Complex sentence: Nearly 40% of the children and young people had half or fewer seizures with the diet (even when less radical) compared with the group not assigned to the diet, although only about 10% were still on the diet after a few years.
Split into simpler sentences: Nearly 40% of the children and young people had half or fewer seizures with the diet compared with the group not assigned to the diet. Only about 10% were still on the diet after a few years.