During the 1970s, the “grapefruit diet” began making headlines in the United States and gained a reputation as a good way to lose weight. While health experts widely regard it as an ineffective type of fasting diet, people who have tried this eating approach use it for the purpose of losing 10 pounds or more in a short amount of time, according to Purdue. On the grapefruit diet, you consume large quantities of grapefruit and grapefruit juices in an effort to burn more fat, the Cleveland Clinic notes.
But like most other fad diets that focus on a low calorie intake, the grapefruit diet hasn’t been proven to be safe or effective. While grapefruit is a healthy food choice, eating too much of any one food — even fresh fruits — won’t provide your body with the variety of nutrients it needs. Too much grapefruit can also cause gastrointestinal reactions, such as diarrhea or nausea, due to its high vitamin C content, per the NIH.
While grapefruit consumption alone won’t help you burn more fat, research does show that including grapefruit in your diet can help you shed excess pounds. For example, researchers behind one small randomized controlled trial found that participants with obesity who ate half a fresh grapefruit before each meal for 12 weeks lost an average of 1.6 kilograms (kg), or about 3.5 pounds (lb), compared with a control group who lost 0.3 kg, which is less than 1 lb.
According to one theory, this may be thanks to an ingredient in grapefruit called nootkatone. Results from a past study noted that nootkatone stimulated energy metabolism in a mouse model. Metabolism is the group of processes by which the body uses energy or burns calories; the faster your metabolism, the more calories you’ll burn both during rest and while exercising, per Harvard Health Publishing. These findings show the potential weight loss effect of grapefruit, and how this fruit can complement a healthy diet. (Keep in mind, though, that this is just a theory, and further research is needed to determine exactly how grapefruit may lead to weight loss.)
Also, a 1 cup serving of red or pink grapefruit with juice has 2.5 g of fiber, making it a good source of the nutrient, notes the aforementioned USDA data. Fiber-rich, low-calorie foods like grapefruit and other fruits can help promote weight loss efforts by keeping you feeling full longer, compared with empty-calorie foods like sodas and cookies, which can leave you hungry, according to the Mayo Clinic.