denote a great lack of knowledge of the basics of dietetics. At the risk of appearing arrogant, it seems necessary to state some basic principles:

The  body has a vital need, but in variable quantity, of the following three  types of nutrients, in descending order of quantity: carbohydrates (=  sugars), proteins (= proteins) and lipids (= fats): a healthy diet  should be constituted especially  carbohydrates, a little less protein and even less lipids (for  simplicity I will not speak here of fiber and and vitamins or trace  elements, nor of "good" and "bad" carbohydrates). So  to begin with, the fact that meat contains very little (and not "none")  of carbohydrates and a lot of protein and lipids rather pleads against  it.
Since  meat is mostly protein and fat (and extremely low levels of  carbohydrate), an exclusively meat-based diet is particularly  contraindicated (this creates a lot of problems for the Inuit, for  example, and still feeds on food). they mainly seal meat, much healthier than beef or pork, especially those from industrial breeding).
Of course, outside this particular example, meat is usually eaten with another food: rice, potatoes, etc. The  whole question is about the overall balance, not of a dish or a meal,  but of a global diet: it is necessary to average food over several days  to judge if it is balanced. Off,  most of the foods that come as an accompaniment or complement to the  meat are already rich enough, either in fat (eg fries or fried  vegetables, whether in oil or butter, sauces, etc.), either  protein (anything that is rice or wheat, such as pasta, semolina,  bread, etc.), or both (cheese and other dairy products, ...).
In  short, it is not a question of the so-called vegetarian lobby but of  common sense: Western culinary habits (and which are in fact Western  bourgeois culinary habits, because before the twentieth century the meat  was very expensive and most Europeans ate exceptionally) are not particularly healthy.
Of  course, and some answers have emphasized, everything is a question of  dosage: a moderate consumption of meat (and quality, avoid frozen steaks  at 5 Euros per kilo at the supermarket ...) is not bad for health. On  the other hand, contrary to what we read unfortunately still too often,  there is no contraindication to a strictly vetetian diet, since it is  very easy (in fact easier than consuming meat ) to respect the hierarchy of carbohydrates / proteins / lipids by being vegetarian (and yet God knows that I like sausages ;-)
In  fact, almost the entire population of our globalized and industrialized  world has a diet that is very, if not too, protein-rich. The  only places in the world where protein-deficient diets still exist need  to be a few villages in Central America where people are so poor that  they only eat corn (which is very low in protein): I insist the fact that rice and wheat have a protein content that is quite sufficient!