Plants Provide Everything But Vitamin D and Vitamin B12

Vit­a­min D Comes From Sun­shine, Vit­a­min B12 From Bac­te­ria

How can a diet con­sist­ing main­ly of leaves give goril­las enough pro­tein to grow big and strong? It’s because leaves con­tain pro­tein. Leaves are low in calo­ries, but a lot of their calo­ries come from pro­tein. In fact, most ordi­nary plant foods con­tain more than enough pro­tein to meet human nutri­tion­al needs. Nutri­tion sci­en­tists have known for near­ly a hun­dred years that as long as you are eat­ing any rea­son­able plant-based diet, if you take care of the calo­ries, the pro­tein takes care of itself.

It’s hard even to design a plant-based diet that would be defi­cient in pro­tein while pro­vid­ing enough calo­ries. You’d have to include noth­ing but some low-pro­tein fruit, such as apples. Or you could cheat and use sug­ars and fats that have been extract­ed from plants, leav­ing the pro­tein and oth­er nutri­ents behind.

Not only do plants pro­vide enough pro­tein for human nutri­tion, the pro­teins they con­tain are nutri­tion­al­ly “com­plete,” as far as human pro­tein needs go. That means that they con­tain enough of all of the dif­fer­ent amino acid “build­ing blocks” that human bod­ies need.

The only “incom­plete” pro­tein you are like­ly to find on your din­ner plate is gelatin, which comes from ani­mal bones. Gelatin is incom­plete because tryp­to­phan is destroyed in the man­u­fac­tur­ing process. You’d get very sick if you tried to use gelatin as your sole source of pro­tein.

Plant foods also con­tain the min­er­als that are essen­tial for human nutri­tion. Plants absorb these min­er­als, such as cal­ci­um and iron, from the soil. After all, where did the cows get the cal­ci­um that goes into their milk? Where did they get the iron that goes into their flesh?

Plants also pro­vide near­ly all of the vit­a­mins that are essen­tial in human nutri­tion. The excep­tions are vit­a­min B12, which is made by bac­te­ria, and vit­a­min D, which your body can make for itself if you go out­side in the sun­shine. Peo­ple who eat a pure­ly plant-based diet are gen­er­al­ly advised to take a vit­a­min B12 sup­ple­ment. Whether you need a vit­a­min D sup­ple­ment depends on how dark your skin is and where you live. Your doc­tor can do a sim­ple blood test to see whether you have enough of both of these vit­a­mins.