Kate Maura Forde, student dietitian, Glasgow Caledonian University

Grapefruit tend to be like marmite; you either love them or hate them. Breakfasting on half a grapefruit has long been one of the healthiest ways to start the day, a virtuous alternative to tucking into cereal or a cooked breakfast. Grapefruit forms a core part of the “grapefruit diet“, which is a protein-rich meal plan that focuses on consuming grapefruit or grapefruit juice at every meal. The theory being that the fruit’s low-glycaemic index is able to help the body’s metabolism burn fat.

One average grapefruit is approximately 180g and contains 54 calories (McCance & Widdowson, 2002). See table 1. below for full nutritional composition of a grapefruit (McCance & Widdowson, 2002).

Nutrient Amount RNI
Carbohydrate (g) 12.24
Of which sugars (g) 12.24
Fibre (AOAC) (g) 2.34 30g
Protein (g) 1.44 45-55g
Fat (g) 0.18
Vitamin C (mg) 64.8 40mg
Phosphorous (mg) 36 550mg
Potassium (mg) 360 3500mg
Calcium (mg) 41.4 700mg
Selenium (mg) 1.8mg 60-75mg
Folate (ųg) 46.8 200ųg

 

Table 1. Nutritional composition of the average grapefruit, raw, flesh only, and the recommended intake values for the average healthy adult from SACN. (British Nutrition Foundation, 2016) (McCance & Widdowson, 2002).

Macronutrients

The above nutrient list is not extensive but highlights the nutrients considered to be a good source. Beneficial nutrients in grapefruit are abundant. Like most citrus fruits it is low in calories, contains no saturated fats or cholesterol, but rich in dietary fruit fibre called pectin.  (SACN, 2015). An accumulation of studies demonstrated a significant reduction in risk of cardiovascular disease, type II diabetes and colorectal cancer at 30 g of fibre or more per day. This was therefore recommended as a revised adult intake for adults in the UK (SACN, 2015). A lot of the fibre in grapefruit comes from the skin but there is still a considerable amount within the individually bagged segments and the white roughage that binds the fruit together. For this reason, you should leave as much of this intact when preparing your grapefruit for the added benefit (SACN, 2015).

Additionally, while the level is low, grapefruit have a small level of protein that is 1.5grams or ~3% of our daily requirements. This would be useful for those following a vegetarian or vegan diet to ensure they get adequate protein from their diet. Grapefruit has earned the reputation as being a healthy food, and it provides a modest amount of protein compared to other fruit on our list. However, overall you’ll be getting plenty of benefits by eating grapefruit, many of which overshadow anything you’d get from its protein content.

Micronutrients

Grapefruit is a good source of calcium. With 41mg in each fruit that contributes to 6% of your daily intake which is not normally considered as most people get their calcium intake from dairy products. Calcium is the most abundant mineral in the body and is essential for several vital functions. As everybody knows, the body needs adequate dietary calcium develop and maintain healthy bones and teeth. But calcium also plays a vital role in many systems including regulation of some metabolic functions, the transmission of information in the nervous system, the control of muscle contractions (including the heart!) and blood clotting. Furthermore, it has been suggested that adequate calcium intake may help lower high blood pressure, although more evidence is needed to fully substantiate this (BNF, 2016).

Grapefruit is also a fruit that is high in folate (the naturally form occurring of folic acid). In various parts of the world folic acid is added by law to flour and bread e.g. USA, Canada and Chile. The UK is yet to commit to this ‘mandatory’ fortification; however, it is still added to most breakfast cereals and is the primary source of folic acid in the diet. A grapefruit contains nearly ¼ of the recommended daily intake for the general population, however this can be very useful for women who are planning pregnancy. It is recommended that all women of childbearing age who are planning a pregnancy take a daily supplement as it is difficult to achieve 400μg/day from diet alone. There is conclusive evidence that supplements of 400μg/day of folic acid taken before conception and during the first 12 weeks of pregnancy prevent most neural tube defects (e.g. spina bifida) in babies (BNF, 2016).

Besides pregnancy, together with B vitamins, folate is involved with the maintenance of normal blood homocysteine levels. The amino acid homocysteine plays a role in folate metabolism in the body and evidence suggests that raised blood homocysteine is an independent risk factor for cardiovascular disease. High intakes of folate have been found to lower the blood concentration of homocysteine in people and, thus it has been proposed that folic acid supplementation might reduce the risk of cardiovascular disease (BNF, 2016).

Selenium intakes in the UK are far below the recommendations. Selenium content of food is largely dependent on location and soil conditions, which vary widely. Grapefruit wouldn’t normally be considered as a food high in selenium but it does contain modest amounts with ~2mg per whole fruit. The main function of selenium is as a component of some of the important antioxidant enzymes and therefore to protect the body against oxidative damage. It is also necessary for the use of iodine in thyroid hormone production, for immune system function and for reproductive function.

Phytochemical antioxidants

Grapefruit contain many flavonoids which have been extensively studied to understand their role in health which suggest anti-inflammatory, anti-proliferative and anti-carcinogenic and antimicrobial activity (Gattuso, et al., 2007). Nairingin is one of the major bitter compounds and significantly contributes to the juices sensory taste quality. The combination of flavonoids ensures that grapefruits have a strong anti-oxidant property. Optimum intake of anti-oxidant is possibly linked with health benefits such as certain cancers and cardiovascular diseases (Uckoo, et al., 2012). Studies have also shown Nairingin to have a lipid-lowering effect on the body and increases the anti-oxidant enzyme activities in those with high cholesterol (Uckoo, et al., 2012).

Lycopene is another powerful antioxidant and is the main contributor to the pink and red hues found in grapefruit. Lycopene also has been suggested to prevent the carcinogenesis process and the atherosclerosis process by protecting critical components in the body including lipids, low-density lipoproteins (LDL), proteins and DNA (Venket Rao & Agarwal, 2000). Lycopene levels in the blood have also been inversely related with the chronic disease risk. Although the antioxidant properties of lycopene are thought to be primarily responsible for its beneficial properties, evidence is accumulating to suggest other mechanisms such as modulation of intercellular gap junction communication, hormonal and immune system and metabolic pathways may also be involved (Venket Rao & Agarwal, 2000).

Tips to including more grapefruit in your diet

Just half of a grapefruit is 1 of your 5 a day, however if you find them particularly bitter, here are a few tips to still include them as part of a healthy balanced diet

  • Add to a fruit salad with other sweet fruits such as pineapple to increase the sweetness.
  • Squeeze half a fresh grapefruit into your glass of OJ in the morning.
  • Add some peeled slices to some low fat greek yoghurt and a teaspoon of honey.
  • Or if you don’t mind the bitter, add to a salad for lunch. Grapefruit pairs well with avocado.

Unfortunately, there is a small catch when it comes to grapefruit. You must be careful consuming any grapefruit in your diet if you are taking certain medications. Most commonly if you are taking a statin to reduce cholesterol level. Grapefruit contains compounds known as furanocoumarins that block some of the enzyme processes in the body. When grapefruit or its juice is consumed, the body’s enzyme’s ability to break down the drug for elimination is decreased. Therefore, blood levels of the drug may rise, resulting in the risk for new or worsened side effects (NHS, 2012)
.

How much is too much grapefruit?

The researchers report that furanocoumarins are present in all forms of grapefruit (freshly squeezed juice, frozen concentrate and whole fruit). One whole grapefruit or 200ml of juice is sufficient to cause enough of an increase in the concentrations of active drugs to influence the body, and therefore could cause side effects. The time between consuming grapefruit and taking the medication, and the frequency of consumption of grapefruit, can also influence their effect (NHS, 2012).

Researchers recommend that it is better to err on the side of caution and never have any grapefruit (or other citrus fruit containing furanocoumarins) when taking drugs known to interact with these types of fruit (NHS, 2012).

What should you do?

When being prescribed a new medication, discuss with your doctor or pharmacist whether there are any foods or drinks you should avoid if you are concerned that your diet may affect your medication (NHS, 2012).

 

References

Benavente-García, O. & J, C., 2008. Update on uses and properties of citrus flavonoids: new findings in anticancer, cardiovascular, and anti-inflammatory activity. Journal of Agricultural and Food Chemistry, 56(15), pp. 6185-6205.

BNF, 2016. Minerals and trace elements- Calcium. [Online]
Available at: https://www.nutrition.org.uk/nutritionscience/nutrients-food-and-ingredients/minerals-and-trace-elements.html?limit=1&start=3
[Accessed 01 March 2017].

BNF, 2016. Vitamins; Folate/Folic Acid page 12. [Online]
Available at: https://www.nutrition.org.uk/nutritionscience/nutrients-food-and-ingredients/vitamins.html?limit=1&start=11
[Accessed 01 March 2017].

British Nutrition Foundation, 2016. Minerals and Trace Elements- Potassium page 8. [Online]
Available at: https://www.nutrition.org.uk/nutritionscience/nutrients-food-and-ingredients/minerals-and-trace-elements.html?limit=1&start=7
[Accessed 12 Feb 2017].

Gattuso, G. et al., 2007. Flavonoid composition of citrus juices. Molecules. Molecules, 12(8), pp. 1641-1673.

McCance, R. A. & Widdowson, 2002. McCance and Widdowson’s The composition of foods. Cambridge: Royal Society of Chemistry.

NHS, 2012. NHS Choices: Prescription drugs and grapefruit a ‘deadly mix’. [Online]
Available at: http://www.nhs.uk/news/2012/11November/Pages/Prescription-pills-and-grapefruit-a-deadly-mix.aspx
[Accessed 01 March 2017].

SACN, 2015. Carbohydrates and Health, London: TSO and Blackwell.

Uckoo, R. M., Jayaprakasha, G. M., Balasubramaniam, V. M. & Patil, B. S., 2012. Grapefruit (Citrus paradisi Macfad) Phytochemicals Composition Is Modulated by Household Processing Techniques. The Journal of Food Science, 77(9), pp. 921 – 928.

Venket Rao, A. & Agarwal, S., 2000. Role of Antioxidant Lycopene in Cancer and Heart Disease. Journal of the American College of Nutrition), 19(5), pp. 563-569.

WHO, 2003. Diet, Nutrition and the prevention of chronic dieases, Geneva: World Health organisation.