They all contain the mineral boron which speeds up the brain function in most people and can combat drowsiness. The Institute of Food Research found that people on diets had slowed mental performance, which was comparable to the impairment alcohol can cause. The best route to follow is to boost your activity level rather than skimping on food. Instead of cutting 500 calories from your diet, cut 250 calories and increase your exercise load to burn an additional 250 calories. By doing that, you end up defeating the whole purpose because muscle burns fat, and the less muscle you've got, the fewer calories you're going to burn during exercise.
Caffeine's a drag.
A cup or two of coffee can pep you up, but moderate use of caffeinated beverages can brew into a habit that will snatch your energy. People who have developed a dependency can feel tired and irritable when they don't have a steady flow of caffeine.