Fruit fly study challenges theories of high carb diets

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A study conducted by University of New South Wales (UNSW) researchers suggests that one day people may be prescribed diets according to their genes.

A single mitochondrial DNA mutation common in animals could play a role in obesity and other health problems associated with a diet high in carbohydrates, the study indicates.

UNSW scientists looked at how different diets affected fruit fly populations.

The researchers observed a surprising difference between two sets of the Drosophila melanogaster fruit flies when feeding them alternate diets high in protein and high in carbohydrates.

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Fruit fly larvae with a noted mitochondrial DNA (mtDNA) mutation showed a pronounced increase in development when eating high carbohydrate diet of banana, but stagnated on a high protein diet of passionfruit.

Conversely, fruit fly larvae without the mtDNA mutation thrived on the high protein diet, but dropped in frequency when put on carbohydrates.

UNSW School of Biotechnology and Biomolecular Sciences professor Bill Ballard, who led the study, said the research is a rare demonstration of positive selection at work in evolution.

“What is unique about this study is we’ve identified one mutation in the mitochondrial genome, that when fed a specific diet is advantageous and causes the frequency of flies in a population cage to increase,” he said.

“Then when you swap the diet back to a high protein diet, the flies with the mutation go down in numbers and the other flies without the mutation go up,” said Ballard.

The study, which was a six-year collaboration between authors from research institutions in Australia, the US and Spain, challenges the neutral theory of molecular evolution that says changes in species at the molecular level are random, not caused by natural selection and provide no benefit or disadvantage to the species.

UNSW PhD student Sam Towarnicki, who is equal first author of the paper, explained why this was more than just a random, neutral mutation.

“The selective advantage is this – the larvae possessing the mutation fed on high carbohydrate diet grow up nice and early and become adults before the others on the protein diet [also with a mutation],” he says.

“And we found a 10 per cent difference in the development just in one generation between those two groups, which is huge.

“Because we followed 25 generations, those increases compound over time which delivers much bigger numbers and a huge selective advantage,” said Towarnicki.

Humans share 75 per cent of the same genes as fruit flies, and have the same mtDNA genes.

Ballard said knowledge of a person’s ‘mitotype’ could help explain why a diet high in carbohydrates may induce obesity and diabetes in some but not others.

“The news is not all bad for people harbouring the mutation. Sure, you would need to manage your carbohydrate intake when you are younger, but if you are unfortunate enough to develop Parkinson’s Disease, a high carbohydrate diet will help you maintain weight,” said Ballard.

“So a consequence of our study is to open up a new area for the development of specific diets and drugs to treat Parkinson’s’ Disease,” he said.

“The most obvious implication from our work is that people should start to manage their diets to match their genotypes to fulfil their specific goals.”

The paper, titled Genotype to phenotype: diet-by-mitochondrial DNA haplotype interactions drive metabolic flexibility and organismal fitness, was published by PLOS Genetics.