It is not uncommon for dietary recommendations to be made on the basis of just one or two of a food's constituents. Yet most things that pass our lips are complex chemical concoctions, which means that judging foodstuffs on just a small portion of what they contain may lead to not altogether accurate assessments of their likely effects on health. I spied an example of this misappliance of science in the Journal of Urology.
Researchers found that dosing up individuals with pure caffeine brought about biochemical changes in their urine that would be expected to increase the risk of kidney stones. So the authors recommended strict limits on tea and coffee consumption for those with a history of kidney stones. In stark contrast to this advice, several studies link tea and coffee quaffing with lower kidney stone risk.
The apparent ability of coffee and tea to protect against kidney stones is quite likely something to do with the fact that the principal component of these beverages is water. Drinking tea or coffee stimulates fluid flow through the kidneys and bladder, which is likely to reduce the risk of stones. Another option is simply to drink more water. In one study, this reduced the chances of kidneystone recurrence by more than half.
Kidney-stone risk is also related to what we eat. Stones come in several forms, the most common being composed of calcium and a substance called oxalate. Individuals with a history of such stones may be be advised to limit their consumption of calcium-rich foods (eg dairy products, seeds and green vegetables). However, this recommendation does not appear to be scientifically sound: studies show that those with higher intakes of calcium tend to be at reduced risk of calcium oxalate stones. Calcium binds to oxalate in the gut, barring its entry into the body. Scientists theorise that calcium in the diet can actually protect against the formation of calcium oxalate stones.
Magnesium and vitamin B6 help convert oxalate into substances that do not contribute to stone formation. Nuts are rich in both, and also contain useful quantities of potassium, which has also been linked with a reduced risk of kidney stones. Other sources of potassium include fruit and vegetables.
Studies in which individuals have supplemented with vitamin B6 and/or magnesium have produced promising results, with one study showing that a combination of the two reduced kidney stone recurrence by 90 per cent. I recommend supplementing with 400-500mg of magnesium and 25-50mg of vitamin B6 each day. The evidence suggests that nutritional approaches help ensure that those prone to kidney stones have no hard feelings.
Dear John
Recently you recommended diluting fruit juices with water. However, in the past you have recommended not drinking water with meals. Can you clarify this for me?
Philip McLaughlin Preston
The reason I recommend not drinking much water (or any fluid) with meals is that this risks diluting the stomach acid and digestive enzymes that are important in the digestion of food in the digestive tract. Good digestion helps ensure that we extract maximum nutritional value from food, and also reduces the risk that undigested food will create problems with toxicity in the body.
The main nutritional components in fruit juice (other than water) are sugars that require little or no digestion prior to absorption. In other words, diluting juice is unlikely to impair the body's ability to digest it. This will, however, reduce its sugar concentration, and slow the rate at which it liberates sugar into the bloodstream. Tempering blood-sugar release will help to reduce the amount of insulin the body needs to secrete in response. This reduces the risk of problems associated with insulin excess, such as weight gain and diabetes.
Nutrition news
While not all women are able to or wish to breastfeed, there is a wealth of evidence which suggests that this practice has distinct health advantages over bottle-feeding. Studies show that breastfeeding can help to protect against a range of conditions including allergic conditions, such as asthma. In a recent study published in the American Journal of Public Health, researchers examined the relationship between breastfeeding and asthma in a group of children followed from birth to six years of age.
Overall, each month of exclusive breastfeeding was found to be associated with a 4 per cent reduced risk of asthma. One potential explanation for this might be that breast milk contains factors that contribute to the health of a child's immune system. Also, exclusive breast-feeding delays the introduction of cow's milk products, and this may reduce the risk of a child becoming sensitive to such foods (in practice, sensitivity to cow's milk products is a common factor in childhood asthma). Whatever the explanation, this recent research supports the notion that breastfeeding reduces the risk of allergic disease in children.
