Tart and tangy grapefruit juice adds a punch of vitamin C and potassium to your breakfast. While grapefruit juice could be a healthy addition to your diet, it's not a replacement for exercise and a whole-foods weight-loss plan. Grapefruit juice may curb your hunger slightly so you eat less at meals, but it doesn't notably raise your metabolism to help you burn more calories.
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Grapefruit Juice's Nutritional Analysis
A 1-cup serving of grapefruit juice contains 96 calories, 156 percent of the daily value for vitamin C and 11 percent for potassium. Pink or red versions also contain 22 percent of the DV for vitamin A. Both white and pink juices provide small amounts of calcium and iron.
With 23 grams of carbohydrates, 22 grams of which are sugar and 0 grams of fiber, grapefruit juice is missing some of the most beneficial qualities of a whole fruit. One cup of grapefruit sections offers almost 19 grams of carbohydrates but only 16.5 grams of sugar and 2.5 grams of fiber. When you're trying to lose weight, fibrous foods like grapefruit help fill you up by slowing digestion. The whole fruit also carries fewer calories -- just 76 per cup of sections, and both the juice and whole grapefruit offer small amounts of B vitamins.
Grapefruit's Effects on Metabolism and Weight Loss
Research shows that drinking grapefruit juice or eating grapefruit before a meal might assist with weight loss, but why this happens is unclear. It doesn't seem to be because the grapefruit boosts your metabolism. A study published in the Journal of Medicinal Food in 2006 showed that obese patients who consumed 8 ounces of grapefruit juice or 1/2 of a grapefruit before each meal lost about 3.5 pounds after 12 weeks, without making other notable changes to their diets. Participants in the study who consumed a grapefruit capsule before meals also lost weight -- but just 2.2 pounds over the 12 weeks. Individuals in the study who had just a placebo did not lose significant weight.
In this study, prediabetic participants who consumed grapefruit, grapefruit juice and grapefruit capsules also improved insulin resistance.
Combine Grapefruit Juice With a Low-Calorie Diet
Creating a calorie deficit is one of the most effective ways to lose weight. You boost your metabolism, or the calories your body burns daily, by adding more activity and reducing the number of calories you eat. A study published in a 2011 issue of Nutrition and Metabolism showed that combining a low-calorie diet with a glass of grapefruit juice or snack of whole grapefruit before meals helps boost weight loss. Note that a glass of water consumed before the meals also resulted in similar significant weight loss. The researchers concluded that a low-calorie premeal snack could effectively help with weight loss, but that snack did not have to be grapefruit. Grapefruit wasn't shown to have some magical metabolic-boosting property, either.
Interestingly, the grapefruit juice- or grapefruit-consuming group experienced additional benefits to their cholesterol profile that weren't seen in the water-drinking group. They had small increases in their high-density lipoprotein -- or good cholesterol -- levels.
Grapefruit Isn't for Everyone
Before you start swigging grapefruit juice in an effort to lose weight, remember that its calories do contribute to your daily intake total. Drinking an 8-ounce glass before every meal adds nearly 300 calories a day. If you didn't reduce your intake at meals or exercise more, this could lead to a weight gain of 0.6 pound per week.
Grapefruit juice and whole grapefruit can interact with certain prescription and nonprescription drugs. Compounds in grapefruit cause your body to absorb more of the active ingredients in the drugs, giving you a higher concentration in your bloodstream. Before adding grapefruit juice to your diet, talk to your doctor if you're taking any prescriptions -- especially if they include medications for lowering your cholesterol or blood pressure, organ-rejection drugs and anti-anxiety drugs. In the case of certain medications, such as some antihistamines, grapefruit juice reduces effectiveness.