Relevance of Dual Protein in Blood Glucose Maintenance and Satiety

Introduction

Proteins form majority of the structure of muscles and other vital tissues in the body. They are also the building block of hormones, enzymes, and haemoglobin. They can also be utilized as a source of energy, though a secondary one.1 With proper combination of sources, vegetable proteins possess similar benefits as protein derived from animal sources (eggs, milk, meat, fish and poultry).1 The effectiveness of a protein is decided by finding its quality and rate of digestibility. The protein quality refers to the bioavailability of amino acids that it supplies. This is important when determining the nutritional benefits it can provide. While, digestibility refers to how a source of protein is best utilized by the body.1 Protein Digestibility Corrected Amino Acid Score (PDCAAS) has been adopted as the preferred method for determining the protein value in human nutrition.

Types of Protein:

1) Plant or vegetable proteins
They are complex proteins consisting of legume proteins, pulse and cereal.2 Soy is most widely used as vegetable protein source.1
Soy protein isolate (Supro) is derived from soybeans (leguminous)3 that is highly purified soy protein. Isolated soy protein is at least 90% protein by weight. It is the only vegetable food that has all essential amino acids. The quality of soy protein is higher than other plant proteins and comparable to animal protein. According to PDCAAS scale, soy protein is rated with a score of 1.0, the highest possible rating. It also has good digestibility.1,3,4  The protein which is predominantly present in soybean are storage proteins, namely 7S globulin (conglycinin) and 11S globulin (glycinin), which forms 80% of total proteins. Other storage proteins in lesser amount include 2S, 9S, and 15S. Soy protein is also associated with fatty acids, isoflavones, saponins, and phospholipids.52) Milk protein

Two important milk proteins are whey and casein.
Whey protein is a set of globular proteins made up of α- lactoalbumin and β-lactoalbumin. It has composition of well-balanced amino acids along with high-content essential amino acids. It is also composed of bovine serum albumin, immunoglobulins and lactoferrin (enzyme).6-8 Whey protein digests very quickly giving a fast, high and transient release of amino acids.1 It also stimulates rapid protein synthesis but a larger part of it is used as fuel as it is oxidized.1

Casein is a phosphoprotein. Casein at its phosphorylated site binds to calcium forming calcium phosphate–micelle complexes that increases the digestibility of casein.6,8 It is absorbed slowly in the body as casein micelle has an attractive property to form a clot or gel in the stomach which makes it power pack in the supply of nutrients. Casein micelle clot gives a steady release of amino acids in the blood so that protein formation continues for a prolonged period of time.1 Thus, casein results in a greater protein accumulation over a longer period of time.1

Casinate is made up of β-casein, κ-casein, α-S1-casein, α-S2-casein and basic 7S globulin glycinin.9 It is regarded as a slow protein, based on digestion and absorption rates. Caseinate causes prolonged and slow release of amino acid in blood.10

Amino acid profile of different proteins:

Amino acid profile of milk proteins:
On the basis of human amino acid requirements, digestibility, and bioavailability both whey protein and casein are designated as high quality proteins as they incorporate high proportion of essential amino acids. However the difference in physiological effects of both milk proteins is attributed to the difference in their amino acid composition. Whey protein contains relatively higher proportion of the branched chain amino acids (BCAA) like leucine, isoleucine, and valine as compared to casein. The branched chain amino acids and particularly leucine is shown to trigger increase in protein synthesis in type 2 diabetes mellitus. Among other essential amino acids casein contains a high proportion of histidine, methionine, phenylalanine, and valine than whey protein. In addition, casein also has high content of several non-essential amino acids like arginine, glutamic acid, proline, serine, and tyrosine.11
Amino acid profile of soy protein: Soy protein is considered a complete protein as it contains most of the essential amino acids that are present in animal proteins. However, soy proteins contain low levels of methionine/glycine and lysine/arginine ratios as compared to casein.5

Role of protein in blood glucose maintenance
The impact of proteins on the metabolism of glucose depends on the composition of amino acid, kinetics of protein digestion and utilization of amino acids in the gastrointestinal tract.2 It is a well-proven fact that protein stimulates the secretion of insulin, a peptide hormone that is released from the b-cells of the pancreas, which in turn regulates the metabolism of glucose by decreasing the plasma glucose concentration.2,8,12,13

Insulin also potentiates the uptake of amino acids and in the synthesis of muscle protein. Amino acids, especially branched chain amino acids (leucine) and arginine, promotes the secretion of insulin.12

The process through which insulin secretion is stimulated by proteins are:12


 

Role of milk proteins in blood glucose maintenance:
Both the milk proteins, whey and casein stimulate increased insulin secretion that not only have potential to alter glucose uptake by tissue but also control the rise in postprandial blood glucose. Whey protein reduces glucose concentration in blood due to its structure of branched chain amino acids consisting of leucine, isoleucine, valine, lysine, threonine that are potent amino acids in stimulating insulin.11
Whey is more potent than casein in increasing the glucose uptake by tissues and decreasing the concentration of plasma glucose as whey is digested more quickly causing increase in insulin release than casein that are digested slowly.2

Role of Soy protein in blood glucose maintenance:

Soy protein is useful in nondiabetic and diabetic individuals in the control of blood sugar. According to Chang et al., soy diet helps individuals with impaired glucose tolerance and reduced insulin sensitivity.14

Genistein, which is the most abundant isoflavone in soy15 has antidiabetic property with its direct role in pancreatic β-cell proliferation and insulinotropic effect15 with glucose-stimulated insulin secretion. Genistein also has a therapeutic role for managing the complications of diabetes.  It helps to relieve diabetic peripheral painful neuropathy, revert proinflammatory cytokine and restoration of the nerve growth factor (content of the diabetic sciatic nerve).16

Protein and satiety

Satiety or feeling of fullness with protein is greater as compared to carbohydrates and fat.6,18

Milk proteins especially whey proteins are more satiating as compared to other sources of protein. According to Veldhorst et al., whey protein had a greater effect in suppressing hunger than casein or soy.  Whey proteins induce satiety signals that are responsible for short- and long-term food intake regulation. Glycomacropeptide, a peptide that is found in whey protein, induces satiety by causing a release of hormone cholecystokinin which is involved in the control of intake of food.6,7
Soy protein may improve satiety by optimizing gut peptide response and increasing gut transit time. Also soy protein has shown to decrease the levels of peptide ghrelin, which is associated with hunger.19

Thus, diet that is high in protein causes less desire to eat causing increased post-meal and long-term satiety.20 This is achieved by a protein diet through following ways:7
 

References

  1. Hoffman JR, Falvo MJ. Protein—which is best? J Sports Sci Med. 2004;3(3):118-30.
  2. Jahan-Mihan A, Luhovyy BL, Khoury DEl, Anderson GH. Dietary proteins as determinants of metabolic and physiologic functions of the gastrointestinal tract. Nutrients. 2011;3(5):574-603.
  3. Montgomery KS. Soy protein. J Perinat Educ. 2003;12(3):42-45.
  4. Messina M. Soy and health update: evaluation of the clinical and epidemiologic literature. Nutrients. 2016;8(12):E754.
  5. Velasquez MT, Bhathena SJ. Role of dietary soy protein in obesity. Int J Med Sci 2007;4(2):72-82.
  6. Davoodi SH, Shahbazi R, Esmaeili S, Sohrabvandi S, Mohamamd Mortazavian A, Jazayeri S, et al. Health-related aspects of milk proteins. Iran J Pharm Res. 2016;15(3):573-91.
  7. Chung Chun Lam SMS, Moughan PJ. Whey protein and satiety: implications for diet and behaviour. In: Preedy VR, Watson RR, Martin CR, editors. Handbook of behavior, food and nutrition. Vol 1. New York: Springer; 2011. p. 1107-24.
  8. KIM JH, Bode L, Ogra PL. Human milk. In: Wilson CB, Nizet V, Maldonado YA, Remington JS, Klein JO, editors. Remington and Klein’s infectious diseases of the fetus and newborn infant. 8th ed. Philadelphia: Elsevier, Inc; 2016. p. 189-213.
  9. Hsieh CH, Wang TY, Hung CC, Jao CL, Hsieh YL, SX Wu, et al. In silico, in vitro and in vivo analyses of dipeptidyl peptidase IV inhibitory activity and antidiabetic effect of a sodium caseinate hydrolysate. Foof Funct. 2016;7(2):1122-28.
  10. Kanda A, Nakayama K, Sanbongi C, Nagata M, Ikegami S, Itoh H. Effects of whey, caseinate, or milk protein ingestion on muscle protein synthesis after exercise. Nutrients. 2016;8(6):E339.
  11. McGregor RA, Poppitt SD. Milk protein for improved metabolic health: a review of the evidence. Nutr Metab (Lond). 2013;10:46.
  12. Carlson SK. Identifying protein needs in persons with diabetes. In: Powers MA, editor. Handbook of diabetes medical nutrition therapy. 2nd ed. Maryland: An Aspen Publication; 1996. p. 320-34.
  13. Franz MJ. Protein: metabolism and effect on blood glucose levels. Diabetes Educ. 1997;23(6):643-51.
  14. Chang JH, Kim MS, Kim TW, Lee SS. Effects of soybean supplementation on blood glucose, plasma lipid levels, and erythrocyte antioxidant enzyme activity in type 2 diabetes mellitus patients. Nutr Res Pract. 2008;2(3):152-57.
  15. Gilbert ER, Liu D. Anti-diabetic functions of soy isoflavone genistein: mechanisms underlying effects on pancreatic β-cell function. Food Funct. 2013; 4(2): 200–212.
  16. Wang Q, GE X, Tian X, Zhang Y, Zhang J, Zhang P. Soy isoflavone: the multipurpose phytochemical (review). Biomed Rep. 2013;1(5):697-701.
  17. Harland JI, Haffner TA. Systematic review, meta-analysis and regression of randomised controlled trials reporting an association between an intake of circa 25 g soya protein per day and blood cholesterol. Atherosclerosis. 2008;200(1):13-27.
  18. Veldhorst MAB, Nieuwenhuizen AG, Hochstenbach-Waelen A, van Vught AJAH, Westerterp KR, Engelen MPKJ, et al. Dose-dependent satiating effect of whey relative to casein or soy. Physiol Behav. 2009;96(4):675-82.
  19. Nutraceuticals World [Internet]. USA: NW; c 2017 [updated 2008 Jan 12; cited 2017 Oct 26]. ISO Soy Protein Promotes Satiety; [about 16 screens]. Available from: https://www.nutraceuticalsworld.com/issues/2008-12/view_supplier-research/iso-soy-protein-promotes-satiety/.
  20. Leidy HJ, Carnell NS, Mattes RD, Campbell WW. Higher protein intake preserves lean mass and satiety with weight loss in pre-obese and obese women. Obesity (Sliver Spring). 2017;15(2):421-29.
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