What is proteins large, complex molecules that play many critical roles in the body Meat and poultry — such as beef, pork, chicken, and turkey — are excellent food choices as part of an overall healthy weight loss diet. Meat and poultry provide protein and many vitamins and minerals, including vitamin B12, magnesium, and potassium. Protein is an important part of a healthy diet. Proteins are made up of chemical 'building blocks' called amino acids. People must normalize eating proteins because body uses amino acids to build and repair muscles and bones and to make hormones and enzymes. They can also be used as an energy source.