When you think about diet or nutrition, your thoughts are mainly towards what foods you consume on a regular basis. But over the past few decades there has been increasing emphasis not just on our food intake but also our fluid intake as being an important factor towards good or bad health.

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For a number of years, we have been told about the benefits of drinking tea and especially green tea but there is still a number of people who live with the misconception that coffee is bad for your health. If you ask anyone the question, what is the most commonly consumed drug in the world, you get various answers such as cigarettes, alcohol, marijuana, cocaine or possibly even heroin. The true answer, however, is caffeine, typically delivered through coffee but also present in smaller amounts in tea and a number of soft drinks. The benefits of caffeine are very much related to the delivery system and for example it is my opinion that energy drinks (which are loaded with caffeine) should be banned.

Regardless, it is important to look at the science regarding the health benefits or detriments of the variety of food and fluids we consume on a regular basis. A recent study from Japan published in the British Medical Journal Open Diabetes Research documented just under 5000 participants with Type 2 diabetes over the age of 20. The average age of the people in this survey was 66 years old and the follow-up was just over 5 years.

Included in the study was information regarding existing health conditions, the level of exercise performed, the intake of cigarettes and alcohol, sleep duration, weight and symptoms of depression. Four dietary questionnaires were performed during the follow up period including the consumption of coffee and green tea.

The primary end point of this study was the death rate over the follow-up period. There were just over 300 deaths out of the 5000 people. The results were very interesting demonstrating those who consumed 2 cups of coffee per day on average had around a 40% reduction in death; 2–3 cups of green tea and 2 or more cups of coffee led to a 51% reduction in death but the biggest results were those who consumed 4 cups or more of green tea per day along with 2 cups or more of coffee per day was associated with a 63% reduction in death rate.

There are two aspects to analysing this study. The first being why should there be potential benefits from consuming this amount of green tea and coffee per day and also can we actually believe the results of a trial such as this?

Firstly, although a standard cup of coffee contains round 100 mg of caffeine and a standard cup of green tea contains round 8 mg of caffeine, it is almost certainly not the caffeine content that has the enormous benefit. Both coffee and green tea (and normal tea for that matter) contain very concentrated plant chemicals known as polyphenols. There is increasing scientific data to show the enormous benefit from the regular consumption of polyphenols with a number of studies in the general public (not specifically diabetics as in this study) had on average a 30% reduction in mortality by consuming high amounts of polyphenols present in all fruit and vegetables in varying degrees. Clearly, polyphenols in green tea and coffee are very concentrated and in relatively high doses and thus the benefits.

Polyphenols in general have marked metabolic benefits and in particular affect the master metabolic switch known as AMP kinase which has a strong effect in activating many aspects of fat, carbohydrate and protein metabolism.

But, the down side of a study such as this is that it is purely observational, relying on a person’s truthful assessment of their dietary intake and also their accurate recall. But, most people are not going to lie about how many cups of green tea and coffee they have every day and most people can recall what type of fluid they consume on a regular basis. The study was controlled for the other lifestyle factors I initially mentioned and thus (although not a randomised controlled trial — the gold standard of medicine), it does strengthen the notion that consuming green tea and coffee on a regular basis does have significant, and what appears to be profound, health benefits.

Finally, although this study was only performed in diabetics, it has long been said that diabetics are the canaries in the coal mine of health. In the old days, the miners used to take canaries into the coal mine and if there was a gas leak the canaries would die before the miners, warning them that there was danger within the mine and they had to leave immediately. Diabetics develop all common diseases long before the rest of the population and this study is a good reminder of the benefits of many principles of healthy lifestyle and in this particular case choosing the appropriate fluid as part of our daily dietary intake.

It has often been said, you are what you eat but it also appears that you are what you drink.