Diets touting the fat-burning benefits of grapefruit have been around for decades. Proponents claim it contains fat-burning enzymes that will boost weight loss efforts. Research indicates that grapefruit juice might possess these properties but this link requires more substantial investigation.
The Grapefruit Diet
Registered dietitian Maureen Callahan, writing for Health.com, explains that a specific diet involving grapefruit has been around since about the 1930s. The creator remains unknown and she notes that many different versions circulate around the Internet. Basically, these diets call for consuming grapefruit in some form before every meal. The diet plans typically outline meal suggestions that eliminate many types of foods, such as certain carbohydrates.
Callahan notes that while grapefruit might possess some fat-burning capability, the weight loss on these types of diets most likely results from calorie restriction---most plans call for eating only about 1,200 calories, much less than typically recommended.
Research
A 2004 study conducted at the Nutrition and Metabolic Research Center at the Scripps Clinic in California found that grapefruit might possess some fat-burning capabilities. Study leader Dr. Ken Fujioka and his team studied 100 participants who either drank a serving of grapefruit juice or ate a half a grapefruit with each meal over the course of 12 weeks; besides slightly bumping up physical activity, they ate their typical diet. Participants on average lost over 3 lbs. with many participants losing more than 10.
Weight Loss Mechanism
According to the study, grapefruit appears to regulate insulin levels, excess of which have been linked to increased fat storage. Insulin levels dropped in the participants consuming the grapefruit. Smaller spikes of insulin cause the body to use glucose more efficiently, leading to less stored as fat.
Considerations
While this one small study found that grapefruit might have fat-burning properties, it does not represent a magic bullet that will allow you to eat whatever you want and still lose weight. Most proponents of consuming grapefruit have subscribed to one of the many incarnations of the calorie-restricted diet that come along with it---any diet where you eat less than you burn will result in weight loss. If you do want to consider adding grapefruit to your weight loss efforts, stick with juice or the fruit. The capsules probably do not have the same chemical make-up as whole versions of the fruit.
Warnings
Grapefruit contains enzymes that interfere with metabolization of many types of drugs. This leads your body to store more of the drug than it normally would. This build up can increase effectiveness to dangerous levels and increase risk of side effects. Simply spacing your consumption between medications and grapefruit consumption might not suffice like it does in other instances and you might have to stay away from grapefruit completely. Examples of possible interactions include certain medications used for depression, anxiety, seizures, high cholesterol and immune system disorders.
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