The pineapple and tuna fish diet is limited to three days, with the goal of quickly dropping a few pounds 1. If you follow the diet you will undoubtedly lose some weight. But you’ll quickly gain it back because you’re losing mostly water weight. While that’s a significant downside, this diet does have a few benefits. The combination of pineapple and tuna fish is rich in nutrients and has enough carbohydrates to keep you energized 1.

Pineapple and Tuna Diet Basics

As you would guess from its name, this diet consists of eating nothing but pineapple and tuna for three days 1. Some advocates claim you can lose up to 9 pounds during that time, but each person's results will vary. A description of the diet on the website of Dr. Rafael Bolio notes that the plan consists of eating 2 kilograms of pineapple spread throughout the day, plus 2 ounces to 4 ounces of tuna once a day 1. Two kilograms, or 2,000 grams, equals 12 cups of pineapple chunks. Four ounces of tuna is about 3/4 cup, according to the U.S. Department of Agriculture.

Calories and Weight Loss

Twelve cups of pineapple chunks and 4 ounces of light tuna packed in water contain a total of 1,088 calories. Even though this is low in calories, this diet does not get results in three days by cutting calories. If you reduce your daily intake by 500 calories, you’ll lose about 1 pound a week, reports the University of Michigan 6. Whether the pineapple and tuna diet means you’re eating 500 or 1,000 fewer calories each day, it will still take more than three days to see results 1. If you lose weight in three days, you've only lost water weight. Pineapples can boost the water loss because they're natural diuretics.

Plenty of Nutrients

Twelve cups of pineapple supplies 260 grams of carbohydrates, including 195 grams of energy-providing sugar. The tuna ensures you’ll get about 60 percent of your daily protein and all of your daily requirement for vitamin B-12. Since you're eating such a large amount, the pineapple becomes a rich source of vitamin C, vitamin A, folate, potassium, magnesium, iron and calcium 1. With 28 grams of fiber in 12 cups of pineapple, women get an entire day’s fiber, while men consume 74 percent of their daily intake. If this is more fiber than you're used to eating, it may cause gas or diarrhea. With this much fiber it’s also important to drink 6 to 8 glasses of water, according to Oklahoma State University 7.

Considerations and Warnings

You will not consume too much mercury from the tuna if you limit the diet to three days. You can eat up to six servings per month of canned light tuna, reports the Natural Resources Defense Council 8. Albacore tuna is limited to half that amount because it has more mercury. Pineapples are the primary source of a substance called bromelain, which may interact with blood thinning medications. If you take these medications, do not start the diet until you consult your health care provider. Bromelain is a potent enzyme that breaks down proteins. As a result it may irritate your tongue or mouth. It can also upset your stomach or cause an allergic reaction. People who are allergic to latex are at a higher risk for being allergic to pineapples, reports the American Latex Allergy Association.