What are the differences and similarities between carbohydrates,proteins and fats?

Like nitrogen is present in protein but not in carbohydrates.

Ok, there's carbon and hydrogen in all of them, that's the only similarity. They are known collectively as macro-nutrients.

Carbohydrates are basically, oxygen, carbon and hydrogen and they're the bodies primary source of energy. This means that they're the first source of energy used which is why if you eat foods high in simple sugars you get a sugar rush. All carbs metabolize down to glucose, some faster than others.

Fats are called lipids. Lipids are very heterogeneous (this means that there's not much similarity between them). Some examples of lipids are steroids, seed oils, pork fat, cholesterol, etc. The main thing in common with them is that they don't mix with water. They are readily stored in fat cells in the form of tryglicerides and are used when carbs are all used up. They also yield the highest per gram amount of energy (it escapes me right now).

In a chemical sense, fats are lipids derived from animals (saturated, solid at room temperature) and oils are derived from plants and seeds (insaturated with some exceptions, and liquid at room temperature. Insaturated are healthier because they contain HDL which cleans your arteries (prevents artherosclerosis).

Proteins are made up of aminoacids, 20 make up the vast amount of human proteins. Enzimes (the most famous being digestive enzimes) are proteins, skin is covered in protein, hair is protein, cilia and flagella are protein, basically EVERYTHING is protein, after water the human body is basically protein. They're only used up as energy when everything else is used up.

When athletes eat/drink protein, it's to give them building materials in order to increase the amount of stuff inside their cells which will enable them to produce more energy.

okay....protein repairs body tissues and build muscle mass.carbohydrates gives out energy,and fats ensure u are not underweight.basically,carbohydrate is the most important,followed by protein and fats

fat has 9 calories per gram
protein and carbs have 4 calories per gram.