Grapefruit
Grapefruit (Citrus × paradisi, Rutaceae) is an accidental hybridized cross between pomelo (C. maxima) and orange (C. sinensis) cultivated in the 18th century.1,2 The tree grows to over 30 feet, with glossy leaves and white, yellow, or pink fruit.1 While and the species originated in the West Indies, it also grows in California, Florida, Texas, Brazil, and Israel. High in vitamins C and A, grapefruit has been promoted to help with weight loss, diabetes, cardiovascular disease, and mortality.2 The fruit also contains small amounts of vitamin E, thiamin, riboflavin, niacin, potassium, phosphorus, copper, manganese, and zinc. Pink grapefruit has the added benefit of the antioxidants lycopene and beta-carotene, as well as the phytonutrients limonoids, hespertin, and naringenin.
Grapefruit has been part of weight loss programs as early as the 1930s when the "Hollywood Diet" was introduced.3 Metabolic syndrome is characterized by abdominal obesity, high-density-lipoprotein cholesterol, high blood pressure, and elevated fasting blood sugar. In a 2003 prospective, 12-week, randomized, double-blind, placebo-controlled trial, conducted at the Scripps Clinic in San Diego, California, obese subjects (one-third with metabolic syndrome) received either grapefruit capsules (500 mg) plus 7 oz. apple (Malus domestica, Rosaceae) juice, placebo capsules plus 7 oz. apple juice, placebo capsules plus 8 oz. grapefruit juice, or half of a fresh grapefruit plus placebo capsules, three times per day before meals. Results showed that consumption of half of a fresh grapefruit before meals three times per day resulted in a 3.5 lbs. loss in body weight and an improvement in insulin resistance in obese subjects with or without metabolic syndrome. Another randomized, open-label, parallel-arm design trial which tested whether grapefruit or grapefruit juice consumed as a preload could affect weight loss found that either was equally efficacious resulting in an overall weight loss of 7.1% of initial body weight in obese adults.4 Grapefruit preload also increased high-density lipoprotein cholesterol, an aid in reducing cardiometabolic risk.
Results from a randomized, double-blind, controlled crossover trial on the consumption of blond grapefruit by postmenopausal women published in 2015 demonstrated that the flavonoids in grapefruit juice may aid in the reduction of arterial stiffness.5 Following six months of grapefruit juice consumption, pulse wave velocity measurements of carotid and femoral arteries were significantly decreased compared to control. However, no other parameters changed.
Grapefruit juice does have known effects on medications and other substances, including increasing the serum concentration of calcium channel blocker drugs by inhibiting CYP3A4, the cytochrome P450 isozyme that metabolizes the medications.6
Reference
1Lawless J. The Encyclopaeidia of Essential Oils. Shaftsbury, Dorset, UK: Element Books Ltd.; 1992.
2Ware M. Grapefruit: Health benefits, facts, research. Medical News Today website. http://www.medicalnewstoday.com/articles/280882.php. December 31, 2015. Accessed March 8, 2016.
3Fujioka K, Greenway F Sheard J, Ying Y. The effects of grapefruit on weight and insulin resistance: relationship to the metabolic syndrome J Med Food. 2006;9(1):49-54.
4Silver HJ, Dietrich MS, Niswender KD. Effects of grapefruit, grapefruit juice and water preloads on energy balance, weight loss, body composition, and cardiometabolic risk in free-living obese adults. Nutr Metab (Lond). 2011;8(1):8. Doi: 10.1186/1743-7075-8-8.
5Habauzit V, Verny M-A, Milenkovic D, et al. Flavanones protect from arterial stiffness in postmenopausal women consuming grapefruit juice for 6 mo: a randomized, controlled, crossover trial. Am J Clin Nutr. July 2015;102(1):66-74.
6Christensen H, Asberg A, Homboe AB, Berg KJ. Coadministration of grapefruit juice increases systemic exposure of diltiazem in healthy volunteers. Eur J Clin Pharmacol. 2002;58(8):515-520.