Many patients with Parkinson's Disease (PD) report an increased consumption of fast-acting sugars. This tendency to consume sweet, high-sugar foods occurs in some patients even before the onset of cardinal motor symptoms. Some recent studies have demonstrated that PD patients have an increased consumption of fast-acting carbohydrates compared to healthy controls. However, the reason for this change in eating behavior has not yet been adequately explained. It is discussed that the increased sugar intake leads to an increased dopamine release in the brain via an increase in insulin and thus to an improvement in clinical symptoms. This study investigates the influence of fast-acting carbohydrates on insulin and glucose blood levels as well as motor and non-motor symptoms in patients with PD using an oral glucose tolerance test and a placebo oral glucose tolerance test in a crossover design.

Inclusion Criteria:

• Diagnosis of Parkinson's Disease, stage Hoehn & Yahr 1.5-3
• Ability to pause antiparkinsonian medication in the morning without relevant impairment
• Capacity to give consent (determined in doubt by two independent neurologists, MOCA ≥18) and written informed consent.
• Patients are between 50 and 80 years of age, with exceptions for a maximum of 5 additional patients enrolled per group
• For stratification into patients with and without sweet craving, a 3-day dietary protocol should be completed once by the patients
• Group I: increased hunger for sweets.
• Group II: no increased hunger for sweets.

For the stratification into patients with and without increased hunger for sweets, participants are asked to answer the following questions:

1. Do you have sudden attacks of cravings for sweets?
2. Would you say that your consumption of sweet food has increased in recent years?
3. Would you describe your consumption of sugary food as increased or excessive?

If one of the questions is answered with yes, participants will be assigned to group I, if all questions are answered with no, participants will be assigned to group II.

Exclusion Criteria:

• Other significant neurological diseases primarily affecting the central nervous system (e.g., multiple sclerosis)
• Diagnosis of diabetes mellitus or prediabetes
• Use of medications that affect glucose metabolism, such as antidiabetics, glucocorticoids, ciclosporin, tacrolimus, sirolimus, beta-blockers, thiazide diuretics, beta-2 adrenoreceptor agonists, theophylline, Clozapine, olanzapine, paliperidone, quetiapine, risperidone, tricyclic antidepressants, mirtazapine, mianserin, carbamazepine, gabapentin, pregabalin, valproic acid, lithium, antiretroviral drugs, statins
• cardiac or brain pacemakers

The study population includes Parkinson's Disease patients with and without sweet cravings. Recruitment of patients takes place in the outpatient clinic for movement disorders at the University of Kiel.