Grapefruit are a type of citrus fruit which originated in Barbados. They were actually an accidental creation, where sweet orange and pomelo (or shaddocks) were crossed with one another.
There are many variations of grapefruit; pink, red, white, pomelo and oroblanco, and they all have slightly different appearances, tastes and textures.
Although once known as ‘the Forbidden Fruit’, all the varieties of grapefruit have one thing in common; they come with a myriad of health benefits and are an excellent addition to any diet.
Nutritional Information
Half a grapefruit (red or pink variety, 123g) contains 52 calories. They have no saturated fat, just 4% RDA carbohydrate, 8% RDA dietary fibre and are extremely good sources of vitamins. In fact, they contain 28% RDA Vitamin A, and a massive 64% RDA Vitamin C.
Nutrition In-Depth
Vitamin A is a nutrient also known as retinol, and is vital for a wide variety of bodily functions. It is actually the name for a group of fat-soluble retinoids (hence retinol) and its functions include promoting and improving the immune response, vision, reproduction and communication between cells (National Institute of Health, 2013).
It makes up the protein rhodopsin which absorbs light into the retina, and due to its role in supporting cell growth and function, is vital for many functions of organs such as the heart, lungs and kidneys.
Vitamin C is another nutrient which is known as L-ascorbic acid, but unlike Vitamin A, Vitamin C is a water-soluble nutrient. The human body cannot create Vitamin C, and so it is very important that the diet contains enough. As grapefruits contain 64% RDA, they are an excellent way to fulfil this need.
Vitamin C is important for the body in a number of ways (National Institute of Health, 2013). Firstly, it is required for the biosynthesis of collagen. In other words, without vitamin C, collagen couldn’t be created. Collagen is a protein which provides structure to tissue and is necessary for wound healing.
Secondly, Vitamin C has great antioxidant powers. This means that it can help to fight molecules called free radicals, which are naturally created within the body but can cause diseases such as diabetes and cancer.
Benefits of Grapefruit
Alongside the health benefits associated with Vitamin A and Vitamin C, grapefruit have specific qualities which mean they are excellent for a variety of health problems:
1. Lowers High Cholesterol
Cholesterol is the name for a fatty substance which is found in the blood. It cannot dissolve in the blood, and must be transported to and from cells by carriers called lipoproteins (American Heart Association, 2014). There are two types of cholesterol; low-density lipoprotein (LDL) cholesterol, and high-density lipoprotein (HDL) cholesterol.
LDL cholesterol is often referred to as the ‘bad’ cholesterol, and HDL as the ‘good’ cholesterol. This is because LDL cholesterol contributes to a process called atherosclerosis, where there is a build-up of fat in the arteries which hardens, causing the arteries to narrow.
This can restrict blood flow to and from the heart and eventually lead to heart disease. HDL cholesterol, on the other hand, can help to reduce LDL cholesterol levels by removing it from the arteries and taking it to the liver where it is broken down.
There is also evidence that low levels of HDL cholesterol can increase the risk of heart disease, whereas high levels can reduce the risk (e.g. Boekholdt et al, 2013).
Triglycerides are also very important for heart health. Triglycerides are the form that fat exists in most areas of the body. They have a role in creating energy for the body to use, whereas cholesterol is needed to build certain cells and hormones such as oestrogen.
Triglycerides are created following consumption of fatty foods and carbohydrates. Unlike cholesterol, all triglycerides increase the risk of heart disease, and often high levels are associated with low levels of good HDL cholesterol (Bass, 2011). It is thought that this combination often runs in families and is one of the reasons for genetic predispositions to heart disease.
In America, over 30% of adults have excessive levels of LDL cholesterol, and less than a third of these people are successfully managing the condition (CDC, 2015). In England over half of all adults have high cholesterol, and every year over 160,000 people die from heart and circulatory disease, which has been exacerbated or caused by high cholesterol (Heart UK, 2015).
Furthermore, a study by Tirosh et al (2007) found that of over 13,000 participants, higher levels of triglycerides led to a 4 times greater risk of heart disease and stroke compared to those with lower triglyceride levels.
Fortunately, it is possible to reduce the levels of cholesterol and triglycerides in the blood, thereby reducing the risks of heart disease and death. Lifestyle choices such as reducing alcohol intake and exercising more can help, but so can changing the diet.
Eating a diet which is low in saturated fat, high in fibre and contains many fruits and vegetables is recommended by many healthcare professionals in order to reduce or prevent high cholesterol (NHS, 2015). Amongst the foods that make up this heart-healthy diet, there are some specific items which are particularly beneficial for lowering cholesterol, and one of those is the grapefruit.
A longitudinal study conducted by Murphy, Barrraj and Rampersaud (2014) over 5 years assessed the impact of grapefruit on a number of outcomes (some of which will be reported in other sections of the article). They found that female participants who consumed grapefruit or grapefruit juice (as assessed by two screening interviews, 3 to 10 days apart) had significantly higher levels of HDL cholesterol as compared to non-grapefruit consumers.
This is a useful study as it used an extremely large sample size (12,789 adults) which suggests that the results are likely to be applicable to the general population. It was also a naturalistic study which investigated people within their own lives, rather than within the setting of a laboratory experiment. This ensures that the results are likely to occur in very naturalistic, every-day settings.
Further studies can support the results from this longitudinal research. For instance, Gorinstein et al (2006) investigated the impact of red, yellow, or no grapefruit consumption on lipid levels of patients who had undergone coronary bypass surgery (and so already had very bad cholesterol and triglyceride levels).
It was found that compared to the control group, those who consumed the red or yellow grapefruits had significantly lower overall lipid profiles. Specifically, total cholesterol, LDL cholesterol and triglyceride levels were all reduced.
Furthermore, it was found that the red grapefruit was particularly effective as it contains higher levels of bioactive compounds which hold antioxidant properties. This may be one mechanism by which grapefruit can improve the lipid profile.
2. Helps Maintain A Healthy Body Weight
Excessive body weight is becoming a global epidemic. There are nearly 2 billion overweight adults worldwide (World Health Organisation, 2015), which is approximately one in four people. Of these, 600 million are obese, a condition which has more than doubled since 1980. Tackling excess body weight is vital, as it can lead to a huge variety of health problems; heart disease, diabetes, cancer, and musculoskeletal disorders to name a few.
Although many people find it extremely difficult to lose weight, making changes to the diet can make a big difference. It is particularly important to choose foods which can help your body to actively burn fat, rather than those which are simply low in calories. Grapefruit has this property, making it an excellent addition to the diet of anybody trying to lose weight.
Returning to the longitudinal study by Murphy et al (2014) which was mentioned previously, this research provides evidence that grapefruit do not only reduce cholesterol levels. They also lead to significant changes in body composition on a number of parameters.
Specifically, grapefruit consumers had a lower body weight, smaller waist circumference and lower BMI (Body Mass Index) compared to those who did not eat grapefruit. Unfortunately for men, this result was only found in female participants.
One reason for weight loss following grapefruit consumption may be that they help the body to remove excess water. In a study by Silver, Dietrich and Niswender (2011) participants were split into three groups; those who consumed grapefruit, grapefruit juice, or a water preload for twelve weeks.
All groups lost weight, had significantly smaller body size and had a reduced waist circumference compared to the beginning of the 12 weeks, however there was no difference between groups. Due to the fact that grapefruit did not differ to water on weight loss may suggest that, as grapefruit is approximately 91% water (University of Kentucky, 1991), it is the water content which helps to improve weight loss.
Water consumption is not something which many people think about when trying to lose weight, but it can actually have a serious impact on success. When the body is dehydrated, it needs to hold on to as much water as it can in order to function effectively. As human beings are approximately 60% water (the USCS Water Science School, 2015), it is clearly very important for us.
Just some of the functions of water in the body include allowing the body’s cells to grow, reproduce and survive, regulating body temperature, converting food into components required for survival, and helping to deliver oxygen. As the body holds on to water when it is dehydrated, it can lead to bloating. By consuming water, the body will actually lose water weight. It seems a little counterintuitive, but research has shown that water consumption can lead to weight loss.
For instance, Dennis et al (2010) found that when water consumption was increased during a low-calorie diet (by adding a 500ml drink before every meal), weight loss was significantly greater than when water was not added.
Specifically, there was a 44% greater decline in weight over the 12 week research period for water consumers compared to non-consumers and they also found that energy intake was decreased. This may be because drinking water meant participants were less likely to drink other calorie-filled drinks, or it may have been that water consumption actually helped them to feel less hungry.
Not only does the water content of grapefruit make them excellent for weight loss, but they also contain antioxidant compounds known as polyphenols. In a study by Dallas et al (2013), participants were given Sinetrol-XPur, a citrus extract containing grapefruit compounds (alongside red orange and orange compounds).
For 12 weeks the participants consumed the extract alongside their meals twice daily, and body composition was measured. It was found that, when compared with the placebo, the citrus extract led to a significant reduction in hip circumference, waist circumference and abdominal fat.
Furthermore, inflammatory markers were reduced. This suggests that the antioxidant properties of grapefruit are effective in helping the body to burn excess fat.
3. Improves Symptoms Of Influenza
Influenza is a viral respiratory infection which is characterised by fever, muscle pains, tiredness and weakness, headache and a dry or chesty cough. Although for most people symptoms only last about a week, for those with a weakened immune system, the virus can be fatal.
Roughly 5 to 20% of the American population suffer from the flu each year (CDC, 2015) and over 200,000 people are admitted to hospital as a result of flu-related complications. Treatment for the flu varies from drinking plenty of fluids and resting, to prescription antiviral drugs which work by stopping the virus from multiplying and spreading throughout the body. They can both shorten the duration of the illness, and help to prevent it spreading to other people.
As with all medications, however, there are side-effects to these antiviral drugs. It is much more beneficial to try and prevent the flu from occurring by ensuring you receive your annual flu shot. This can also save each US state up to $957.5 million dollars per year (Mao, Yang, Qui and Yang, 2012) and the UK £1.35 billion pounds each year (The Co-operative Pharmacy, 2010).
However, not everyone is eligible to receive the free flu vaccine. For the flu shot, this includes people who have children younger than 6 months, and people with allergies to the ingredients within the vaccine (which could include those allergic to gelatine, antibiotics, and even egg).
For the nasal spray, this includes adults over 50 years of age, people with allergies to any ingredients (including those allergic to eggs), people with weakened immune systems, children younger than 2 years old, and children on long-term aspirin treatment (CDC, 2014).
In any of these cases, and even for those who do receive it, ensuring that you practise good health habits can make a significant difference to your risk of contracting the flu. These health habits include regular hand washing, exercise, sleep, managing stress, and eating a nutritious diet (CDC, 2015) high in Vitamin C, which is known to be an anti-viral agent (Guerriero, Capone, Colanna and Castello, 2014).
Li, Maeda and Beck (2006) gave five-week old Vitamin C deficient mice either plain water, or water infused with Vitamin C for three weeks. They then infected the mice with influenza, and assessed the immune response to the virus.
They found that the mice which had been supplemented with Vitamin C had worse lung pathology 1 and 3 days after infection, but that at 7 days their lung function was significantly better than the mice which had not been supplemented with Vitamin C. This suggests that a deficiency in Vitamin C can decrease the effectiveness of the immune system to fight off influenza.
These results were taken a step further by Hemelä and Louhiala (2013) who investigated whether enhancing Vitamin C in non-deficient patients could improve pneumonia incidence and pathology (influenza is the main precursor to pneumonia, and so they have similar pathological profiles).
They reviewed three prophylactic (preventative) trials and two therapeutic (treatment) trials, and found that all five trials showed a significant positive effect of Vitamin C. In other words, for the three preventative trials they found that Vitamin C supplementation was extremely effective at preventing pneumonia, and for the two therapeutic trials they found that it was very good at improving symptoms of the infection.
Although no studies have been conducted which specifically assess the impact of grapefruit consumption on influenza, due to their high Vitamin C concentration it is extremely likely that consumption will improve symptoms, and may even prevent contraction of the virus.
4. Could Help Prevent Stroke
A stroke is an extremely serious event where a blood clot causes the blood supply to the brain to be significantly reduced or cut off (NHS, 2013). There are a variety of risk factors associated with a stroke, including being older, high blood pressure, smoking, being overweight, high cholesterol and diabetes.
In England, around 110,000 people have a stroke and it is the third largest cause of death in the country. Although strokes are not always fatal, they can often leave patients with chronic side-effects including muscle weakness, speech problems, memory and cognitive problems, vision problems, and difficulty in regulating emotions and behaviour (The Stroke Association, 2015).
Treatment for stroke is variable in its success, but it includes medicines called thrombolysis for removing blood clots (which have a 1 in 7 success rate), antiplatelets such as aspirin which reduce the risk of new clots forming, anticoagulants which have a similar role, antihypertensives to reduce blood pressure, and statins to reduce cholesterol.
Some strokes are caused by a narrowing of the carotid artery in the neck, and if the narrowing is particularly severe, treatment may include surgery to unblock the artery. As strokes are difficult to treat, the treatment is not always effective and there are often chronic side effects following the event. It is therefore very important to do everything possible to prevent one from occurring.
Reducing risk factors by making healthy lifestyle choices is particularly important, and adopting a healthy diet is one such change that can make a big difference.
Some foods which have been shown to be particularly beneficial for reducing the risk of stroke are vegetables, soy, fruits, and to a lesser extent, fish, animal products and whole grains (Sherazi, Haim, Boothby and Sherazi, 2012).
Citrus fruits are thought to be particularly beneficial for preventing stroke because some of them contain a type of antioxidant called a flavanone. This is a subclass of flavonoid, and they are found in both oranges and grapefruit.
A prospective research study on nearly 70,000 women was conducted by Cassidy et al (2013), where their flavonoid intake was assessed alongside stroke incidences. They found that although there was no link between total flavonoid intake and stroke risk, women who consumed more flavanones (found in oranges and grapefruit) did have a significantly lower risk of stroke (19%).
Further support for grapefruit as a protective food against stroke is in a review by Raza et al (2012). They discuss evidence which suggests that naringenin, a specific type of flavonoid found in grapefruit, may be very effective against inflammatory conditions.
Inflammation has a significant role in stroke, as the brain becomes inflamed during and after, which can contribute to prolonged side-effects and permanent brain damage (Jin, Yang and Li, 2010).
Alongside evidence that these antioxidants are cardio protective (as mentioned in the section about cholesterol), it seems possible that grapefruit may well contain stroke-preventing nutrients and as such should be included in the diet of those at risk.
5. Fights Cancer
Cancer is the biggest cause of premature death (i.e. death before 75 years of age) in the UK (NHS, 2014) and according to the Office for National Statistics (2014) it was the most common ‘broad cause of death’ at 29% of all deaths.
In the USA, the American Cancer Society (2015) estimates that over 310,000 men will die from cancer in 2015, as will over 270,000 women. Globally, there are around 14 million new cases of cancer each year, and over 8 million people died from cancer in 2012 (WHO, 2015).
Cancer Research UK (2015) claims that more than one in two people born after 1960 will be diagnosed with some form of cancer during their lifetime. It is clearly a huge global problem, yet more than 30% of these deaths could be avoided by making changes to risk factors (WHO, 2014). For lung cancer, this figure rises to a massive 70% of cases due to tobacco smoking.
Some of the biggest risk factors for developing cancer include tobacco use, alcohol consumption, unhealthy diet and physical inactivity. Diets which contribute to higher incidences of cancer are those which usually include large portions (particularly of high calorie foods), sugar sweetened beverages, processed meats, high levels of red meat consumption, too many refined grains, and low levels of fruit and vegetable consumption (less than 2.5 cups per day, American Cancer Society, 2014).
Everybody knows that a diet high in fruits and vegetables is important, but it is not always clear as to why this is. The reason they are good for reducing cancer risk is because of a three-factor combination; firstly, they contain very little salt, secondly, they have a lot of fibre, and thirdly, they contain more cancer-fighting nutrients than any other foods (Cancer Research UK, 2015).
Cancers caused by a poor diet include bowel cancer, mouth and upper throat cancer, larynx cancer, lung cancer, stomach cancer, and oesophageal cancer.
Stomach cancer has been linked to high consumption (more than 6g a day) of salt. The link is thought to occur because too much salt increases the growth and activity of bacteria called Helicobacter pylori (H. pylori). Salt can also damage the stomach lining, making the stomach more vulnerable to H.pylori. The bacteria can lead to inflammation, which in turn can cause stomach ulcers and ultimately stomach cancer.
Consuming more fibre is very important for preventing bowel (colorectal) cancer, which is the fourth most common cancer in the UK (Cancer Research UK, 2015) and the third most common in the USA (American Cancer Society, 2015). It is also the second biggest cause of death of all cancers in the USA.
Fibre comes in two forms; soluble and insoluble. Soluble fibre dissolves in water, and is important as it can reduce the amount of cholesterol in your blood, and can help to relieve constipation. As well as relieving the discomfort associated with constipation, but as stool is helped to move through the gut, it reduces the amount of time that the bowel is in contact with harmful chemicals within the stool.
Insoluble fibre helps to make stools more bulky, which also helps them to move through the bowels more efficiently. It helps to keep the bowels healthy and prevent digestive problems. Fibre also feeds the healthy bacteria in the gut which is responsible for destroying microbes, yeast and candida which can cause cancer, and they can synthesise important cancer-fighting agents such as folic acid and vitamin K.
The nutrients found in fruits and vegetables are very important for fighting cancer. Research cited by Cancer Research UK (2015) suggests that 1 in 20 cancers are due to diets which are too low in fruits and vegetables.
This is because the diets lack antioxidants which can fight cancer-causing free radicals, nutrients which can protect DNA against cancer-causing damage, nutrients which can repair DNA when it has been damaged, and nutrients which can block the formation of cancer-causing chemicals.
These nutrients include carotenoids (which give many fruits and vegetables a distinctive orange colouring), folate, vitamin C, vitamin E, selenium, and flavonoids.
Grapefruit are a very good example of cancer-fighting fruit, because they contain naringenin, limonin, and the red and pink varieties also contain beta-carotene and lycopene. Grapefruit can help to prevent cancer in a variety of ways.
Firstly, as it is a successful weight-loss promoting food, it can reduce the risk of cancers related to being overweight and obese, such as breast, colorectal, kidney, and pancreatic cancer (Cancer.net, 2015).
Secondly, they have very high fibre content at 6% RDA per 100g. They have a ratio of approximately 1:6 insoluble to soluble fibre. This means they provide the benefits of both types of fibre to help protect against bowel cancer.
Thirdly, the cancer-fighting nutrients they contain have been proven to reduce the risk of colorectal cancer (American Institute of Cancer Research, 2014). Furthermore, there is good evidence that they may be helpful for reducing the risk of cancers of the mouth, larynx, pharynx, oesophagus, lung and stomach.
Laboratory research is currently investigating the impact of powdered grapefruit, limonin and naringenin on a variety of cancers, and the result have been very positive.
6. Helps With Skin Problems
Grapefruit are extremely rich in Vitamin C, and this makes them a brilliant food for improving the health and appearance of skin. Skin is the biggest organ on the human body, and is the first line of defence for the immune system.
It is made up of three layers. The outer layer is called the epidermis and is made from a protein called keratin. The second layer is called the dermis, and is comprised of collagen and elastin, which provide the skin with strength and elasticity. This is also where body hair and sweat emerge from. The internal layer of the skin is called the subcutis, and is a layer of fat which works as a fuel reserve, as insulation for heat, and as a cushion for damage.
Everybody knows the importance of skin, and it is also clear that without the correct care it can become damaged, meaning it will not work effectively. Vitamin C is an important nutrient to maintain the health of skin because without it, we would not be able to create collagen.
As mentioned above, collagen gives skin its strength and elasticity. Collagen production decreases as we age, and this is why older skin tends to be more saggy and dry than younger skin. It is also more prone to damage and disease; according to Ward (2005), 70% of the elderly population have a skin condition.
As well as providing structure to the skin, collagen is also one of the main components of wound healing. It is the building block of new skin, and attracts cells to the wound. These cells, called keratinocytes, perform a number of functions including debridement (cleaning the wound of dead and damaged cells), angiogenesis (the formation of new blood vessels), and reepithelialisation (the construction of new skin over the wound). As well as triggering these processes, collagen also acts as a scaffold over which new skin can be formed.
Due to the numerous functions collagen performs in the skin, having enough Vitamin C so it can be created, is vitally important. Not only does Vitamin C create collagen, but it also has it’s own direct role in skin protection. It is a very powerful antioxidant, meaning it can fight off the damage done to the skin by free radicals.
These are molecules which are missing an electron, and try to take electrons from other cells in the body. When they pair with electrons from incompatible cells, they can cause that cell serious damage. Over time, this can build up into diseases such as cancer.
Free radicals occur naturally in the body as a by-product of respiration, but their numbers can be increased when the body is exposed to radiation, a poor diet, little exercise and other factors.
The sun can cause damage to the skin when there is an excessive exposure of UV (ultraviolet) rays. There are two types of UV, both of which cause different types of skin damage; UVA ages skin, whilst UVB burns it.
Popular sunscreens claim to protect against both UVA and UVB, and although they are generally effective, incidence of skin cancer has been increasing over the past 40 years (Cancer Research UK, 2013). Males are now seven times more likely to develop skin cancer, and females are 4 times more likely. As a result of this growing need for more effective sun protection, research has been conducted on how sunscreens might be improved.
One Malaysian study, for instance, investigated how Vitamin C can change the effectiveness of sunscreen. Kamsiah et al (2013) compared both international and local sunscreens on levels of Vitamin C and Vitamin E (another nutrient thought to be protective against UV) and they found that sunscreens which had higher levels of Vitamin C had significantly higher SPF values.
SPF stands for Sun Protection Factor, and is a measure of how much longer one can (theoretically) stay out in the sun without sun damage when wearing the sunscreen. For instance, an SPF of 50 means that, in theory, the sunscreen should allow you to stay in the sun without damage for 50 times longer than if you wore no sunscreen.
A clinical review of Vitamin C research was conducted by Farris (2005) and it was found that it is extremely effective in protecting against both UVA and UVB. It was also found that it can help to promote the production of collagen, improve uneven skin tone, and even improve the symptoms of a variety of inflammatory skin conditions.
As one grapefruit contains more than 100% RDA Vitamin C for an adult consuming approximately 2000 calories a day, it is a wonderful food for improving the appearance of skin, and even fighting skin conditions.
Some Things to be Aware of
Although grapefruit do have a number of well-researched health benefits, there are some individuals who need to be careful about how much grapefruit they consume.
Grapefruit is known to interfere with an enzyme called CYP3A4 (FDA, 2015). This enzyme is responsible for metabolising drugs within the small intestine, and so when the enzyme is inhibited, more drugs can enter the blood stream.
This can lead to a potentially dangerous level of drug within the blood, particularly for medicines which require repeat administration. For medications containing fexofenadine, grapefruit actually has the opposite effect and can reduce the absorption of drugs into the blood stream. This can reduce their effectiveness. This is not due to interference of CYP3A4, but rather interference of a specific group of drug transporters in the body.
Grapefruit will affect different people in different ways depending on how much ofCYP3A4 they have in their intestine and how many drug transporters they have. In order to be safe, however, it is important to ask your doctor or pharmacist if it is possible that grapefruit may interfere with your medication.
Some medicines known to be affected by grapefruit include some statin drugs (simvastatin, atorvastatin and pravastatin), some blood pressure drugs (nifedipine), some transplant rejection drugs (cyclosporine), some anti-anxiety drugs (buspirone), some anti-arrhythmia drugs (amiodarone) and some antihistamines (fexofenadine).