Granny Smith apples were found to contain high levels of a compound that promotes good bacteria in the gut, helping people feel fuller for longer
An apple a day keeps the doctor away, goes the saying.
But a new study has found more specifically, that a Granny Smith a day could be the key to preventing obesity.
The bright green, crisp variety helps people feel full, inhibiting the urge to eat.
They were found to promote friendly bacteria, which invokes the feeling of being full.
The study, published in the journal Food Chemistry, revealed that the non digestible compounds in the fruit, which include fibre and polyphenols, do not get broken down by stomach acid.
When they reach the colon they are fermented by bacteria in the colon which helps friendly bacteria in the gut to grow.
Scientists at Washington State University tested several different varieties of apple on mice, to see which caused the most growth of friendly bacteria.
Granny Smiths worked better than Golden Delicious, Gala, Braeburn and other popular varieties, they discovered.
The variety, known for its slightly tart flavour, had a particularly high fibre content and compounds like polyphenols which do not break down when eaten, they reported.
The team analysed mouse droppings after feeding the animals, some of which were obese, different types of fruit.
They discovered the balance of bacteria in the colon of obese people is often 'disturbed' in a way that can disrupt the metabolism and make people feel hungry.
It was revealed that the faeces of overweight mice that had eaten Granny Smith apples had changed and become similar to that of slim mice.
The discovery could lead to future treatments for weight problems.
Professor Giuliana Noratto, from Washington State University said: 'We know that, in general, apples are a good source of these non digestible compounds but there are differences in varieties.
'Results from this study will help consumers to discriminate between apple varieties that can aid in the fight against obesity.
'The non digestible compounds in the Granny Smith apples actually changed the proportions of fecal bacteria from obese mice to be similar to that of lean mice.'
The discovery could help cut disorders linked to obesity, including low grade inflammation.
'What determines the balance of bacteria in our colon is the food we consume,' said Professor Noratto.
Scientists at Washington State University believe the findings might help combat obesity. File picture
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