Soyabeans have a beneficial fatty acid composition. They are low in saturated fat and contain mostly polyunsaturated fatty acids in particular the essential fatty acids, linoleic acid (omega-6) and alpha-linolenic acid (omega-3).
Because extensive research has shown that soya protein can lower blood cholesterol levels, the American FDA (Food and Drug Administration, USA, 1999) and the JHCI (Joint Health Claim Initiative, UK, 2002) have approved following health claim: “ the inclusion of at least 25g of soya protein per day, as part of a diet low in saturated fat, can help reduce blood cholesterol levels ”.
The complete mechanism for this plasma cholesterol reduction isn’t yet clear. Evidence indicates that soya protein is responsible for this beneficial effect. Research has indicated that the soya protein can increase LDL-receptor activity (1,2).
Soya protein contains small subunits and recent evidence has shown that these soya subunits might have a substantial role in the cholesterol-lowering effects of soya protein (3,4). After ingestion, soya proteins are hydrolyzed in the intestine and small peptides, containing 4 to 6 amino acids, are absorbed into the portal circulation. In vitro findings indicate that these peptides increase LDL-receptor activity in the liver, responsible for the cholesterol-lowering effect of soya protein (3).
While a meta-analysis of clinical studies published prior to 1995 (5) suggested that soy protein consumption may decrease serum LDL-cholesterol values by 13%, more recent studies (6) using currently available soy products indicate that soy protein intake is likely to reduce serum LDL-cholesterol values by 6-7%. The reductions seem to be more efficient when the intake is spread throughout the day. Reduction is fasting serum triglycerides of about 10% and increases in HDL-cholesterol of about 3% also can be expected with soyfood intake. In 2007 a review re-evaluated 33 studies published in the last 10 years and concluded that the cholesterol-lowering effect of soy products was in line with the results of Anderson from 1995. The more recent studies have been performed in patients with modest hypercholesterolaemia (severe hypercholesterolemic patients are treated with statins) resulting in less pronounced cholesterollowering effects but in line with previous findings (7).
Furthermore a new meta-analysis (2008) of randomised controlled trials that evaluate the effect of soy protein consumption on blood cholesterol confirmed that modest intakes of soy protein have beneficial effects on blood lipids. This meta-analysis (8), unlike previous analyses, has focused on studies where the intake of soy protein or soyfoods was practically achievable (15 to 40g soy protein per day), with an average intake of 26.9g. An approximate reduction in LDL of 6% was found which is an equivalent to a reduction in risk in coronary heart disease of around 12-15%. In addition a regression analysis was carried out to determine if there was a dose response relationship between soya intake and the extent to which LDL cholesterol was reduced. From this analysis no association between soya protein intake and the extent of LDL reduction was reported, indicating that an intake of 15g soya protein is just as effective as 40g in reducing LDL. This is very important for the consumers as it demonstrates that to achieve a beneficial reduction in LDL cholesterol it is not necessary to target an intake of 25g every day and lower intakes, particularly if sustained over a period of time, can be effective in blood lipid modification (8).
Other benefits:
Soya is rich in unsaturated fatty acids and low in saturated fatty acids. Soya oil contains 62% PUFA’s (poly-unsaturated fatty acids), of which 54% linoleic acid (an omega-6 fatty acid) and 8% alpha-linolenic acid (an omega-3 fatty acid), two essential fatty acids.
PUFA’s exert a beneficial effect on blood lipids. Polyunsaturated fatty acids have a lowering effect on the triglyceride level. In addition, a diet rich in alfa-linolenic acid reduces platelet aggregation which reduces the risk of thrombogenesis.
Health Claim :
Research indicates that the consumption of high quality soya protein rich in amounts of 10 grams twice daily can deliver significant effects on serum lipoproteins. The combined use of soya protein, soluble fiber and plant sterols can decrease serum LDL-cholesterol values by 25-30%, equivalent to the effect of a “statin” drug (3,9).
In October 1999, the American Food and Drug administration (FDA) has decided to approve a health claim linking consumption of soya protein with a reduced risk of heart disease. They recommend a daily intake of 25 gram (eg. divided over 4 intakes).
In July 2002 the Joint Health Claim Initiative (JHCI) in UK has also approved this cholesterol lowering health claim for soya “the inclusion of at least 25g of soya protein per day, as part of a diet low in saturated fat, can help reduce blood cholesterol levels ”.
To learn more about those two health claims, please choose the following links :
American Food and Drug Administration health claim
Joint Health Claim Initiative health claim
References
- Lovati MR, Manzoni C, Canavesi A et al. Soyabean protein diet increases low density lipoprotein receptor activity in mononuclear cells from hypercholesterolemic patients. J Clin Invest 1987; 80; 1498-502
- Baum JA, Teng H, Erdman JW et al. Long-term intake of soya protein improves blood lipid profiles and increases mononuclear cell low-density lipoprotein receptor messenger RNA in hypercholesterolemic, postmenopausal women. Am J Clin Nutr 1998; 68: 545-51
- Anderson JW. Diet first, then medication for hypercholesterolemia. J Amer Med Assoc 2003; 290: 531-3.
- Lovati MR, Manzoni C, Gianazza E et al. Soya protein peptides regulate cholesterol homeostasis in Hep G2 cells. J Nutr 2000;130: 2543-9.
- Anderson JW, Johnstone BM, Cook-Newell ME. Meta-analysis of the effects of soy protein intake on serum lipids. N Engl J Med 1995;333:276-82.
- Taku K, Umegaki K, Sato Y, Taki Y, Endoh K, Watanabe S. Soy isoflavones lower serum total and LDL cholesterol in humans: a meta-analysis of 11 randomized controlled trials. Am J Clin Nutr 2007;85:1148-56.
- Sirtori CR, Eberini I, Arnoldi A. Hypocholesterolaemic effects of soya proteins: results of recent studies are predictable from the anderson meta-analysis data. Br J Nutr 2007;97:816-22.
- Harland JI, Haffner TA. Systematic review, meta-analysis and regression of randomised controlled trials reporting an association between an intake of circa 25g soya protein per day and blood cholesterol. Atherosclerosis 2008:04:006.
- Jenkins DJA, Kendall CWC, Marchie A et al. Effects of a dietary portfolio of cholesterol-lowering foods versus lovastatin ons serum lipids and C-reactive protein. J Amer Med Assoc 2003; 290: 502-10.