In order for the body to function at a optimum level, a slightly alkaline body is vital for good health. The problem with meat and processed foods, especially red meats, is that they are acidic in the body. So while you gain a good source of protein and iron, eating a lot of acid forming foods means your organs become stressed, bloating and weight gain occur, which down the track can lead to chronic illnesses and generally your peace of mind is lost. Whereas maintaining a mainly alkaline diet means purification and detoxification, helping the body to function at its optimum level.
There are many plant based sources out there that will provide protein and essential amino acids. Good fats are also essential, it actually helps to keep the bad fats at bay and encourage weight loss. I think it's important that as we learn more about these things we have to change how we think about food as well. Just because we've always been told something doesn't mean it's right, just because everyone has always done it a certain way doesn't mean it's the best way. This video is one of many great examples out there which breaks the old ideas we have about exercise and food.