For most people, weight is not static, but fluctuates over time. As individuals age, their metabolic needs decrease, but their energy intake typically remains constant or increases (Bosy-Westphal et al., 2003; Elia, Ritz, & Stubbs, 2000). As a result, until old age, adults tend to gradually gain weight as they age. Similar to weight at any one given point in time, there are considerable individual differences in the extent to which BMI fluctuates across the lifespan.
