Apparent metabolisable energy corrected to zero nitrogen retention (AMEn) was used to select chickens for high (D+) or low (D-) capacity to digest a wheat diet. Consequences of this selection on digestive tract (gizzard and small intestine), feeding behaviour (number of pecks to the feed, number and length of meals and time between meals) and excretion (dry excreta weight, nitrogen and phosphorus excretion, and excreta water content) has been measured on birds from the 7th generation of selection, fed ad lib. or by meals either with wheat or corn diets. D- birds pecked and consumed feed 16-19% more and had 29% smaller gizzards than D+ birds. Differences between lines for digestibility, nitrogen, and phosphorus excretion were stronger for wheat diet given ad lib., smaller with other treatments. For example, phosphorus excretion was 52% higher in D- when fed ad lib. with wheat, 16-33% for other diets. Independently from line or treatment, phenotypic correlations indicated a strong link between AMEn and raw, nitrogen, and phosphorus excretion (-0.43 to -0.99). Correlations between AMEn and feeding behaviour or anatomy were dependent on line and/or treatment. AMEn was correlated with feed consumption and number of pecks to feed only in D- birds (-0.45 to -0.76). AMEn was correlated with gizzard weight in D+ but with small intestine weight in D- birds. Therefore, our results indicated that selection on AMEn affected environmental impact, feeding behaviour and anatomy of birds, but that mechanisms involved in both lines are nrobablv different.