Monday, 3 May 2010

What we do and don't know about food

Leamington Pump Rooms viewed across the river
I now have a cold, not too serious, but annoying. Saturday it dripped, yesterday my nose bunged up, today I'm back to dripping with the extra joy of a very deep voice.

Still revising, and thanks to Facebook I'm aware of what some of my peers are up to. Many seem to be completing coursework in time for handing in this week, and haven't started revising. I'm well aware that I'm not a standard sort of student, given that I have been there before and am now quite content to work by day and stay in most nights. Even so, we now have a week of lectures, then a free week, and then our first exam. Fourteen days from now, I will be immersed in the first paper, and then there are four more. Granted, there's a week between the fourth and fifth exams, but just fourteen days left to revise for four exams, two or three of which (depending on optional choices) are double modules with a year's worth of lectures to revise?

Anyway, as Mr A reminds me, that isn't my problem, or 'NMFP' as we have learned from 'The Thick Of It' (series 1), which is one of our current DVD watching pleasures. It's pretty brutal, so after one half-hour episode we have to wait a few days until we're ready to see the next one. If 'Yes, Minister' is like a ride on a miniature railway, then 'The West Wing' is a Japanese bullet train and 'The Thick of It' is the scariest roller-coaster you can imagine. We are also watching the 1981 ITV series of 'Brideshead Revisited', which is relaxing to the level of soporific, but so beautifully written and acted. I can't read for pleasure at the moment - by the end of a day's revising, I can hardly bear to look at words any more.

In academic news, since last time, I have done a day of mind-stretching Molecular Nutrition (perhaps I'll write about that another time), and two days of nutritional issues around infant feeding, childhood obesity, cancer and the Developmental Origins of Health and Disease. This last, known as DOHAD, proposes that conditions in the womb have a permanent 'programming' effect on the genome, predisposing the foetus to develop conditions such as heart disease and diabetes in adulthood. Further, the theory goes that this foetal programming is actually heritable, which goes against all prior assumptions that the DNA code is not influenced by environment.

Traditional theories are based on genetic inheritance - if a naturally thin person is force-fed until fat, we would expect their offspring to inherit thinness, not fatness - their genetic inheritance, rather than environmental conditions. This theory says that a foetus in the womb which is subject to maternal undernutrition somehow 'expects' poor nutritional conditions when it is born. It is 'programmed' in the womb to make best use of nutrients when it is born, thus predisposing it to obesity when all the fat and salt they could desire is actually available. So a thin woman having a baby with a similarly thin partner eats badly when pregnant, and the child grows up to be fat, and what's more, their grandchildren will inherit fatness rather than thinness.

If I'm not convincing in my explanation, it's not surprising, as I'm not entirely convinced myself. Other aspects of this module that I've been revising have been equally frustrating. You'll probably have seen some news item about this nutrient or that food causing or protecting us from cancer. While the experts agree about smoking and sunbathing, nutritional factors are much harder to untangle.

It's perfectly possible to feed mice a specific diet for the course of their natural lives and compare cancer incidence with other genetically identical mice fed a different diet. Perhaps we find that a diet high in saturated fat always causes an increase in cancer rates compared with a diet low in saturated fat. Knowing that mice are not the same as humans, we'd like to see if these results are applicable to us. Well, we can't. The main problems are a) we eat food rather than nutrients, b) researchers cannot control what subjects eat for more than a few days, c) food records are notoriously unreliable and d) researchers and research money rarely last for the length of time needed to run a reliable experiment.

So every two minutes someone reaches some conclusion somewhere about which foods cause cancer, and it's published in all the popular magazines, and the trouble is that on its own, each individual piece of research is unhelpful. It's only when you put together a large number that a balance of probabilities can come up with a reasonable estimate of the real effect. Out of 13 human studies looking at consumption of cereals, 3 studies concluded that they lower the risk of colon cancer, 3 studies suggested a higher risk, and 7 found there was no significant effect at all. Even then we don't know which bit of the cereal to focus on - is it the soluble or insoluble fibre, the folate, or some other component? It's no wonder that people think that we're always changing our minds about what they should eat.

There are, however, two themes consistently running through virtually every subject I've studied over three years. The first is that not fat = good and fat = bad, and the second is that moderate physical activity is good for you. If only it were that easy.

3 comments:

jay said...

If only! Over the course of my life I've heard so many theories about food/cancer/obesity and many of them stated as fact. One which I dared to believe in (because I wanted it to be true and it sounded so reasonable) stated categorically that if you fed a newborn solely on breast milk for a minimum of three months, 1) they would not get fat and 2) babies who didn't get fat in the first three months would never be obese no matter how much they ate later in life because the number of fat cells a person has is finite, and would be determined during that time.

Ha!

Both my sons were solely breast fed for way longer than three months and neither got fat during that period, but both are now seriously overweight. I don't care what they say, the tendency to be overweight is genetic, for some people. Simple as that.

Caz said...

How interesting! I usually switch off at the merest mention of anything scientific but the mention of skin cancer caught my interest. I have recently had a freckle removed due to early melanoma and am interested in the possibility of which foods may protect us from skin cancer. However, any 40 something Australian is likely to expect a melanoma at some stage due to our lifestyle and it was unheard of to wear a hat or sunscreen when I was a child. Now, however, it's a different story and I or my children don't go outside without either.
I hope your cold gets better soon.

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