Monday, 22 August 2011

Barker hypothesis and thin-fat bodies

Viewers here in the UK can, for a limited time, watch this weeks edition of Horizon on BBC2. It is a really interesting programme this week on our first nine months of being, including the theory postulated by Prof. David Barker - the Barker hypothesis of how our birth weight might predict our health later in life. The long and short of theory is simply that low birth weight might increase our risk of various conditions such as coronary heart disease and type 2 diabetes. The reasons why are perhaps slightly more complicated.

It is an interesting theory with a number of lines of evidence potentially supportive. The programme highlighted the studies conducted in Pune, India including this one by Yajnik and colleagues* which suggested that low birth weight children showed a greater level of impaired glucose tolerance, a potential early indicator of future diabetes complications. The paradox is that in India, most of the population are living pretty healthy lives by Western standards: thin bodies, a diet following and exceeding the Western 5-a-day slogan in terms of fruits and vegetable intake and good standards of physical activity, yet have quite high rates of more 'Western' diseases like heart disease and type 2 diabetes considered to be related to our more sedentary lifestyles.

Having said that when you look closer at those 'thin' people, looking at things like the percentage of body fat, these are in fact thin people with fat people bodies: normal body mass index (BMI) but higher percentages of body fat. The programme highlighted one potentially important factor related to birth weight; micronutrients and particularly ideas that low maternal vitamin B12 and low folic acid might make offspring more prone to the thin-fat body and the onward health effects suggested.

A second line of evidence was that derived from the studies on the wartime famine in Holland (sorry, the Netherlands) and the suggested effects on children born to mothers who experienced the famine. This study by Ravelli and colleagues** kinda sums it up: mums exposed to famine especially during the later stages of pregnancy resulted in offspring with decreased glucose tolerance as adults.

I don't claim to understand all the concepts highlighted in the programme and relevant to the Barker hypothesis and there is some evidence to the contrary. What is perhaps most interesting is that we live in a world where our access to food has never been better, certainly over the past 60 years or so, yet ironically the food we eat, or rather the food our mother's or grandmothers ate, might be so deficient in certain nutrients that our physical health and longevity may be at risk. The challenge is to know more about potential mechanisms (including things like the efficiency of the placenta) and make the necessary dietary changes for the sake of future generation health.

* Yajnik CS. et al. Fetal growth and glucose and insulin metabolism in four-year old Indian children. Diabetic Medicine. April 1995.
** Ravelli ACJ. et al. Glucose tolerance in adults after prenatal exposure to famine. Lancet. January 1998.