Like many vegetarians, I am constantly being asked how I get enough protein in my diet. To the surprise of these omnivores, protein is surprisingly easy to get in the vegetarian diet (it is iron and B vitamins which are usually more of a concern). However, because few plant-based proteins are “complete”, it is important that vegetarians make sure they are eating a variety of protein-rich foods and some, especially athletes, may wish to take a protein supplement.
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What are Proteins?
After water, proteins are the most abundant type of molecule in our body and are found in every single cell. They have two main functions in the body. First, they serve as building blocks for our cells, and thus are vital for healthy growth. Secondly, they are a main source of energy for the body, second only to carbohydrates.
Each protein is made up amino acids which are strung together. Once the protein is ingested, enzymes break them down into amino acids. The amino acids are absorbed by the small intestine which then sends them into the blood stream so they can be used by the body. The individual amino acids reorganize themselves into proteins, with each protein having its own specific function.
The two main types of proteins are:
- Structural proteins: Form cells
- Storage proteins: Store energy which can be broken down and used by the body during metabolism
Other types of proteins include:
- Enzymes: These proteins cause chemical reactions in the body, such as metabolism and DNA replication
- Antibodies: These proteins help white blood cells to kill antigens
- Contractile Proteins: These proteins allow muscle movement
- Hormones: Hormone proteins regulate various bodily functions
- Transportation proteins: These proteins help transport other chemicals throughout the body, such as hemoglobin.
- Receptors and Signal proteins: These proteins communicate with other types of chemicals in the body
The 20 Amino Acids
Proteins are made up of strings of molecules called amino acids. There are 22 different amino acids which make up nutritional proteins. However, two of these amino acids (Pyrrolysine and selenocysteine) are not used in humans.
Of the 20 amino acids used by humans, 9 are considered “essential,” meaning that they cannot be produced by the body and must be consumed as food. 4 of the amino acids are “non-essential,” meaning that the body can make them from essential amino acids. The remaining 7 amino acids are “conditional,” meaning that they can be made by the body but sometimes must be supplied through diet in certain peoples who cannot make adequate amounts.
|Essential Amino Acids||Non-Essential Amino Acids||Conditional Amino Acids|
*These amino acids are essential in infants and developing children
A complete protein is a protein which contains all 9 essential amino acids needed by humans. Most foods do contain at least small amounts of all 20 amino acids. However, they are only considered “complete” if they provide enough of each essential amino acid to support bodily function.
Most animal-based foods are complete proteins. However, few vegan foods provide complete proteins. So long as vegetarians and vegans are eating a variety of different proteins throughout the day though, they should have no problem getting all the essential amino acids they need.
Some of the plant-based sources of complete protein include:
- Hemp seeds
Again, it isn’t necessary to eat complete proteins so long as you are combining different vegetarian protein sources. For example, whole grains tend to have most essential acids except for lysine, whereas legumes typically are missing methionine. By eating grains and legumes together (or at different times of the day), vegetarians and vegans would be able to get all essential amino acids.
Protein Requirements for Vegetarians and Vegans
Institute of Medicine recommends that adults get a minimum of 0.8 grams of protein for every kilogram of body weight per day (about .36 grams per pound). Based on these general guidelines, a 120 pound person would need about 43 grams of protein per day.
However, protein requirements can vary drastically depending on the age, gender, and activity level of the individual. For example, a male athlete will require much higher amounts of protein than an inactive woman of the same weight. The Sports Nutrition Guidebook puts the protein needs of adults at these levels based on activity level:
- Sedentary adult 0.4 g/lb.
- Active adult 0.4-0.6 g/lb.
- Growing athlete 0.6-0.9 g/lb.
- Adult building muscle mass 0.6-0.9 g/lb
Here are the dietary intake recommendations for protein from the Institute of Medicine:
Should You Take a Protein Supplement?
Studies show that vegetarians tend to have less protein in their diets than omnivores (10-12% vs. 14-18% of calories coming from protein). Despite the lower intake of protein, most vegetarians probably don’t need to take a protein supplement so long as they are eating a balanced diet which consists of a variety of high-quality proteins. The exception to this is vegetarian athletes because they need additional protein to support tissue repair.
It may be difficult for vegetarian athletes to get enough protein to meet the 0.6-0.9 grams/lb. recommendation. For example, a male athlete weighing 165 pounds would need upwards of 148 grams of protein per day to sustain high-intensity workouts. This would mean eating in a day:
- 3 cups quinoa (24 grams)
- 2 cups baked beans (24 grams)
- 4 slices whole grain bread (12)
- 8 Tbsp. peanut butter (32 grams)
- 1 cup of tofu (40 grams)
- 2 cup soy yogurt (16 grams)
It would be easier to instead take a vegetarian complete protein supplement, such as hemp powder at about 15 grams per scoop.
Dangers of Excessive Protein
The Institute of Medicine hasn’t identified any maximum intake level of protein. However, there is ample evidence that a high-protein diet can be harmful to the body. Certain amino acids get oxidized in the body. The body responds neutralizes the oxidation by releasing calcium. Over time, this could lead to osteoporosis.
Further, the high levels of calcium in the body could cause kidney problems, such as kidney stones. The American Diabetes Association recommends not exceeding the 0.8gram/kilogram recommendation in people with kidney disease.
Non-Protein Amino Acids
- Taurine & Carnitine
- Carnosine & beta-Alanine