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Green tea and body weight management

Obesity is increasingly being recognized as a significant health challenge facing all ages of the population, and it is a risk factor for several chronic disorders. It has been linked to 44 different diseases affecting 12 of the body's major organ and tissue systems.
Currently there is no functional food available for obesity, such as there is for cardiovascular disease or cancer. The culture of over-eating and a sedentary lifestyle is compounding the effects of a diet that contains a large percentage of high energy processed and conventional foods. Nutritional research strategies that target aspects of the physiology of obesity are critically important if a workable solution to this health challenge is to be found.
Green tea has been used for thousands of years in Asia as both a beverage and herbal medicine. Over the past few years, dozens of studies have been conducted on green tea's antioxidative and chemopreventive effects. Research has shown the beverage to be effective against a number of conditions, ranging from lowering cholesterol and capturing free radicals to reducing the risks of certain types of cancers.
In this article I am going to shed some light on the impact of green tea on weight management and obesity. Many studies have been conducted on the obesity and the effects of tea extracts and their polyphenols (active ingredients) with very positive results. In addition, some studies have carefully examined the effects of tea consumption on body weight or energy expenditure (EE) in humans.
A team at the University of Geneva studied the effects of green tea on ten healthy young men who ranged in body type from "lean" to "mildly overweight." For six weeks, the men took two capsules consisting of either green tea extract plus 50 milligrams of caffeine; 50 milligrams of caffeine alone; or a placebo with each meal. The researchers measured the men's energy expenditure (EE - the number of calories used in a 24-hour period) in a respiratory chamber. They also gauged the men's respiration quotient, or RQ. (RQ is a measurement of how well the body utilizes carbohydrates, proteins and fats). A lower RQ means that more fats are being metabolized by the body for energy. Results showed that those men taking the green tea extract experienced "a significant increase in 24-h EE" and "a significant decrease in 24-h RQ" over those taking only caffeine or the placebo. Men taking the green tea extract also used more fat calories than those using the placebo. In their conclusion, the scientists stated, "Green tea has thermogenic properties and promotes fat oxidation beyond that explained by its caffeine content and that it may play a role in the control of body composition via sympathetic activation of thermogenesis, fat oxidation, or both."
Thermogenesis is the term used by scientists to describe the activity of brown fat (Brown Adipose Tissue; BAT), which includes dozens of biochemical and metabolic events. The basic outcome of these events is the generation of thermo units, in other words, the creation of heat in your body. BAT has only one purpose - to create heat. To do that, it must use calories. Where does it get the calories to burn? From white fat (White Adipose Tissue). White fat is BAD FAT; the fat you can see on your body; the fat you want to get rid of.
In one study, the anti-obesity effect of an extract from green tea was evaluated in moderately obese subjects. The body weight was decreased by 4.6% and waist circumference by 4.5% when 2 capsules were taken twice daily for 12 wk as part of a regular, self-selected diet. Laboratory studies have shown that this extract exerts a direct inhibition of gastric and pancreatic lipases and a stimulation of thermogenesis. The authors suggested the green tea extract to be a natural product for the treatment of obesity by inhibition of lipases and stimulation of thermogenesis.

Recently, a 12-week double-blind study was performed in which 17 healthy subjects ingested one bottle of green tea containing 690 mg polyphenols /day and another group of 18 subjects as control group to investigate the effect of tea polyphenols on body fat reduction in humans. It has been found that body weight, body mass index, waist circumference, body fat mass, and subcutaneous fat area were significantly lower in the green tea extract group than in the control group. The researchers concluded that tea consumption of tea rich in polyphenols might be useful in the prevention and improvement of lifestyle-related diseases, mainly obesity.
Although more research is necessary to determine the component (s) responsible for the anti-obesity activity and also the differences between types of tea with respect to their effect on EE should be investigated further, these findings nevertheless raise the interesting possibility that tea could be used as a combination agent for treating obesity.


Dr Abdul Molan is a senior research officer in the Institute of Food, Nutrition and Human Health, Massey University.


 

 

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