Maltodextrin is about 12% fermentable (according to Austin Homebrew and somewhere else that I'm too lazy to look up and cite right now), so you may see just a little action when you add it, but the other 88% goes to adding body to your brew.
As mentioned above, lactose is typically used to sweeten beer, and will work fine unless you're lactose intolerant.
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Revolving Door Brewery
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