Green tea cuts the risk of obesity and a number of inflammatory biomarkers linked with poor health, according to a new study published in the Journal of Nutritional Biochemistry.
Mice fed a diet of 2 percent green tea extract fared far better than those that ate a diet without it, a finding that has prompted an upcoming study of green tea’s potential benefits in people at high risk of diabetes and heart disease.
The benefits seen in the research appear to stem from improved gut health, including more beneficial microbes in the intestines and less permeability in the intestinal wall – a condition typically called ‘leaky gut’ in people.
Richard Bruno, the study’s lead author, said: ‘This study provides evidence that green tea encourages the growth of good gut bacteria, and that leads to a series of benefits that significantly lower the risk of obesity.’
Negative changes in the gut microbiome have been previously linked to obesity, and green tea has been shown to promote healthy bacteria. The Ohio State team wanted to explore whether there was an argument for green tea preventing obesity, inflammation and other factors connected to poor metabolic health.
‘The results of studies looking at obesity management so far have been a real mixed bag. Some seem to support green tea for weight loss, but a lot of other research has shown no effect, likely due to the complexity of the diet relative to a number of lifestyle factors. Our goal is to figure out how it prevents weight gain. This will lead to better health recommendations.’
Bruno and his colleagues suspected that green tea might prevent obesity and protect against inflammation in the gut based on previous studies, so they devised an experiment that examined green tea’s effects in male mice fed a normal diet and a high-fat diet designed to cause obesity. (Female mice are resistant to diet-induced obesity and insulin resistance, a precursor to diabetes, so they weren’t included.)
For eight weeks, half of the animals ate a high-fat diet designed to lead to obesity and half were fed a regular diet. In each of those groups, half ate green tea extract mixed in with their food.
Then the researchers measured body and fat tissue weight, insulin resistance and other factors that included:
- Gut permeability, or how ‘leaky’ the gut was
- Endotoxin translocation, or the movement of a gut bacteria-derived component to the bloodstream, where it provokes inflammation and insulin resistance
- Inflammation in the fat tissue and intestines
- The composition of the gut microbes, which are known to contribute to a variety of health factors
The mice fed a high-fat diet supplemented with green tea gained about 20 per cent less weight and had lower insulin resistance than mice fed an otherwise identical diet without tea.
Those mice also had less inflammation within fat tissue and the intestine. Furthermore, the green tea appeared to protect against the movement of endotoxin, the toxic bacterial component, out of their guts and into the bloodstream.
Plus, the researchers found evidence of stronger guts in these mice. Leaky gut is a problem in humans that contributes to widespread low-grade inflammation and has been implicated in a number of health problems.
The researchers also found that the green tea appeared to contribute to a healthier microbial community in the guts of the mice fed a high-fat diet. Mice fed the normal, or low-fat, diet supplemented with green tea also had benefits including reduced weight gain and lower endotoxin levels and markers of leaky gut, but these were relatively modest compared with the effects seen in mice fed the high-fat diet.
Green tea consumption in the experiment would be equivalent to about 10 cups of green tea throughout the day for a person, Bruno said.