In this clinical cross-over study, we will compare the efficacy of different oral nutrition regimens for night-time glucose control in adult GSD 1 patients. Three different over-night nutrition regimens (=interventions) will be compared in each patient sequentially, (1) uncooked corn starch (UCSS, "Maizena"), (2) modified corn-starch, (3) other carbohydrate (starch) containing meal. During each intervention, glucose profiles will be continuously monitored by continuous glucose monitoring (CGMS). The duration of each intervention is 3d (mimimum) to 6d (maximum), depending on the quality of night-time glucose control and the technical quality of glucose sensor readings. Between the interventions, the patients follow their normal prescribed diet.

Inclusion criteria:

• Glycogen storage disease type 1 (type 1a and 1b)
• Stable nighttime glucose control without frequent or severe hypoglycaemia under current dietary treatment, according to capillary glucose measurements.

Exclusion criteria:

• Unstable night-time glucose control during the last 8 weeks with frequent (> 4x weekly) hypoglycaemia during night-time, or a hospitalisation due to unstable glucose control during the last 4 weeks, or any episode of severe hypoglycaemia (requiring assistance or loss of consciousness) during the last 4 weeks.
• Pregnancy or breast feeding
• Drug or alcohol abuse
• Acute gastrointestinal problems (e.g. acute gastroenteritis)
• Known malignancy (e.g. hepatocellular carcinoma)