True and False, Human beings have a large part in negatively harming the environment through intentional and unintentional actions (Over-Forestation, Pollution, Introducing chemicals and new sediments, and elimination of key species), Human kind has also helped to protect and improve our environment by actively creating and looking for solutions to decrease natural energy usage (solar power, etc).
False, we do a lot for the environment as well, in fact every organism has both positive and negative impacts, without a single organism the whole food web would go horribly wrong. Artificially we also have good and bad impacts, cars aren't the only thing that exist, we do help the environment out sometimes as well ;)
Will not get all the necessary nutrients and vitamins and minerals like vitamin C and iron. your cholesterol will raise. will get obese. will be eating mostly fats and empty calories and will not feel as energised.