I'd agree feed ad-lib with a 18% protein diet or higher (pigs need a diet of 20% protein at a young age until about 50kgs, then it decreases to around 16-18% protein, though if its a breed that turns to fat quickly then 18% protein would be fine). Its about 3lb of fruit and veg to 1lb of nuts.
Traditional pigs dont start laying fat until around 45-50kgs so up until this point your ok to ad-lib feed, though some of the modern breeds wont start laying down the fat till nearer 70kgs and more. As up until these weights the feed is going into growth of muscles and other important areas.
You can feel pigs to check on their condition, feel lighlty around their shoulders, spine, and hips if you can feel them then they are ok, if you can see them poking out then either increase feed or continue on ad-lib, if you have to press hard to feel the bones then they are overweight, reduced the feed.. if you have to push soo hard the back bends then they really need to go on a diet.
Ours pigs were going through about 5-6kgs a day each when put on growers feed at 12 weeks (should have been 10 weeks when we first bought them in). We reduced their feed down to 4.5kgs each, then 3kgs each by 20 weeks, and for 3 days only went on to 1.5kgs to reduce some fat, but will now be on 2-3kgs a day till slaughter (in 4 weeks time).
When on ad-lib they dont squeal for food, but once its reduced they will.
Dont restrict when they are young thats when they are doing the most growing and need it for their young bodies to build on.