The Collison Newsletter February 2016


GRAPEFRUIT Health Benefits*


Grapefruit, citrus paradisi, is a subtropical citrus tree known for its sour to semi-sweet fruit. It is an 18th century hybrid between sweet orange, citrus sinensis, and pomelo, citrus maxima.

It is called a grapefruit simply because it grows in clusters.

The fruit of the grapefruit tree, herein referred to as 'grapefruit', is yellow-orange skinned and spheroid in shape, with a diameter between 10-15cm. There are seed and non-seed varieties. The flesh of the grapefruit is segmented and acidic. The colour of the pulp and juice varies from white, pink and red. Its albedo (the white matter under the skin, the mesocarp or pith) is about 6-12mm thick. There is varying sweetness, the red variety being the sweetest.

The grapefruit has many valuable nutrients: trace elements, vitamins (especially vitamin C), phytochemicals, antioxidants, the fibre pectin and, in the pink/red varieties, lycopene.

Nutritional Values of Grapefruit (raw, white) per 100 grams (see


138 kJ (33kcal)





Thiamine B1


Riboflavin B2

Niacin B30.269mg
Pantothenic acid B50.283mg
Pyridoxine B60.043mg
Folate B90.01mg
Vitamin C33.3mg
Vitamin E0.13mg
Vitamin A0.002mg
Trace Elements
Zinc0.07 mg
Carotene (alpha & beta)0.022mg

It also contains citric acid and essential oils like limonene, pinene, and citral. The phytonutrients in this fruit are limonoids, flavonoids, glucarates and, in the pink/red variety, lycopene.

Grapefruit is an acid fruit. However, after digestion, it is strongly alkali-forming. It is thus a useful food that can be part of the recommended diet that should be made up of 75-80% alkali-forming foods (see my September 2005 newsletter Acid / Alkaline Balance - The Ideal Diet).

Grapefruit has a glycemic index rating (GI) of 25. Thus it is regarded as a low GI food, one which will not raise the blood sugar or insulin level significantly when consumed.

Health Benefits of Eating Grapefruit

  • Vitamin C

Grapefruit is an excellent source of vitamin C. This vitamin helps support the immune system and is effective in reducing cold symptoms or the severity of cold symptoms. It is an antioxidant and assists in the prevention of free radical damage that triggers the inflammatory cascade. Free radicals can oxidise cholesterol and lead to plaques that may rupture causing heart attacks, hence vitamin C is beneficial in promoting cardiovascular health.

  • Lycopene - found in the pink and red grapefruit varieties

Lycopene is a carotenoid phytonutrient. (White grapefruit does not provide this nutrient.) Lycopene has anti-tumour activity. It has a high capacity to fight oxygen free radicals. Research has shown lycopene to reduce a man's risk of developing prostate cancer. (Other sources of lycopene include lycopene-rich fruits such as tomatoes, apricots, watermelon, papaya, and guava - see my December 2009 newsletter Lycopene - A Powerful Antioxidant.)

  • Antioxidant activity

Lycopene is a powerful antioxidant. However, white grapefruit also have strong antioxidant properties. Not all fruits are the same. They differ markedly in the variety of phenolic compounds and antioxidant activity. When the different fruit juices were analysed from this point of view, grapefruit was one of the highest scorers. (Just what antioxidants are, and how they work, has been discussed fully in my January 2007 newsletter Free Radicals Antioxidants.)

  • Phytonutrients

These include limonoids and flavonoids. These are said to inhibit tumour formation by promoting the formation of glutathione-S-transferase, a detoxifying enzyme. This enzyme activates the liver to help make toxic compounds more water soluble for excretion from the body. The pith of all citrus fruits, but especially grapefruit, contains glucarates, which research suggests may help prevent breast cancer. The limonoids are readily bio-available, which may account for their being powerful anti-carcinogens.

  • Pectin

This is a soluble fibre. It can assist in cholesterol control. It binds bile salts in the gut (which take part in the digestion of fat) and so prevents them from being reabsorbed back to the liver that produced them originally, an enterohepatic circulation. Being bound, the bile salts are lost from the body and so the liver has to produce more, which it does from cholesterol. Both the white and pink/red positively influenced the cholesterol levels, but the red grapefruit was more than twice as effective in lowering triglycerides levels.

Grapefruit and Drug Interactions

Interactions can happen when medicines mix with certain foods or drinks, and grapefruit is one example of this. A review article published in the Canadian Medical Association Journal (November 2012) highlights more than 85 medicines that can interact with grapefruit, with 43 of these having potentially serious consequences.

Grapefruit contains furanocoumarins.

Furanocoumarins are a class of organic compounds produced by a variety of plants. Many are toxic and are produced by the plant as a defence mechanism against various types of predators, ranging from insects to mammals. They have other biological effects as well. For example, bergamottin and 6', 7'-dihydroxybergamottin are responsible for the "grapefruit juice effect" in which these furanocoumarins can interfere with the way your body metabolises or processes certain drugs in the intestines or liver before they reach the blood stream. When this happens, more of a medicine may get into your body, making it work too strongly or causing unwarranted side effects.

This happens because of their effect on 'CYP3A4' - an enzyme involved in metabolising many medicines. Medicines need to be taken orally to be affected by grapefruit because grapefruit mainly affects this enzyme in the gut. Bitter oranges and limes may also cause interactions with medicines. Other citrus fruits such as sweet oranges and lemons do not have the same effect. Consuming any part or form of grapefruit can cause an interaction.

Certain medicines are more likely to have serious interactions with grapefruit than others. The following is a list of the "Medicine Category" of these medicines:

  • Anti-cancer medicines
  • Antibiotics
  • Antimalarials
  • Antiviral medications
  • Cholesterol and lipid medications
  • Medicines for heart conditions
  • Anti-hypertensive medications
  • Anti-clotting medications
  • Anxiety medications
  • Cough and cold medications
  • Opioid pain relievers
  • Medicines for psychotic conditions
  • Nausea and vomiting medicines
  • Immune system modifying medications.

For full details of the drugs in the above medicine categories and other medications refer to and type in "grapefruit and medicine interactions".


Tart and tangy with an underlying sweetness, grapefruit has a juiciness that rivals the ever popular orange. The health benefits of grapefruit are many. The Latin name citrus paradisi suggests that it is a taste of paradise.

Care should be exercised if you are taking certain medications.


*Copyright 2016: The Huntly Centre.

Disclaimer: All material in this newsletter is provided for informational or educational purposes only. Consult a health professional regarding the applicability of any opinions or recommendations expressed herein, with respect to your symptoms or medical condition.


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