Restricted yess, but the Lines diet certainly wasn't as nearly as restricted as some lowcarb diets.
'In 1925 in the early days of insulin, it was usual to give equal numbers of black and red portions, for example, ten black and ten red, providing 100 g carbohydrate/approximately 1500 calories; this was the line ration diet.'
'As insulin became more available, more blacks (carbohydrate) were given than reds. As each black portion contained 10 g carbohydrate and 40 calories and each red (protein and fat) 111 calories the scheme could be used to supply any number of calories for any type of diet'
'For patients on insulin, the diet should start with 15 black portions/ten red portions and distributed to balance the action of whichever type of insulin used (see Table 2). More black portions, 20 or 25, would be required for a patient with an active physical life.'
'For patients needing to lose weight, the usual diet prescription was 100 g carbohydrate/1000 calories.'
Incidently the author of the lines diet RD Lawrence was a type 1 (diagnosed just before insulin was 'discovered') and the co founder of the BDA (diabetes UK).
If you have some time.You might also like to look at changes from the professional point of view here are 20+ accounts from doctors, dietitians, nurses etc who trained from the 40s onwards
http://www.diabetes-stories.com/research-all.asp
Harry Keen is very interesting since he was involved with all sorts of developments
Patricia Torrens describes the Lines diet in action and moves forward a little
Gillian Mcguinness describes the exchange diet and subsequent thinking.