Inclusion Criteria:  Age: ≥1 and ≤ 6 years of age. Weight at baseline between ≥ -3 and < -1 SD WHO-score (mild to moderate undernutrition). Informed consent provided.  Exclusion Criteria:  Underlying medical illness affecting growth, according to the clinician's opinion. Known lactose intolerance / cow's milk allergy. Use of (other) ONS 1+ (1 kcal/mL) at enrolment and/or during the three months before enrolment. Insufficient ability to understand or communicate in English and/or Bahasa Malaysia. Participating in any other clinical study