Pregnant women who eat American diet are FAR more likely to have obese babies - even when they stay fit and don't overeat

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Pregnant women who eat a typical American diet are more likely to have an obese child, a study warns.

A growing swell of research has shown a woman's diet before, during, and shortly afte pregnancy may influence whether offspring become obese.

And new research by The Scripps Research Institute has laid bare how damaging a Western diet can be - even if the mother remains physically active and doesn't overeat. 

Until now, researchers believed overweight women were more likely to have obese children. 

But lead author Dr Eric Zorrilla warns their findings show diet appears to be the most important factor. 

New research by The Scripps Research Institute has laid bare how damaging a Western diet can be - even if the mother remains physically active and doesn't overeat

The researchers tested their theory on two sets of rats.

One set was selectively bred to be obesity-resistant to a high-fat diet and another was unusually vulnerable to high-fat meals.

Within each group, some were fed a Western diet - rich in red meat, dairy, processed foods, salt, with few fruits, vegetables, fish, and whole grains.

Some were fed a diet lower in fat and higher in grains.

They found that all rats given a Western diet in the weeks leading up to pregnancy, during pregnancy and during nursing had offspring more prone to obesity.

And that obesity lingered well into their offspring's adulthood. 

This occurred even if the mothers themselves did not overeat and maintained a healthy weight, body fat and insulin status.

In fact, the researchers found that giving females a typical American, or Western, diet appeared to set the next generation up for lifelong obesity issues. 

'Your diet itself matters, not just whether you are gaining excess weight or developing gestational diabetes,' said lead author Dr Eric Zorrilla.   

The Western diet seemed to set in motion a metabolic 'program' that lasted throughout the rat's life. 

Although these rats slimmed down during puberty and early adulthood, they still showed a lower metabolic rate and higher food intake during that time, which led to a return of obesity in mid-adulthood.

'What we found interesting was that you sometimes see the same thing in humans, when a kid goes through a growth spurt,' said study first author Jen Frihauf of the University of California, San Diego.

They also found that the Western diet made it harder for obesity-vulnerable rats to reproduce. 

'This wasn't the focus of the study, but it supports the idea that a Western diet promotes infertility in mothers vulnerable to diet-induced obesity,' said Dr Zorrilla. 

Now, the team will explore which aspects of the American diet trigger these effects - and the molecular changes in the offspring responsible for them. 

Dr Zorrilla said the findings should raise awareness of the importance of a healthy pre- and post-natal diet. 

He said doctors may want to discuss nutrition with all women who are pregnant or are planning to become pregnant, not just those already overweight.

'Doctors often use weight gain as a hallmark of a healthy pregnancy,' said Frihauf. 

'But we realized there was something going on in utero that wasn't detectable in the mother's weight.'

Frihauf added that few pregnant women, even in the United States, eat a high-fat, high-sugar diet all day, every day. 

'We're not trying to tell pregnant women not to occasionally splurge on a piece of cake,' she said.