High or low metabolic rate are the sceintific terms. I can't think of anything quite as colloquial as the German.

If this is in reference to animals, it would be efficient feeders vs. delicate feeders. In reference to humans you might go with people with efficient and poor digestion.

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Note added at 2002-12-29 02:20:25 (GMT)
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This is from a German/English website on cattle

Galloways produce prime beef due to their excellent digestion of fodder even if the nutritive substances available
are poor.

http://www.galloway.de/asite/quell/info/_queleng.htm

those with poor metabolic systems.
With respect to animals you could use "good fodder (or forage) processors versus bad fodder (or forage) processors

Hi there, I thought it was rather the other way round?! A "guter Futterverwerter" is someone who has a very efficient metabolism and can therefore consume less food i.e. processes/metabolises the food in a way to use it more efficienty and therefore puts on more weight.

Hi Antoinette,

You definitely got it wrong. Someone who is said to be ein guter Futterverwerter gets very easily overweight because the metabolism extracts most of the energy from the food. I know it from personal experience. "Verwerten" means "to utilize" ie. someone who utilizes the food intake very well is producing a lot of energy from less food - someone who functions like a 4 liter engine :-) On the contrary, someone who is said to be "ein schlechter Futterverwerter" operates like a 18 liter engine and can eat cake the whole day without getting fat.