Green Tea - Snake Oil or Truth?
01 December 2020
by Dr Monique Hope-Ross
Today we separate the proven from the unproven, using Cochrane reviews, a global source of knowledge, existing so that health care decisions get better. A Cochrane review is a meta-analysis of the best studies and sound scientific conclusions are made. These conclusions are regarded as the highest level of evidence in the medical and scientific world.
Green Tea - Snake Oil or Truth?
Tea drinking has legendary origins dating to the reign of Emperor Shennong, five thousand years ago. Potential health benefits range from fat loss, to helping you to live longer and cancer prevention. Green tea features widely within the pages of glossy magazines, but rarely in the medical literature. So does green tea, a would-be elixir of life, live up to the hype or is it just snake oil?
Green tea, Camellia sinensis contains polyphenols, or plant antioxidants. Antioxidants are natural chemicals which reduce inflammation and protect us against cancer. Antioxidants help to neutralise and reduce the effect of oxidants, or free radicals; compounds which cause inflammation and promote the growth of cancers. Thus, there is a scientific rationale for the benefits of green tea, in supporting a healthy metabolism. The active compounds in green tea include catechins and caffeine. Catechins also act to increase metabolism, thus increasing energy consumption which may be useful for weight loss.
Studies on green tea, to promote weight loss have been analysed as part of a Cochrane review by Jurgens et al. These studies on weight loss use green tea extracts, which contain high doses of the active compounds in green tea, far in excess of that found by drinking even copious amounts of green tea. The conclusions of the review were that a very small, statistically non-significant weight loss was induced, and this weight loss is not clinically important. Furthermore, green tea did not have any effect on maintenance of weight loss. We are not surprised by these conclusions at whisperer HQ; there is no magic pill to lose weight, otherwise everyone would be lean!
It’s scary that the likelihood of developing cancer is approaching 1 in 2 people. Filippini et al in a Cochrane review found evidence of a beneficial effect of green tea on some cancers but these findings were limited by the study methods. Some studies showed reduced cancer risk, particularly in prostate cancer, some showed no benefit, and some showed an increased cancer risk. Green tea extracts were associated with adverse reactions, such as skin reactions, raised blood pressure and liver abnormalities. Their final conclusion was that there is limited evidence of a beneficial effect of green tea consumption on the overall risk of cancer.
A Cochrane review by Hartley et al shows that green tea reduces total cholesterol, LDL (bad cholesterol) and blood pressure. These factors are implicated in the development of heart disease and by reducing risk factors, heart disease may be prevented. While the studies show that green tea can reduce risk factors for heart disease, prevention of heart disease has yet to be proven. The conclusion was that the limited evidence suggests that tea has favourable effects on cardiovascular risk factors. Further research was recommended.
What does this all mean for me?
Green tea has favourable effects on cholesterol, LDL and blood pressure, risk factors which contribute to heart disease. Green tea contains natural antioxidants which may have health benefits, such as prevention of heart disease and cancer. Green tea does not help you to lose weight. More research on the subject has been recommended. So, just like whisperer HQ, some do the green tea thing and some don't. Overall, it is probably beneficial, but we certainly will be looking for more evidence. Keto supper with apple cider vinegar dressing
Summary of Green Tea Research
- Green tea has favourable effects on cholesterol
- Green tea does not help you to lose weight
- More research on the subject has been recommended.
- Overall Beneficial
The Latest on Vinegar
While the blood sugar lowering effects of vinegar have been known for over a century, it is not an approved medical treatment, but vinegar is in the news this month. Cheng et al looked at the blood sugar lowering effect of vinegar in numerous studies and found that vinegar, in particular apple cider vinegar, reduces blood sugar in people with diabetes and long-term diabetic control was also improved.
However, further work is necessary before vinegar enters mainstream medicine. We do not understand fully how vinegar works, but it is thought that is inhibits digestive enzymes, thus slowing sugar absorption and also increases glucose uptake by muscles, by increasing insulin sensitivity.
Vinegars differ and there are studies that show apple cider vinegar to be more beneficial than other vinegars, but the evidence is weak. Apple cider vinegar is made by combining apples with yeast, to which bacteria are added. 'Mother' is apple cider vinegar which is organic, unfiltered and contains good bacteria, enzymes and protein. It may also have benefits as a probiotic.
So should you add vinegar to your diet? There is good evidence showing that the addition of 10-30mls (1-2 tablespoons) of vinegar to a high carbohydrate meal reduces both the spike of blood sugar and insulin. Good news, so it might make sense to use vinegar with a treat meal. Add vinegar to your Thanksgiving meal (perhaps with a vinegarette salad dressing?) and your waistline and metabolism may thank you for it!
We worry about the safety of taking 10-30mls vinegar in the long term, and there are side effects, which have not been fully studied. In the short term, it is probably safe. In the long term, potential problems include tooth erosion, gastric problems, burns and bone loss. So, whilst we enjoy lots of vinegar in our salad dressings at Whisperer HQ, and additional vinegar may be beneficial, we need more data before we can recommend this. Watch this space!
In the News: Published this Month
Bisphenol (BPA), a chemical found in 90% of Americans is a major public health concern, due to its widespread usage and potential toxicity; it is typically found on the inside of cans. In spite or our ubiquitous exposure to this chemical, studies on the topic are sparse. Bao et al evaluated BPA exposure and the risk of death. Higher BPA exposure was significantly associated with an increased risk of all causes of death.
Sugary drinks consumption has increased worldwide in recent years and the detrimental metabolic impact is well established. Artificially sweetened beverages are marketed as a healthy alternative but may be equally detrimental. Chazelas et al report that higher consumers of sugary drinks and artificially sweetened drinks have a higher risk of a first case of stroke, heart attack and other cardiovascular episodes.