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Soy as a Solution: Heart Disease and Reducing Cholesterol Levels

Tinsae Demissie

 

 

Heart Disease: The Threat

Chronic illnesses progress over a lifetime and require life-style changes and continual treatment that may persist for a lifetime. Heart disease is on of these illnesses. Heart disease has become a substantially increasing problem for the world, and a major threat for Americans. As the leading cause of death in the United States, heart disease accounts for over 30% of all deaths and is a major contributor to disability (http://www.cdc.gov/heartdisease/).

Age-adjusted death rate

Ratio

Hispanic/2

to

Percent of

Percent non-

 

Rank/1 Cause of death (based on the International Classification of Diseases, Tenth Revision, 1992)

Number

total deaths 2004 crude death rate

2004

change from 2003 to 2004 Male to female Black to white Hispanic white

... All causes

2,397,615

100.0 816.5

800.8

-3.8 1.4 1.3 0.7

1 Diseases of heart (I00-I09,I11,I13,I20-I51)

652,486

27.2 222.2

217.0

-6.6 1.5 1.3 0.7

2 Malignant neoplasms (C00-C97)

553,888

23.1 188.6

185.8

-2.3 1.4 1.2 0.6

3 Cerebrovascular diseases (I60-I69)

150,074

6.3 51.1

50.0

-6.5 1.0 1.5 0.8

4 Chronic lower respiratory diseases (J40-J47)

121,987

5.1 41.5

41.1

-5.1 1.4 0.7 0.4

5 Accidents (unintentional injuries) (V01-X59,Y85-Y86)

112,012

4.7 38.1

37.7

1.1 2.1 0.9 0.8

6 Diabetes mellitus (E10-E14)

73,138

3.1 24.9

24.5

-3.2 1.3 2.2 1.5

7 Alzheimer's disease (G30)

65,965

2.8 22.5

21.8

1.9 0.7 0.8 0.6

8 Influenza and pneumonia (J10-J18)

59,664

2.5 20.3

19.8

-10.0 1.4 1.1 0.9

9 Nephritis, nephrotic syndrome and nephrosis (N00-N07,N17-N19,N25-N27)

42,480

1.8 14.5

14.2

-1.4 1.4 2.3 0.9

10 Septicemia (A40-A41)

33,373

1.4 11.4

11.2

-3.4 1.2 2.2 0.8

11 Intentional self-harm (suicide) (*U03,X60-X84,Y87.0)

32,439

1.4 11.0

10.9

0.9 4.0 0.4 0.5

12 Chronic liver disease and cirrhosis (K70,K73-K74)

27,013

1.1 9.2

9.0

-3.2 2.2 0.9 1.6

13 Essential (primary) hypertension and hypertensive renal disease (I10,I12)

23,076

1.0 7.9

7.7

4.1 1.0 2.8 1.0

14 Parkinson's disease (G20-G21)

17,989

0.8 6.1

6.1

-1.6 2.3 0.4 0.6

15 Assault (homicide) (*U01-*U02,X85-Y09,Y87.1)

17,357

0.7 5.9

5.9

-1.7 3.7 5.6 2.7

... All other causes (residual)

414,674

17.3 141.2

...

 

 

Heart disease is a term that applies to a number of abnormal conditions affecting the heart and the blood vessels of the heart, mostly resulting in the compromise of blood flow to the heart.Coronary Heart Disease, known commonly as CHD, is the most common type of heart disease (http://www.cdc.gov/heartdisease/). CHD occurs when the coronary arteries, those which supply blood to the heart muscle, become hardened and narrowed due to plaque (a mixture of fatty substances including cholesterol and other lipids) that builds up along the walls of the arteries over time.

Because cholesterol can’t dissolve in the blood, it has to be transported to cells by lipoproteins that serve as carriers (http://www.lycos.com/info/cholesterol--blood.html). There are two types of lipoproteins. Low-density lipoprotein, or LDL, is known as “bad” cholesterol while High-density lipoprotein, or HDL, is known as “good” cholesterol. LDL is known as bad cholesterol because it can also build up along the walls of the blood vessels over time. The People with heart disease tend to have high levels of LDL and low levels of HDL. Plaque buildup and the narrowing and hardening of the arteries is called atherosclerosis (http://www.herbal-supplements-guide.com/correcting-low-hdl-and-high-ldl.html). As a consequence of this build up of plaque the flow of blood and oxygen to the heart becomes greatly reduced and eventually, without intervention, completely blocked. With decreased blood flow many people suffer angina which is manifested through sharp chest pain and discomfort because the heart muscles are not receiving enough blood (http://www.health-alliance.com/learnabout/learn_disease.htm). When the arteries become blocked CHD usually leads to heart attack.

 

Preventing Heart Disease; The Claim:

The key to reducing the risk of heart disease seems to lie in reducing ones levels of LDL (bad cholesterol) and increasing levels of HDL (good cholesterol). Aggressive means to improve high cholesterol is usually diet therapy coupled with medication. But anyone can monitor their cholesterol levels by making informed dietary choices. One of the primary ways LDL cholesterol levels can become too high in blood is through eating too much of two nutrients: saturated fat and cholesterol. Saturated fats and cholesterol are found mostly in animal products. For many Americans, animal products were a good source of protein the diet. Vegetarians and “health nuts” have known for years that foods rich in soy protein offer a good alternative to meat, poultry, and other animal-based products. The term soy is used to refer to derived from the soybean.  Unlike other beans, soybeans contain all the amino acids essential to human nutrition. Soy protein products can replace animal-based foods which also have complete proteins but tend to contain more fat, especially saturated fat. Soy foods have been consumed as part of the diet as source of high-quality protein throughout Asia and in other parts of the world for centuries. (http://www.soyfacts.com.au/what/intro.html)                                                                                                                           

However the roar came 1999 when the FDA approved the labeling of foods with 25 grams or more of soy protein as being protective against heart disease.  The FDA based their claim on epidemiological and animal studies that seemed to indicate that diets low in animal protein and high in soy protein showed significant decreased levels of LDL (bad cholesterol), overall cholesterol levels, and triglycerides. (http://www.soyfacts.com.au/heart/claim.html)  

Echoing this claim, in 2000 the American Heart Association released a statement in which they recommend incorporating food containing soy protein in a diet low in saturated fat and cholesterol. Following these FDA’s stamp of approval, the soy market gained great momentum and many soy products claiming to prevent heart disease appeared on the market. (

 

 

How is this Possible? : The suggested Mechanisms:

While the exact mechanism by which soy protein reduces LDL levels is still unclear to scientist, there have been postulations at a possible mechanism. It has been noted that soy protein is richer in L-arginine (a protein amino acid) than animal protein, which is richer in L-lysine. Some animal studies have indicated that a dietary increase in L-arginine is accompanied by a decrease in cholesterol levels. Other studies have also demonstrated that under some conditions like hypercholesterolemia high intakes of L-arginine could enhance endothelial-dependent vasodilation thus contributing to the ability of soy protein to combat plaque and LDL buildup

 

 

The soy isoflavones may also contribute to the lipid-lowering activity of soy protein . Soy isoflavones are phytoestrogens found in soybeans. Phytoestrogens are plant-derived nonsteroidal compounds that possess estrogen-like biological activity and possibly some antioxidant activity. Oral estrogens have been shown to decrease total cholesterol and LDL-cholesterol. The soy isoflavones may have similar actions. BUT, it is important to note that some studies have shown that soy isoflavones themselves do not have the same cholesterol-reducing activity as the combination of soy protein and soy isoflavones. There seem to be accompanying effects of these substances that are not understood at this time. Antioxidant activity may also contribute to the possible anti-atherogenic effect of soy protein. (http://www.pdrhealth.com/drug_info/nmdrugprofiles/nutsupdrugs/soy_0325.shtml)

 

 

How Valid Are These Claims? A meta-analysis of clinical studies of Soy Protein and Isoflavones:

Kenneth Carroll reviewed a number of studies, initially breaking off these studies into two categories; studies done on 1) normocholesterolemic subjects (those with normal levels of cholesterol and 2) hypercholesterolemic subjects (those already hiving high levels of cholesterol). Carroll reviewed 5 studies done on normocholesterolemic individuals. Of the five studies all but one concluded that there was little to no difference between the cholesterol levels of individuals who replaced animal proteins in their diet with soy protein isolate.  In one of the five studies reviewed on normocholesterolemic subjects, Miyazima et al [15] reported plasma cholesterol levels that were 10% to 12% lower in a soy-protein diet than with a control diet of animal protein. On average, based on the review by Carroll it seems that a soy-protein diet in place of animal protein does not significantly reduce bad cholesterol in the blood. When reviewing studies done on hypercholesterolemic subjects, there was a significant difference. Most of the studies revealed a significant decrease in LDL levels when soy protein replaced animal protein in the diet, with an average decrease between 10 and 16% with a few studies showing decreases as much as 20% to 30%.  One study in particular pointed out that the magnitude of the response tends to inversely correlated with the degree of hypercholesterolemia.  There were however a few studies in which it was concluded that there was no significant difference between the soy-protein diet and the control. For these studies, Carroll provided possible explanations for the gap in results. One possibility is that differences in level of dietary protein may help to explain the variability in results. Relatively little effect on plasma cholesterol was observed with 10% animal protein in combination with soy protein.  Carroll also evaluated the form of soy protein preparation. soybean protein preparations ranging from isolates containing more than 90% protein to textured preparations of dilapidated soy flour containing just over 50% protein were used in the trials. Isolated soy protein was often used by workers who reported little or no response. Another possible reason for the variable results obtained in human dietary experiments is that they may be influenced by interactions with other dietary components.

In conclusion studies reveal that substituting soy protein for animal protein in the diet can lower blood levels of total cholesterol and bad cholesterol (LDL) in individuals with high cholesterol but it has little to no effect in those with normal cholesterol levels. Diets high in protein and low in fat have been able to reduce blood cholesterol by 20 percent or more.

Possible Side Effects:

The claims made for soy protein give the impression that its undoubtedly beneficial. Is it? Or are there any possible side-effects? It is prudent to investigate both the positive and negative claims about soy protein and weighing both before a solid conclusion can be made.  Many advertisers and proponents of soy protein claim that for individuals who are not allergic to soy, no serious short-term or long-term side effects have been reported from eating soy foods. However, many have also researched the long term negative side-effects of soy protein and published their findings. For example some claim that soybeans contain moderate amounts of a natural substance called purine and that purine can make gout worse and thus people with gout should consume soy products. (cite here). Others also claim that phytoestrogens have been found to have adverse effects on various human tissues, some also claim that soy protein contains phytates which block the body's uptake of minerals and oxalate which contributes to kidney stones. (http://bodybuilding.com/fun/author25.htm).

 

Studies on the negative effects of Soy:

In 2005, a study was conducted at Washington University to investigate the possibility that consuming soy products increased the formation of kidney stones. Oxalate is a component of kidney stones. This study concluded that although some soy foods contain large concentrations of oxalate and phytate but not enough to be detrimental to health. The study reviewed thirty commercial soy products which contained from 2 to 58 mg of oxalate and 76 to 528 mg of phytate per serving.  There was no significant formation of stones in the kidney noted from consumption of these products. Aside from this study, there have been very few studies to evaluate the claims of adverse health outcomes as a result of soy and the few studies that do exist have proved inconclusive.

 

Conclusion:

In conclusion, there seems to be a positive correlation between soy protein substitution for animal proteins and levels of bad cholesterol that contribute to heart disease. My research shows however, that this correlation seems to only be present in individuals who already have high levels of cholesterol.  There seems to be no body of research proving soy to be detrimental to health as some claim, but there still much research needing to done before we can rule out the possibility. As of now, the benefits of sot products seem to outweigh and possibility of negative consequences for those suffering from high levels of cholesterol.

 

 

 

 

References:

1)    Al-Wahsh, Ismail (2005) Soy oxalate and phytate and risk of kidney stones. Ph.D. dissertation, Washington State University, United States -- Washington. Retrieved September 24, 2007, from ProQuest Digital Dissertations database. (Publication No. AAT 3204135).

2)    Carroll, Kenneth K (1991). Review of Clinical Studies on Cholesterol-Lowering Response to Soy Protein. American Dietetic Association. Journal of the American Dietetic Association, 91(7), 820.  Retrieved September 24, 2007, from Health Module database. (Document ID: 2727139).

3)    Kristi Reynolds,  Ashley Chin,  Karen A Lees,  Aline Nguyen,  et al. (2006). A Meta-Analysis of the Effect of Soy Protein Supplementation on Serum Lipids. The American Journal of Cardiology, 98(5), 633-640.  Retrieved September 24, 2007, from Health Module database. (Document ID: 1155019991).

 

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