Giant anteaters (Myrmecophaga tridactyla) are among those mammals for which a particularly low metabolism has been reported. In order to verify presumably low requirements for energy, we used eight anteaters (2 males, 6 females; aged 1-14 years; body mass between 46-64 kg) in a total of 64 individual trials, in which a variety of intake levels was achieved on various diets. Digestible energy (DE) intake was quantified by measuring food intake and faecal excretion and analysing representative samples for gross energy, and animals were weighed regularly. Maintenance DE requirements were calculated by regression analysis for the DE intake that corresponded to zero weight change. Differences between individuals were significant. Older anteaters (n=3 animals aged 12-15 years in 29 trials) had lower relative requirements than younger ones (n=5 animals aged 1-7 years in 35 trials); thus, giant anteaters resemble other mammals in which similar age-specific differences in energy requirements are known. However, estimated maintenance requirements were 347 kJ DE kg-0.75 d-1 in the anteaters, which is low compared to the 460-580 kJ DE kg-0.75 d-1 maintenance requirements of domestic dogs. The lack of knowledge that metabolic requirements are below the mammalian average could make species particularly susceptible to overfeeding, if amounts considered adequate for average mammals were provided. Non-scientific reports on comparatively fast growth rates and high body masses in captive Giant anteaters as compared to free-ranging animals suggest that body mass development and feeding regimes in captivity should be further assessed.