Many nutrients in salad ingredients are fat soluble. This means they are more efficiently absorbed if eaten with fats and oils. Oil based dressings assist in this process, whereas low fat dressings do not. Adding cream cheese or olive oil, or both, to your salad will boost your nutrient absorption (and improve the flavour, of course).
http://onlinelibrary.wiley.com/doi/10.1002/mnfr.201100687/abstract;jsessionid=DFF141893CF8831B5EF03F87F75B7BE6.d02t01
http://www.purdue.edu/newsroom/research/2012/120619FerruzziSalad.html
http://onlinelibrary.wiley.com/doi/10.1002/mnfr.201100687/abstract;jsessionid=DFF141893CF8831B5EF03F87F75B7BE6.d02t01
http://www.purdue.edu/newsroom/research/2012/120619FerruzziSalad.html