Protein

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Description and Use:

Proteins are one of the three macronutrients, those nutrients needed in relatively large amounts to support normal function and health. The other two are carbohydrates and fats. Like carbohydrates and fats, they are mainly composed of carbon, hydrogen and oxygen but additionally they also contain nitrogen. Nitrogen absorption or loss is usually what is measured when determining protein utilization and requirements. Proteins can also contain traces of sulfur, iron and phosphorus. Proteins are found in every cell and tissue of the body. Their main functions in the body are to;

  • Grow, repair and maintain bodily tissues. This includes the growth of hair and nails, healing of wounds and the general replacement of broken down tissues that occurs in normal daily activity.
  • Maintain fluid and electrolyte balance
  • Maintain acid/base balance
  • Act as antibodies in the immune system (white blood cells)
  • Act as enzymes and hormones (insulin, glucagon, etc.)
  • Aid in transport and storage of nutrients
  • Provide energy when there is insufficient supply of carbohydrates or fats

If needed, the body can convert protein into energy. Normally, carbohydrates and fats provide energy for the body. However, in the below cases, protein is used;
1. Excess protein. Protein in excess of the body's protein requirement will be converted to energy. Unlike carbohydrates which can be stored as glycogen and fats which can be stored as triglycerides, excess protein cannot be stored for future use.
2. Insufficient carbohydrates or fats to meet caloric needs. If protein is the main component of the diet, it can be used for energy. This can happen in some cultures like the Eskimos, where meat is the main food source or in unusual diet plans like Atkins.
3. Starvation. Tissues (muscles, liver) in the body can be broken down for energy.

Protein does not burn cleanly like carbohydrates and fats and can put an added strain on the liver and kidneys. When carbohydrates and fats are burned, the by-products are simply carbon dioxide and water. However, when protein is burned, there are ammonia and urea by-products. For protein to be used as fuel, the nitrogen component must first be removed. It is converted to ammonia and transported to the liver where it is converted to urea. Urea is then screened out by the kidneys and eliminated in the urine. The protein with the nitrogen removed, can then be burned like a carbohydrate for energy. If necessary, unlike fats, it can be converted to glucose which is needed for brain function. When used for energy, protein provides 4 kcal/gm, the same as carbohydrates. It is important to consume sufficient carbohydrates and fats to provide your caloric needs. That way, protein consumed can be used specifically for protein requirements.

When transitioning to a vegetarian diet, often the first concern people have is getting enough protein. This need not be a concern. Over the years, there have been numerous studies on vegetarian groups and they have borne out that a varied and adequate vegetarian diet can easily provide sufficient protein. See the stance of the American Dietetic Association. Lacto-ovo vegetarians easily consume enough protein and vegans with a little planning can also easily meet their protein requirements. A vegetarian diet can provide strength and endurance as well as any other diet. Famous vegetarians include some bodybuilders (Bill Pearl, Andreas Cahling) and Olympic athletes (Carl Lewis, Edwin Moses).

Structure of Protein:

Proteins are large complex molecular chains of amino acids. The body's proteins are made from 20 different amino acids. 9 of these are considered essential, meaning they cannot be manufactured in the body from other substances and must be consumed in the diet. They are; histidine, isoleucine, leucine, lysine, methonine, phenylalanine, threonine, tryptophan and valine.

In digestion, proteins are broken down into their constituent amino acids then the body reassembles them to make its own proteins. This reassembly uses our DNA as the blueprint, so each person's protein is unique. To synthesize protein, the 9 essential amino acids must be present and in the correct ratio to each other. A protein source that contains the 9 essential amino acids and in the right ratio is considered a complete protein. Examples would be egg whites, milk products and soy. If one or several of the 9 essential amino acids is low compared to the ideal ratio then they will be the limiting factor in how much protein is usable. If only part of the protein source is usable, it is referred to as an incomplete protein. Examples would be some legumes, vegetables and grains. However, even though legumes may be considered as incomplete, the quality of protein in some (lentils, garbanzo beans, black-eyed peas) is almost equal to that of meat.

In a process called mutual supplementation, several incomplete proteins can be combined to create a complete protein. For example; legumes are low in methonine and cysteine but adequate in isoleucine and lysine. Rice is low in isoleucine and lysine but adequate in methonine and cysteine. By combining rice and legumes, a complete protein is formed. This principle is particularly useful for vegetarians who do not consume any eggs, milk or dairy products. Interestingly, this combining principle is common in several cultures;
   Rice and dal - India
   Beans and tortillas - Latin America
   Hummus (garbanzo beans) and pita - Mid-East
   Blackeyed peas and cornbread - U.S., South
   Peanuts and grains like millet - Africa
   Rice or noodles with soy products - Asia

It is not necessary to combine incomplete proteins in the same meal (though that would be optimal) however they should be eaten in the same day. There is a pool of available amino acids in the bloodstream but they are not stored and saved for future use. It is also not necessary to do any elaborate weighing or measuring to combine proteins. Most varied vegetarian diets provide adequate protein. Following some general principles of eating legumes with some grains, etc. is simply a smarter way for increasing the quality and thus the amount of the usable protein being consumed.

Digestion of Protein:

No digestion occurs in the mouth. Protein foods are chewed crushed and mixed with saliva to ease swallowing and increase their surface area for more efficient digestion.

In the stomach, hydrochloric acid denatures the strands of protein and activates the protein digesting enzyme pepsin. Pepsin breaks the proteins into single amino acids and shorter strands of amino acids called polypeptides.

Absorption of amino acids occurs in the small intestine. The pancreas and small intestine produce additional enzymes to further break down the polypeptides into their individual amino acids. Amino acids are transported to the liver via the portal vein. The liver can;
  • Convert amino acids to energy, glucose or fat
  • Build new proteins
  • Release amino acids to the blood stream where they can be transported to others cells as needed.

Additional notes for weight lifters.

Recommended Intakes:

The Recommended Dietary Allowance (RDA) for protein is .8 gm/kg. In the past, it was thought that regardless of whether a person was active or inactive, the RDA was the same. However, recent studies indicate that growing children, women who are pregnant or lactating and endurance/strength athletes will need slightly more. An endurance athlete should get 1.5gm/kg, a strength athlete 1.8gm/kg. As a percentage of total calories consumed, protein should be in the 10-15% range. This assumes approx 20-30% is fat and 55-70% is carbohydrate. For people who consume an adequate calorie intake, in this general ratio, protein needs are easily met or exceeded. Consuming more than 2 gm/kg, approximately twice the RDA, is not recommended. People consuming higher levels of protein should drink more water to flush urea from the kidneys.

As an example calculation; an adult male of 180 lbs. would need about (180 lb/2.2 kg) * .8 = 65 gm of protein per day. This represents 65 * 4 kcal/gm = 260 calories. In an average 2000 kcal/day diet this is about 260/2000 = 13%. A 140 lb. person needs about 50 gm/day. The weight used in these calculations assumes the normal or lean body weight for a given height and bone structure. Being overweight does not increase one's protein requirement.

Deficiency symptoms: Insufficient protein over time can result in
• Hair and nails not growing normally.
• Healing of wounds and injuries can be impaired.
In extreme cases,
• Edema - a disorder where fluids build up in the tissue spaces of the body, causing fluid imbalances and swollen appearance.
• Marasmus - the gradual wasting away of the body due to severe malnutrition or inadequate absorption of food. Child will look emaciated.
• Kwashiorkor - Typically seen in children 1-3 yrs old in impoverished countries where the most visible symptom is a swollen belly. There are many other symptoms also.

Excess symptoms: Too much protein can cause several problems
• Cholesterol levels can increase if the sources of protein are mostly animal products which have associated saturated fat.
• Added strain on the liver which must convert ammonia (very toxic) to urea for elimination by the kidneys.
• Kidney disease, including kidney stones, is a risk for those who are susceptible. Diabetics have a higher risk for kidney disease and may benefit from a lower protein diet. Their need for protein is more than average but an intake of 15-20% is adequate.
• High dietary intake of animal protein can promote the formation of kidney stones.
• Calcium loss which can increase the risk of osteoporosis. Studies have shown that a high protein diet increases the amount of calcium lost in the urine. This is because the protein by-products create an acidic condition in the blood and so calcium is then pulled from the bones to neutralize the pH levels.

Sources of Protein:

Protein is common in many foods including grains and vegetables. So when eating a varied diet, the amount of protein can easily add up over the course of a day. Listed below are sources that contain a significant portion of protein, like more than 5 gm per serving.

Vegan sources include;
Nuts - almond, brazil, cashew, filbert, peanut (actually a legume), pecan, pine, pistachio, walnut
Seeds - sunflower, pumpkin
Legumes - adzuki, black, black-eyed, cannellini, garbanzo, kidney, lentil (red and brown), lima, mung, pinto, soybean, split pea (green and yellow), toor dhal (split pigeon peas), urad dhal (black gram), white (navy or Great Northern)
Soy products - soy milk, tofu, tempeh, soy cheese, soy yogurt, protein powder
Grains - oatmeal, pasta, quinoa, rice (white or brown), wheat
Veggie meats (soy or gluten based) - hot dogs, burgers, sliced turkey/ham, sausage, bacon, meat balls, chik'n strips and many more!
Additionally, lacto-ovo sources include;
Dairy - milk, yogurt, cheese, cottage cheese, kefir
Eggs
Veggie meats with dairy
Protein content of common vegetarian foods:

FOOD SERVING PROTEIN (g)
Nuts & Seeds    
   Almonds 1 oz, ~ 1/4 cup 6
   Cashews 1 oz, ~ 1/4 cup 5
   Peanut butter 2 Tbsp 8
   Pumpkin seeds 1 oz 8
   Sunflower seeds 1 oz 5
   
Legumes (Cooked)    
   Baked beans (white) 1/2 cup 6
   Black beans 1/2 cup 8
   Black-eyed peas 1/2 cup 7
   Edamame, shelled 1/2 cup 11
   Garbanzo beans 1/2 cup 7
   Kidney beans 1/2 cup 9
   Lentils 1/2 cup 9
   Refried beans (pinto) 1/2 cup 6
   Soybeans 1/2 cup 14
   
Soy Products    
   Soy milk 1 cup 8
   Tempeh, cooked 3.3 oz 18
   Tofu 3.5 oz (1/4 block) 9
   
Grains    
   Oatmeal, cooked 1 cup 6
   Pasta, cooked 1 cup 8
   Quinoa, cooked 1 cup 9
   Rice, cooked 1 cup 5
   Whole-wheat bread 1 slice 4
   Burger bun, TJ* 1 bun 8
   Hot dog bun, TJ* 1 bun 6
   
Dairy Products    
   Milk 1 cup 8
   Yogurt 1 cup 12
   Cheese 1 slice, 3/4 oz 5
   Cottage cheese 1/2 cup 14
   Egg 1 large 6
   
Veggie Meats    
   Hot dog (Litelife) 1 link 8
   Burger (Gardenburger) 1 patty 5
   Burger (Morningstar) 1 patty 10

Source: USDA National Nutrient Database for Standard Reference, Release 26
Note: USDA refers to edamame as 'Soybeans, green' and black-eyed peas as 'Cowpeas'.
* TJ - Trader Joes's Honey Wheat

Summary:

Based on the above information, here are some general (vegetarian) guidelines;

  • A vegetarian diet can easily provide adequate protein. Lacto-ovo vegetarians have the least concern and generally do not have to watch protein intake. Vegans may need to plan more carefully and should have an idea of how much protein their daily diet is providing. Soy substitute products (milk, yogurt, cheese, veggie-meats) and tofu can easily contribute more than enough.
  • Protein requirement for an adult is .8 gm/kg. That's about 65 gm for a 180 lb. person, 50 gm for a 140 lb person. Children, pregnant or lactating women, and strength/endurance athletes will require slightly more.
  • Eat sufficient carbohydrates and fats to provide your caloric needs. That way, protein consumed can be used specifically for protein requirements. A general calorie ratio of 65/20/15 for carbohydrates/fats/protein when maintained at most meals insures a good balance.
  • Legumes make an excellent addition to one's daily diet. In addition to protein, they provide needed fiber. Combining them with some grains like rice, bread, pasta etc. will improve their protein quality.
  • Eat a serving of raw nuts or seeds daily. A handful of nuts or a couple of tablespoons of a nut butter provides a healthy source of protein and also contributes some essential fatty acids. Nuts should be chewed well for good digestion.
  • Be moderate in protein sources which also contribute saturated fat. Choose low-fat or non-fat dairy products.
  • Protein powders are generally unnecessary for diets that provide adequate protein. In moderation, they may be an aid to bodybuilders and strength atheletes.
  • Do not consume excessive amounts of protein. Protein beyond double the daily requirement puts an added strain on the liver and kidneys. It can also be a factor in bone loss.

Disclaimer:

The contents of this Web site are not intended to offer personal medical advice. You should seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this Web site.

References:

  1. Thompson, Janice L., Melinda M. Manore and Linda A. Vaughn. "Proteins: Crucial Components of All Body Tissues" The Science of Nutrition San Francisco, CA : Pearson Benjamin Cummings 2008
  2. Duyff, Roberta L. "The Vegetarian Way" American Dietetic Association Complete Food and Nutrition Guide Hoboken, NJ : Wiley 2006
  3. Weil, Andrew. "Protein Revisited: How Much Is Enough?" Eating Well for Optimum Health New York : Quill 2001
  4. Craig, Winston J. "Plant Proteins are a Plus" Nutrition and Wellness Berrien Springs, MI : Golden Harvest Books 2008
  5. Messina, Virginia, and Mark Messina. "Protein in Vegetarian Diets" The Vegetarian Way New York : Three Rivers Press 1996
  6. Willet, Walter C. "Choose Healthier Sources of Protein" Eat Drink and Be Healthy New York : Free Press 2001
  7. Melina, Vesanto, and Brenda Davis. "Power from Plants...legumes, nuts and seeds" Becoming Vegetarian Summertown, TN : BPC 2003
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