Proteins – The Building Blocks of Life

[icon name=”user” class=”” unprefixed_class=””]   Dr. Hasina Akhtar, Ph.D.

protienProteins is a common term used every day for health and diet. Innumerable suggestions pour in when topics related to ‘proteins’ and health are discussed. But, are we well informed about proteins and its relevance to our health?  Might not be. Through this article, let us get informed about proteins.

WHAT ARE PROTEINS?

Proteins are described as building blocks of life. They are large, complex molecules found throughout the body from hair to toe. They are critical for all the body function and are recruited in all the biochemical reactions taking place in the cells. They are required for structure, function and regulation of each and every organ, tissue and cells of the body. The body needs protein for growth and development – to make new cells, repair the damaged tissue and cells. Proteins are made up of thousands of smaller units called amino acids. Amino acids are attached to each other to form long chains of proteins. The sequence of amino acids in the chain determine the protein’s specificity, its uniqueness, 3 dimensional structure and function. There are 20 different types of amino acids1. So when proteins are broken down or digested, amino acids remain and the body uses these amino acids to make new proteins.

what-are-pro

There are three types of amino acids

ESSENTIAL AMINO ACIDS

The body cannot make these amino acids and hence, must be supplied through diet. The nine essential amino acids are histidine, isoleucine, leucine, methionine, phenylalanine, threonine, tryptophan and valine.

NONESSENTIAL AMINO ACIDS

These are produced by the human system. The three nonessential amino acids include alanine, asparagine, aspartic acid, and glutamic acid.

CONDITIONAL AMINO ACIDS

These amino acids are usually not required by the body but only in cases of illness and stress.2

Depending on the type of function of the protein in the body, the proteins can be described as follows1:

  1. Antibodies: These are proteins that bind to specific foreign particle such as bacteria or viruses invading the body during infection and help protect the body.
  2. Enzymes: Enzymes are proteins that help in all the biochemical reactions in the body and regulate and conduct cellular processes of the body.
  3. Signaling proteins: These are messenger proteins such as hormones that signals to communicate and coordinate the biological processes between different cells and tissues.
  4. Structural Proteins: These proteins provided structure and support to the cells. The example of these proteins are actins and the proteins that form part of the cell membrane which along with the lipids form lipoprotein structure.
  5. Storage/Transport proteins: These are proteins that bind to the other small molecules within the cells and transport them out of the cell membrane.

PRODUCTION OF PROTEINS IN THE BODY: ‘A CENTRAL DOGMA’

It is fascinating to know how the body can manufacture the proteins. The genes in the body has all the required information to make these complex molecules. The process of translating information from the genes to make the protein is highly regulated and tightly controlled within each cell. Proteins are made in two steps – Transcription and Translation1. These two process at the molecular level are referred to as Gene expression.

Transcription: During this process the information stored in the genes(DNA) is coded to small molecules called mRNA(messenger Ribonucleic acid) in the cell’s nucleus. The mRNA carries information from the DNA in the nucleus out to the cytoplasm of the cell1.

Translation: In this step the mRNA interact with specialized complex called the ribosomes to form mRNA-ribosome complex. Now the ribosome reads the sequence of the mRNA bases. Each sequence has three bases called codon. Each codon codes for particular amino acid and the tRNA(transfer RNA) assembles protein chain one amino acid at a time, until it encounters a stop codon. The stop codon does not code for any amino acid but signal to stop the protein assembly.

This transfer of information from DNA to RNA and then to protein is one of the crucial processes in the body and is referred to as ‘Central Dogma’.1

A HEALTHY DIET- PROTEIN RECOMMENDATIONS:

A healthy, well balanced diet should provided enough proteins necessary for the body functions according to the weight and age. Although, non-vegetarian foods such as meat and fish are good source of proteins, vegetarians can get enough proteins through beans, lentils and other plant products. The amount of protein to be consumed each day depends upon your health and age. The Institute of Medicine recommends that an adult should get a minimum of 0.8 grams of protein for every kilogram of body weight per day(8 gms protein for every 20 pounds of body weight).4 In the United States, the recommended daily allowance of protein is 46 gms/day for women over 19 years of age and 56 gms/day for men over 19 years of age.5

Young children and toddlers should take 2 servings of protein rich food such as turkey, eggs, fish chicken, lamb, baked beans and lentils.3  Teens need 45-60 gms/day of protein in order to grow and maintain muscles. Children should be encouraged to eat variety of protein foods in their diet. Some of the healthy options for meat protein include turkey or chicken or buffalo meat, lean cuts of beef or pork, fish or shell fish.

RECOMMENDED SERVING SIZES FOR PROTEIN:

  1. Cooked lean meat, poultry or fish- 2-3 ounces
  2. Cooked dried beans- 1/2 cup
  3. Egg-1
  4. Peanut butter-2 tablespoon
  5. Cheese-1 ounce

PROTEIN DEFICIENCIES AND  HEALTH  PROBLEMS:

Large number of people do not take enough proteins in their diet and protein malnutrition is a common problem. Protein deficiencies lead to decreased immunity, weakening of the heart and respiratory system, loss of muscle mass and growth failure.

PROTEINS QUALITY AND DISEASES:

Evidences suggest that eating healthy high protein sources like chicken, beans, fish or nuts instead of red meat can lower the risk of cardiovascular disease, diabetes and premature deaths5, 6, 7. Farvid and group has reported that  replacement of one serving/day of total red meat with one serving of combination of poultry, fish, legumes, and nuts was associated with a 15% lower risk of breast cancer overall and a 23% lower risk of premenopausal breast cancer.8 High protein diet for long period of time leads to leaching of calcium from the bones leading to Osteoporosis However. the findings to support this claim are still controversial. Some studies suggest that increase protein intake increases the risk of fractures whereas others link high protein to increased bone mineral density and stronger bones.9, 10, 11

Some people exhibit environmental and food allergies. The protein in food and environment(pollen grains have surface proteins) are responsible for allergies. Apart from these, there are little evidence regarding the effect of dietary protein in development of chronic health issues.

EXCESSIVE PROTEIN INTAKE:

The body has optimum requirement of each of the dietary components, and this is true for proteins also. If you intake more proteins then required, it will be converted to sugar and fats. Excessive intake of dietary protein leads to prostate cancers.12 Additionally, consuming excessive proteins generates more nitrogenous waste product which added extra load for the kidneys. A study on athletes on high protein diet found that the athletes were chronically dehydrated with excessive protein  intake.13

PROTEIN , WEIGHT AND EXERCISE:

Mozaffarian and group in their study on life style, diet changes and long term weight gain in men and women reported that consumption of red and processed meat over the course of time gained more weight-one extra pound every four years as compared to those who ate more nuts gained less weight – about half a pound less every four years.14 One study showed that eating one daily serving of beans, chickpeas, peas, lentils may help in better weight management and weight loss.15 A study at Kent University suggest that protein recommended dietary allowance may actually be 50 to 100 % higher for individuals who exercise on regular basis. Although, a definitive recommendations regarding the optimal protein intake for various athletic groups are not yet possible due to controversial finding between old and new studies, it appears that exercise and individuals attempting to increase muscle mass and strength needs increase protein intake.16

For individuals engaged in sports and exercise regime, a daily dose of around 1g of protein per 1kg of body weight is recommended. Protein is particularly important after exercise since muscles need it to recover and grow. A portion of protein (15-25g) is recommended within 30 minutes of exercise.17 A high protein diet in combination with resistance exercise such as lifting weights, can help build healthy muscles and support weight management. Consuming approximately 20 to 30 grams of high-quality protein at each meal can help you build and maintain muscle.18 Healthy high quality dairy proteins can help preserve muscles and reduce muscle loss during aging. The high quality Dairy foods include milk, flavored milk, cheese, cottage cheese, yogurt and Greek-style yogurt The high-quality protein also found in foods such as dairy foods, eggs, lean beef and pork, skinless poultry, fish and soy can be convenient options to meet the protein needs.18

DIFFERENT PROTEIN SOURCES:

pro-sources

 

  • Eggs: An egg a day- A medium egg has around 6gm of protein. Eggs are the best source of protein since it has  all 20 amino acids in the most digestible form.
  • Milk , cheese and Yogurt: Milk and other dairy foods are packed with protein and  are also good source of calcium.  Chocolate milk is the age-old delicious recovery drink after exercise since it contains energy-replenishing carbohydrates and a blend of both slow and fast release whey and casein proteins. Yogurt, a combination of casein and whey protein is a great source of lactose free protein and hence it can work for people with lactose intolerance.
  • Soya: Soya is a great alternative source of protein for dairy intolerant people. Eating soya protein foods such as tofu and soya-based drinks can help to lower cholesterol and reduce the risk of heart disease.
  • Beans: One-half cup of beans contains as much protein as an ounce of broiled steak. Additionally, these nutritious nuggets are loaded with fiber to keep you feeling full for hours. Pinto beans, black beans, kidney beans, lentils, split peas, or garbanzo beans are all rich source of protein.
  • Fish and seafood: Fish and seafood are good sources of protein and are typically low in fat. Salmon is well known for its heart-healthy omega-3 fatty acids.
  • Pistachio nuts and other nuts: Mostly nuts are rich source of protein. But nuts such as pistachios is a great choice since about 50 pistachio nuts will provide 6gms of protein, plus sodium and potassium, the electrolytes lost in sweat during exercise. Nuts and seeds, including almonds, hazelnuts, mixed nuts, peanuts, peanut butter, sunflower seeds, or walnuts (nuts are also high in fat) are good source of proteins.
  • Pork, Chicken and Turkey: The pork contains high quality protein with branched chain amino acids, which play a significant role in supporting muscle recovery. It is one of the richest source of Leucine, an amino acid particularly helpful in stimulating muscle repair after exercise. Eggs, chicken and lean beef also provide good amounts of leucine. Chicken and turkey are good source of white meat poultry.

 

REFERENCES

  1. http://ghr.nlm.nih.gov/handbook/howgeneswork/protein
  2. https://www.nlm.nih.gov/medlineplus/ency/article/002222.htm
  3. http://www.helpguide.org/articles/healthy-eating/nutrition-for-children-and-teens.htm
  4. Institute of Medicine,Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (Macronutrients). 2005, National Academies Press: Washington, DC.
  5. Food, Nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective.2007,World Cancer Research Fund, American Institute for Cancer Research.: Washington, DC.
    Bernstein, A.M., et al., Major dietary protein sources and risk of coronary heart disease in women.Circulation, 2010.122(9): p. 876-83.
  6. Pan, A., et al., Red meat consumption and mortality: results from 2 prospective cohort studies.Arch Intern Med, 2012.172(7): p. 555-63.
  7. Pan, A., et al., Red meat consumption and risk of type 2 diabetes: 3 cohorts of US adults and an updated meta-analysis.Am J Clin Nutr, 2011. 94(4): p. 1088-96.
  8. Farvid MS, Cho E, Chen WY, Eliassen AH, Willett WC. Adolescent meat intake and breast cancer risk. Int J Cancer, 2015.
  9. >Bonjour, J.P., Protein intake and bone health.Int J Vitam Nutr Res, 2011.81(2-3): p. 134-42.
  10. Kerstetter, J.E., A.M. Kenny, and K.L. Insogna, Dietary protein and skeletal health: a review of recent human research.Curr Opin Lipidol, 2011.22(1): p. 16-20.
  11. Darling, A.L., et al., Dietary protein and bone health: a systematic review and meta-analysis.Am J Clin Nutr, 2009.90(6): p. 1674-92.
  12. http://news.wustl.edu/news/Pages/22443.aspx
  13. http://www.webmd.com/diet/20020422/high-protein-diets-cause-dehydration
  14. Mozaffarian, D., et al., Changes in diet and lifestyle and long-term weight gain in women and men.N Engl J Med, 2011.364(25): p. 2392-404.
  15. Li SS, Kendall CW, de Souza RJ, Jayalath VH, Cozma AI, Ha V, Mirrahimi A, Chiavaroli L, Augustin LS, Blanco Mejia S, Leiter LA, Beyene J, Jenkins DJ, Sievenpiper JL. Dietary pulses, satiety and food intake: a systematic review and meta-analysis of acute feeding trials.Obesity, 2014. Aug;22(8):1773-80.
  16. PW Lemon Protein and exercise: update 1987.– Medicine and Science in Sports and Exercise, 1987
  17. http://www.bbcgoodfood.com/howto/guide/best-sources-protein
  18. Protein and Exercise – National Dairy Council http://www.nationaldairycouncil.org
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