Consumption of marine protein in humans and animals can result in an apparent older radiocarbon (14C) age due to reservoir offsets. In order to correct for this, an estimate of the marine protein intake should be used to correct the 14C age for reservoir offsets, which is ordinarily done using δ13C or δ15N values. However, these two isotopic proxies can be influenced by a number of factors which can hamper estimation of the correct marine protein intake. A small dataset of 12 samples from the Limfjord, Denmark, ranging in age from Mesolithic to Viking Age, was used to test the use of δ2H values to quantify marine protein intake and determine the reservoir corrections. Each of the three stable isotopic values (δ2H, δ13C, δ15N) was used to estimate the percent marine protein intake, which produced three different calibrated 14C ages. The calculated percent marine protein intake differed between the use of the stable isotopic ratios with a maximum difference of 42.1% between the use of δ15N and δ13C, 23.8% between δ2H and δ13C, and 46.2% between δ2H and δ15N. In some cases the calculated percent marine protein intake changed the sample’s archaeological period, although there was generally still overlap in the archaeological periods for samples used in this study.