as part of a trial and were told to consume the same amount of calories from starchy carbohydrates such as bread and potatoes could not do it, Mann said. "They really didn't like it. They felt full. They weren't complaining about anything to do with addiction – they just felt stuffed with food."

Soft drinks containing sugar are not energy-dense in the same way, Mann argues, "but it seems that probably the body doesn't sense calories that come from sugary drinks, so that if one has a Coke with all the vast amount of sugar that it contains you don't register that you've had all these calories".

Sugary drinks, Mann believes, contribute to obesity in younger people, but not in the over-50s, who drink fewer. "But if you look for instance at New Zealand, where I am – Pacific youth for example, who are among the fattest people in the world – sugary drinks probably contribute an enormous amount, as indeed in American youth. How much it contributes to British youth I'm not quite sure but it probably is a significant contributor to youth of all nationalities."

Sugar Nutrition, which used to be called the Sugar Bureau and is funded by the industry, seized on the review's finding that it is the calories consumed that make people fat, rather than something about sugar itself. "Therefore products containing sugars should be consumed within an individual's energy-balanced diet and not in addition, in order to maintain a healthy body weight," it said in a statement.

The UK still officially uses an 11% limit on sugar set 22 years ago by the SACN's predecessor on the basis of tooth damage, although the NHS Choices website refers to 10%. Sugar Nutrition says that "numerous groups" including the European Food Safety Agency and UN Food and Agricultural Organisation have reviewed it since and found no health reason for any limit. "These expert reviews have concluded that the levels of sugars currently consumed are not implicated in any of the lifestyle diseases such as obesity, diabetes, coronary heart disease or cancer," it said.

However, the European Heart Network report in 2011 on diet, physical activity and the prevention of heart disease recommended a sugar limit of less than 10% and set a tentative ambition of reaching 5% in the future.

Mike Rayner, director of the British Heart Foundation health promotion research group at Oxford University and an adviser on the report, believes obesity is caused by too many calories from all kinds of foods. Nevertheless, he is a leading light in the campaign for a soft drinks tax, which would affect consumption.

"The problem with sugar is its calories really and it's easily digestible," he said. "And it tends not to come with anything particularly useful, so sugary drinks are problematic because they are an easy way of getting calories – not because it's sugar but because it's calories. I know there is a difference of opinion. I think nutritionists are rather squabbling over how many angels you get on the side of a pin."

Simon Capewell, professor of clinical epidemiology at Liverpool University, argues there is evidence that taxes on foods with high fat, sugar and fat content will work. But, he says, "industry is doing all it can to stop that happening, including funding scientists. The tactics of the Big Food and Big Soda multinationals are thus very similar to those employed by Big Tobacco. How much longer will society tolerate industry profiting from making children obese?" he asked. "These obese children then face premature deaths, deaths which are 100% preventable."

"Regulation and taxation both work. All we need now is a UK government which is genuinely committed to promoting the public's health, rather than supporting their industry friends' profits."