Obesity, Body Weight and BMI
Worldwide prevalence of obesity has increased by more than doubled since 1975. According to the World Health Organization (WHO), there were more than 1.9 billion adults (above 17 years old) that were overweight in 2016. Of these, over 650 million were obese. Overweight and obesity are defined as having a bodyweight greater than what is considered healthy for a certain height.
The weight gain generally occurs when there is an excess intake of kcals (energy from food). Excessive energy will be processed and stored in the body as fat, regardless of the type of food consumed. There are 2 types of fat based on the location of where it is stored in the body: visceral and subcutaneous. Visceral fat is stored around the internal organs in the abdomen, and subcutaneous fat is stored beneath the skin. Visceral fat has been linked to a list of adverse health conditions. The more visceral fat accumulated, the higher the risk of developing non-communicable diseases such as cardiovascular diseases, diabetes and musculoskeletal disorders, to name a few (2, 6).
A simple way to check whether you are in a healthy weight range for your height would be the body mass index (BMI). It is defined as a person's weight (kg) divided by the square of his height (m2), and it is the same for both sexes and for all ages of adults. A BMI at or greater than 25 (23 for Asians) is considered as overweight, and a BMI at or greater than 30 (27.5 for Asians) will be considered as obese (3,8). Even though BMI provides a useful population-level form of measurement for overweight and obesity, it should be considered as a rough guide. It is important to keep in mind that BMI is a measure of excess weight rather than excess body fat as it does not take into account of the overall body composition (body fat and lean mass). In a study done by Bosch et al. which assessed the body composition difference in NFL football players, none of them had a BMI within the normal range (they were all classified as either overweight or obese). However, their body fat percentage classifications are considered relatively normal or lean (except for the linemen group) (4). Therefore, different individuals may have a different degree of fatness even though they might have similar BMI classification.
To determine body fat more accurately, supplement BMI with other measurements such as the skinfold thickness and waist-hip ratio. By measuring the skinfold thickness using the caliper, we can estimate body fat percentages. Depending on age, gender and ethnicity, healthy body fat percentage ranges from 20 – 26% for women and 8 – 14% for men with ‘Normal’ BMI (>18.5 - <25) (5). Keep in mind though, that skinfold method can only measure subcutaneous fat for overall body composition. Although it is simple to set up and conduct, the type of caliper used and the skill of the measurer can affect the measurement. It is recommended to engage a qualified professional who is certified by the International Society for the Advancement of Kinanthropometry (ISAK) to conduct the test to ensure accuracy and consistency of the measurements.
One of the reasons for measuring body fat is to keep a check on your health. The waist-hip ratio is a common measure of fat distribution (3). It is a quick, simple and inexpensive method of measurement used to identify any potential heart disease risk related to obesity. It reflects the degree of abdominal fat a person has by taking your build (hip) into account. The bigger the waist measurement is to the hip, the greater risk of cardiovascular diseases (2, 6). Alternatively, we can also easily measure our waist circumference as a way to quantify abdominal fat (3). A waist circumference greater than 102 cm (90 cm for Asians) for men and 88 cm (80 cm for Asians) for women increased the risk for weight-related comorbidities (1, 3, 7).
It is common to have BMIs within the normal range, and yet a high percentage of the bodyweight is of body fat. In order to assess according to body fat and to avoid misclassification, it is recommended to use BMI and along with other forms of measurements.
After understanding the fundamental of weightloss, find out more about how we discuss the weightloss management strategies in the next topic!
References
1) Alberti, K. G., Zimmet, P., & Shaw, J. (2006). Metabolic syndrome—A new world-wide definition. A Consensus Statement from the international diabetes federation. Diabetic Medicine, 23(5), 469-480.
2) Balkau, B., Deanfield, J. E., Després, J. P., Bassand, J. P., Fox, K. A., Smith, S. C., . . . Haffner, S. M. (2007). International day for the evaluation of abdominal obesity (IDEA): A study of waist circumference, cardiovascular disease, and diabetes mellitus in 168,000 primary care patients in 63 countries. Circulation, 116(17), 1942-1951.
3) Clinical guidelines on the identification, evaluation, and treatment of overweight and obesity in adults-The evidence report. (1998). Obesity Research, 6(S2), 51S-179S.
4) Dengel, D. R., Bosch, T. A., Burruss, T. P., A. Fielding, K., E. Engel, B., L. Weir, N., & Weston, T. D. (2014). Body composition and bone mineral density of national football league players. Journal of Strength & Conditioning Research, 28(1), 1-6.
5) Gallagher, D., B Heymsfield, S., Heo, M., A Jebb, S., R Murgatroyd, P., & Sakamoto, Y. (2000). Healthy percentage body fat ranges: An approach for developing guidelines based on body mass index. The American Journal of Clinical Nutrition, 72(3), 694-701.
6) Janssen, I., Katzmarzyk, P. T., & Ross, R. (2004). Waist circumference and not body mass index explains obesity-related health risk. The American Journal of Clinical Nutrition, 79(3), 379-384.
7) Waist circumference and waist-hip ratio: Report of a WHO expert consultation. (2008). Retrieved from Geneva, Switzerland:
8) WHO. (2004). Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. Lancet, 363(9412), 157-163.