The idea that was a "scientific" study is laughable. MacDougall only looked at 6 people. Two of them he couldn't weigh due to technical troubles. Of the four he managed to weigh, one lost weight and then gained it back (soul got kicked outa heaven??) Two lost some weight and then continued to lose more (were those bodies schizophrenic? Was there a bunch of people's souls all in one body having an orgy?)
MacDougall chose the one and only of the 6 cases where the data fit his preconceived notion and declared victory. When one knows the answer they want, they can easily cherry pick data to create the result they desire.
The sad part is almost 120 years later there's still suckers born that buy this crap.