Objective Parental decision-making around extended formula feeding (12 months+) has not been explored previously. This study tested the hypotheses that extended formula milk use (i) is associated with poorer appetite and (ii) supplements lower food intake.

Methods Appetite was assessed with the Child Eating Behaviour Questionnaire (CEBQ) in 3854 twin children aged 16 months. Diet was assessed from 3-day diaries in 2714 children at 21 months. Parents reported their children's weight at 24 months. Associations between formula feeding and (1) appetite, (2) energy intake and (3) weight were examined. 35 mothers were interviewed when the children were 7 years old to explore retrospectively their reasons for extended formula feeding.

Results Formula consumers (13% of the sample) scored significantly differently than non-formula consumers on five of the six CEBQ subscales, indicating lower appetite avidity: ‘food responsiveness’ (2.02 vs 2.22, respectively),‘enjoyment of food’ (3.99 vs 4.20), ‘satiety responsiveness’ (2.89 vs 2.65), ‘slowness in eating’ (2.63 vs 2.46) and ‘food fussiness’ (2.34 vs 2.14). Formula consumers had a significantly lower percentage of daily energy intake from food (70% vs 74%); however, total daily energy intake did not differ significantly from non-consumers (4315 vs 4373 kJ). At interview, mothers reported supplementing their child's diet with formula because of ‘picky eating’ and concerns about inadequate food intake.

Conclusions High formula milk intake is associated with picky-eating behaviours, but seems to act as a substitute for rather than a supplement to solid food. Prospective and intervention studies are needed to determine whether extended formula feeding has an enduring impact on weight trajectories, eating behaviours or health.