Wednesday, February 23, 2011

Life is a gas, and it's healthy

Borborygmi. One of my favourite words. Borborygmi are the gurgling sounds of gas travelling along your intestines. The rumble can be most pronounced during a conversation lull at the dinner table. Hark, I hear borborygmi.

Gas inside your digestive system is normal. It comes from two main sources: 1) the air you swallow during eating or drinking; and 2) gas produced by bacterial fermentation in the large bowel, the back end of your digestive system. Smaller amounts come from CO2 production when your stomach acid is neutralised in the small intestine.

Air swallowing

One obvious way of swallowing air is through aerated drinks such as soft drink, champagne and beer. This usually comes back into the atmosphere via eructation (burping to you). Air can also be swallowed during eating, more commonly in those that eat quickly or talk a lot during the meal. If it isn’t burped out then it will pass from your stomach and into the small intestine.

Bacteria gas

Once the contents of your small intestine pass the appendix and into the large intestine, the resident bacteria feast on the fibre and small amounts of starch and protein that doesn’t get digested. When bacteria feed they produce gas. In fact, 75% of flatus is bacterial gas. As the contents move along the large intestine (aka colon) water is absorbed so the waste becomes more solid and the gas becomes entrapped in large bubbles.

Some bacterial gas is absorbed back into the blood and exhaled. This is the basis of a breath hydrogen test. If you have, say, suspected lactose intolerance your breath is tested for its hydrogen content because if lactose has reached the colon the bacteria will consume the lactose and generate far more hydrogen than normal.


Most of flatus is oxygen, nitrogen (the two main components of air), hydrogen, methane and carbon dioxide. Some sulphur containing gases provide the head-jolting aroma. You want to know: why baked beans? The legume family have plenty of fibre and two types of carbohydrate that don’t get digested well – stachyose and raffinose – which then become bacteria food with the end product being gas.

Here’s the physics of what happens to gas down the back end. The abdominal muscles and the anal sphincter contract at the same time, thereby raising the pressure of the gas against the anal sphincter and then, at the magic moment, the pressure gradient sends out the air at high speed through a very narrow slit too small for solid waste to escape. Hopefully. The high speed gas causes the edges of the anus to vibrate. Maybe fart should be pronounced with a distinctive rolled “r”.

What does it all mean?

Gas is normal. You can reduce the amount of swallowed air by avoiding fizzy drinks and eating slower. Colonic gas is from bacteria eating undigested food ie fibre, which is exactly what the health authorities want you to eat. As one author said: “Flatulence rich in bacterial gases might be the price for the large bowel water reabsorption. It seems that little can be done to reduce flatulence.”

So if you eat plenty of fibre-containing food, you will release more methane into the air, vis-à-vis, don’t think you can solely blame global warming on the cows.


Medical Hypotheses 2006; 67: 235-239

American Journal of Gastroenterology 2007; 102: 842-849

Public gas in Malawi

On the 5th February 2011 it was reported that public farting will become an offence in the southern African country of Malawi.

“The government has a right to ensure public decency”, said George Chaponda the justice and constitutional affairs minister. “Would you like to see people farting in public anywhere? It was not there during the time of dictatorship because people were afraid of the consequences. Now because of freedom people would like to fart anywhere.”

It’s at this moment you look at the calendar. Nope, 1st of April nearly two months away. A lost Monty Python skit? Teenage pranksters hacked into Reuters?

Apparently it is a true story ( and this fuss is about an amendment to a current law on public farting passed in 1929. This old law says: “Any person who voluntary vitiates the atmosphere in any place as to make it noxious to health of persons in general dwelling or carrying a business in the neighbourhood or passing along a public way, shall be guilty of a misdemeanour.” (vitiate = spoil or impair the quality)

My prediction is that dog ownership will increase in Malawi (you know the rest of the story). And next time your workmate vitiates the atmosphere, remember that it is the aroma of freedom, according to George.

Tuesday, February 15, 2011

Cuppa tea

I’m a big fan of black tea due to my English heritage, where you weren’t supposed to leave the breakfast table if there was still tea in the pot. For one of my badges in Cubs I had to prove at the age of seven that I could brew the perfect cup of tea: pre-warm the pot, add x teaspoons of leaves (x = one teaspoon per person + one for the pot), add boiling water, stir, leave to brew for five minutes, pour into cup through tea strainer. Haven’t lost the art.

Why does tea contain caffeine?

It is quite natural for you to assume the caffeine in tea is there just to give you a lift. The tea bush in China was producing caffeine long before humans came by. Its caffeine is to dissuade bugs from nibbling on the leaves. You are drinking a form of pesticide! Don’t worry, all plant foods produce compounds to try and keep the bugs at bay. Some produce compounds to keep humans at bay. For example, chokoes, which are sometimes passed off as edible.

Making your tea leaf

There are different ways to prepare the tea leaf. For black tea, leaves are macerated, allowing the enzyme phenolase within leaf cells to mix with polyphenolic compounds, and left for a few hours to ferment. The leaves are then heated to halt the action of phenolase (enzymes, being proteins, are denatured by heat). Voila! You have black tea, a favourite in the UK, NZ and Australia.

Green tea, an Asian favourite, and white tea (from the youngest bud and two top leaves) are heated before any fermentation occurs. Oolong tea is fermented for only 30 minutes before being heated. All four teas come from the same plant, Camellia sinensis. All four teas have flavonoids, those antioxidant compounds that have created an excited stir in the science world for the last 20 years.

The type and amount of flavonoid polyphenols in tea differ depending on the type of tea and area it is grown. Right now it is impossible to suggest that one type flavonoid had an advantage over another; they probably have multiple positive actions. Thearubigins are the main pigments in black tea. They contribute most of the colour, as well as the astringency and “body”, of the tea.


All four teas also contain caffeine. Love to have a nice bottle of Grange Hermitage for every time someone said to me that they take green tea because they are avoiding caffeine. The caffeine levels of each tea are similar at the leaf level, with white tea being the lowest, around 15mg per brew, because it is usually steeped for a short period. Green tea has around 40mg/cup after three minutes brewing, while a strong cup of black tea may have 60mg of caffeine.

How much caffeine will be present in your cuppa will depend on how long you brew the tea, type of tea, how much tea you brew and possibly even the region the tea was grown (Assam in north east India had the highest leaf level of caffeine in one study).

What does it all mean?

For a long time both tea and coffee unfairly had a bad name, mainly due to their caffeine content. Herbal teas were seen as a “healthy” substitute because they don’t contain caffeine. The consensus is that 300-500 mg of caffeine a day is no threat to healthy adults, although for some even 150 mg of caffeine can disrupt sleep.

Tea is the second most widely consumed drink in the world. No, Coke is not the first, it’s water. Being so popular, tea has attracted a lot of research, some of it showing that tea drinkers have less risk of heart disease, Parkinson’s Disease, type 2 diabetes and even have stronger bones. It is way too early to say that every cuppa will definitely help you to avoid disease, but the comforting thing to me is that nothing suggests that having a few cuppas a day is a problem.

You want to hear a number don’t you? OK, there is broad agreement that up to five cups a day is healthy. Just do what I do – choose big cups.

Reference: Coultate T. Food: The Chemistry of its Components, RSC Publishing 2009

Eating lessons in Kenya

Recently I popped over to Kenya to be PA for my wife, Toni, who was there as part of a Curtin University delegation. While she worked, I asked Fredie (sic) to show me the real Kenya, not the tourist stuff. We called into a roadside restaurant for nyama chomu, which is salted roast meat, in this case goat. With that we had fried potato balls with tomato sauce, mashed potato with peas and corn and a drink (see photo). They had run out of ugali, a solid corn flour dough, thankfully. I would have been the first mzungu to have been in there for weeks, maybe years, yet it was very relaxing being African.

“So where are the knives and forks Fredie?”

“Use hands.” Stupid mzungu.

“Which hand Fredie?”

“Either. And not like that, grab a handful.”

After eating a modest amount of food, having that constant visitor fear of whether I might regret this meal during the night, I expressed to Fredie that I was done.

“You have to finish the meat. You don’t leave meat in Africa.”

Sawa, sawa. So much to learn.

And I was the only one of the delegation to have polite guts for the fortnight.