- Many laboratory rats subsist only on specially prepared blocks of food, sometimes referred to as lab blocks or rat blocks. Unlike with mixes or other food preparations, rats can't sift through and pick out only the parts they want, so they are more likely to get the nutrition they need. The bulk of the block is generally corn and soy, with additional nutrients added. Because of the low cost and simplicity of rodent blocks, many laboratories provide only this type of sustenance.
- Lab rats are sometimes fed mixed grains to add variety to their diet. Commonly used grains are barley, oats and whole-wheat flakes. These loose grains add much needed fiber and protein to the diets of the rodents. Handlers pay close attention to ensure that the grains are not sprayed with pesticide or filled with preservatives.
- Fresh fruit, like blueberries, has been proven to prevent illness in rats. It is sometimes given as a preventative measure and as a means to increase the variety in the diet of the laboratory rodents. Handlers do exercise caution, however, as some fruits have been shown to be harmful. Oranges, for example, can have harmful effects on male rats, though the effect on female rats is positive. Fruits are given in moderation, as they are high in natural sugars.
- Like fresh fruit, fresh vegetables add variety and necessary nutrients to the lab rat's diet. Rats will eat most vegetables: kale, broccoli, tomatoes and cabbage are staples in the diet of a typical rat.
- Lab rats deserve a treat every now and then, and for these rodents, nearly anything can double as a reward. Cookie bits or commercially available treats supplement the nutritional component of the rat diet with a bit of fun. Used sparingly, these nutritionally dubious additions keep the rats motivated.