-LRB- CNN -RRB- -- Nearly one-fifth of American 4-year-olds are obese , and children of color are at higher risk , according to new research . Obese children are at risk for early onset of diabetes , fatty liver and musculoskeletal problems . Researchers calculated the body mass index from a sample of 8,550 Hispanic , black , white , Asian and Native American 4-year-olds . The children were born in 2001 , and in 2005 , their height and weight were measured -- 18.4 percent of them were obese . `` Significant differences in the prevalence of obesity between racial/ethnic groups were evident at 4 years of age , '' the researchers wrote in the April issue of the Archives of Pediatrics and Adolescent Medicine . Using body mass index , they found that 31.2 percent of American Indian/Native Alaskans , 22 percent of Hispanics , 20.8 percent of blacks , 15.9 percent of whites and 12.8 percent of Asians were obese . `` It 's surprising that there are large differences by racial/ethnic group by that age , '' said Sarah Anderson , an assistant professor of epidemiology at The Ohio State University and lead study author . Anderson and co-author Robert Whitaker 's analysis showed that children were becoming obese even before encountering soda and candy vending machines in schools . `` These results really do point to the need for us to focus attention on early childhood and the need for research to understand how these differences can emerge so early , '' Anderson said . `` To do that , we may need to understand the different family and cultural factors that are at play in these children 's lives . '' The cause for the early health disparities is hard to pinpoint , childhood obesity experts said . `` It 's always possible there are biological factors within ethnic groups , '' said Dr. Tom Robinson , director of the Center for Healthy Weight at the Stanford University School of Medicine . `` We know most of the changes that have occurred in body fat tend to occur from being in an environment that promotes very easy access to high-caloric foods and limited opportunities for physical activities . '' Michael Rich , an associate professor of pediatrics at Harvard Medical School , called the disparities between ethnic groups disturbing . `` The expectations , lifestyle , behaviors are different on a cultural and socioeconomic basis , '' he said . `` Kids who live in the inner city , whose neighborhoods are perceived as dangerous , stay at home more , sit more , eat more snacks , because that 's all they can get at the local bodega . There are no supermarkets to get produce . That 's what mom is eating , so that 's what kid is eating . What we 're dealing with here is whole life issues . '' Previous research has shown that older children are becoming less active and spending more time in front of a computer or TV . `` That is displacing physical activity , '' said Dr. Sarah Barlow , director of the Obesity Center at Texas Children 's Hospital in Houston . `` You can imagine strollers , less outdoor play -- all those kinds of things that have shifted how much activity younger kids are getting . At the same time , portion sizes are increasing for everybody . '' According to data from the Centers for Disease Control and Prevention , adults fare no better . Approximately 45 percent of blacks , 36.8 percent of Mexican Americans and 30 percent of whites are obese . `` It 's a very bad sign if we see obesity at a young age , '' Robinson said . `` When we see children obese at age 4 , we 're likely to see complications -- high blood pressure , abnormal lipids -- which can lead to heart disease and stroke , diabetes in children . '' Diseases commonly seen in 40 - or 50-year-olds are presenting in 6 - and 7-year-olds . Obese children are developing type 2 diabetes , fatty liver disease and musculoskeletal problems , which occur because their bodies ca n't carry that much weight , doctors said . Calculate your child 's body mass index . `` The heavier you are as a child , the likelier that extra weight will follow you through life , '' Robinson said . `` That 's why we see adolescents who need weight-loss surgery , because they have life-threatening complications from obesity . '' If you have an obese child ... The first step is for the parents to acknowledge that the child is overweight , instead of making excuses or comparing him or her to heavier children . Many of the parents of obese children are overweight themselves , which makes that acknowledgment difficult , said Rich , who is also director of the Center on Media and Child Health at Children 's Hospital in Boston . `` While it 's important to focus on it and take it seriously , it 's also important not to give up or feel hopeless , '' he said . `` Then you wo n't try . You want to look at it for what it is and not be defeated by it . '' When you 're trying to help your child achieve a healthy weight , remove the stigma attached to obesity . `` It should always be about health , not about losing weight , '' Rich said . `` You 're trying to build the positive . '' He recommended the 5-2-1-0 plan . Eat at least five servings of fruits and vegetables , cut screen time down to two hours or less , exercise at least one hour , and have zero soda and sugary drinks . Such changes , which are not seismic shifts to lifestyles , can help the child get into a health weight . `` It 's easier to start that way , rather than try to change habits when they 're 8 or 12 or 16 , '' said Barlow , an associate professor of pediatrics at the Baylor College of Medicine in Houston , Texas . While it 's possible for some kids to outgrow the excess weight , she warned parents not to count on that . `` We 've seen over time that the environment does n't promote that , '' she said .