Is grapefruit effective in helping to lose weight? I have read that it acts as a catalyst to the burning process. Plus, it gives an individual energy, which helps to burn more calories. Anyway, I am always stumped with this question. Many of my clients have said it helps them lose weight. I simply want to know why.
The grapefruit diet that is supported by the Florida citrus web site is supposedly a low fat, low calorie (1200 to 1800 or more) diet with fruit, namely grapefruit, included. The weight loss from this type of diet is from the decreased calories (less fat, etc.). This seems to be a modified version of the Dietary Guidelines and is probably much healthier than the other popular grapefruit diets. (I do take issue with some of the myths proposed by Denise Austin on their site, however).
Most other versions of a "grapefruit diet" are based on the idea that grapefruit has an enzyme that burns fat. These versions of the grapefruit diet are much more restrictive, allowing only a few types of food and prescribing about 800 calories (see the first two links below). I found no studies or diets that used grapefruit independently of a calorie deficit. The biggest reason people lose weight on such a "grapefruit diet" is because they are eating less.
I consulted several nutrition texts and performed search on Medline. All sources agreed that there is scant to no evidence that grapefruit increases fat burning in any significant amount.
There are some studies that show grapefruit alters a different enzyme system in the body (the third link below). This accounts for the proper recommendation to avoid grapefruit with many types of prescription drugs.