I have been facing this problem from times immemorial. Whenever I copy a table with data, either numbers or text, from Excel to Powerpoint, most of the time I get numerous spaces before the data, which never existed in the Excel file.
It takes a lot of time to get rid of them. I follow some of these, with mixed success:
Using the replace function, but mostly it gets rids of all the spaces among other text also
Manually deleted each space
Trying to keep the numbers in simple Number format, eliminates space before numbers, but this does not solve the spaces before text issues
I've faced this with Office 2007, 2010, and 2013.