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.

加拿大一个新的研究提出,煮鸡蛋和煎鸡蛋中的蛋白质可能能够降低血压，以及还可能具有降低心血管疾病风险的潜能。

关于鸡蛋的传统观点，尤其是针对它所含的胆固醇，引出了一些建议：避免进食鸡蛋以促进心脏健康。但是在《农业与食品化学杂志》上刊登的新研究提出，鸡蛋的蛋白质可能有利于心血管的健康。

Jianping Wu 和 Kaustav Majumder 的研究发现，在煎鸡蛋和煮鸡蛋中的蛋白质可被胃部和小肠中的酶催化转换，产生具有抑制血管紧张素转换酶(ACE)活性能力的多肽。ACE抑制剂的作用是通过抑制血管紧张素Ⅰ转换为有效的血管收缩剂（血管紧张素Ⅱ），从而改善血液循环和血压。阿尔伯大学的研究人员写到：“研究结果显示，熟鸡蛋在体外降解的实验中产生了许多有效的ACE抑制肽，这些多肽可能具有防止心血管疾病包括高血压的作用。”

当收缩压大于140mm汞柱，舒张压大于90mm汞柱时，就被界定为高血压。高血压是心血管疾病的最大风险因素。在欧洲，高血压导致了每年近乎50%的死亡。有报告显示，欧盟每年的经济大约有1690亿欧元被投入到对高血压的治疗中。

Kaustav Majumder和Jianping Wu 补充：“这个研究的发现提供了更多的证据，表明鸡蛋是一种促健康食品的优质来源。”

以上所提到的促进心血管健康的作用仅限于针对鸡蛋中的蛋白质，而煎鸡蛋中的脂肪和油脂成分的作用不在考虑范围中。

研究详情

埃蒙顿基地的研究员运用胃部和小肠模型来模拟人类肠道状况，使煎鸡蛋和煮鸡蛋被穿过该模拟肠道，测定消化过程产生的肽。

据研究员说，煎鸡蛋中的蛋白质比煮鸡蛋中的蛋白质具有更强的ACE抑制剂。两者在这方面的差异可能源于烹煮温度的不同：煎鸡蛋时温度达到170℃而煮鸡蛋为100℃。另一种原因推断认为，可能是由于加热速率的差异。据Majumder和Jianping Wu说，煎鸡蛋经过接近完全的热处理，而在煮鸡蛋时产生了从蛋壳到蛋黄的温度梯度。他们补充：“煮鸡蛋的蛋黄或者接近卵黄的白蛋白可能没有完全变性，导致煮鸡蛋样本较低的消化率和ACE抑制剂的较低活性。”Jianping Wu强调，需要进一步进行活体实验来证明这个假设。

鸡蛋蛋白可以降低血压这一课题的研究是由阿尔伯塔省畜牧业发展基金（ALIDF）和家禽研究中心赞助经费。

揭开胆固醇“谬论”

英国研究人员最近报告说，最新的证据显示，没有发现人们对吃鸡蛋和胆固醇水平升高存在忧虑。英国萨里大学的Bruce Griffin教授在《营养学通报》（2009年第34期，66～77页）中写到吃鸡蛋和胆固醇水平升高有关联并且最终可能导致心血管疾病发生的说法，是基于过时的资料提出的。萨里大学的研究人员总结到：“我们必须消除环绕着鸡蛋和心脏疾病的迷雾，让鸡蛋重回到我们的食谱当中，为人们健康均衡的饮食作出有价值的贡献。”