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Smaller twin girls have greater risk of adult obesity

Blossom outside Clocktower

Monday 27 July 2009 9:22am

Monday 27 July 2009

Female twins who were small at birth have a greater risk of adult obesity, a University of Otago-led international study of 3170 female twins aged 18 to 80 in the United Kingdom suggests.

The study, to be published in the August issue of the American Journal of Clinical Nutrition, was undertaken by scientists in the United Kingdom and the University of Otago. It found that twin girls with a lower weight at birth were found in later life to have higher amounts of fat compared to lean body tissue than the twins who were heavier at birth. Conversely, those who were heavier at birth had a higher ratio of lean body mass to fat mass once in adulthood.

"A girl who is a twin, with a birth weight of 2.5kg, will have around 500 grams less fat in adulthood than a twin girl with a smaller birth weight of 1.5kg," says Dr Skidmore.

The average weight for a twin girl is 2.5kg. All the twins had their adult weight and total fat measured using dual-energy X-ray absorptiometry, and were asked to recall their birth weights for the purposes of the study.

Study leader, Dr Paula Skidmore, of the University of Otago's Department of Human Nutrition, says the higher proportions of fat in adulthood for these smaller babies was not drastically different when compared with their adult counterparts who were larger at birth; the differences in adulthood for smaller babies amounted to hundreds of grams rather than kilograms of fat mass when measured against the heavier twins.

"But we can definitely say the twins who were smaller as babies had a propensity to accumulate more fat throughout the life cycle, whereas those with a higher birth weight had a more favourable body composition in adulthood," Dr Skidmore says.

"So birth weight has a relatively small effect on adult weight - but there are other important factors such as good nutrition and physical activity which have a greater bearing."

The study also found that the proportions of fat and lean body mass recorded in all twins were not due to differences in nutrition between twins in a pair within the uterine environment. Instead, the shared post-natal environment of the twins as they grew into adulthood was more likely to contribute to their fat to lean mass ratios. These factors may include diet, exercise and socio-economic status.

Dr Skidmore says previous studies have shown that those who are born small but who then grow rapidly during early childhood may be at increased risk of adult obesity and this may explain the findings from this study.

Twins were used in this study because they provided a natural control group where researchers could see what factors were important and which were not in the shared common environment. However, researchers could not pinpoint which factors, such as diet or exercise, had the greatest bearing on fat to lean mass levels in adulthood.

For more information or interview, please contact

Dr Paula Skidmore
Department of Human Nutrition
Tel 03 479 8374

Jo Galer
Senior Communications Adviser
Tel 03 479 8263

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