A new study, entitled “Consumption of Clarified Grapefruit Juice Ameliorates High-Fat Diet Induced Insulin Resistance and Weight Gain in Mice” was published in the peer-reviewed journal PLOS ONE by Dr. Rostislav Chudnovskiy and colleagues from the Department of Nutritional Sciences and Toxicology, Graduate Program in Metabolic Biology, University of California, Berkeley. The study provides new evidence for potential health promoting properties of grapefruit Juice (GFJ) in murine high-fat diet (HFD)-driven obesity and non-obesity models.
Dietary supplements, including use of nutraceuticals, nutritional products that provide health and medical benefits, offer promising approaches to ameliorate obesity and to increase health-span. Grapefruit juice (GFJ) is relatively rich in nutrients, including vitamins and minerals and has fewer calories than other many juices. Grapefruit or GFJ consumption has been assumed to have positive effects in health and promote weight-loss and has been mostly associated with a hypo caloric diet, e.i. the “Hollywood diet.” However these assumptions have been based on previous studies that were contradictory and not well-controlled as stated by these authors.
Dr. Chudnovskiy and colleagues reported an animal model in which mice consumed centrifugation clarified GFJ (cGFJ) ad libitum at rates comparable to water consumption of control groups. The group of mice that were drinking cGFJ, butas 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. cGFJ consumption did not modify food intake or absorption. The mice were fed a diet that was either 60 percent fat, high-fat diet (HFD), or 10 percent fat, low-fat diet (LFD), during 100 days, and their metabolic health was monitored throughout the study. The mice that were fed with a HFD the consumption of cGFJ decreased the rate of weight gain, accumulation of hepatic triacylglycerol, a type of fat, fasting blood glucose, and improved insulin sensitivity. While mice fed on a low-fat diet (LFD), the consumption of cGFJ induced a decrease in two-fold of fasting insulin. This is a well-controlled mouse model that enables to assess that GFJ consumption has health-promoting effects, and these effects are mediated by compounds in addition to naringin.
“I was surprised by the findings,” said Stahl, associate professor of nutritional sciences and toxicology and one of the senior’s authors of the study, in the UC, Berkeley press release. “We even re-checked the calibration of our glucose sensors, and we got the same results over and over again.” added Prof. Stahl.
“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,” added Prof. Napolli, UC Berkeley faculty member and co-senior author, in the UC, Berkeley press release.
In this study, the researchers administrated to one group of mice naringin, a bioactive compound in grapefruit juice that has been identified to induce loss of weight, and another group metformin, a glucose-lowering drug often prescribed to Type 2 diabetes patients.
“The grapefruit juice lowered blood glucose to the same degree as metformin,” said Prof. Napolli. “That means a natural fruit drink lowered glucose levels as effectively as a prescription drug,” added Prof. Prof. Napolli.
The group of high-fat-diet mice that received naringin had lower levels of glucose in the blood than the control group, but there was no effect on weight, implying that that 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 Prof. Stahl.
The authors did not find a significant effect of grapefruit juice on weight or other metabolic variables in mice eating low-fat diet although there was a two-fold decrease in insulin levels. “The effects were more subtle for the low-fat diet group,” explained Prof. 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,” added Prof. Stahl. “Basically, we couldn’t see a smoking gun that could explain why or how grapefruit juice affects weight gain,” said Prof. Stahl. “Obesity and insulin resistance are such huge problems in our society, ”said Prof. Stahl. “These data provide impetus to carry out more studies,” concluded Prof. Stahl. The research team intends to pursue this line of research in exploring the positive effects of grapefruit juice in diseases like obesity.