If your energy is low on a diet, you are probably dehydrated or low in salt. The bet is low energy is not low blood sugar. Make sure you drink at least a gallon (128 ounces) of non-caloric fluid every day. Caffeine can help, so don’t be afraid of Diet Coke, Diet Pepsi, coffee and tea. The easiest way to make sure you are getting enough salt (a major side effect of most low calorie diets is sodium depletion, your body dumps salt like a race horse if you lower calories enough) is to drink 4 bouillon cubes in water a day. If you hate bouillon cubes (beef, chicken or vegetable are all the same – they are flavored salt), drink 4 cups of miso soup. Miso soup is the salty soup served at most Japanese restaurants. Most restaurants will be happy to sell you a quart of miso soup to go.