The Grapefruit Diet Makes a Comeback

Grapefruit on a plate
For decades, it was considered a fad, but recent studies suggest that the grapefruit diet has science behind it.. Niva/Cultura/Getty Images

It's one of those diet fads that has never completely gone away: The Grapefruit Diet.

A few decades ago, the Grapefruit Diet was all the rage, offering an unhealthy regimen of grapefruit and yet more grapefruit. The basic idea was that grapefruit was so filling, you could only eat so many per day, thereby limiting calories. Understandably, it didn't gain much traction in the world of weight loss and nutrition practitioners, even as it enjoyed fad status.

But a number of studies over the past decade now support the judicious role of grapefruit in efforts to lose weight, and combat insulin resistance -- suggesting that the Grapefruit Diet is more than a fad or myth.

A study by the Nutrition and Metabolic Research Center at Scripps Clinic released in 2006 confirmed that the simple act of adding grapefruit and grapefruit juice to one's diet can result in weight loss.

The 2006 study found that over 12 weeks, the people who had half a fresh grapefruit or 8 ounces of grapefruit juice with each meal lost around 3.5 pounds -- significantly more weight than the placebo group, which lost almost nothing. However, many patients in the study actually lost more than 10 pounds.

There was also a significant reduction in the insulin level 2 hours after eating, and improved insulin resistance.

"For years people have talked about the grapefruit diet, and some even swear by it, but now, we have data that grapefruit helps weight loss," said Dr. Fujioka, principal researcher at the Nutrition and Metabolic Research Center at Scripps Clinic.

"Our study participants maintained their daily eating habits and slightly enhanced their exercise routine; the only dietary change was the intake of grapefruit and grapefruit juice."

Additionally, the research indicates a physiological link between grapefruit and insulin, as it relates to weight management.

The researchers speculate that the chemical properties of grapefruit reduce insulin levels and encourage weight loss.

The importance of this link lies with the hormone's weight management function. While not its primary function, insulin assists with the regulation of fat metabolism. Therefore, the smaller the insulin spike after a meal, the more efficiently the body processes food for use as energy and the less it's stored as fat in the body. Grapefruit appears to have unique chemical properties that reduce insulin levels, promoting weight loss.

"Our study shows grapefruit can play a vital role in overall health and wellness, and in battling America's ever-growing obesity epidemic," stated Dr. Fujioka. "Whether it's the properties of grapefruit or its ability to satiate appetites, grapefruit appeared to help with weight loss and decreased insulin levels leading to better health. It's good the 'Grapefruit Diet' never lost its popularity among the public."

A 2011 study published in the journal in Nutritional Metabolism found that "pre-loading" -- eating grapefruit or drinking grapefruit juice before each meal, generated 7% weight loss over 12 weeks in the group studied, as well as decrease in body fat, waist circumferences, and cholesterol levels.

A 2012 study in the journal Metabolism found that daily grapefruit consumption (1/2 a grapefruit with each of 3 meals) was associated with modest weight loss , a significant reduction in waist circumference, and a significant reduction in blood pressure.

The Berkeley Study

More recently, animal studies conducted at the University of California, Berkeley and reported in 2014, showed that consumption of grapefruit juice with a high-fat diet resulted in a more than 18% decrease in body weight, a 13-17% drop in fasting blood glucose, and reduced fasting insulin.

Andreas Stahl and Joseph Napoli were the two Berkeley faculty members who led the research.

Napol said: "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."

According to Stahl, an associate professor of nutritional sciences and toxicology, "I was surprised by the findings. We even rechecked the calibration of our glucose sensors, and we got the same results over and over again."

Interestingly, the grapefruit juice also decreased blood glucose levels almost equally to the common diabetes drug metformin (Glucophage). According to Napoli, "that means a natural fruit drink lowered glucose levels as effectively as a prescription drug."

Researchers still don't know exactly what component of the grapefruit may be working. In the past, weight loss on grapefruit diets have been attributed to lowered calories, due to the nutritional density and filling quality of grapefruit. But according to the researchers, they ruled out all these 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 animal feces to check for problems with absorption of nutrients.

"Basically, we couldn't see a smoking gun that could explain why or how grapefruit juice affects weight gain," said Stahl. "There are many active compounds in grapefruit juice, and we don't always understand how all those compounds work."

Of Interest to Thyroid Patients

The regulation of blood sugar and insulin levels is important for thyroid patients who want to lose weight. Weight loss can be frustrating, and sometimes seem almost impossible, for some thyroid patients. Dr. Kent Holtorf described the hormonal interaction in the article Long Term Weight Loss for Thyroid Patients: Hormonal Factors That Affect Diets.

If you are interested in adding grapefruit or grapefruit juice to your diet, make sure that you are not taking other medications that interact with grapefruit or grapefruit juice. There is some evidence that regular consumption of grapefruit may have a slight impact on thyroid absorption, but researchers say it's not clinically significant. Still, if you greatly increase your consumption, you should consider getting thyroid levels rechecked to evaluate any possible impact of the grapefruit juice. And, to be sure you understand any possibly interactions with other medications you take, I suggest you download a free copy from People's Pharmacy of their Graedon's Guide to Grapefruit Interactions (Adobe PDF file).


Chudnovskiy, R. et. al. "Consumption of Clarified Grapefruit Juice Ameliorates High-Fat Diet Induced Insulin Resistance and Weight Gain in Mice," PLOSOne, October 08, 2014 Online

Dow CA et. al. "The effects of daily consumption of grapefruit on body weight, lipids, and blood pressure in healthy, overweight adults." Metabolism. 2012 Jul;61(7):1026-35. doi: 10.1016/j.metabol.2011.12.004. Epub 2012 Feb 2.

Fujioka K, et. al. "The effects of grapefruit on weight and insulin resistance: relationship to the metabolic syndrome." Journal of Medicine and Food, 2006 Spring;9(1):49-54 Online

Silver HJ, et. al. "Effects of grapefruit, grapefruit juice and water preloads on energy balance, weight loss, body composition, and cardiometabolic risk in free-living obese adults." Nutr Metab. 2011 Feb 2;8(1):8. doi: 10.1186/1743-7075-8-8.

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