Proteins in boiled and fried eggs may reduce blood pressure and potentially reduce the risk of cardiovascular disease, suggests new research from Canada.

Traditional views on eggs, and particularly their cholesterol content, has led to some recommendations to avoid eggs in order to boost heart health, but new research published in the Journal of Agricultural and Food Chemistry, suggests that proteins from eggs may benefit cardiovascular health.

According to findings by Jianping Wu and Kaustav Majumder, proteins in fried and boiled eggs can be converted by enzymes in the stomach and small intestine to produce peptides with angiotensin converting enzyme (ACE)-inhibitory activity.

ACE inhibitors work by inhibiting the conversion of angiotensin I to the potent vasoconstrictor, angiotensin II, thereby improving blood flow and blood pressure.

“Our results showed that in vitro digestion of cooked eggs could generate a number of potent ACE inhibitory peptides which may have implications for cardiovascular disease prevention, including hypertension,” wrote the researchers from the University of Alberta.

High blood pressure (hypertension),defined as having a systolic and diastolic blood pressure (BP) greater than 140 and 90 mmHg, is a major risk factor for cardiovascular disease (CVD) - a disease that causes almost 50 per cent of deaths in Europe, and reported to cost the EU economy an estimated €169bn ($202bn) per year.

“Findings from this study provided further evidence that eggs are an excellent source of health-promoting food,” added Majumder and Wu.

The effects are specific to the proteins in the eggs, and the effect of the fat and oil content of fried eggs was not considered.

Study details

The Edmonton-based researchers used a model system of the stomach and small intestine to simulate human gut conditions. Fried and boiled eggs were passed through the model gut and the peptide products measured.

Protein from fried egg showed greater ACE-inhibition than proteins from boiled egg, said the researchers. This disparity could have been due to differences in cooking temperatures (170 versus 100 degrees Celsius for fried and boiled respectively), or from a difference in heating rate – fried eggs have a “nearly identical thermal treatment”, said Majumder and Wu, while the boiling process produces a gradient from the shell inwards to the core of the egg.

“The core of the egg where the yolk proteins or the white protein part close to the yolk may have not been extensively denatured, result[ing] in a lower digestibility and weaker ACE inhibitory activity of boiled egg samples,” they added.

The results also should that the proteins would be absorbed by the body, allowing the in vivo antihypertensive activity to occur. However, Majumder and Wu stressed that an in vivo study would be needed to confirm this assumption.

The study was funded by the Alberta Livestock Industry Development Fund (ALIDF) and the Poultry Research Centre.

Debunking the cholesterol ‘myth’

British researchers reported recently that concerns over egg consumption and cholesterol increases are unfounded, after reviewing up-to-date evidence.

Writing in Nutrition Bulletin (March 2009, Vol. 34, pp. 66-70), Professor Bruce Griffin from the University of Surrey said that the link between eggs consumption and raised cholesterol levels (hypercholesterolaemia), which ultimately could lead to cardiovascular disease, was based on out-of-date information.

“It is high time that we dispelled the mythology surrounding eggs and heart disease and restored them to their rightful place on our menus where they can make a valuable contribution to healthy balanced diets,” concluded the Surrey researchers.

加拿大一個(gè)新的研究提出,煮雞蛋和煎雞蛋中的蛋白質(zhì)可能能夠降低血壓，以及還可能具有降低心血管疾病風(fēng)險(xiǎn)的潛能。

關(guān)于雞蛋的傳統(tǒng)觀點(diǎn)，尤其是針對(duì)它所含的膽固醇，引出了一些建議：避免進(jìn)食雞蛋以促進(jìn)心臟健康。但是在《農(nóng)業(yè)與食品化學(xué)雜志》上刊登的新研究提出，雞蛋的蛋白質(zhì)可能有利于心血管的健康。

Jianping Wu 和 Kaustav Majumder 的研究發(fā)現(xiàn)，在煎雞蛋和煮雞蛋中的蛋白質(zhì)可被胃部和小腸中的酶催化轉(zhuǎn)換，產(chǎn)生具有抑制血管緊張素轉(zhuǎn)換酶(ACE)活性能力的多肽。ACE抑制劑的作用是通過抑制血管緊張素Ⅰ轉(zhuǎn)換為有效的血管收縮劑（血管緊張素Ⅱ），從而改善血液循環(huán)和血壓。阿爾伯大學(xué)的研究人員寫到：“研究結(jié)果顯示，熟雞蛋在體外降解的實(shí)驗(yàn)中產(chǎn)生了許多有效的ACE抑制肽，這些多肽可能具有防止心血管疾病包括高血壓的作用。”

當(dāng)收縮壓大于140mm汞柱，舒張壓大于90mm汞柱時(shí)，就被界定為高血壓。高血壓是心血管疾病的最大風(fēng)險(xiǎn)因素。在歐洲，高血壓導(dǎo)致了每年近乎50%的死亡。有報(bào)告顯示，歐盟每年的經(jīng)濟(jì)大約有1690億歐元被投入到對(duì)高血壓的治療中。

Kaustav Majumder和Jianping Wu 補(bǔ)充：“這個(gè)研究的發(fā)現(xiàn)提供了更多的證據(jù)，表明雞蛋是一種促健康食品的優(yōu)質(zhì)來源。”

以上所提到的促進(jìn)心血管健康的作用僅限于針對(duì)雞蛋中的蛋白質(zhì)，而煎雞蛋中的脂肪和油脂成分的作用不在考慮范圍中。

研究詳情

埃蒙頓基地的研究員運(yùn)用胃部和小腸模型來模擬人類腸道狀況，使煎雞蛋和煮雞蛋被穿過該模擬腸道，測(cè)定消化過程產(chǎn)生的肽。

據(jù)研究員說，煎雞蛋中的蛋白質(zhì)比煮雞蛋中的蛋白質(zhì)具有更強(qiáng)的ACE抑制劑。兩者在這方面的差異可能源于烹煮溫度的不同：煎雞蛋時(shí)溫度達(dá)到170℃而煮雞蛋為100℃。另一種原因推斷認(rèn)為，可能是由于加熱速率的差異。據(jù)Majumder和Jianping Wu說，煎雞蛋經(jīng)過接近完全的熱處理，而在煮雞蛋時(shí)產(chǎn)生了從蛋殼到蛋黃的溫度梯度。他們補(bǔ)充：“煮雞蛋的蛋黃或者接近卵黃的白蛋白可能沒有完全變性，導(dǎo)致煮雞蛋樣本較低的消化率和ACE抑制劑的較低活性。”Jianping Wu強(qiáng)調(diào)，需要進(jìn)一步進(jìn)行活體實(shí)驗(yàn)來證明這個(gè)假設(shè)。

雞蛋蛋白可以降低血壓這一課題的研究是由阿爾伯塔省畜牧業(yè)發(fā)展基金（ALIDF）和家禽研究中心贊助經(jīng)費(fèi)。

揭開膽固醇“謬論”

英國研究人員最近報(bào)告說，最新的證據(jù)顯示，沒有發(fā)現(xiàn)人們對(duì)吃雞蛋和膽固醇水平升高存在憂慮。英國薩里大學(xué)的Bruce Griffin教授在《營養(yǎng)學(xué)通報(bào)》（2009年第34期，66～77頁）中寫到吃雞蛋和膽固醇水平升高有關(guān)聯(lián)并且最終可能導(dǎo)致心血管疾病發(fā)生的說法，是基于過時(shí)的資料提出的。薩里大學(xué)的研究人員總結(jié)到：“我們必須消除環(huán)繞著雞蛋和心臟疾病的迷霧，讓雞蛋重回到我們的食譜當(dāng)中，為人們健康均衡的飲食作出有價(jià)值的貢獻(xiàn)。”