Plenty of work has been done to show that bees can't tell the nutritional content of protein food, for example:

We evaluated the influence of pollen-based cues on the foraging decisions made by honeybees using a series of two-choice bioassays, performed within a highly controlled indoor environment. We examined behaviours related to the choice and collection of pollen by foragers among six floral species and three artificial substrates (pollen analogues). 

Foragers were incapable of discriminating protein content. We determined changes in the response of foragers to different levels of handling time using different sized screens through which bees were forced to crawl to reach an attractive pollen odour source. 

When odour was presented simultaneously with other stimuli, it was the primary and overriding cue used by bees to select pollen. These results suggest that individual honeybee foragers do not discriminate among pollen sources based on intrinsic differences in quality, but instead evaluate cues that may increase their efficiency of collection and recruitment to such a food resource.

Pernal, S. F., & Currie, R. W. (2002). Discrimination and preferences for pollen-based cues by foraging honeybees,< i> Apis mellifera</i> L. Animal Behaviour, 63(2), 369-390.

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