Pea protein is extracted commonly from the yellow garden pea (Pisum sativum), which contain fleshy greenish seeds (Pisiva®). Consumption of peas in their natural state does not necessarily produce the same health benefits as the protein isolate because potentially bioactive compounds or proteins are present in an inactive state in natural pea produce.
Such compounds are activated by the use of enzymatic digestion. One principal and desirable effect of pea protein is the presence of compounds that act as ACE inhibitors. Inhibition may occur in the conversion of angiotensin I to the potent vasoconstrictor, angiotensin II with resultant improvement of blood flow and lowering of blood pressure. Hill Pharma, Inc. is the supplier of Pisiva® a high quality pea protein concentrate.
Pea Protein Supports the Lowering of Blood Pressure in Humans and Experimental Animals
Researchers at the University of Manitoba (Canada) have studied the effects of pea protein hydrolysate in hypertensive rats and humans and demonstrated a blood pressure lowering effect (Li H, Prairie N, Udenigwe CC, et al, Journal of Agricultural and Food Chemistry, pre-published online, doi 10.1021/jf201911p). These investigators used rats that are genetically predisposed to hypertension (spontaneously hypertensive rats) and administered 100 and 200 mg per kg of weight of pea protein. A maximum reduction of 19 mmHg in systolic blood pressure was noted four hours after consuming pea hydrolysate. Pea protein in its natural state (non-hydrolysed) had no significant effect on blood pressure.
In the experimental animals, the administration of pea protein isolate was associated with lower levels of angiotensin II and an approximate 50% reduction in renin, mRNA levels. It was concluded that control of the output of renin by the kidneys, as a consequence of pea protein hydrolysate administration, resulted in lower levels of angiotensin II (a 45% reduction) by alteration of the renin-angiotensin system.
Smaller reductions in blood pressure were noted in the human studies of pea protein isolate. In the human arm of the studies (Li H, et al, ibid), seven volunteers (age range 30-55 years, systolic blood pressure range 125-170 mmHg) had modest reductions in blood pressure as a consequence of the administration of 1.5 or 3.0g of pea protein hydrolysate over a three week period.
Other Properties of Pea Protein
Studies in vitro (SIMPHYD) and in vivo show that pea protein is effective at inducing satiety with equivalence to whey protein (Ruijschop R, www.nizo.com/explore/cases, 2013, accessed Dec. 6, 2013). In vitro experiments reveal that pea protein agglomerates at its isoelectric point but does not engage in “network formation” like casein. The speed of digestion of pea protein is intermediate between casein (a slow protein) and whey (a fast protein). Measurement of patterns of gut hormone responses showed only small differences between the administration of pea and whey protein meals, implying no major differences in a propensity to cause weight gain by hormonal changes.
Dietary proteins exert influences on lipid metabolism in humans and animals. For example, soy protein has both hypocholesterolemic and hypotriglyceridemic that surpass the actions of casein (Spielman GI et al, Journal of Animal Physiology and Animal Nutrition, 92, 683-93, 2008). Other plant proteins can reduce concentrations of cholesterol and triacylglycerols in rats, e.g. lupin derived protein (Sirtori et al, Journal of Nutrition, 134, 18-23, 2004).
Pea protein is derived from legumes, which includes soybeans and lupins. This origin determines a relatively similar content of amino acids with a relatively low content of methionine and a high concentration of arginine. Furthermore, the ratio of arginine to lysine is much higher in leguminous protein than found in casein. This ratio of arginine to lysine has been proposed as a significant factor in the hypocholesterolemic effect of soy and lupin protein (Spielman GI et al ibid).
Studies in pigs using whole peas in their natural state (P. sativum), show increased levels of very low density lipoproteins (VLDL) and low density lipoproteins. These findings were associated with an increased excretion of fecal steroids (Kingman et al, British Journal of Nutrition, 69, 409-21, 1993). In a separate study, whole raw peas fed to pigs who were on a high cholesterol diet caused lowering of blood cholesterol, LDL, and cholesterol levels in the liver. The complex composition of whole peas (starch, polysaccharides, and plant sterols) makes the individual effects of the different ingredients of whole peas on lipid metabolism unclear.
Spielman GI et al (ibid) have examined the effects of pure pea protein isolate in rats. Rats fed the purified pea protein diet had both a lower concentration of total cholesterol in the liver and VLDL than control animals fed a casein-rich diet. Further findings in this study included the ability of pea protein to stimulate the formation and excretion of bile acids in the liver, thereby reducing hepatic cholesterol concentration and reducing the secretion of cholesterol by actions on VLDL.
Studies of sterol regulating element-binding protein (SREBP)-2 and its target genes 3-hydroxy-3-methylglutary coenzyme A reductase (HMG-CoA) and LDL receptors in the liver revealed an increase in rats fed pea protein. These data suggest that gene expression of SREBP-2 and its target genes HMG-CoA and LDL receptors are a mechanism whereby compensation occurs for an increased loss of cholesterol that is used for bile acid synthesis (Spielman et al, ibid).
Studies at the University of Toronto (Canada) have examined the effects of intact and hydrolyzed pea protein on food intake, glycemic response, and subjective appetite in healthy male volunteers (Luhovyy B, www.clinicaltrials.gov/show/NCT 01298154, accessed Dec. 6, 2013). In brief, it has been found that increasing pea protein leads to decreased pre-meal blood glucose response and reduction of food intake. Further research is recommended to define the effects of intact and hydrolysed pea protein on glycemic responses and appetite in both pre and post-meal circumstances. In addition, the differences between intact and hydrolysed pea protein requires detailed comparisons to be undertaken with other plant proteins, where outcomes have been better defined. Furthermore, recent studies in animals (rats) on a high cholesterol diet showed reductions of blood cholesterol after the administration combinations of pea protein with oat fiber or apple pectin (soluble fiber) (Parolini S, et al, British Journal of Nutrition, online print, doi 10.1017/50007114513000639). It is apparent that these rats showed better control of blood cholesterol with the combination of pea protein with oat fiber or apple pectin compared with circumstances that result from the individual administration of pea protein or soluble fiber.
Pea protein has been found to have a potential role in reducing blood pressure and improving kidney function (Aluko R, 239th National Meeting of the American Chemical Society). Auko R et al (ibid) fed small doses of hydrolysed pea protein to rats with polycystic kidney disease and showed a 20% reduction in blood pressure and improvements in renal function with a 30% increase in urine production. The mechanism of this beneficial action on renal function and blood pressure control may be related to the boosting of the production of cyclooxygenase-1 (COX-1), which could promote renal function.
Benefits and Safety of Pea Protein
It is clear that pea protein has major promise for the nutritional support of healthy blood pressure, lipid metabolism, and renal function. Pea protein is gluten free, hypoallergenic, and well tolerated, without gastrointestinal side effects. Elegant studies of pea protein isolate show that it is not genotoxic (Aouatif, C, et al, Hindawi Publishing Corporation, ISRN Toxicology, vol. 2013, Article ID 817353, DOI 10.115/2013/817353).
Genotoxicity testing of pea protein in bacterial reverse mutation tests, chromosome alteration tests, and micronucleus testing were all negative (Aouatif, C, ibid).
Pea protein has a propensity to cause a build-up of uric acid. Therefore, it has the potential to cause gout (a painful inflammatory condition in joints due to the build-up of uric acid). Individuals taking several protein supplements are potentially at risk of this disorder and it is very important to maintain adequate hydration to help avoid these side effects. With high dosages of plant proteins, calcium intake should be optimal to avoid calcium loss from bones, which may lead to osteoporosis.