Association of Sedentary Behaviour and Habitual Diet With Resting Fat Oxidation in Women With Overweight and Obesity

Obesity is associated with a changing food environment where low-cost, high-energy-dense fast foods are readily available, and physical activity levels are decreasing. Additionally, metabolic flexibility, defined as the organisms ability to switch between metabolic fuels, is impaired in obesity and is known to play a significant role in the development of chronic diseases. In these disease states, a metabolically inflexible condition is typically characterized by a reduced ability to regulate fat oxidation during fasting and carbohydrate oxidation during satiety. Therefore, considering the rising trend in obesity, understanding the factors related to metabolic flexibility becomes critical. It is known that numerous factors such as diet composition, eating habits, physical activity level, and sedentary behavior affect metabolic flexibility. However, unlike dietary and exercise interventions, the number of studies examining the impact of individuals eating habits and physical activity levels on resting fat oxidation is limited, and this topic has not yet been researched in obese individuals.

Moreover, another important concept known to have adverse effects on metabolic health independently of physical inactivity is sedentary behavior. Sedentary behavior is defined as "activities that require low energy expenditure while sitting, reclining, or lying down." However, the extent to which daily sedentary time and interruptions of this time with physical activities affect resting fat oxidation, an important variable of metabolic health, is not known.

In this context, the aim of this study is to comparatively determine the relationship between physical activity levels, sedentary behaviors, habitual diet, and resting fat oxidation in normal-weight and overweight/obese women. A total of 118 healthy women aged 25-50 years (normal weight, n=60; body mass index (BMI) = 18.5 - 24.9 kg/m²) and overweight/obese (n=60; BMI = 25.0 - 34.9 kg/m²) will participate in this study. All participants' body composition and resting metabolic rate measurements will be conducted, and fat and carbohydrate oxidation will be determined. The dietary habits, 4-day physical activity levels, and sedentary behaviors of all participants will be assessed using appropriate measurement methods.

The findings of this project are expected to reveal the extent to which dietary habits, physical activity, and sedentary behavior throughout the day affect resting fat oxidation in overweight/obese and normal-weight individuals. These findings will provide important evidence on how dietary habits and sedentary behaviors can improve resting fat oxidation, an important indicator of metabolic flexibility, without the need for dietary and exercise interventions

Inclusion criteria

Sedentary women aged 25-50 years with a body mass index range of 18.5-24.9 kg/m2 (normal weight) and 25-34.9 kg/m2 (overweight and obese) will be included in the study.

Exclusion criteria

• Smokers,
• Taking any medication or supplements that may affect metabolism,
• Dieting for more than 6 months,
• Pregnant or breastfeeding,
• Amenorrhoea,
• Individuals who meet the physical activity recommendations of the World Health Organisation (at least 150 min of moderate-to-vigorous exercise or at least 75 min of high-intensity exercise per week),
• Individuals with any chronic disease other than obesity will be excluded from the study.