Warning on fruit juice and drug interactions

Sorry to be still on the fruit juice trail, but news this week had a real deja-vu quality about it for me. In the 1980′s, I was involved with a naturopath in the writing of a book called ‘The Medicine Chest’ which looked at the relationship and interaction between foods, vitamins and medicines. One of the things we flagged up then was how food can affect your medication. One example of this is the drug warfarin which interacts with vitamin K, which we get from food, and from the bacteria in our gut. Vitamin K is involved in the formation of special liver proteins, known as coagulation factors, which reduce the risk of haemorrhage or bleeding. Conversely, if you are susceptible to blood clotting, warfarin (because of how it interferes with the formation of these vitamin-K-dependent factors) may be prescribed for you. So you can see that if you increase the amount of vitamin K-rich foods then you can alter the effect that the warfarin will have in your body. Such foods include everyday items like spinach, lettuce, beef, broccoli and soy beans – good foods in themselves but to be discussed with your doctor if you are on warfarin.

Now the scientific world seems to have caught up with the research done by naturopaths over the years, which has always treated food as ‘medicine’ and been much more aware of its effects. Recent research presented at a US conference has now suggested that a chemical in grapefruit, orange, and possibly also apple juice, could stop anti-allergy drugs being absorbed properly. Grapefruit juice is already known to interfere with blood pressure drugs and indeed some medicines carry a warning that taking them alongside grapefruit juice could cause an overdose and normally your pharmacist will point this out to you. However, the latest finding shows that grapefruit juice had the reverse effect on fexofenadine, an antihistamine drug, making it less rather than more potent. Volunteers took the drug with either a single glass of grapefruit juice, or just water.

When it was taken with juice, only half the drug was absorbed, potentially reducing its effectiveness. The active ingredient of the juice, naringin, appears to block a mechanism which moves drug molecules out of the small intestine into the bloodstream and this substantially decreases the absorption of certain drugs.

The three juices mentioned have also been found to affect etoposide, a chemotherapy drug, some beta-blocker drugs used to treat high blood pressure, and cyclosporine, taken by transplant patients to prevent rejection of their new organs. Dr David Bailey of the University of Western Ontario, the study’s author, said: “This is just the tip of the iceberg – I’m sure we’ll find more and more drugs that are affected this way.”

Cholesterol – Keeping the balance naturally

If you watch television, or read magazines, you cannot miss the constant bombardment on the ‘evils’ of high cholesterol. Certainly, out of control levels of high cholesterol are to be avoided, but so too is low cholesterol. It is not the cholesterol itself that is ‘evil’; we actually require normal levels for the production of the hormones testosterone and oestrogen, and it is found in our cell membranes as part of the structure to keep them waterproof.

Without cholesterol, we could not have a different biochemistry on the inside and the outside of the cell. When cholesterol levels are not adequate, the cell membrane becomes leaky or porous, a situation the body interprets as an emergency, and then releases a flood of corticoid hormones to repair the damage.

Cholesterol is therefore essential as it is the body’s chief repair substance: scar tissue contains high levels of cholesterol, including scar tissue in the arteries. So you can see that so cutting out all cholesterol is actually a bad idea. Studies have shown that there is an increased risk of strokes and a compromised immune system when cholesterol drops too low, but as always the answer lies in balance.

If you do have high cholesterol then it can lead to hardening of the arteries and heart disease, but statin drugs, given for the inhibition of cholesterol, – as I have reported before – have their problems too. They have been associated with side effects such as muscle pain and weakness, memory loss, nerve problems and interference with production of Co-Q10.

Natural Solutions?

So, if you don’t want to take drugs to lower your cholesterol, what can you do? Back to the advertisers, who imply that by switching to their margarine, or yoghurt product, you can lower your levels naturally. Well, that depends on what you mean by ‘naturally’. If you read the labels on those products, they contain many chemical compounds, and the ‘healthy’ yoghurt drinks contain not only sugar but sweeteners as well.

So what else is left? Enter the humble grapefruit, wholly natural and a lot cheaper than buying the aforementioned products.

An international team of researchers from Israel, Singapore and Poland put grapefruit to an extremely rigorous cholesterol test. Researchers at the Hebrew University in Jerusalem, recruited nearly 60 subjects who had several things in common: they all had undergone recent coronary bypass surgery, had high cholesterol levels, and had used a cholesterol-lowering statin drug with no success. At the outset of the study, none of the subjects had taken any statins for at least 30 days and they were divided into three groups. Over the 30-day study, everyone followed the same low-fat diet, but one group ate one yellow grapefruit a day, while another group ate one red grapefruit daily. They all ate their normal, everyday diet and the third group got no grapefruit at all.

At the end of the study, the two groups who had eaten the daily grapefruit had lower levels of both total cholesterol and LDL – and it was even more marked in the group who ate red grapefruit. Another benefit seemed to be that triglyceride levels also dropped in the red grapefruit group, but not in the other groups. Triglycerides are blood fats that can leave deposits in coronary arteries, and so increase the risk of heart disease.

Now my problem is that my local supermarket has red, yellow and pink grapefruit so I might have to ask them for advice on whether ‘pink’ hasĀ a diluted effect from the ‘red’ benefits!

More Good Grapefruit News

Oh, and if you are wanting to lose some weight, there was a study at the Scripps Clinic in San Diego four years ago, in which a group of 100 obese subjects were told to stay on their normal diets, and in addition were given either grapefruit or grapefruit juice to have once a day. On average they lost 3lb, and one person lost 10lbs, as opposed to the non-grapefruit trial group who lost less than a 1lb.

Diabetics may also be interested to learn that the subjects in that same study also showed better management of insulin levels. Those in the two grapefruit groups had lower levels of insulin and glucose than they did at the outset, while levels in the non-grapefruit group were unchanged. The Scripps researchers believe that enzymes in grapefruit help control insulin spikes that occur after a meal, which frees the digestive system to process food more efficiently. This means that less nutrients are stored as fat.


Many foods can interact with the effectiveness or efficiency of drugs, and grapefruit are no exception. Chemicals in grapefruit interfere with the enzymes that break down certain drugs in your digestive system and this can result in excessively high levels of these drugs in your blood, and an increased risk of side effects. The following list is a generic overview of the classes of drugs that may be affected. Bear in mind that it may not be all drugs within a particular group, so consult with your doctor if you are taking any of the following types of medication:

Anti-seizure medication – anti-arrhythmia drugs – antidepressants – erectile dysfunction – Calcium channel blockers -HIV medications – HMG-CoA reductase inhibitors used to treat high cholesterol – Immunosuppressant drugs – Methadone Pain relief – Tranquillisers.