Body mass index (BMI) is used to follow trends in body weight in the adult population. The World Health Organisation (WHO) uses the following definitions of overweight and obesity among adults:
BMI is a good indicator when one wishes to measure the proportion of overweight and obese within an age group. However, BMI is not an ideal indicator for individuals because high muscle mass can give a high BMI. Individuals with large muscle mass can have a high BMI without having a lot of fatty tissue.
Waist circumference and waist to hip ratio are used as indicators for health, and are more suitable for evaluating an individual’s weight and health than BMI.
Over half of adult men in Norway are overweight and 15-18 per cent are obese, according to BMI-values. The proportion of women who are overweight is somewhat lower. The figures come from health studies in five counties between 2000-2003. Since 2003 only Nord-Trøndelag has carried out county studies with weighing and measuring.
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The largest health risk is linked to obesity (BMI 30 kg/m2 or higher) that begins early in life. In the age group 30 and 40/45 years, 13-18 per cent are obese. See figure 1.
The proportion of overweight and obese varies between the counties. The average BMI and proportion of overweight and obese are lower in Oslo than in the four other counties where health studies have been carried out - Oppland, Hedmark, Troms and Finnmark.
Figure 2 shows the results for men and women aged 40-45. The measurements were made in 2000-2003. Click "open original" to access results for other age groups.
40-year olds with high education are to a lesser degree obese than groups with lower education. In Oslo, the adult population is heavier in eastern districts than in western, particularly among women.
Among immigrants in Oslo the prevalence of overweight and obesity varies with ethnic background. The proportion with obesity is largest among women from Turkey and lowest among men from Vietnam. Women from Sri Lanka and Pakistan have the highest waist-hip-ratio, as seen from a study among 3000 immigrants from non-western countries (Kumar 2005).
Adult men have increased evenly in weight since the 1960s. Women have increased weight evenly since 1985. These trends are illustrated in figure 3. The proportion with obesity rose from 9-10 per cent in 1985 to 13-22 per cent around 2000, according to figures from health studies of adults.
Since 1995 there seems to be a steeper rise in weight increase. In particular, adult men under 60 years and adult women under 50 years gained weight (Midthjell K 1999).
In 2000-2001, 40-year olds from Hedmark and Oppland weighed 5.0 and 5.8 kg more than 15 years earlier respectively. This relates to an increase in BMI of around 2 kg/m2.
You can find tables in Norhealth that illustrate this. Click on Risk factors in the left margin, then biological measurements and choose Body mass index (BMI).
In 2000, an international expert group, the International Obesity Task Force (IOTF), published a proposal for joint international value definitions for body mass index (BMI) among girls and boys from 2 to 18 years. These BMI-values are also referred to as iso-BMI and originate from BMI-values for adults, adapted to a child’s age and sex.
From the information we have today, 15-20 per cent of Norwegian children in the 8-12 year age group are overweight or obese (Norwegian Directorate of Health 2008, Juliusson 2007, Vilimas 2005).
Results from Norwegian Directorate of Health’s study in 2005-06 of 9-year olds shows that the prevalence of overweight and obesity among children seems to be at the same level in Norway as in Nordic countries and Western-Europe in general.
We have too little information to say whether the weight increase has sharply risen or is continuing.
Approximately 8-14 per cent of Norwegian 15-16-year olds are overweight or obese (Norwegian Directorate of Health 2007, Grøholt 2008, Juliusson 2007). In the Norwegian Directorate of Health’s study more 15-year old boys than girls were obese respectively, this is the opposite of what was found among 9-year olds.
Also for youths we have too little information to evaluate whether the proportion with overweight is still increasing, and if trends are different from county to county.
Studies of 8-12-year olds in Oslo in 2005 show big differences between districts. In the inner west and outer west there are respectively 19 and 15 per cent overweight. In the inner east and in newer suburban areas, the proportion of overweight is 29 and 26 per cent respectively (Vilimas 2005).
The Norwegian Institute of Public Health’s youth studies among 15-16-year olds show the link between overweight and socioeconomic factors (Grøholt 2008).
Among immigrant youths in 15-16-year age group in Oslo, the proportion of overweight varies from 4 to 12 per cent. Immigrant youths from other western countries, Eastern Europe and the Middle East/North-Africa had the highest prevalence of overweight, according to the youth part of the Oslo Health Study, that registered weight and height with the help of questionnaires (Kumar 2004.)
There are also clear socioeconomic and ethnic differences in other countries. In USA, children and adolescents from groups with low education levels or income, and children and adolescents with Mexican and Latin-American origin have the highest prevalence of overweight and obesity (Ogden 2008).
When measurements are compared with a 30 year gap in Bergen, it is found that the group of adolescent children (over 97.5-percentile in weight-versus-height) was two-three times bigger in 2003-06 than in 1971-74. In the top weight groups there were small changes. Comparisons between age groups showed the biggest weight increase among 7-11-year olds (Juliusson, Bjerknes 2008, Juliusson 2007).
Studies in Oslo and Nord-Trøndelag indicate that also among youths, it is the heaviest that have increased most in weight (Heggebø 2003, Bjørnelv S).
In 2008, the Child Growth Study was carried out among eight year olds in the entire country. The results will be available in 2009. To follow trends in children’s height and weight, there are plans to repeat the study every other year. This study is performed in collaboration with WHO in about 25 European countries.
WHO estimates that in certain areas of North-America, Middle East, Australasia and China the prevalence of overweight is three times higher today than in 1980. A group of researchers published a new report in 2008 that shows that in 2005, 937 million adults were overweight and approximately 400 million were obese (Kelly 2008). The increase in overweight among children started in USA in the beginning of the 1980s. Today, 32 per cent of children and adolescents in USA are overweight or obese, since 2000 the proportion has not increased (Ogden 2008).