Why is it so hard to Diet?

Even if you're eating healthy there is still a ton of rules and guidelines to follow. Who's to say we even have it right this time anyway? The original food pyramid was completely unhealthy. The Atkins diet removed all carbs, but vegetables are full of carbs. We keep changing what's healthy and what a good diet consists of, no wonder so many people struggle. Not to mention the impossible task of limiting sodium. I read that the body only needs about 500mg of sodium a day and the maximum recommended amount is 1500mg. Have you ever read the labels of food and condiments? Everything is so full of sodium its almost mind boggling. It would just be nice if all these so called experts could come together and agree on exactly what we should be eating each day so people could have a straight forward guideline to follow.