Less fermentables per gallon of wort -> less alcohol, less residual sugars, and fewer calories (which come from both... though, mostly the alcohol, which there is a lot more of, especially in macro lagers, which don't have much else other than water and CO2 in 'em).
Lite beers typically are brewed and fermented for very high attenuation. So, while they are not high in alcohol, they are high in alcohol relative to the calories, if you know what I mean.
Lite beers typically are brewed and fermented for very high attenuation. So, _________________________ they are high in alcohol relative to the calories, if you know what I mean.