In Norway, a significant proportion of the adult population is currently classified as overweight (~50%) or obese (~23%). Over the past four decades, there has been a significant rise in the prevalence of overweight and obesity in both children and adults. Obesity is associated with a higher risk of chronic diseases such as cardiovascular diseases, type 2 diabetes, respiratory disease, osteoarthritis and specific cancers. Consequently, leading to increased morbidity and reduction in life expectancy. A healthy lifestyle including meeting recommendations for diet and physical activity is considered beneficial the prevention of chronic diseases, and for quality of life. There is limited evidence on weight reduction programs implemented outside specialized healthcare services, however intensive lifestyle modifications have demonstrated promising effects on sustainable weight loss.

The Kickstart Program is a lifestyle program addressing weight reduction, changes in body composition and improved health-related quality of life (HRQoL) by integrating personalized dietary guidance and physical activity (PA) over a three, four or six-month period for registered participants, and can be considered an organized follow-up intervention. The participants receive close monitoring and support from clinical dietitians, physiotherapists and personal trainers. Unlike patients in specialized healthcare, Kickstart participants sign up and pay for it themselves, without any support from referrals or financial aid. This financial commitment is thought to make participants more motivated and facilitate compliance with the program. Recognizing the potential of programs like Kickstart to reduce healthcare costs by preventing lifestyle diseases, especially outside of specialized healthcare, shows why it is important to study how well they work.

The study's findings can be leveraged to assess the influence of lifestyle programs and enhance the support available to adults with obesity.

The study will tighten the knowledge gap concerning how an intervention of intensive dietary changes and PA specifically effects weight loss, FFM and HRQoL within a three-month timeframe.

The overall aim of the study is to investigate the effect of a combined diet and PA intervention for people with a BMI>25 kg/m² on body weight, body composition, RMR and HRQoL.

In Norway, a significant proportion of the adult population is currently classified as overweight (~50%) or obese (~23%). Over the past four decades, there has been a significant rise in the prevalence of overweight and obesity in both children and adults. Obesity is associated with a higher risk of chronic diseases such as cardiovascular diseases, type 2 diabetes, respiratory disease, osteoarthritis and specific cancers. Consequently, leading to increased morbidity and reduction in life expectancy. A healthy lifestyle including meeting recommendations for diet and physical activity is considered beneficial the prevention of chronic diseases, and for quality of life. There is limited evidence on weight reduction programs implemented outside specialized healthcare services, however intensive lifestyle modifications have demonstrated promising effects on sustainable weight loss.

The Kickstart Program is a lifestyle program addressing weight reduction, changes in body composition and improved health-related quality of life (HRQoL) by integrating personalized dietary guidance and physical activity (PA) over a three, four or six-month period for registered participants, and can be considered an organized follow-up intervention. The participants receive close monitoring and support from clinical dietitians, physiotherapists and personal trainers. Unlike patients in specialized healthcare, Kickstart participants sign up and pay for it themselves, without any support from referrals or financial aid. This financial commitment is thought to make participants more motivated and facilitate compliance with the program. Recognizing the potential of programs like Kickstart to reduce healthcare costs by preventing lifestyle diseases, especially outside of specialized healthcare, shows why it is important to study how well they work.

Earlier studies have focused on the effect on body weight og body mass index (BMI). Because of the limitations with BMI, it is also important to study body composition. Body composition refers to the proportion of fat, muscle, bone, and other tissues that make up a person's body weight. It provides information about the distribution and relative proportions of body tissues, which can be important for evaluating overall health status, and progression of fitness during and after lifestyle change. Measurements of body composition can include body fat percentage (%), visceral fat, and fat free mass (FFM), including muscle mass that is the primary variable of interest in this study.

Resting metabolic rate (RMR) is the energy the body uses at rest to maintain vital functions. RMR is the main contributor to total energy expenditure, contributing up to 60-70 %. Other components of total energy expenditure is energy used from physical activity (20-30%) and lastly from the thermic effect of food (10%). Studies have demonstrated a decrease in RMR following weight loss, largely attributed to the loss of FFM, which plays a significant role in metabolic rate. It has been speculated that rapid weight loss induce metabolic adaptations resulting in greater than predicted decreases in RMR.

The concept of HRQoL is frequently utilized to assess how health status influences overall quality of life. Reported low HRQoL is typically found in individuals with multiple chronic conditions and low levels of PA.

In The Norwegian Healthy Life Centre Study by Samdal et al., the objective was to assess the impact of behavioral change interventions at Norwegian Healthy Life Centers on participants' physical activity six months after baseline. The study concluded that individuals with high socioeconomic status increased their physical activity more over the course of six months, but simultaneously consumed more unhealthy food. The intervention did not significantly influence dietary habits, but participants who attended the "good-food course" notably increased their consumption of healthy food. A follow-up study on HRQoL in 2020 revealed a positive association between physical activity and improved HRQoL. All HRQoL dimensions showed enhancement from baseline to the three-month follow-up, and these improvements were sustained at the 15-month follow-up.

By focusing on healthy lifestyle and weight reduction, valuable healthcare resources can be conserved, emphasizing the need for such programs outside specialized healthcare services. This also involves the individual's ability to cope and their overall quality of life. The study's findings can be leveraged to assess the influence of lifestyle programs and enhance the support available to adults with obesity.

The Kickstart program reveals a knowledge gap concerning how an intervention of intensive dietary changes and PA specifically effects weight loss, FFM and HRQoL within a three-month timeframe.

The overall aim of the study is to investigate the effect of a combined diet and PA intervention for people with a BMI>25 kg/m² on body weight, body composition, RMR and HRQoL.

Inclusion Criteria:

• BMI > 25 kg/m2

Exclusion Criteria:

• BMI< 25 kg/m2