NEW YORK (CNN) — Everybody knows that a high-fat, high-sugar diet is not a good idea. It can have a wave of negative consequences on your health, including greater risks of obesity, diabetes and heart disease.

But a new study has found that eating foods rich in fat and sugar during pregnancy could affect not only your health but also your child's, with potential links to attention deficit hyperactivity disorder and conduct problems, such as lying, fighting and stealing, due to changes to a child's DNA.

"The assumption is that prenatal exposure affects a child as they develop," said Edward Barker, a development psychologist at Kings College London, who led the study. "We looked at food exposure on DNA."

Changing expressions

Barker's team analyzed the DNA of 164 people from the Avon longitudinal study of parents and children, which monitors the health of 14,500 families in Bristol, England. Eighty-three children who showed symptoms of conduct disorders early in life were compared with 81 children with milder conduct problems. The diets of mothers were also analyzed.

The study found that poor prenatal nutrition influenced the expression of a particular gene, known as IGF2, involved in both the metabolism of food and brain development, both before and after birth. In both groups, there was a link between changes in gene expression and mothers having a diet rich in fat and sugar. The group with early-onset conduct problems had more extensive changes in expression associated with greater ADHD symptoms when they were older, ages 7 through 13.

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When factors influence the way a gene is expressed, the alterations are called epigenetic changes. One example of this is methylation, which adds to or takes away a molecule called a methyl group that sits on DNA and influences whether genes are active or silent.

"Prenatal high-sugar, high-fat diets do influence methylation around this gene," Barker said.

The number of people compared in the study is small, however, and more studies are needed to confirm the association as well as studies among other populations where nutrition levels are typically lower. "If you look at areas with greater poverty or deprivation, you may find a stronger association," Barker said.

In addition, the researchers stress that the findings are purely an association; they do not confirm that a diet rich in fat and sugar can directly cause ADHD.

"While prenatal nutrition is very important, we need to be cautious about drawing conclusions about the impact of prenatal nutrition on later conduct disorder and ADHD," said Professor David Daley, co-director of the Centre for ADHD and Neurodevelopmental Disorders Across the Life Span at the University of Nottingham, who was not involved in the study.

"I would be extremely concerned about the general public using the findings of this study to blame parents of children with ADHD for their child's problems," he said, adding that a host of other genetic and environmental influences on the development of ADHD may not have been adequately controlled in what was also a relatively small study.

Diet and mental health

Diet is thought to influence a range of psychiatric disorders and mental health problems, including depression, in all age groups. Nutrition is also thought to affect the onset of ADHD in children if they don't eat a balanced diet and instead consume large quantities of processed or fast food.

"This is thought to exacerbate ADHD symptoms in children," Barker said.

One approach to treating the disorders is to change someone's diet to include more folate, fiber and omega-3 fatty acids.

The team hopes the new findings promote awareness of the need to maintain a healthy diet during pregnancy, in addition to childhood, to help prevent the development of ADHD in children. They plan to further investigate particular nutrients that could prove to be beneficial rather than detrimental, such as omega-3 fatty acids, which are known to benefit neural development.

"[But] we hope this raises awareness of the importance of healthy diets for child development," Barker said, adding that "this is important both pre- and post-natally."

But he added that when it comes to factors influencing disorders such as ADHD, many things will be involved in addition to methylation of DNA and nutrition, including violence and poverty.

"There are a lot of correlated risks, and nutrition is just one," he said. "It's hard to isolate the effects of one."

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