I recommend the Weston A. Price Foundation for guidance on nutrition, as well as Nourishing Traditions: The Cookbook that Challenges Politically Correct Nutrition and the Diet Dictocrats by WAPF President Sally Morrell.
Remember that there is no one-size-fits-all diet; some people may do well on a mostly vegetarian diet while others thrive on mostly meat. Do keep in mind that it is more about the ingredients than the calories or nutrition label numbers; in other words, quality over quantity. Also, if you are going to be an omnivore, please be a conscious one. Support local farms and buy your eggs, dairy and meat from local producers who treat their animals humanely and allow them access to the great outdoors. Make sure they are hormone and antibiotic-free, and ideally, fed non-GMO grain and alfalfa. If possible, visit the farm where they are raised to better gain a connection to where your food comes from. There are many CSAs and farmers’ markets in almost every part of the country (and growing, thanks to community support) that offer seasonal organic fruits, vegetables and animal products. You will be supporting your local economy, the health of your family and the health of the planet via your consumer habits.
Check out some of my favorite books on health and nutrition. These books changed my life!