The human body uses 20 amino acids—the building blocks that form protein. They are found in a variety of food sources, including animals and plants. Essential amino acids are those the body cannot make itself, which means they must be taken in through food sources or supplements. They come primarily from animal sources like meat, as well as from dairy and eggs. The body can manufacture the remaining 10 nonessential amino acids. The problem is that many plant protein sources don’t contain the full spectrum of essential aminos when eaten separately. This is why food variety and careful planning are so important. 

Food combining is the concept that eating certain foods together over the course of a single day will help vegetarians get all the essential amino acids needed for proper growth, development, and health. For example, grains and cereals are very low in the essential amino acid lysine, while beans, peas, and peanuts are a rich source. Likewise, legumes don’t contain the essential amino acids tryptophan, methionine, and cysteine, but nuts and seeds do; therefore they are complementary to each other. Some commonly recommended food combinations include black beans with rice, pasta with peas, and whole-wheat bread with peanut butter.

But not everyone agrees with the food- combining approach. “I think it’ s a wasted effort,” says McGee. For many, worrying about food combining just overcomplicates the vegetarian lifestyle and reduces the chances of sticking with it, she notes. Instead, “Focus on taking in quality, natural food with all three macronutrients over the course of the day. This will best provide lasting energy and muscle-building nutrition.”

Research published in The Medical Journal of Australia backs the idea that there is no need to consciously combine different plant proteins at each meal as long as a variety of foods are eaten from day to day and overall energy needs are being met. This is because the human body maintains a pool of amino acids that can be used to complement dietary protein.

To keep the rest of your diet in balance, you still need a healthy mix of carbs and fats. Lisa Dorfman, R.D., author of Legally Lean and a Vegetarian, recommends 1.5 to 2 grams of carbs per pound of body weight and 0.3 to 0.5 grams of fat per pound of body weight per day. For a 140-pound woman, that’s about 210 to 280 grams carbs a day and 42 to 70 grams fat.

But the most detrimental mistake vegetarian women tend to make is not eating enough total calories—approximately 2,200 calories per day for a 140-pound woman exercising regularly, according to the U.S. Department of Agriculture.