Does milk reduce the nutritional value of green tea?
From the “WTF would you do that” files…
Short answer: it doesn’t, but…
It really depends upon what you consider to be “nutritional value”, which, speaking as someone who has worked as a food scientist and who has studied the principles of nutrition, isn’t really a well defined scientific term except when used solely as a scientific term.
Nutrition, scientifically defined, is something that enables living organisms to have the required (metabolic) energy to survive and continue living. Water, although absolutely essential to living beings (even tardigrades need water to move around and “live”, despite their ability to hibernate without it) is not “nutritional” because water alone doesn’t provide energy that is usable in metabolic processes. Paradoxically though, although energy is involved in oxidation and oxidation-reduction chemistry is absolutely essential to metabolism, the oxygen in air is not considered “nutritional” since the long history of nutrition actually predates the discovery of oxygen and the understanding of the role of oxygen and oxidation-reduction (“redox”) chemistry in nutrition. It’s also ubiquitous here on planet earth.
Nutrition is typically divided into different types of substances that bring (caloric) energy, and therefore typically involves three classes of items: carbohydrates (sugars), fats, and proteins. Nutrition is extended to certain micronutrients known to be essential to life as well, such as salts (such as sodium and potassium, calcium and magnesium, etc.,), vitamins, and minerals. Anything that is an essential building block of living things, except for water and air, is “nutritional”.
While green tea contains trace quantities of micronutrients and contains a significant amount of redox-active chemicals, green tea does not contain a significant amount of calories by itself to be considered “nutritional”- you’d die of malnutrition nearly as quickly if you only drank green tea as if you only drank plain water. Both milk and cream on the other hand, contain significant quantities of nutrition, and you would survive for significantly longer periods of time if you drank milk or cream instead of water.
There is a separate question that is frequently asked, which is whether or not green tea is “anti-nutritional”. Some species of animal, when they attempt to consume a diet high in a class of compounds known as tannins (which includes tannic acid, but notably not all tannins are tannic acid, see, e.g. the Rec.food.drink.tea FAQ) will experience a reduced ability to get the calories those animals need to survive. In general, though, most animals (including humans) don’t experience a significant reduction in nutritional value when consuming tea, and the “tannins” in tea are very different, nutritionally, from the slightly anti-nutritional tannic acid found in some plants.
Since this anti-nutritional effect of tannins is thought to be caused by strong binding of tannic acid to proteins resulting in indigestible complexes of tannic acid and protein, and because the proteins and calcium in milk and cream have been observed to bind (largely reversibly!) to tea compounds, this false folk-wisdom logic has reversed in recent years to draw a completely opposite yet also incorrect conclusion- that because green tea contains redox-active “antioxidants” and it is widely thought among nutritionists that “antioxidants” help to prevent some of the damage which occurs in all oxidative metabolism, that antioxidants including vitamins such as Vitamin C and E, the carotenes, and antioxidant tannins and polyphenols found in wines, fruits, vegetables (and teas) are “healthy”, that therefore adding milk or cream to tea should therefore reduce the “healthy”, “nutritional” value of the antioxidants in tea. This conclusion is completely unsupported by the majority of evidence, in a number of ways. There is no conclusive evidence that antioxidant vitamins, or other so-called antioxidant polyphenols, play a significant role in human nutrition nor play a significant role in the progression of old age, heart disease, cancer, or any other disease, though there is known to be some small effect. There is no conclusive evidence that the known binding of polyphenolic antioxidants to proteins plays any significant role in hindering the absorption of either milk proteins nor polyphenols into the body- the fraction of polyphenols absorbed by the body and measured in the blood is small and are metabolized and excreted very rapidly no matter what they are co-consumed with. There is no conclusive evidence that milk reduces the small effect of tea polyphenols, though such effects have been widely reported (see Really?: Adding Milk to Tea Destroys its Antioxidants) and are based in part upon work performed in conjunction with scientists at Unilever with whom I have worked directly, who concluded that milk has no effect. Even if there is a small reduction in absorbed polyphenols from tea due to milk or cream, there is a huge overall variance in the fraction of tea compounds that are absorbed which could depend on both individual variations in diet and metabolism as well as activity of gut microbial variations (the “microbiome”), and only a small fraction of tea polyphenols are absorbed even under the best of conditions.
So, in short, there might be some small effect upon an effect which is, in itself, small, so small that neither the nutritional value of green tea nor the effect on that small effect of anything which might be consumed at the same time as that green tea has been studied to the point which we can conclude anything with scientific certainty or consensus. I’d go even further, and say that anything you might hear about the magic healthful properties of tea is complete and utter nonsense- it is healthy and completely nutritionally valid to drink plenty of liquids, which can include tea and any other plant-based beverage, provided they don’t contain excessive amounts of sugar, but it’s not going to cure your cancer or heart disease and it certainly isn’t going to make you live happily forever to drink tea, with or without milk.
Two more minor points: first, there’s a lot of evidence to suggest that consuming animal products causes a heavy environmental burden, and I’m sure there are many (vegans, especially) who would consider cow’s milk or cream in your tea to be repugnant. While I am no vegan, despite generally agreeing with the growing consensus of the environmental effect of animal-based food, the thought of putting cream in green tea is something that I find personally, aesthetically repugnant. Ew. Just don’t do that, that’s gross. Nutritionally, it’s perfectly fine, but yuck, yuck, yuck.
Second, there’s a lot of evidence to show that significant portions of the world are currently eating too much, or if not too much- at least too much of an incorrect mix, of nutritional components. This is a relatively new development, because prior to 1980 or so, the combination of war, famine, and poverty were so commonplace that it was only a very few people worldwide that were actually lucky to be eating a sufficient number of calories to encourage them to live to the point where other diseases begin to predominate as a cause of poor health. Prior to the 1920s or so, food in the United States represented in excess of 80% of the total expenditure of the average person’s budget, a number that is now closer to 5% in the US and Europe and has been falling for decades worldwide. (That’s not to say the problem of famine or hunger are “solved” by any stretch of the imagination!) As a result of this trend, the typical problem that faced nutritional scientists over the past few centuries (how do I get enough calories of food into everyone’s belly such that nobody suffers malnutrition) is quickly being replaced by a new problem (how do I get people to eat the right nutrition such that they have optimal health over their entire typical lifespan of 70–90 years?) As such, the questions of “what is nutrition”, as a science, are changing, and depending on whether you are talking to a “classical” nutritionist (counting myself in that, for the most part) or a “modern” nutritionist you might get a different answer.
answer originally published on Quora, at https://www.quora.com/Can-a-food-expert-nutritionist-doctor-etc-explain-why-adding-cream-to-hot-green-tea-diminishes-the-nutritional-value/answer/Matt-Harbowy.
matt harbowy is a tea chemist, scientist, activist, and data management expert. He is one of the founders of the non-profit Counter Culture Labs, working to bring fairness and egalitarian ideals to people interested in learning about science and biotechnology. He is also a top writer on the question and answer site, Quora.
