Calories are a highly important part of the game: using calories you can gain higher Ranks.
Herbivores have four types of food: Grass, Flowers, Fruit, and Mushrooms. Mushrooms yield 400 calories, while Fruit yields 800 calories. Flowers give 128 calories per Flower (32 calories per bite), and are arguably the worst plant food. Grass gives 216 calories per whole plant, and yields 72 calories per bite, and are the basic food. Eating poisoned plant material will add 25 to your Toxicity Gauge per bite.
Water offers no calories to Herbivores. Drinking tainted water will add 15 to your Toxicity Gauge.
Carnivores can eat any dead animal other than robotic dogs, Homo Erectus, their own species, and animals that have a friendly relationship with them (such as, the Cat cannot eat the Fat Cat, and vice versa.) Depending on the animals' size they offer a different amount of calories. For instance, a Chick offers the lowest amount of calories, with only 56 kcals per Chick, while a Mammoth offers some of the most, with 560 per bite. Consuming meat tainted by Toxicity will add 25 to your Toxicity Gauge per bite.
Water offers zero calories for Carnivores. Drinking tainted water will add 15 to your Toxicity Gauge.