Ask A Scientist© Biology Archive

Question:  What are the negative effects in humans of only eating plant 
products?
H Teacher

Answer 1:
If you are excluding dairy from your meals, I understand that it may be 
difficult to get the right mix of essential fatty acids and amino acids 
and that it is difficult to get enough calcium.  However, many people are 
strict vegetarians and although it is takes some planning to get the right 
kinds and amounts of nutrients when ALL animal products are left out of 
the diet, it is not impossible. The problems occur when the vegetarian in 
question does not take care to get the right nutrients, because it is more 
difficult then when animal products are used.
Stacie

Answer 2:
Aha!!  (I'm back from a long vacation, and have to drag out my soapbox) 
There are vegetarians and there are vegetarians, I say... in other words, 
they come in two flavors: the dumb vegetarian and the smart vegetarian.
 
WARNING: PERSONAL ANECDOTE
I knew someone once who decided to become a vegetarian.  Knowing next to 
nothing about proper nutrition, this person decided that she would become 
a vegetarian, for health as well as acquired moral reasons.  So she 
figured the local salad bar would do her just fine, and lived on a diet 
of plain lettuce and tomatoes, with a little vinaigrette dressing on top 
to make it a little more interesting.  It didn't last long - she collapsed 
in the middle of a high school history lesson on the Yom Kippur War.  
Not realizing that certain nutrients (quite a few, really..) are missing 
from lettuce and tomatoes, she began suffering from the obvious 
consequences of malnutrition.
 
Okay, the SMART vegetarian has read up on all the literature regarding 
this life choice, and has learned that in order to maintain a healthy 
balance of nutrients, carbohydrates and ions in the body, a wide variety 
of foods are needed.  Protein is not impossible to come by in the 
vegetable world, but must be procured in adequate amounts of the right 
kind of protein -- what are known as complete proteins.  Beans and legumes 
contain certain portions of a complete protein, while rice contains 
another.  Together, they provide the necessary protein in a balanced diet.  
A wide selection of fruits and vegetables, as well as fungal foods 
(don't forget the lowly mushroom, or the yeast that rises your bread).  
And if you aren't totally Vegan (and go for milk) don't forget that 
calcium, amino acids (like tryptophan, for one), fats, and A COMPLETE 
PROTEIN are ingredients which go into milk.
 
Now, how about servings?  I have found, in my own personal and 
un-scientific research on this very subject, that many vegetarians appear 
thin and rather pale, almost to an unhealthy degree.  Why?  One of two 
reasons: either they are the dumb variety of vegetarian, or they are the 
smart variety, but aren't eating enough -- vegetable matter may contain 
the right ingredients for a healthy diet, but they may also not contain 
them in as large quantities as meat does, and consequently, you will 
require more in order to get enough of what you need.  My friend Jeff is 
an excellent example -- he is a vegetarian who drinks milk, and when he 
eats, watch out!! He might suck the tablecloth in with the rest of his 
plate.  He knows he needs a certain amount of protein and other major 
nutrients, and the only way he can get it with his diet is to eat a large 
volume of the stuff every day.  And he looks and feels great!!
Hope this answered your question.
Wordsworth