12 - Physical activity, obesity and weight maintenance

Summary

Introduction

Obesity is recognized as a major health problem in western society. Maintenance of an acceptable body weight is therefore an important aspect of a healthy lifestyle.

Overweight and obesity result from a state of positive energy balance in which total energy intake from food has exceeded expenditure over a prolonged period. Although this equation of energy balance is simple, it has not been proved which one of the two factors, energy in or energy out, is responsible for the imbalance and the consequent high energy stores. There are many factors associated with the energy intake and expenditure and the interaction of these two factors which makes this equation complex. Furthermore, the positive balance is a gradual process over many years. In the longitudinal Zutphen study of middle-aged men over 25 years, a significant increase of 2.8kg was noticed (Kromhout et al., 1990). Assuming this to be an increase in fat stores, suggests an imbalance of about 70 MJ or 8kJ per day. With the most precise methods that are available today, this imbalance is not measurable. Even if the weight increase in the upper three percentiles of this cohort of about 15 kg is considered, the imbalance on a daily basis is about 50 kJ. The precision of a 24h measurement of energy expenditure in a respiration chamber is at best in the order of 2 to 3% leading to absolute differences of 100–150kJ.