Effectiveness of Grapefruit Diet Studied at Vanderbilt Medical Center

In order to validate, or perhaps disprove, the belief that consuming grapefruit is a sensible weight loss strategy, researchers at Vanderbilt University Medical Center have launched a two-year, three-arm randomized controlled study to see just how consumption of grapefruit and grapefruit juice affects appetite, dietary intake, weight loss and body composition.

The origin of the grapefruit diet dates back to the food fads of the 1970s, when it was popular to eat grapefruit with every meal or eat nothing but grapefruit for several days in a row. The grapefruit diet has been described by some nutrition professionals as a mysterious urban dieting legend that was reported to contain enzymes that burn fat away or speed up metabolism. Despite the notion by many people that eating grapefruit leads to significant weight loss, only one or two modest scientific studies have supported this widely held belief.

“The myth of the grapefruit diet has been around for decades. If you search the Internet, you will find diet-related websites that offer menu plans focused on eating grapefruit for weight loss,” said Heidi J. Silver, Ph.D., R.D., research assistant professor of Medicine at Vanderbilt University School of Medicine’s Center for Human Nutrition and the study’s principal investigator. “But in all this time there has never really been any solid science to support this assumption, other than one study conducted by the Scripps Clinic in California which was completed in 2004. Notably, the Scripps study did show greater weight loss in the groups of participants who ate grapefruit or drank grapefruit juice for 12 weeks.”

Silver believes that the reason the grapefruit diet became so widely popular is because the fruit is tasty and low in calories. “Grapefruit only has about 66 to 84 calories per serving of grapefruit,” she explained. It is also inexpensive and grows in many common varieties, including the seedless white marsh from Florida and the ruby red and pink blush, grown in Texas. The white, pink and red are also grown in California and Arizona. Grapefruit is high in fiber, high in water content, and low in concentrated sugars, Silver said. It is also high in vitamins and minerals like vitamin A, vitamin C and some of the B complex vitamins.

This means that grapefruit is a “nutrient dense” food, she said. “The concept of nutrient density is very important in nutrition research now. It indicates how much of a nutritional impact a particular food item has by volume or per gram weight of the food,” she said. “Other studies have found that people consistently eat the same volume of food day after day. It may be true that eating grapefruit or drinking grapefruit juice offers an early sensation of satiation, that feeling of fullness early into eating a meal that curbs the amount of food intake at meals,” she said.

Silver’s study consists of two separate phases. In phase I, the focus is on a weight loss intervention, to determine whether eating grapefruit or drinking grapefruit juice results in greater weight loss compared to placebo. Participants will meet with registered dietitians weekly for individualized weight loss plans. Both dietary intakes and physical activity will be measured carefully. “In the animal studies that have been done, with mice and rats, the investigators observed that the animals had increased activity in their cages after they ate or smelled grapefruit; this increased their daily energy expenditure,” Silver said.

Phase II of the study will examine whether grapefruit and grapefruit juice actually play a role in curbing appetite through satiation or satiety. There will be approximately 90 participants recruited in phase I of the study. About one-half of this original cohort will eventually graduate on to the study’s second phase. Silver explained, “The individuals who progress along to phase II will have their food and fluid intake weighed before and after meals and snacks to see if the consumption of grapefruit really can curb appetite.”

Funded by the Florida Department of Citrus, the study will use a total of 4,158 white marsh grapefruits and 893 bottles of grapefruit juice that are being shipped each month from Florida. “The grapefruit they sent us for use in this study are beautiful whole fruit, picked at the ripest part of the season” said Silver. “For the purpose of this study, it is important that the grapefruit is all from the same growers’ lot. This is for size and weight consistency, and also to make sure that if there turns out to be a metabolic effect, that it will be from the same maturity of fruit. The grapefruit juice is also being provided in a similar manner to assure consistency in the food product.”

To be considered for this study, a prospective candidate must be 21-50 years old, have a body mass index of 30 to 39.9 (corresponding with NIH classifications for Obesity Class I and II), and must not be a smoker or drinker or currently taking prescription medications which have a known propensity to interact with consumption of certain bioactive compounds found in grapefruit or grapefruit juice.

“People who meet the NIH’s classification of Obesity Class I and II are individuals who are at high and very high risk for the metabolic syndrome. The metabolic syndrome is characterized by a group of metabolic risk factors like being overweight, having high blood pressure, or having high cholesterol or triglycerides in the blood that increase the incidence of comorbidities such as type 2 diabetes and cardiovascular diseases like coronary heart disease,” Silver said. “It is estimated that at least 22 percent of adults in the U.S. have metabolic syndrome.”

Upon acceptance into the study, participants will receive individualized nutrition education, counseling and supervision from registered dietitians; including nutrition and diet assessment, development of a comprehensive reduced-calorie meal plan, blood analysis, a tailored plan for increasing physical activity and body composition analysis.

For more information about participation in the grapefruit study please contact Silver’s research team at (615) 936-0985.


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Jerry Jones or Craig Boerner