Human paleofeces from the Neolithic site Çatalhöyük, Turkey. Picture from Lisa-Marie Shillito, Newcastle University UK The reason this analysis is possible at all is due to the digestive system not being entirely efficient, in the sense that not everything that passes through the digestive system is destroyed. Not all of the surviving material is recognizable, but some of it is. This material is generally the best indicator archaeologists can use to determine ancient diets, as no other part of the archaeological record is as direct an indicator. 
The 9th-century Viking Lloyds Bank coprolite, now at Jorvik Viking Centre, York The reason this analysis is possible at all is due to the digestive system not being entirely efficient, in the sense that not everything that passes through the digestive system is destroyed. Not all of the surviving material is recognizable, but some of it is. This material is generally the best indicator archaeologists can use to determine ancient diets, as no other part of the archaeological record is as direct an indicator. Human paleofeces from the Neolithic site at Çatalhöyük, Turkey. Picture from Lisa-Marie Shillito, Newcastle University UK
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Human paleofeces from the Neolithic site Çatalhöyük, Turkey. Picture from Lisa-Marie Shillito, Newcastle University UK
The 9th-century Viking Lloyds Bank coprolite, now at Jorvik Viking Centre, York
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Human paleofeces from the Neolithic site at Çatalhöyük, Turkey. Picture from Lisa-Marie Shillito, Newcastle University UK