Consuming grapefruit and grapefruit juice for weight loss purposes has been long promoted since the 1930s as a healthy addition to the diet to encourage body fat reduction.
Most versions of the "grapefruit diet" include ingesting 1/2 a grapefruit or 8 ounces of juice before meals. Along with low-carb/low-calorie foods and ample protein intake, this dietary regimen is reported to help individuals lose an average of 10 pounds in as little as 10-12 days.
But is this claimed benefit based on truth or hype?
According to our research, there is some loose evidence that grapefruit may facilitate a positive impact on weight loss.
While we would definitely not pursue it as some kind of "miracle weight loss food" all on its own, it may be something to consider experimenting with if you are looking to shed unwanted pounds.
Here are some of the proposed weight-reducing compounds believed to be responsible.
Grapefruit contains a unique compound known as NOOTKATONE which, along with grapefruit mercaptan, provides some of the fruit's flavor and aroma.
The significant aspect of nootkatone is that it can activate an enzyme called AMPK (or 5' adenosine monophosphate-activated protein kinase). In a study on mice, nootkatone triggered AMPK was identified to stimulate energy metabolism and help with diet-induced obesity.
Grapefruits contain the flavonoids naringenin and naringin. Naringenin is a strong antimicrobial and antioxidant. It is very concentrated in the seeds which are used to make grapefruit seed extract supplements.
The bitter component in grapefruit comes in part from the NARINGIN compound. This is what gives the grapefruit flesh its predominant bitter-sweet taste compared to other types of citrus. And, if you recall, bitter-tasting foods and drinks help to stimulate digestive enzymes which may account for some claims on its fat-burning potential.
Both naringenin and naringin have been shown to provide strong anti-inflammatory and antioxidant actions. (*)
The consumption of grapefruit and raw grapefruit juices initially became a popular food and drink to include on weight loss regimens because it is one of the lowest-calorie fruit varieties.
One half of a raw grapefruit (123 grams), according to nutrition data, contains about 52 calories, 2 grams of fiber and 13 grams of total carbohydrates.
There are also claims that grapefruit's acidic qualities, which come from components such as ascorbic acid, citric acid and compounds like limonin, help to boost metabolism and break down dietary fat. This however has not yet been scientifically validated.
As far as overall grapefruit nutrition goes, they are very high in the antioxidant VITAMIN C. Half a grapefruit contains about 38.4 mg vitamin C or 64% the Daily Value and 8 ounces of raw unpasteurized grapefruit juice contains about 93.9 mg or 156% the Daily Value (based on an adult 2,000-calorie diet). Individuals who consumed adequate amounts of vitamin C are known to burn fat more efficiently during exercise. (*)
Pink/red varieties also contain antioxidants such as beta-carotene and lycopene.
Grapefruit pith and pulp membranes are a source of PECTIN, a soluble dietary fiber that can influence weight loss because it slows down gastric emptying and makes you feel full for a longer period of time. In earlier research, a grapefruit pectin-supplemented diet was found to encourage a decrease in cholesterol levels which can likewise be beneficial for obese conditions.
While grapefruit can be healthy to consume for some individuals as part of a balanced diet and a regular exercise program, the whole fruit pulp or its freshly pressed juice is not going to in and of itself reduce excess bodyweight.
Also, it is important to note that many of the studies on the fruit are on animal models not on human subjects. (*) In addition, there are likewise mixed outcomes. For example, one randomized control trial offered some associations with weight reduction, whereby another study suggested no significant impact.
Grapefruit or grapefruit juice for weight loss is known to interact adversely with certain medications by causing too little or too much of the particular drug in the bloodstream. This may also occur even when grapefruit and any interactive drugs are spaced out.
It is caused by grapefruit's naringin flavonoid but also furanocoumarins like bergamottin. These grapefruit-specific compounds basically can inhibit key drug-metabolizing enzymes, like CYP3A4.
Because there is a long list of pharmaceuticals that may not be appropriate to consume with grapefruit, it is best to consult your physician if you are taking any type of prescription or over-the-counter drugs.
Keep in mind, FDA approved medicines require labeling which will clarify not to consume with grapefruit or grapefruit juice.
Periodically consuming grapefruits or grapefruit juice can be a beneficial addition to a health-promoting diet.
The pulp of grapefruits can be consumed whole for added fiber content. Likewise, grapefruit can also be juiced with the pulp strained out OR you may wish to leave some pulp fiber in the juice to reduce the immediate glycemic effect.
Most "grapefruit diet" protocols recommend half a grapefruit or 8 ounces of grapefruit juice for weight loss results. Grapefruit or juice is typically consumed three times a day before each meal, which is commonly restricted to high protein/low carbohydrate foods. This is of course an aspect which may also account for some of the diet's weight loss benefits.