Protein: Is More Better?

Chip Law, TVS Nutrition Advisor

Haven't we all been asked, "Where do you get your protein?", when people find out we're vegetarian? This is such a common question that one would think protein deficiency is rampant in the United States. In reality, we are so concerned with getting enough protein that most Americans consume 2-3 times more than we actually need! If protein is a good thing, more must be better, right? Wrong! Very wrong!

Excess protein (particularly animal protein) is now linked to increased risks of osteoporosis, kidney disease, heart disease, and certain cancers. Animal protein differs chemically from plant protein. The byproducts of animal protein digestion are more sulfuric and cause bone calcium to be excreted to remove these toxic byproducts from the body. After many years of this process, the bones become brittle and osteoporosis may begin.

There are also many "tag-along" nutrients of animal protein which are potentially hazardous to your health, including saturated fat and cholesterol which contribute to heart disease and some cancers. Animal protein is devoid of any fiber, a component of plant foods which decreases serum cholesterol levels, decreases the risk of colon cancer, and is important for proper digestive function3.

How much protein do we need?
Based on the latest RDAs 4, protein requirements for adult males is 63 grams/day, and for adult females 50 grams/day. Individual protein needs can be calculated by multiplying .8 grams times the number of kilograms of body weight 5; this includes a 25% margin of safety for individual variation, so that the RDA meets the needs of 97.5% of the healthy population. This figure was also rounded up from 0.75 g/kg to simplify calculations1. Given your body weight in pounds, W, this is the recommended amount of protein that you should consume per day:

W / 2.2 lbs/kg x 0.8 gm/kg = grams of protein per day

We will see shortly that this can easily be satisfied by a vegetarian diet; infants (1.2-1.5 g/kg)4 and athletes (1.0-1.5 g/kg) 1 need more protein, but this can also easily be met.

What about "high quality" protein?
The food we consume contains about twenty different amino acids, the building blocks of proteins. Of these twenty, our bodies can make eleven, called nonessential amino acids; the other nine are essential amino acids (EAAs) that we must get from food.

The terms "high quality" or "complete" protein refer to a protein source that contains all nine essential amino acids. It is usually thought that animal proteins are the only source of complete protein and that to get all of the EAAs from plant sources one has to carefully weigh, measure, and combine foods. This myth, which persists even among health care professionals, was erroneously reinforced when Frances Moore Lappe wrote Diet for a Small Planet in the late 1960s. Although she supported a vegetarian diet, she advocated the notion of "protein combining", or consuming two "incomplete" proteins (beans and rice) at the same time to achieve adequate EAA balance. Due to convincing refuting research, Ms. Lappe retracted her statements in the 1981 revision of her book. It is now widely accepted among the nutrition community that protein combining is unnecessary.

If we look at the amino acid composition of plant foods, we see that plant proteins provide all nine EAAs (in fact, all food proteins, except gelatin -- which many vegetarians don't eat -- contain all nine EAAs). Although one or more EAAs may be present in small amounts, it is possible to meet your protein requirements consuming one plant food, provided you eat enough of this food. (This is not advisable, since other nutrient imbalances could result from such a limited diet, but I am just using this to prove a point.) If you consume adequate total calories to maintain your body weight and eat a variety of foods, you should easily meet your protein needs.

Which plant foods are the best protein sources?
Most plant foods contain some protein. Even broccoli contains protein. (Foods that do not contain significant amounts of protein are most fruits, all oils, and beverages like soda, coffee, and alcohol.) Plant foods that contain plenty of protein include beans and legumes, soy products (tofu, tempeh, soymilk), nuts, seeds, and whole grains. Vegetables also contain protein, but in smaller amounts. Let's look at the exact amount of protein in some of these foods.

Food Serving Size Protein (gms)
Tofu, firm cup 20
Soymilk 1 cup 10
Tempeh 4 oz. 12-24
Lentils cup 9
Peanut butter 2 Tbsp. 8
Chickpeas cup 7.5
Pinto beans cup 6
Quinoa cup 5.5
Oatmeal cup 5
Whole wheat bread 1 slice 2.5
Broccoli cup 2.5
Spinach cup 2.5

It is easy to see that by consuming a plant-based diet with a variety of foods, one can readily meet their protein needs. So the next time someone asks you that nagging protein question, remember that:

  1. Protein is found in most foods.
  2. The RDA for protein is 50 gms/day for women and 63 gms/day for men.
  3. By consuming adequate total calories to maintain your weight and eating a variety of plant foods each day, protein needs can easily be met.
  4. Excess protein (especially animal protein) can be hazardous to your health by increasing your risk of osteoporosis, kidney disease, heart disease, and certain cancers.

Also, remember that some of the largest mammals on earth (elephants, giraffes, hippopotami, and cows) are vegetarians and fulfill their protein requirements on plant foods alone. Not only can we easily meet our protein needs, but we enjoy many health benefits from avoiding animal proteins.

Footnotes (Hit "Back" on your browser to return)
1) Messina, M. and W. Messina. The Dietitian's Guide to Vegetarian Diets: Issues and Applications.
Aspen Publishers, Gaithersburg, MD, 1996.

2) Melina, V., B. Davis and V. Harrison. Becoming Vegetarian.
The Book Publishing Co., Summertown, TN, 1995.

3) Mahan, L.K. and S. Escott-Stump. Krause's Food, Nutrition, & Diet Therapy.
9th ed. W.B. Saunders Co., Philadelphia, PA, 1996.

4) Recommended Daily Allowances

5) Zeman, F.J. and D.M. Ney. Applications in Medical Nutrition Therapy.
2nd ed. Prentice-Hall, Englewood Cliffs, NJ, 1996.