O leite e seus derivados podem destruir antioxidantes presentes nas frutas, vegetais e grãos.
Milk Products may Destroy Antioxidant Benefits in Fruits, Vegetables and Grains
Milk cancels out the heart protective benefits of tea drinking
Several studies have found that tea is beneficial in terms of heart health. Since there has been evidence showing that milk and milk products may block the body`s ability to absorb antioxidants, researchers in Germany decided to see what adding milk would do to the heart protective capabilities of tea. They reported their results in the June, 2007 European Heart Journal.
In the study, 16 healthy women drank either half a liter of freshly brewed black tea, black tea with 10 percent skimmed milk, or only boiled water on three different occasions under similar conditions. The researchers then assessed the function of the cells lining the brachial artery in the forearms of the women, through the use of high resolution ultrasound both before and two hours after tea consumption.
The researchers found that black tea was able to significantly improve the ability of the arteries to relax and expand, a condition that suggests positive cardiovascular health. This ability depends on an enzyme, eNOS, that synthesizes the chemical messenger, nitrous oxide. However, when milk was added, this positive effect was completely absent. They concluded that milk counteracts the favorable health effects of tea on vascular function and demonstrated that proteins in milk, called caseins, were responsible for canceling out the positive effects of the polyphenols in tea.
Casein in milk binds polyphenols rendering them ineffective
These proteins bind specifically to tea chemicals, especially a catechin called EGCG. Catechins are a kind of polyphenol, a group of chemicals long thought to underlie the beneficial effects of a plant based diet. EGCG is the primary antioxidant in green tea.
When this research team took their study into the lab, they found that tea also relaxed rings of aorta in rats, and increased the activity of the eNOS enzyme in cultured arterial cells by fourfold. But when the tea had 10% of skimmed milk added to it, it had none of these effects on rat aortas or cells.
When the study was interpreted and reported by the University of Rochester Medical Center, it was noted that milk not only blocks tea`s benefits for blood vessels, it also destroys the antioxidant effects of tea and may negate its caner-protective effects as well.
The Rochester report quotes Dr. Robert Vogel, a professor of medicine at the University of Maryland Medical School who agrees that tea is one of the greatest sources of antioxidants. In countries where they drink a lot of tea, heart disease is decreased, except for the British Isles, where it is typical to add milk to the tea. His advice is to add lemon to tea, but not milk or cream.
Researchers in the past had claimed that milk had no effect on tea because it did not change the overall concentration of polyphenols in the blood. However, in an interview Dr. Stangl, the leader of the German research team, stated that what is important is the presence of specific polyphenols, such as EGCG, and milk does block those.
The study team is looking at whether green or black tea is better to drink. Previous studies may have been confounded by the fact that black tea is often consumed with milk, while green tea is not. Studies based particularly on responses of informants as to tea drinking habits, not considering the milk addition as a factor, may have biased several research studies that showed green tea as containing greater amounts of beneficial polyphenols and producing more desirable outcomes.
Polyphenols are more than antioxidants
Polyphenols have recently been termed "lifespan essentials". They work in the body to enhance health in complex ways, and they do more than scavenge free radicals. Their specific heath benefits are being actively researched. So far it is known that polypheonols work to protect the systems of the body from chronic diseases, particularly heart disease and cancer.
To attain or preserve optimal health, foods containing polyphenols should be eaten daily, as these compounds are only active in the body for a short period of time. Blood levels of polyphenols will peak soon after they are consumed, and then decrease as they are metabolized or excreted from the body. Some polyphenols are not even absorbed into the bloodstream at all, but merely pass through the digestive tract, protecting against colon cancer.
Polyphenols are found in unprocessed fruits, vegetables, whole grains and legumes. They tend not to be destroyed by moderate cooking or heating, and cooked foods may offer a more bioavilable source of some polyphenols. To a large degree, polyphenols are why it is so important to eat a plant based diet.
It may be time to rethink how we combine our foods
Although it is possible that the studies with blueberries and tea are isolated incidents, such a conclusion seems to go against the tenets of nature which are presented in broad statements. This suggests that a more likely conclusion would be that proteins in milk have a great affinity for many polyphenols found in both fruits and vegetables. It implies that if one chooses to eat fruits and vegetables for their health promoting benefits, no dairy product should be involved in the process until the body has had a chance to make full use of the polyphenols presented.
Fresh green salads may lose much of their antioxidant power when cheese is added, as may peaches with cream or yogurt with fresh fruit. Coffee may lose its health benefits when milk or cream are added. The implications of these findings are huge once a person decides to interpret them as meaning that no fruits and vegetables should be eaten near the time milk products are consumed.
We already know that milk chocolate contains very few polyphenols compared to dark chocolate. This may be because polyphenols in chocolate bind with milk protein and become inactive.
For more information:
Lorenzo M, Jochmann N, von Krosigk A, Martus P, Baumann, G, Stangl K, Stangl V, "Addition of milk prevents vascular protective effects of tea", European Heart Journal.
Skip Milk in Black Tea, Boost Antioxidant Power, University of Rochester Medical Center.
How to Boost Your Intake of Polyphenol Antioxidants, wikiHow.com.