5 replies to this topic

[everythingeverything]

It is thought that drinking tea with milk may nullify some of its health benefits. However, I really don't like the taste of green tea without milk, which leaves me the choice of either taking green tea supoplements or possibly drinking green tea with soy milk. Are their any reliable studies detailing whether or not soy milk has a negative impact on the health benefits of green tea?

[Skötkonung]

I think the jury is still out on whether drinking green tea with milk is bad. As you know, many vitamins / antioxidants and minerals are fat soluble. So in theory, combining them with fat such as that found in milk could enhance absorption.

For instance, a 2002 study suggests that brewed tea, when added to the fat cells of laboratory rats, raises insulin activity by more than 15 times. Adding lemon to the tea did not affect the insulin-potentiating activity. But adding 50 grams of milk decreased the activity by 90%. This would appear to be good for weight loss.

From the research I have reviewed, there appear to be over 200 bio-active compounds in tea of which catechin is assigned the most healthful benefits. Casein in milk binds to tea catechin, reducing their concentration and effectiveness.

So if you drink tea with milk, try using soya milk. Soya milk contains lecithin that has a different molecular structure to casein, and so is unlikely to bind to tea catechin the way casein does.

Studies:
Dubey P, Sundram KR, Nundy S. Effect of tea on gastric acid secretion. Digestive diseases and sciences. 1984 Mar; 29(3):202-6.

Lorenz 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. 2007 Jan;28(2):219-23. Epub 2007 Jan 9.

van het Hof KH (1998). Bioavailability of catechins from tea: the effect of milk. Eur J Clin Nutr 1998:52:356-9.

Hollman PC (2001). Addition of milk does not affect the absorption of flavonols from tea in man. Free Radic Res 2001;34:297-300.

Tsung Cheng (2006). All teas are not created equal. The Chinese green tea and cardiovascular health. International Journal of Cardiology;108:301-308.

Cabrera Carmen (2006). Beneficial Effects of Green Tea - A Review. Journal of the American College of Nutrition;25(2):79-99.

Anderson RA, Polansky MM (2002). Tea enhances insulin activity . J Agric Food Chem 50:7182-7186.

[everythingeverything]

Thanks very much for your contribution!

[Connor MacLeod]

It is thought that drinking tea with milk may nullify some of its health benefits. However, I really don't like the taste of green tea without milk, which leaves me the choice of either taking green tea supoplements or possibly drinking green tea with soy milk. Are their any reliable studies detailing whether or not soy milk has a negative impact on the health benefits of green tea?

I had the impression that the main culprit was the milk proteins. Because of this I now use milk cream, i.e. heavy whipping cream, with my black tea. This has 0 grams of protein.

[JLL]

I think the jury is still out on whether drinking green tea with milk is bad. As you know, many vitamins / antioxidants and minerals are fat soluble. So in theory, combining them with fat such as that found in milk could enhance absorption.

For instance, a 2002 study suggests that brewed tea, when added to the fat cells of laboratory rats, raises insulin activity by more than 15 times. Adding lemon to the tea did not affect the insulin-potentiating activity. But adding 50 grams of milk decreased the activity by 90%. This would appear to be good for weight loss.

From the research I have reviewed, there appear to be over 200 bio-active compounds in tea of which catechin is assigned the most healthful benefits. Casein in milk binds to tea catechin, reducing their concentration and effectiveness.

So if you drink tea with milk, try using soya milk. Soya milk contains lecithin that has a different molecular structure to casein, and so is unlikely to bind to tea catechin the way casein does.

So are you saying that the decreased insulin activity is good for weight loss? I thought it was the other way around. I don't understand the entire process completely, but based on the studies I've read, we know that a) green tea increases insulin sensitivity and b) green tea (without milk) helps with weight loss. For example, green tea reduces the absorption of fat in calorie restricted rats.

Calorie-restricted rats supplemented with green tea and Awa tea lost more weight and fat mass than non-supplemented rats. Green tea and Awa tea also decreased plasma leptin concentrations. No significant differences were seen between the two types of tea, suggesting that other polyphenols than catechins (which are mainly found in green tea) also have health benefits.

Although fat intake was similar in all three groups, rats supplemented with tea had larger amounts of fecal lipids, which suggests that green tea and Awa tea effectively inhibited the fat absorption rate.

Similarly, green tea has been shown to increase insulin sensitivity and fat burning during exercise in humans.

A green tea extract containing 890 mg polyphenols (catechins) increased fat oxidation from moderate-intensity exercise compared to placebo in healthy young men. Green tea extract also reduced insulin area under curve during a 2-hour oral glucose tolerance test and improved insulin sensitivity. Green tea may thus help with weight loss, both by increasing fat metabolism during exercise and maintaining healthy insulin levels.

So at the same time there's an increase in insulin sensitivity AND weight loss. Therefore, it seems to me that getting rid of this improved insulin sensitivity would also get rid of the weight loss benefits.

Anyway, in the paper you referred to, both ordinary milk and soy milk inhibited the increase in insulin activity from green tea.

When milk was added to the tea, insulin potentiation was decreased. One teaspoon (5 grams) of milk decreased activity by 33%, while 50 grams of milk decreased the activity by more than 90%. Both whole milk and skimmed milk had the same negative effect, as did nondairy creamers and soy milk. Lemon juice, on the other hand, had no effect.

In the same paper the authors speculate on the somewhat contradictory effects of green tea:

The authors mention that other studies have shown that when humans are given tea catechins prior to eating starch, the elevation of insulin is suppressed. So how can tea both increase insulin activity and suppress insulin levels? According to the authors, a possible explanation is that because tea increases the activity of insulin, less insulin is needed to get the same results as before. That is, when tea is present, the pancreas makes less insulin but the insulin does its job better.

But, as you say, the question of whether to use milk or not is still not clear in my opinion. Yes, milk appears to have a negative effect on the insulin benefit of green tea, but on the other hand, green tea and black tea increase antioxidant levels in plasma even when milk is added. Still, just to play it safe, it makes sense not to add cow milk or soy milk to tea - that is, if you're drinking it for the health benefits and not the taste.

There's a couple of ways I know to improve the bioavailability of green tea catechins. The first one is ascorbic acid, which protects catechins from degradation. Citric acid doesn't appear to do much, however, so squeezing lemon into a cup of tea seems to be useless (except for taste, of course). I know there's one study that claimed lemon juice is effective, but if I remember correctly, that was based on a computer model of some kind.

After two hours, half of the catechins had degraded. Adding citric acid to the buffer didn't protect them from being degraded in any significant way. However, ascorbic acid improved the stability of the catechins for up to 20 hours.

The second way is black pepper, which doesn't only improve the absorption of curcumin; piperine also improves the bioavailability of green tea catechins.

Piperine, a component of black pepper, increases the bioavailability of epigallocatechin gallate in mice. The more piperine was given, the more EGCg was found in plasma. Accordingly, the excretion of EGCg in feces was significantly reduced.

You may also want to spread your green tea intake throughout the day, since the peak in antioxidant activity occurs 20-40 minutes after drinking green tea and apparently there is a saturation point for the absorption.

Interestingly, though, there was no difference between the participants who consumed 400 ml of green tea and those who consumed only 300 ml (due to the bitter taste). The authors suspect that this may be due to the absorption mechanism being saturated at the lower dose; this may mean that it's better to spread your daily 10 cups of green tea throughout the day instead of drinking it all at once.

[Skötkonung]

Hey JLL,
I had assumed insulin activity and insulin sensitivity are two different things. Insulin activity implies heightened insulin levels. Since insulin is a storage hormone, the higher your insulin levels, the more fat accumulation will occur. This makes it antagonistic to weightloss.

Insulin sensitivity is a term for the body's ability to respond to blood glucose by producing insulin.

Here is the study in question:

Tea enhances insulin activity.
http://www.ncbi.nlm....pubmed/12428980

In the study, the authors note that milk decreased the insulin-potentiating activity of green tea by approximately 90%. They also note that plain green tea increases insulin potency. I could see how that might be beneficial for health in that blood glucose in stabilized. However, heightened insulin potency means our body is much quicker to store that glucose as adipose tissue.