Comparison of Biphasic Insulin Aspart 30 Individually Adjusted by the Subject and the Trial Physician, Both Combined With Metformin in Subjects With Type 2 Diabetes

Inclusion Criteria: * Diagnosed with type 2 diabetes for a minimum of 12 months prior to Visit 1 (screening) * Currently treated with a basal insulin analogue for at least 3 months prior to Visit 1 (screening) * Stable treatment (no change in dose or regimen) with a total daily dose of at least 1500 mg metformin or maximum tolerated dose (minimum 1000 mg) ± additional OAD treatment. The metformin treatment must have been stable for at least 2 months prior to Visit 1 (screening) * HbA1c higher or equal to 7.0% and below or equal to 10.0% (one re-test within one week of screening visit was allowed. The last sample was to be conclusive) * Body Mass Index (BMI) below or equal to 40.0 kg/m\^2 * Able and willing to eat at least 2 main meals each day during the trial * Able and willing to adhere to the protocol including compliance with performance of self measured plasma glucose (SMPG), injection regimen and titrating themselves according to the protocol * Experience in performing self measured plasma glucose (SMPG) Exclusion Criteria: * Treatment with any thiazolidinedione (TZD) and glucagon-like peptide-1 (GLP-1) receptor agonists or pramlintide within the last 3 months prior to Visit 1 (screening) * Impaired hepatic function defined as alanine aminotransferase (ALAT) above or equal to 2.5 times upper referenced limit (one re-test within one week of screening visit was allowed. The last sample was to be conclusive) * Impaired kidney function with serum creatinine above or equal to 133 micromol/L (1.5 mg/dL) for males and above or equal to 124 micromol/L (1.4 mg/dL) for females (one re-test within one week of screening visit was allowed. The last sample was to be conclusive) * Cardiac problems or uncontrolled treated/untreated severe hypertension (defined as systolic blood pressure higher or equal to 180 mmHg and/or diastolic blood pressure higher or equal to 100 mmHg) * Previous use of pre-mixed insulin products (pre-mixed insulin analogues or pre-mixed human preparations) or bolus insulin. Previous use of pre-mixed or bolus insulin products was allowed only in case of hospitalisation or a severe condition requiring intermittent use of pre-mixed or bolus insulin products for less than 14 consecutive days, but not during the last 3 months prior to screening visit (Visit 1)