CUTTING calories rather than promoting exercise must be the cornerstone in the fight against Scotland's obesity epidemic, health experts will tell MSPs today.

Cancer Research UK will urge policymakers to priority a reduction in calorie consumption over exercise, pointing to the findings of the World Health Organisation that the rise in obesity globally "is too large to be explained by declines in physical activity".

The charity is also calling for Scottish schoolchildren to be "routinely weighed and measured" at the end of primary school to pinpoint youngsters with an unhealthy BMI. This is already done in England, but in Scotland is restricted to P1 pupils only.

Read more: Research finds even light drinkers may be triggering irregular heartbeats

Prof Linda Bauld, professor of health policy for cancer prevention at Stirling University, will give evidence on behalf of the charity today at the Scottish Parliament's obesity inquiry.

In a paper submitted in advance, Cancer Research UK said: "While a comprehensive obesity strategy should seek to increase physical activity, particularly through supporting active travel, this should not be the focus of Government intervention.

"Reducing excessive calorie consumption through reducing consumption of foods high in sugar, salt and fat (HFSS foods) should be the priority as it is likely to have the biggest impact on obesity rates in Scotland."

The call was echoed by dieticians who warned that "you can’t outrun a poor diet". In its submission to the inquiry, the British Dietetic Association Scotland said: "More health gain will be achieved by weight loss (in those with excess weight) than by physical activity alone."

Cancer Research UK is also backing state-led interventions including tough restrictions on supermarket junk food promotions, which are more widespread in Britain than anywhere else in Europe.

In Scotland, an estimated 40 per cent of all calories consumed are said to come from food and drink purchased on special offer.

Read more: Research finds even light drinkers may be triggering irregular heartbeats

Cancer Research UK said: "Given the competition between supermarkets, regulation is likely to be the most effective way to reduce unhealthy price promotions across Scotland ... In the first instance, the Scottish Government should restrict the use of multi-buy discounts such as ‘two for one’ for HFSS foods."

The call is supported by obesity campaigners.

Professor David Haslam, chair of the National Obesity Forum, said: "Previously I would have said that self-regulation was best - I wasn't in favour of a 'big stick' approach. But now, with overweight and obesity levels continuing to rise we are facing an epidemic and I think that we do have to take a 'big stick' approach to tackling it, through regulation and other public health interventions. It's too serious to leave to people to fix on their own."

However, the move would face opposition from retailers.

Read more: Research finds even light drinkers may be triggering irregular heartbeats

Ewan MacDonald-Russell, head of policy for the Scottish Retail Consortium, said: “We are not persuaded the focus right now should be on increasing costs for customers, particularly at a time where household budgets are under pressure."