Because for fitness enthusiasts, protein is one of the most important nutrients. They are necessary for muscle growth and repair, so it is generally recommended to take enough protein in the diet to help achieve fitness goals.

Both beef and chicken breast contain high-quality protein. Among them, beef is also rich in meat iron, which can help the human body synthesize hemoglobin and is an important part of health. However, beef and chicken breast also contain a lot of saturated fat, and excessive intake may increase the risk of heart disease and diabetes.

In contrast, milk is also a very good source of protein, and contains a lot of calcium, vitamin D and other trace elements. However, compared with beef and chicken breast, milk has lower protein content and relatively more fat and sugar content. Therefore, if you just want to increase protein's intake, you need to drink more milk than usual and control other diets with high sugar and fat, so as to effectively achieve your fitness goals.

In addition, for some people, drinking milk may not be easy to digest. This is because the lactose contained in milk may make some people feel uncomfortable or cause slight lactose intolerance. Therefore, in some cases, milk is not an ideal source of protein.

Generally speaking, although milk is also a very good source of protein, it is sometimes not the best choice, because beef and chicken breast provide more protein, are easier to digest and are rich in other nutrients. I believe you can also make a reasonable choice on the intake of protein, because of your personal taste and physical condition.