Grapefruit juice may protect against diabetes

"Grapefruit juice 'could be the key to weight loss','' is the misleading headline in The Daily Telegraph, as mice fed a combination of a high-fat diet and grapefruit juice still put on weight. Though their blood sugar levels were lower than controls…

“Grapefruit juice 'could be the key to weight loss’,'' is the misleading headline in The Daily Telegraph.

It reports on a study in which mice fed a combination of a high-fat diet and grapefruit juice still put on weight  albeit at a lower rate than mice fed a sugary drink. Their blood sugar levels and insulin sensitivity were also better regulated than mice that did not drink grapefruit juice.

The mice were given either a high-fat diet or a low-fat diet in a range of experiments.

Mice fed a high-fat diet and grapefruit juice had an 18% reduced rate of weight gain compared with mice given sugary water with the same number of calories as the grapefruit juice. They also had 13% lower fasting blood sugar levels. There was no effect on weight gain in mice fed a low-fat diet.

Drinking grapefruit juice improved insulin sensitivity in mice, regardless of their diet (in people, reduced insulin sensitivity can be a sign of impending diabetes).

Grapefruit juice lowered blood sugar as effectively as metformin, a drug widely used to treat people with type 2 diabetes. However, none of the mice actually had diabetes, so this research has little immediate relevance to humans with the condition.

For the time being, people with diabetes should not swap their metformin for grapefruit juice on the basis of this study.


Grapefruit juice and medication

Grapefruit juice has been known to increase the levels of medication in the blood, which can be potentially dangerous.


Some of the medicines affected are statinsamiodarone (for irregular heartbeats), Viagra (sildenafil), sertralinediazepam and calcium channel blockers.


If you are considering adding grapefruit juice to your diet, you should first read the patient information leaflet of any medication you are currently taking.

Where did the story come from?

The study was carried out by researchers from the University of California and was funded by the California Grapefruit Growers Cooperative, although it had no role in the study design, data collection, analysis or decision to publish.

The study was published in the peer-reviewed science journal PLOS ONE. This is an open-access journal, so the study is freely available to all.

Both the Mail Online and The Daily Telegraph’s headlines incorrectly state that grapefruit juice can help people lose weight. Leaving aside the fact that this study involved mice, rather than humans, none of the mice actually lost any weight  they just differed in the rate they put on weight.

The Daily Express’ headline was also irresponsible, as it suggests that grapefruits “tackle diabetes as well as a leading drug”, with an accompanying picture of a smiling woman (not a mouse) tucking into a grapefruit. None of the reports seemed to mention that the work was funded by the California Grapefruit Growers Cooperative. This doesn’t mean that the study results aren’t correct, but it's worth mentioning so people can make their own conclusions.

The Mail Online does, however, include a balancing comment from the British Dietetic Association, which said that until further trials are carried out in humans, it's too early for people to try grapefruit diets.

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