In the Belly Fat study, the effects of two different caloric-restricted diets on metabolic health will be examined in male and female subjects with increased abdominal adiposity (BMI >27 kg/m2). Metabolic health is defined as health of the primary metabolic organs the liver, gut and the adipose tissue, examined in a static state as well as after the application of a challenge test.

The diets are equally caloric-restricted, but differ in nutrient composition. It is hypothesized that one of the two diets causes a larger improvement in organ health and reduction in liver fat.

Rationale: It is known that in particular visceral fat (abdominal obesity) and fat deposition in non-adipose tissue such as the liver are important factors related to metabolic health, such as the degree of insulin resistance, dyslipidaemia and other well-established cardio-metabolic risk factors. The arise of pathological consequences of abdominal obesity are a result of a disturbance in the elegant interplay between metabolic organs, such as the liver, adipose tissue and gut. Several nutrients have demonstrated to exert positive or negative effects on the health and functioning of metabolic organs. A diet (whole dietary approach) can thus be a power tool to improve the health status of individuals with abdominal obesity by improving organ health.

Objective: The primary objective of this study is to compare the effects of two different diets on the static metabolic health status as assessed by determination of organ health and, more specifically, of lipid accumulation in the liver. The application of a mixed meal challenge test will be used to gain insight in the dynamic metabolic health status. A secondary objective is to determine the reaction (brain activity) of individuals with abdominal obesity after visual and olfactory food-cues.

Study design and intervention: Randomized, parallel design consisting of three groups:

1. 40 subjects, 12-wk nutritional intervention based on dietary advice: diet with 30% caloric restriction and a Western style nutrient composition
2. 40 subjects, 12-wk nutritional intervention based on dietary advice: diet with 30% caloric restriction with a nutrient composition aimed at improving organ health and reducing liver fat
3. 30 subjects, control group, no nutritional intervention (optional: dietary advice at the end of the study period)

Measurements on metabolic health will be conducted at baseline and after 12-wk intervention and include:

• MR imaging for determining body fat distribution
• MR spectroscopy for quantification of liver fat
• Blood sampling (plasma and PBMCs) before and several timepoints after mixed meal challenge
• Adipose tissue sampling before and after mixed meal challenge
• Vascular measurements before and after mixed meal challenge
• Urine and feces sampling

Study population: Males and females, 40-70 yrs old, BMI > 27 kg/m2

Inclusion Criteria:

• Age 40-70y at the time of recruitment
• BMI >27kg/m2 or waist circumference >102cm (males) or >88cm (females)

Exclusion Criteria:

• Diabetic (normoglycemic according to WHO criteria (OGTT, fasting blood glucose< 7 mmol/L, after 2 hr <11.1 mmol/L)
• Daily intake of alcohol of >30g (men) or >20g (women)
• Tobacco smoker
• Abuse of drugs
• Any medical conditions or (metal) devices interfering with or posing a risk for the participant in 1H-MRS/MRI scanning (e.g. claustrophobia, pace maker, surgical screws/pins, artificial joints or heart valves, etc.)
• Diagnosed with any long-term medical condition (i.e. cardiovascular disease, gastrointestinal disease, renal dysfunction)
• Use of medications known to interfere with glucose or lipid homeostasis (i.e. corticosteroids)
• Allergic to fish oil or unwilling to consume fish oil supplements
• Unwilling to comply with dietary guidelines
• Restricted to a vegetarian dietary regime