Consumer Reports explained that fresh fruit at a supermarket or grocery store may not be particularly fresh. From the moment it's picked, food sits in processing facilities, planes, trucks and stores for days losing nutrients. However, frozen food is flash frozen when picked and can last months without significant nutrition loss. Frozen vegetables, such as spinach, also work great in smoothies as a cold addition to the other ingredients. Fresh, local produce eaten quickly is optimal, but frozen vegetables are a viable option as well.