GRAPEFRUIT JUICE STEMS WEIGHT GAIN IN MICE FED A HIGH FAT DIET
Fad diets come and go,
but might there be something to the ones that involve consuming grapefruit and
grapefruit juice? New research at the University of California, Berkeley,
suggests that a closer look at grapefruit juice is warranted.
A new study, to be
published in the peer-reviewed journal PLOS ONE, found that mice
fed a high-fat diet gained 18 percent less weight when they drank clarified,
no-pulp grapefruit juice compared with a control group of mice that drank
water. Juice-drinking mice also showed improved levels of glucose, insulin and
a type of fat called triacylglycerol compared with their water-drinking
counterparts.
If these findings
sound somewhat familiar, it may be because the link between grapefruit juice
and weight loss -- or just decreased weight gain -- has been touted in
Hollywood diets before. However, the earlier studies behind those claims were
often small, not well-controlled and contradictory, according to Andreas Stahl
and Joseph Napoli, the two UC Berkeley faculty members who led the new
research.
This latest work was
funded by the California Grapefruit Growers Cooperative, but the UC Berkeley
researchers emphasized that the funders had no control or influence over the
study design or research findings. Both Stahl and Napoli said they went into
this research with some skepticism.
"I was surprised
by the findings," said Stahl, associate professor of nutritional sciences
and toxicology. "We even re-checked the calibration of our glucose
sensors, and we got the same results over and over again."
Napolli added that
"we see all sorts of scams about nutrition. But these results, based on
controlled experiments, warrant further study of the potential health-promoting
properties of grapefruit juice."
Pitting juice against
water
The study authors
randomly divided mice into six groups, including a control group that drank
only water. Those drinking grapefruit juice got a mixture diluted with water at
different concentrations, and sweetened slightly with saccharin to counteract
grapefruit's bitterness. The researchers also added glucose and artificial
sweeteners to the control group's water so that it would match the calorie and
saccharin content of the grapefruit juice.
At the end of the
study period, the mice that ate the high-fat diet and drank diluted grapefruit
juice not only gained less weight than their control counterparts, they also
had a 13 to 17 percent decrease in blood glucose levels and a threefold
decrease in insulin levels, which reveals greater sensitivity to insulin. (In
Type 2 diabetes, the pancreas makes extra insulin to compensate for increased
resistance to the hormone.)
The researchers gave
one group of mice naringin, a bioactive compound in grapefruit juice that has
been identified as a key agent in weight loss, and another group metformin, a
glucose-lowering drug often prescribed for those with Type 2 diabetes.
The mice were fed a
diet that was either 60 percent fat or 10 percent fat for 100 days, and their
metabolic health was monitored throughout the study.
"The grapefruit
juice lowered blood glucose to the same degree as metformin," said Napoli,
professor and chair of nutritional sciences and toxicology. "That means a
natural fruit drink lowered glucose levels as effectively as a prescription
drug."
Weight effects only
seen in high-fat diet
The group of
high-fat-diet mice that received naringin had lower blood glucose levels than
the control group, but there was no effect on weight, suggesting that some
other ingredient in grapefruit juice is also beneficial.
"There are many
active compounds in grapefruit juice, and we don't always understand how all
those compounds work," said Stahl.
The study did not find
as big an impact on mice that ate a low-fat diet. Those that drank the
grapefruit juice saw a two-fold decrease in insulin levels, but there was no
significant change in weight or other metabolic variables.
"The effects were
more subtle for the low-fat diet group," explained Stahl. "Mice are
incredibly healthy animals with naturally low levels of bad cholesterol. So if
they are eating a healthy, low-fat diet, it will take more to see a significant
effect on their health."
The researchers said
they ruled out the typical explanations for weight loss in their study. It
wasn't the amount of food consumed, since the ingested calories among the different
groups were about the same. The level of activity and body temperatures were
comparable, and the authors even checked the calories eliminated in the feces
of the mice to check for problems with the body's absorption of nutrients.
"Basically, we
couldn't see a smoking gun that could explain why or how grapefruit juice
affects weight gain," said Stahl.
The researchers said
they hope to continue the investigation into grapefruit juice. "Obesity
and insulin resistance are such huge problems in our society, " said
Stahl. "These data provide impetus to carry out more studies."
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