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.