Animals are specially adapted to the diet that they eat. This means that their mouths, digestive systems and even the rest of their bodies have special adaptations that allow them to capture, consume and extract nutrients from their food. In fact Darwin, when he was first working out how natural selection worked, noticed that the beaks of finches on the Galapagos were specially adapted to the type of food they ate. Birds with long, slim beaks fed on insects, whereas those with large, wide beaks used them to crush seeds.

Many animals are adapted to a herbivorous diet - that is, they only eat plants. Herbivores generally have large, flat, teeth for breaking down the cellulose walls of plant cells, and long intestines for extracting the nutrients from food that doesn’t contain many nutrients. For example, cows are specially adapted to live on a diet of only grass - their teeth are large and flat for breaking down cellulose, and they have four stomachs and special bacteria in their digestive systems to extract as many nutrients as possible. Some animals take this to the extreme - for example sloths, which only eat very nutrient poor leaves. Sloths are slow for a reason - not only do they move slowly and have a very slow metabolism to avoid expending energy, but they have an extremely slow digestive system, meaning they can extract nutrients from even incredibly low energy plant material. As a result of this, sloths only defecate everyone to two weeks. This means they don’t fart, because any buildup of gas would be a huge problem! Instead, they reabsorb the gas from their gut and breathe it out.

Other animals are adapted to eat meat. Carnivorous animals usually have sharp teeth, or beaks, for slicing through meat and tearing through the skin of their prey. They usually have a much shorter digestive system, with only one stomach chamber, as it is easier to extract nutrients from meat than from plant material. As with herbivores, their gut flora is specially adapted to break down their diet as efficiently as possible, and they produce lots of protease enzymes, which are the enzymes that break down protein. A lot of the breakdown of meat produces sulfur, which can make for the production of some very smelly flatulence.  

If an animal doesn’t have the right diet, it will be lacking in nutrients and will die. For example, if we ate only grass, like a cow, we would get sick very quickly as our digestive systems are specially adapted for eating a variety of foods, and our teeth and stomachs aren’t very good at breaking down plants, which would lead to malnutrition. Pandas are a type of bear, and so their ancestors ate meat, but pandas have evolved to eat only bamboo. Because of this they have the digestive system of a meat eater - only one stomach and a short intestine. For a long time, scientists didn’t know how pandas managed to survive eating bamboo all day every day. Similar to sloths, they have lowered their metabolism and activity levels to reduce their energy expenditure. However, that doesn’t make up for the lack of protein in their diet. To get around this they are very picky eaters - they choose the bamboo with the highest protein content. They eat the shoots of the species of bamboo that is growing at that time of year, and switch once the bamboo gets older and has a lower protein content.

Although animals are broadly classified as carnivores (eating other animals), herbivores (eating plants), or omnivores (eating both plants and other animals), many animals that are often thought of as carnivores, such as wolves, will also eat some plants. You may have seen your own cat or dog eating grass in your garden. In recent years it has been acknowledged that many animals that people previously thought were herbivores will eat meat if they get an opportunity. From deer to hippos most animals that usually munch exclusively on a plant-based diet have been seen indulging in a meat-based snack from time to time - it’s thought that it supplements their diet with vitamins and minerals that they can’t get from just eating plants.

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