The grapefruit diet, which advocates eating mostly grapefruit for a period of one to three weeks, is a fad diet and not a safe or healthy way to lose weight. However, including 100 percent grapefruit juice -- ruby red or regular -- in your healthy diet does have some merit. Drinking grapefruit juice before meals can lower your caloric intake, help you lose weight and improve some of the markers of metabolic syndrome. Check with your doctor before including grapefruit juice in your diet because it can interact with some medications.
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Ruby Red vs. Regular
Ruby red grapefruit juice and regular grapefruit juice are almost identical in their nutritional values. Although ruby red varieties often taste sweeter than regular grapefruit juice, both contain 90 calories and 17 grams of natural sugars per serving, which accounts for nearly all of the 22 grams of carbs. Because there's no dietary fiber in grapefruit juice, the remaining 5 grams of carbs are in the form of starches. Both types of juice provide 1 gram of protein per serving, 100 percent of the daily value for vitamin C and 8 or 9 percent of the daily value for potassium. Both juices provide 6 percent of the daily value for thiamine, folate and magnesium as well.
Reduced Caloric Intake
In a study published in "Nutrition & Metabolism" in February 2011, 85 obese adults were given either grapefruit, grapefruit juice or water before each daily meal for a period of 12 weeks. Researchers found that although the subjects' total amount, in weight, of food eaten did not change over the 12 weeks, the energy density, or the amount of calories per gram of food, did change significantly. The participants ate 20 to 29 percent fewer calories. Researchers noted that there wasn't a big difference among the grapefruit, grapefruit juice and water; but if you like grapefruit juice better than water, the findings show that it may help you control caloric intake just as well as water when you drink it before meals.
UC Berkeley researchers conducted a study in which they fed mice a high-fat diet and then gave them either water or clarified grapefruit juice -- with the pulp removed -- as their single source of liquids. The results, published in the journal "PLOS ONE" in October 2014, revealed that the grapefruit juice-drinking mice gained 18 percent less weight than those that drank water. The authors were unable to pinpoint the exact cause of the decreased weight gain, but they recommended further research into the role grapefruit juice might play in the obesity epidemic.
Improved Metabolic Parameters
Metabolic syndrome is a collection of risk factors that increase your chances of heart disease, diabetes and stroke. In the 2014 "PLOS ONE" study, grapefruit juice also proved beneficial for decreasing blood sugar and improving insulin sensitivity, both of which help prevent or control diabetes. In fact, grapefruit juice was just as effective at controlling blood sugar as a popular prescription glucose-lowering drug. The 2011 "Nutrition & Metabolism" study showed that grapefruit juice before meals also helps raise good cholesterol, called HDL, high levels of which can reduce the risk of heart disease and stroke.
Choose 100 percent grapefruit juice and not a grapefruit juice "cocktail" with added sugars. Too many added sugars in the diet can contribute to weight gain, obesity, diabetes and heart disease. Also, do not drink grapefruit juice when taking certain medications because it can interfere with the medication's effectiveness. Examples of medications in this group include some statins, certain blood-pressure-lowering drugs, some organ transplant rejection drugs and some antihistamines, anti-anxiety and anti-arrhythmia medicines.