The glycaemic index (GI) appears to be stuck in legal limbo following a vote in the European Parliament on the controversial nutrition and health claims regulation.
The proposed regulation does not permit direct references to GI and it is not yet known whether phrases such as "sustained energy release" or "keeps you fuller for longer" will make it on to the so-called positive list of generally accepted health claims or whether manufacturers will have to go through a lengthy prior approvals process.
The UK's Food Standards Agency (FSA) said: "It's not clear where GI sits legally. It's much bigger in the UK than in other member states.
"The term low-GI itself refers to both the nature and function of the product and it isn't clear whether we're talking about nutrition or health claims."
The FSA has asked the European Commission to put together a group of experts to discuss how the positive list will be compiled. This must be finalised within three years of the regulation coming into force.
"We've had informal discussions about the criteria for deciding what should go on the list, but there needs to be consistency between member states," the FSA said. "We also need to establish where things like GI fit in."
Claims about soy, oats, omega-3s and wholegrains already adopted by the UK Joint Health Claims Initiative are widely expected to make it on to the positive list, but just because a claim is already well established in the UK does not mean it would survive in the same form, according to Leatherhead Food International's business manager for legislation Jean Feord.
"Claims about gut health might be restricted to specific strains of bacteria, for example," she said.
The authorisation process for new health claims will be split into two, with a fast-track scheme for some new claims that will take a maximum of eight months and a process likely to take far longer for claims relating specifically to children or to disease risk reduction.
As a transitional measure, existing nutrition claims can remain on the market for two years and existing health claims for three years.
The UK's Food and Drink Federation welcomed minor changes made to the controversial nutrient profiling clause of the regulation, but said the devil would be in the detail.
"We need to ensure that profiling will not restrict manufacturers from innovating and providing consumers with the foods they want," it said.
The European Union's Council of Ministers is expected to adopt the nutrition and health claims regulation in the autumn.