Maybe. It is enough that the human body has evolved to a diet containing food of various origins. When refusing to eat animal food, the body experiences a deficiency of certain chemicals, some of which are not synthesized in the human body at all. To the greatest extent, this concerns the amino acid balance. The most complete answer can be obtained only on your own, having read, first, a sensible university textbook on biochemistry, and then something on human anatomy and ecology
Maybe, if the diet is not worked out taking into account the characteristics of your body. Providing an acceptable diet that excludes food of animal origin is a rather laborious task, and your food costs can increase significantly.
Problems with lack of essential amino acids and vitamins are solved with the use of pharmaceuticals.
Veganism is also often associated with increased gluten intake, which can negatively affect the digestive system. I have a friend who was a vegan for 12 years, but due to excessive consumption of gluten, he got gastrointestinal problems. I had to add fish and seafood to the diet, on the recommendation of the doctor (it was in Australia, I think the doctor was competent enough). You can, of course, avoid foods containing gluten, but they are not available everywhere and, again, your food budget will have to be increased.
They say it can. But I will say right away - any unbalanced diet is harmful to health. You can avoid eating animal products and only eat fried potatoes. You will faint pretty quickly, but they will say that this is because you were vegan.
We need to immediately clarify the terminology. Vegetarianism - refusal of meat / fish. Veganism is the rejection of any animal products. Anyone. The only problem I know with veganism is vitamin B12. I am not a physician, I do not have a laboratory to check all the information myself, and different sources say different things. But personally, after reading a number of materials on the issue, I have the following beliefs.
B12 is a rather important vitamin. I do not remember exactly what he is responsible for, but his lack can lead to serious, and in the terminal stage even irreversible consequences. It is found not only in animal products. But from plant food, the human body is not able to assimilate it. Since the body of anyone who grew up on a traditional diet contains serious reserves of this vitamin, after a complete rejection of animal products, a person may not experience its deficiency for several more years. But sooner or later it ends, and there will be problems. There are arguments about developing countries - they say there are vegans not out of conviction, but simply because they cannot afford. And nothing, they live somehow. It should be borne in mind that insects are also a source of B12. And the lower the level of development of the country, the higher the percentage of insects in any food collected from the fields, since the fields are less cultivated, and the legislation is easier to deal with. Then, in the same India, the unsanitary conditions are much higher, and, forgive me, feces, particles of which can somehow get on the hands, and then into the body, is also a source of B12. Also in the oral cavity, if you do not brush your teeth very well, some amount of this vitamin is also formed from the natural microflora. I repeat that the required amount is extremely small, but it is still necessary.
Again, in modern society, this problem is easily solved, since vitamins can be bought, or a series of injections can be given once every couple of years. Vegan Petya does just that. Petya is smart. Be like Petya. Other vegans who say they can do just fine without it, I don't understand a little. And I hope that they will be fine.
I cross my fingers and wash down a boiled egg with milk.