With advancing age most aspects of the peptidergic regulation of energy balance 
are altered. The alteration involves both the peripheral peptides derived from 
the adipose tissue or the gastrointestinal tract and the peptides of the central 
nervous system (brainstem and hypothalamus). In general, the expression of 
orexigenic peptides and their receptors decreases with age, while that of the 
anorexic ones rather increases, but not simultaneously and not in a linear 
fashion. Apart from such quantitative changes, the efficacy of the related 
peptides may also change with age. These changes are not necessarily linear, 
either: instead of continuous decline or increase of its effects, the effects of 
a peptide may become less pronounced in some phases of aging and much enhanced 
in other ones. Comparing the individual peptides, the phasic alterations in 
their anabolic or catabolic roles in the regulation of energy balance may 
exhibit dissimilar time-patterns. In addition, within the overall anabolic or 
catabolic effects, the feeding and metabolic actions of certain peptides may not 
change simultaneously. Altogether, as compared with young adults, in middle-aged 
animals or individuals the anabolic processes (increased food intake with 
decreased energy expenditure) seem to prevail, which processes may contribute to 
the explanation of age-related obesity, while in the old ones the catabolic 
processes (anorexia with enhanced metabolic rate) dominate, which possibly 
explain the aging anorexia, frailty and sarcopenia.