Protein group is the friendliest group from weight management prospective. Consumpton of proteins results in reasonable satiety, it does not produce unreasonable food cravings. Proteins mostly come from animal or seafood sources, but many vegetables have significant amount of protein as well. If we do not consume enough proteins our body has a natural ability to create them from carbs and fats. There are few aminoacids that we unable to synthesize on our own (essential aminoacids) and they, just like vitamins and Omega 3 fatty acids, need to come with food. The major debates whether the vegeterian diet is healthy were not about the amount of proteins that vegeterians get, but rather whether vegeterians are able to have sufficient amount of essential amino acids with their diet. So, we can generates proteins on our own, but anyone who tried to attempt body building knows that the best way to build muscles is to provide the body with sufficient dietary proteins.
The daily requirement for proteins is roughly around 1g/kg. USDA recommends to include around 5.5 oz of meat or other protein equivalent food/day, which roughly 2 palm size portion. Many Body builders decide to include in their diet around 1g/pound of proteins.
One gram of proteins produces around 4 calories of energy.
To digest 10 gram of protein in the absence of carbohydrates the human body needs to burn another 2.5-3 grams of proteins. This is so called "thermal effect" of protein digestion because this energy is eventually being released as heat.
The end result is that another approximately 25% of the energy derived from proteins is wasted for heat production.