Eating vegetarian one day a week can bring health benefits. According to Monique Ryan on eatright.org, "eating no meat one day a week is not only about subtracting from your diet, but adding to it" (Ryan, 2016). What she means by this is that while you are eliminating your meat consumption one day a week, you can substitute that meat by consuming more vegetables, whole grains, beans, and lentils. 

Whole-wheat bread, whole-grain pasta, brown rice, etc. can help to prevent heart disease, certain cancers, and diabetes. Adding lentils or beans can also contribute to your protein intake. Vegetables such as kale, collards, and broccoli can also be good sources of calcium (Ryan, 2016).

 
http://www.eatright.org/resource/food/nutrition/vegetarian-and-special-diets/going-meatless

Kristin - Meatless Monday Intern