30 August 2011
ByAppeared in BioNews 622
BBC2, Monday 22 August 2011
Forget 'you are what you eat'. Rather 'you are what your mother ate'. That was the dramatic message of the BBC's latest episode of Horizon 'The Nine Months That Made You', broadcast on Monday 22 August. The documentary was an account of the Barker Theory that birth weight determines health in later life.
The programme began by introducing Professor David Barker whose early work laid the foundations for this theory. In the late 1980s, he uncovered a relationship between birth weight and lifetime risk of coronary artery disease using data from Hertfordshire Birth Records. Since the publication of this research, Professor Barker has been involved in attempts to assess how widely his theory can be applied across different countries and cultures.
The first piece of supporting evidence came from a village in rural India. The villagers ate a near-perfect diet and led active lifestyles yet had an unexpectedly high rate of type 2 diabetes; a condition typically associated with an unhealthy lifestyle. Dr Ranjan Yajnik, who researches this phenomenon, told us low birth weight could be the culprit again.
He said the evidence suggests a mother's poor diet during pregnancy leads to underweight babies who grow up to have a 'thin-fat' phenotype. Despite being slim, they have a higher proportion of fat for their body weight compared to a person of the same weight in the West. This high fat proportion predisposes them to developing conditions like type 2 diabetes and coronary artery disease.
While this was an intriguing idea, the programme's delivery felt laboured and confusing. For example, we were told the villagers ate a 'perfect diet' and the mothers had poor nutrition during pregnancy. These two conflicting statements were never reconciled.
An explanation of why a low birth weight should automatically lead to a 'thin-fat' adult was also missing. Furthermore, the documentary failed to explore whether genetics could play a role in the 'thin-fat' phenotype or whether this body type is found outside of India. Instead, we were told the simple story that mothers' diet determines adult health.
The next piece of evidence used to back up Professor Barker's theory came from the Netherlands. During World War Two, the country was gripped by famine and food was tightly rationed to just 400 calories a day. We were told recent research headed by Dr Tessa Roseboom showed people in the womb during this famine have a higher incidence of chronic illnesses like type 2 diabetes, coronary heart disease, breast cancer and even schizophrenia.
Dr Roseboom's study was an important natural experiment for assessing the long-term effects of famine on subsequent generations. But the programme didn't discuss whether these disease associations occur only after extreme caloric restriction or whether they could apply to normal variations in mother's diet.
Next we were told about ongoing research to establish whether personality is determined before birth. The work is at an early stage and it is too soon to draw any conclusions about the effect of the prenatal environment on personality. This was followed by an interesting, but brief, discussion of the protective role of the placenta during development.
The final section of the programme returned to India where Professor Caroline Fall was coordinating a dietary intervention program. By providing daily snacks before and during pregnancy, the researchers hope to supplement each mother's diet with essential nutrients to improve the health of her children.
The documentary highlighted some interesting research, including this dietary intervention program. But I found the lack of detail unsatisfactory: the programme gave no hint of possible biological mechanisms linking prenatal environment with adult health.
The programme also lacked balance: what was touted at the beginning of the programme as a 'provocative' new theory soon became presented as though it were a widely-accepted scientific fact.
There was little-to-no discussion of other factors that could contribute to later life health outcomes. For example, genetic factors were dismissed in a few brief sentences, despite a sizeable body of evidence linking genetic factors to body weight, distribution of body fat and chronic health conditions.
There was also no mention of the wealth of epidemiological research stressing the importance of postnatal environmental factors (which commonsense tells us are likely to be correlated with mother's diet).
Furthermore, in an attempt to simplify the science and grab the viewers' attention, we were repeatedly told that current diet and lifestyle do little to affect our health. This comes across as crude and irresponsible when obesity rates and liver disease cases are soaring.
It would be more realistic to say that, even if prenatal environment proves to be the strongest predictor of health, it is unlikely to be the only predictor of health.