In this randomized, single-blinded basic research study, healthy normal-weight human participants are exposed to a high-fat/high-sugar (HF/HS) snack or a low-fat/low-sugar (LF/LS) snack twice a day for eight weeks in addition to their regular diet. All participants are tested at baseline, after 4 weeks and after 8 weeks of dietary intervention.

At all time points the investigators acquire the following parameters:

• Body weight and composition,
• Blood parameters to control for metabolic changes,
• Visual analog scales (hunger, satiety, tiredness, etc.),
• Fat and sugar concentration preference,
• Functional Magnetic Resonance Imaging (fMRI) during a learning and a gustatory perception task.

The investigators hypothesize that the habitual consumption of a small HF/HS snack will reduce the preference for low-fat concentrations and will have an impact on brain response to the anticipation and consumption of palatable food. Moreover, the investigators hypothesize, that HF/HS diet will have an impact neuronal encoding of learning independent of food cues. The investigators expect these alterations independent of body weight gain suggesting a direct effect of HF/HS diet on neuronal circuits.

In this randomized, single-blinded basic research study, healthy normal-weight human participants are exposed to a high-fat/high-sugar (HF/HS) snack or a low-fat/low-sugar (LF/LS) snack twice a day for eight weeks in addition to their regular diet. The investigators test the effect of this dietary intervention on body weight, metabolic parameters such as insulin sensitivity, blood cholesterol and triglycerides, the preference of fat and sugar taste, the brain response to milkshake anticipation and consumption, and as the neuronal coding of prediction error learning. Here, all participants are tested at baseline, after 4 weeks and after 8 weeks of dietary intervention using behavioral tasks, fMRI and blood sampling. The investigators hypothesize that the habitual consumption of a small HF/HS snack will reduce the preference for low-fat concentrations and impact brain response to the anticipation and consumption of palatable food. Moreover, the investigators hypothesize, that HF/HS diet will have an impact neuronal encoding of learning independent of food cues. The investigators expect these alterations independent of body weight gain suggesting a direct effect of HF/HS diet on neuronal circuits.

Inclusion Criteria:

• right handed
• non-smoker (for the last 1 year not smoked more than 2 cigarettes per month)
• Body Mass Index between 20-27 kg/m2 (healthy weight)

Exclusion Criteria:

1. serious or unstable medical illness (e.g., cancer);
2. past or current history of alcoholism or consistent drug use;
3. current and history of major psychiatric illness as defined by the DSM-IV (Diagnostic and Statistical Manual) criteria including eating disorders,
4. medications that affect alertness (e.g., barbiturates, benzodiazepines, chloral hydrate, haloperidol, lithium, carbamazepine, phenytoin, etc.) and any psychoactive drugs or anti-obesity agents;
5. history of major head trauma with loss of consciousness;
6. ongoing pregnancy;
7. known taste or smell dysfunction;
8. a diagnosis of diabetes;
9. any known food allergy, certain food sensitivities (lactose);
10. pregnant or nursing women,
11. history of metalworking, injury with shrapnel or metal slivers, and major surgery;
12. history of pacemaker or neurostimulator implantation.