Look up Dr John McDougall. He has a book called The Starch Solution. Also look up the "Raw Till 4" diet. That way you can eat low fat, without any grains. Yes a high fat diet will be hard on your liver BUT if you need to get more calories, then avocados are much less harmful than animal products (oils aren't good either).
But you can definitely get in enough cals on a starch based diet and you can eat a lot of fruit if you want to. If you are eating mostly vegetables at the moment, you might not be getting enough calories.
Yes protein is neccessary but we do not need that much. Most people eat too much protein and it is hard on kidneys.
Other doctors to look up: Dr Neal Barnard, Dr Caldwell Esselstyn, Dr Michael Greger on youtube (nutrition facts).