• Saturday, May 25, 2024
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Could grapefruit juice curb the effects of a high-fat diet?

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The research team, led by Joseph Napoli and Andreas Stahl, both of the Department of Nutritional Sciences and Toxicology at the university, published their findings in the journal PLOS ONE.

Grapefruit has been hailed for its weight-loss effects since the 1930s, forming a part of the famous Hollywood Diet. Studies claimed that grapefruit consists of a fat-burning enzyme that promotes rapid weight loss.

But Napoli and Stahl say the validity of such studies can be questioned. “Relatively few human studies have examined the effects of grapefruit or grapefruit juice consumption per se on metabolism in well-controlled experiments, and these have produced intriguing but contradictory results,” they note.

In this study, the team set out to improve understanding of the metabolic effects of grapefruit juice consumption.

Grapefruit juice curbed weight gain, lowered blood glucose in mice fed high-fat diet

The researchers tested the effects of clarified, pulp-free grapefruit juice diluted with water at different concentrations on five groups of mice fed either a high- or low-fat diet for 100 days. The grapefruit juice was sweetened with saccharin to make it less bitter.

These effects were compared with one group of control mice, which were fed a high-fat diet but were given water to replace grapefruit juice. The team added glucose and artificial sweeteners to the water so it had the same calorie and saccharin content as the grapefruit juice.

At the end of the study, the researchers found that mice fed a high-fat diet that drank grapefruit juice gained 18% less weight than mice on a high-fat diet that drank water. As well as greater weight loss, grapefruit-drinking mice fed a high-fat diet also showed a 13-17% reduction in blood glucose levels and a three-fold reduction in insulin levels.

Grapefruit juice had no effect on weight for mice fed a low-fat diet, although these mice did show a two-fold reduction in insulin levels.

The team tested the effects of a compound found in grapefruit juice – naringin – on one group of mice fed a high-fat diet. Naringin has previously been linked to weight loss. Another group of mice fed a high-fat diet were given metformin – a drug used for lowering glucose levels in people with type 2 diabetes.

The researchers found that naringin lowered blood glucose levels in the mice just as much as metformin. “That means a natural fruit drink lowered glucose levels as effectively as a prescription drug,” says Napoli.

The researchers note, however, that naringin alone appeared to have no effect on the weight of mice fed a high-fat diet, meaning there is another compound in grapefruit that promotes weight loss.

“There are many active compounds in grapefruit juice, and we don’t always understand how all those compounds work,” notes Stahl.

Why does grapefruit juice appear to curb weight gain from a high-fat diet?

The researchers admit that they are unable to say why grapefruit juice appears to halt weight gain.

They note that all mice had similar calorie intake and exercise levels, so these can be ruled out as explanations. They say it cannot even be put down to an issue with nutrient absorption, as they checked the calories that had been eliminated in feces.

“Basically, we couldn’t see a smoking gun that could explain why or how grapefruit juice affects weight gain,” says Stahl. However, this is something they plan to investigate in future research.