Crossbred growing barrows weighing an average of 15 kg were divided into four groups of eight pigs in a completely randomised experiment in a 2 x 4 factorial design (20 or 55 kg, fed 0, 205, 410 or 760 g/kg Jerusalem artichokes). Apparent digestibility of dry matter, organic matter, energy and crude protein was progressively decreased and apparent digestibility of crude fibre and neutral detergent fibre was progressively increased by adding Jerusalem artichokes. The lower dry matter in faeces of pigs fed Jerusalem artichokes was associated with a higher faecal bulk and is suggested as being responsible for the lower digestibility of nutrients and energy in pigs fed high Jerusalem artichoke diets. Except for energy, pigs at 55 kg body weight had significantly higher or lower apparent digestibility of nutrients than pigs at 20 kg, when Jerusalem artichokes or sugar cane molasses were the main energy source in the diet, respectively. Increasing Jerusalem artichokes increased daily faecal flow of short chain fatty acids and ammonia and reduced faecal pH. It is concluded that there is significant adaptation to high amounts of Jerusalem artichokes in the diet with age.