Effect of Exercise and Training on Fat Oxidation During Overfeeding - the FeedEX Study

Effects of Short-term Overfeeding With or Without Exercise on 24-hour Fat Oxidation and Fat Balance Before and After 10 Weeks of Training - The FeedEX Study

Rationale: Body weight is not well regulated in all individuals. In an obesogenic environment, where overeating is common, some individuals are more prone to weight gain and therefore overweight than others. Yet, the reasons behind this are unclear. "Resistant" individuals often have higher physical activity levels (PALs). It seems that - at higher levels of physical activity and therefore energy expenditure - satiety signals are more precisely regulated, making one better at matching energy intake with expenditure. In other words, active people may not overeat where sedentary people would. However, this does not explain the differences in weight gain observed when subjects all have to overeat (imposed overfeeding). It could be that active people are better able to cope metabolically with the extra calories because of already higher levels of carbohydrate and fat oxidation compared to their inactive counterparts.

Objectives: 1/ To study the effects of overfeeding (normal diet composition) on substrate balance and oxidation and more specifically fat balance and oxidation; 2/ to study the effects of exercise and training on fat oxidation during overfeeding (normal diet composition).

Study design: This controlled intervention study will follow a cross-over design. Each subject will spend 5 nights and 4 days in a respiration chamber on two occasions, separated by a 10-week training period.

Inclusion Criteria:

• Caucasians
• Male
• Healthy
• 18-30 years
• BMI 21-27.5 kg.m-2
• Sedentary lifestyle: the following serve as (non-strict) guidelines: "Low category of activity" according to the short version of the International Physical Activity Questionnaire (IPAQ); VO2max (ml.kg-1.min-1) below: 45 - AGE (yrs) / 3 corresponding to a fitness category below "fair" (i.e. "poor" or "very poor") as defined by Schvartz and Reibold. For example for an 18 year-old male, VO2max below 39 ml.kg-1.min-1.
• Stable body weight (<5% change in the last 6 months)

Exclusion Criteria:

• Following a (weight-loss) diet
• Using medications
• Smoking
• Consuming more than 3 units of alcohol per day
• Diagnosed with any chronic diseases known to affect energy metabolism (intake/expenditure) such as diabetes, cardiovascular disease, cancer, or thyroid disease.
• Trained or regularly physically active (according to the IPAQ)