Future school meal standards are likely to be based on nutritional guidelines devised by the healthy food charity Caroline Walker Trust (CWT).
The School Meals Review Panel, a group of 30 nutrition, catering and education experts, looks set to recommend the CWT's nutrient-based standards in the absence of an alternative.
"There's no other data out there, so our recommendations are likely to be used as the blueprint," said Helen Crawley, the author of the CWT's latest report.
The report states that the fat content of school lunches should be no more the 35% of pupils' daily calorie intake,, while the carbohydrate content should be no less than 50%.
CWT guidelines, which were used as the yardstick in Scottish schools, also recommend that salt should not be placed on tables and that free water should be available to all children.
The trust will launch a report on 16 September called Eating Well in School - Nutritional and Practical Guidelines, which is also expected to inform the Government's final decision.
A source close to the panel said Education Secretary Ruth Kelly will reveal which nutritional standards the Government will adopt at the Labour party conference in Brighton on 28 September.