Seventh-day Adventists traditionally are lacto-ovo vegetarians (eating dairy and eggs but no flesh foods). Some very conservative Adventists are dietary vegans (no animal products at all). When I was growing up, they were called “strict vegetarians.” Adventist non-vegetarians eat beef, chicken/turkey, and fish with fins and scales, but do not eat pork or shellfish, among other flesh foods described in Leviticus 11 and Deuteronomy 14. There is a wide spectrum of opinion about vegetarianism/veganism.

Start with this comprehensive overview (for vegetarians and pescatarians):

10 HIGH-PROTEIN LOW-CARB VEGETARIAN FOODS (PROTEIN CHARTS)
https://www.ditchthecarbs.com/low-carb-protein-for-vegetarians/

Ellen G. White and Vegetarianism
https://www.ministrymagazine.org/archive/1986/04/ellen-g.-white-and-vegetarianism

Food For Thought: Meat-Based Diet Made Us Smarter
http://www.npr.org/2010/08/02/128849908/food-for-thought-meat-based-diet-made-us-smarter

How Safe is Eating Meat?
http://www.bbc.com/news/health-28797106

Meat Alternatives Explained: Tofu, Tempeh, and Seitan
http://www.popsugar.com/fitness/Nutritional-Comparison-Tofu-Tempeh-Seitan-Recipes-18692390

Red Meat Causes Cancer?
http://www.drperlmutter.com/red-meat-causes-cancer/

Red Meat Does Not Cause Disease
http://liveto110.com/red-meat-does-not-cause-disease/