Being a vegetarian (or vegan!) shouldn't prevent you from getting the nutrients you need from your food
Q: I’m going to start following an ovo-lacto vegetarian diet (no fish, poultry, or beef—but I’ll eat eggs and dairy). What nutritional deficiencies should I look out for?
A: Eggs and dairy products are packed with vitamin D, calcium, and vitamin B12, so by keeping those foods in your diet you already have two powerful nutritional tools at your disposal to help keep nutrient deficiencies at bay. However, there are four other nutrients you should pay special attention to.
It isn’t difficult for a person following a vegetarian diet to meet their essential protein needs (46 grams a day for women). However, more recent protein research suggests that a daily protein intake of more than 90g per day evenly spread out across three meals, at least 30g per meal, is the optimal approach to support your muscle (and help it repair after exercise). This can be difficult if you're relying purely on plant sources of protein. Including dairy products and eggs daily into your diet will help you more easily achieve these meal based protein targets. (Whip up some protein with these 20 Quick and Easy Ways to Cook Eggs.)
The recommended dietary allowance (RDA) for iron for vegetarians is 1.8 times higher that than that for non-vegetarians. This is because vegetarians generally absorb little-to-no heme iron (animal sources of iron). Some of the best plant (non-heme) sources of iron are nuts, beans, and fortified grains. When eating these foods, keep in mind that vitamin C can more than double non-heme iron absorption by your body. (On the flip side, calcium and phytates—anti-nutrients found in grains and beans—can decrease it.)
While this is a tried and true supplement for enhancing muscle strength and size, in vegetarians it is also key to improving brain function. Your body makes a small amount of creatine each day. To meet the rest of its creatine needs, it relies on dietary sources, namely meat. If you don’t get additional creatine from your diet, you body may not be able to make enough to meet its optimal needs, leading to creatine deficiency. In two different studies, creatine supplementation in vegetarians helped improve memory and brain function. Supplementing your diet with 5g of creatine monohydrate with your largest carbohydrate meal of the day will help optimize your body’s creatine stores.
EPA/DHA are famously known as the two healthy fats that make up fish oil. When you follow an ovo-lacto vegetarian diet, it's easy to get ample omega-3 fats from foods like walnuts, chia seeds, and flax seeds—but the omega-3 fat you're getting from these foods isn't the right kind. The omega-3 fat from those sources isn't EPA or DHA, but instead a shorter omega-3 called ALA. Research shows that our bodies don't convert ALA to EPA or DHA very effectively. Fortunately green algae is a powerhouse for producing DHA (which you body can easily convert to EPA); take easy-to-find DHA supplements derived from algae as part of your daily regimen. (Get your daily dose of nutrient-rich fats with these 8 New Healthy Oils to Cook With.)