This month’s column is devoted to two issues locals have asked about recently.
Nitrites and nitrates
Nitrates hit the headlines recently when health authorities in France publicised a new study that supported earlier warnings from the World Health Organisation linking nitrates in ham, bacon and other processed meats with increased risk of colon (bowel) cancer.
Nitrates are added to many processed foods as a preservative. The highest levels are found in processed meats. Nitrites are also still used and give the pink colour to ham and bacon, but in lower quantities than in previous times.
Some vegetables, including beetroot and leafy greens like spinach and kale, also contain nitrates. Other sources include beer and contaminated drinking water. Nitrates are also used extensively as a source of nitrogen in fertilisers.
Nitrites and nitrates differ slightly in their chemistry with nitrates having an extra oxygen (NO3) compared with nitrites (NO2).
Nitrates are more stable and are fairly harmless in themselves. They are regarded as problems because they can be converted to nitrites by bacteria in saliva, enzymes in the small intestine and predominantly by bacteria in the colon.
Nitrites can be ‘good’ because they can form nitric oxide which helps control heart rhythm. But they can also be ‘bad’ because they can be converted to compounds called nitrosamines, which increase the growth of undesirable cancer-causing bacteria in the colon.
To add to the complication, nitrosamines form from the amino acids in proteins. The protein bound to iron in meat, especially red meats, is a major source of nitrosamines in the colon and is a reason why a diet high in red meat increases the risk of colon cancer.
Although they are sources of nitrates, vegetables do not add to risk. Indeed they protect us from the risk because their vitamin C and many of the polyphenols they contain actually stop nitrates being converted to the harmful nitrites. Vitamin E in nuts and wholegrains has a similar protective role in preventing nitrates being converted to nitrites.
Take home message: nitrites and nitrates in vegetables are not a problem, but they are a potential problem in meats, especially processed meats. The best bet is to keep processed meats to a minimum, and always consume vegetables at the same meal as a red meat (where the safest serving should occupy not more than a quarter of a normal-sized plate). And for many reasons, wholegrains and nuts add extra protection.
Lactose intolerance
The only natural source of lactose is the milk of mammals. Lactose is a double sugar (or disaccharide) composed of glucose and galactose. It is broken down to these component sugars in the small intestine under the influence of an enzyme called lactase. After weaning, when mammals have no more need of lactase, its production gradually declines.
However, the ability to digest milk has evolved in many populations, dating back to ancient times. This evolution has occurred due to variants in the lactase-producing gene that enables cells to continue producing high levels of lactase in people who consume the milk of domesticated cows, goats, sheep or camels.
The timing of this evolved lactase persistence is uncertain. Milk-producing animals were domesticated 10,000 -12,000 years ago, although they were probably initially valued for meat rather than milk.
Scientists have speculated that people who consume milk from animals continued to produce lactase and therefore gained a new source of calories, protein, calcium and many other minerals and vitamins. These individuals would then pass their variant of this genetic ability to continue producing lactase to their offspring who would then be healthier than those who had not the advantage of this nutrient-rich food.
However, a new study published in the journal Nature analysed human DNA samples from 1,700 ancient Eurasian people and also 7,000 animal fat residues from 13,181 fragments of pottery from 554 different archaeological sites dating back to the beginnings of animal domestication. Their genetic studies did not find any evidence of lactase persistence in early animal farmers.
When colleagues checked the United Kingdom’s Biobank health and genomic data for 500,000 people, they noted little correlation between milk consumption and lactose tolerance, and no clear health or fertility benefits for those who tolerated lactose.
Their conclusion is that the early dairy farmers would have simply put up with the unpleasant but not deadly symptoms of undigested lactose – gas, bloating and diarrhoea. By contrast, those who were already malnourished or suffering other infections may well have died from the added burden of the diarrhoea that would have accompanied consumption of milk. From this new work, the researchers suggest a genetic mutation to continue to produce lactase may be as recent at 1,000 B.C.
Checking other findings, these researchers (who I don’t think have been funded by the dairy industry) also back other findings showing many people who believe they are lactose intolerant do not need to avoid milk.
Lactose intolerance is not an allergy where even small amounts of the problem food can be hazardous. Allergic reactions occur to the protein in a food. A small number of infants do develop allergies to the protein in cows’ or goats’ milk, and an even smaller number may be allergic to the protein in their own mother’s milk. This is quite different from lactose intolerance.
A number of studies have shown that small amounts of lactose are almost always well tolerated in those with lactose intolerance.
As described earlier, lactase breaks lactose to its component sugars in the small intestine. In those who produce little or no lactase, the undigested lactose will pass to the large intestine where it is broken down by ‘good’ bacteria. Indeed, a little lactose helps these beneficial bacteria to thrive. All tasks associated with ‘good’ bacteria lead to production of gas. This is normal and an essential by-product of a healthy bowel. These gases must escape and should be allowed to do so – although our social norms mean we’d prefer it to be done in private!
The discussion that led to this article arose at a lunch when a friend said she was sad that she had to avoid cheese because of her lactose intolerance. She was unaware that most cheeses have minimal lactose and are fine for those with lactose intolerance. The only exception could be ricotta, which is made from the whey portion of the milk (which contains the lactose). Even then, you’d need to eat a large quantity of ricotta to cause any reaction.
Genuine yoghurt that contains ‘live’ strains of bacteria is also rarely a problem, as the bacteria will partially digest the lactose to its component sugars and reduce the need for lactase. Check the ingredient list and avoid products that do not specify ‘live’ cultures. It’s also a good idea to check if inulin has been added as a thickener, as it is derived from artichokes – and responsible for their nickname of ‘fartichokes’.
For people with lactose intolerance, double-blind studies of milk with and without lactose show that small amounts (1/2 to 1 cup) produce few if any symptoms, but do help increase ‘good’ bowel bacteria.
Dr Rosemary Stanton OAM
