If you want all the nutrition, eat the fruits and vegetables.
Most true juicers strain out, arguably the best part (the fiber). The pulverizer-style, non-straining juicers keep the fiber but are essentially high-powered blenders. The pulverizers are supposedly the healthiest option, but I haven't ever seen a cheap one.
That being said, the little bit of heat that a blender is going to add isn't going to reduce the nutrition all that much (sitting on the grocery store shelves and in the veggie bin probably does worse).
Another option is adding very cold ingredients such is ice or frozen juice or frozen veggies or fruit in with your fresh fruits and veggies. Even very cold juice or water would help That way the cold ingredients will offset the heat created by the blender's motor. As will pausing the blender between pulses to allow the heat to dissipate.
Last edited by kaplods; 04-02-2012 at 08:55 PM.