The obesity epidemic has been widespread in many countries, and has several adverse consequences. So many factors, some probable, others verified and documented, are known to contribute to the obesity problem in developed and developing countries. Nutritionists and other health professionals need to be skilled in understanding these various causes and their health implications. They should also be able to assess excessive body weight in clinical and other settings. Armed with this knowledge, health professionals should therefore be able to advise consumers and clients struggling with weight management on cost-effective preventive strategies to prevent or reduce incidence of obesity. In addition, nutritionists should be able to advise food manufacturers to make and market healthy food products. This paper will address the growing concern on obesity epidemic by reviewing the presumed and published or proven causes of obesity and the various methods for measurement of obesity. Strategies for preventing obesity will also be discussed. Such strategies would include lifestyle changes, physical activity, diet and behaviour modifications as well as reading food labels and proper food selection. Preventive strategies for obesity and overweight when properly implemented are very cost effective especially at personal and community levels and will ensure good health and wellness in many populations.

Keywords: assessment, obesity, epidemic, overweight, presumed, proven causes, prevention, weight management, health & wellness

ACE , american council on exercise; BIA, bioelectric impedance analysis; BMI, body mass index; BMR, basal metabolic rate; CAT SCAN, computerized axial tomography scan; CDC, center for disease control and prevention; DASH, dietary approach to stop hypertension; DEXA, dual energy x-ray absorptiometry; DGA, dietary guidelines for americans; HC, hip circumference; HFCS, high fructose corn syrup; HP2020, healthy people 2020 guidelines; IOTF, international obesity task force; MRI, magnetic resonance imaging; NCHS, national center for health statistics; NGO, non governmental organizations; NHLBI, national heart lung blood institute; NLIS, nutritional landscape information systems of who; OECD, organization of economic cooperation and development; TLC, therapeutic lifestyle change diet for cholesterol; USA, united states of america; USDA, united states department of agriculture; WC, waist circumference; KG, kilogram; LB, pound; M, meter; W, weight; D, density; V, volume; WHO, world health organization; WHR, waist to hip ratio; WHtR, waist to height ratio

Obesity and overweight trends have reached epidemic proportions in many countries,^1–8 and have serious health and socio-economic consequences. In addition, obesity has negative medical, psychological and quality of life consequences, drains health care resources and reduces life expectancy. The International Obesity Task Force (IOTF) projects that obesity rates worldwide would increase very significantly by 2025 unless appropriate intervention is taken.⁹ In the USA, between 2011 & 2012, the percent of US adults aged 20years and above who are obese was reported to be 35.1 %, while the percent of US adults who had excess body weight (overweight and obesity)in the same period was 69.0% according to published reports.^2,10 Obesity and related chronic diseases are no longer a problem of affluent countries alone, as poor developing countries, middle income countries or countries undergoing economic transition, are also affected by the epidemic.^4,6–8 Global, national and state public health agencies as well as their nutritionists, researchers and educators have raised awareness or taken immediate action to arrest the increasing weight trends and obesity in adults, the youth and children.^11–16 Despite the high prevalence of obesity in many parts of the world, segments of populations (such as geriatric, very sick people, preschool children, pregnant & lactating women) suffer from underweight.^7,17–19 In some developing countries, various types of unhealthy weight such as obesity, overweight and underweight, can coexist concurrently in different segments of their populations.^7,18–21 There are so many factors that cause or contribute to obesity. A previous paper had discussed obvious and hidden calories as causes of obesity.²² This paper will review various other causes of obesity, both probable and proven causes, and will discuss various methods of measurement of obesity in clinical, research, community or field settings. In particular, it will discuss strategies to prevent obesity and excessive weight gain to ensure health and wellness in many populations. A better understanding of the assessment and causes of obesity will lead to a concerted action to prevent and fight the obesity epidemic.

Methods of assessing obesity and overweight in adults

Obesity can be determined by many methods, some of which are quite simple, while others are complex or sophisticated. These methods of assessment include the body mass index or BMI, other anthropometric methods, skin fold callipers that measures percent body fat and high technology or advanced methods.

The BMI method of assessing obesity/overweight

 Obesity and overweight are commonly estimated by a metric known as body mass index or BMI. The BMI is one of the anthropometric measurements used in clinical calculations. (In anthropometry, body weight, height, length, circumferences and thicknesses of parts of the body are measured and used to estimate body fat and general weight status such as normal weight, underweight overweight and obesity). The BMI is a measure of a person’s weight relative to the person’s height. This index is highly correlated with the amount of body fat, and is used to assess risk of diseases related to excess body fat, but it is not a direct measure of fat. High BMI correlates with obesity and higher health risks such as some cancers, cardiovascular diseases, diabetes, hypertension, stroke, sleep apnea, degenerative joint diseases, infertility, respiratory problems, skin problems, gall bladder disease and other conditions.

Scientifically, BMI is calculated in the metric system as body weight in kilograms (Kg) divided by the person’s height in meter squared (m²). {Hence BMI = kg/ m²}. In the imperial system of measurement, BMI is calculated as body weight in pounds (lb) divided by height in inches squared (in²) and the result is multiplied by the number, 703, to get the BMI. {Hence BMI= (lb/in²) x703}. Total body weight includes non-lean body mass (storage fat and subcutaneous fat) and lean body mass (bone, muscle, organ, skin, fluid, non fat cells, & non-fat tissues).

BMI classifications

Healthy weight: In most populations of the world, a person with healthy weight is regarded as one whose BMI value lies between 18.5 and 24.9. A BMI value higher than 25.0 predisposes a person to high fat accumulation and a higher risk of metabolic diseases such as metabolic syndrome, heart disease, diabetes, hypertension, stroke, hernia, sleep apnea, gall bladder disease, intestinal obstruction and certain cancers. It should however be noted that for some reasons, a few people with a BMI of 25.0 or greater are not predisposed to the above risk.

Overweight: An overweight person is someone whose BMI lies between 25.0 and 29.9; the overweight person is about 10% greater than expected ideal body weight; the person may eventually become obese if no intervention to reduce weight occurs. The term overweight is different from over fat.

An over fat person is someone who has a higher percentage of body fat than is normal or healthy compared to the average person of same sex, age and gender. To determine over fat, a person’s total body fat is measured and compared to expected percent fat by age, read off a chart. If a man’s percentage fatness is 20% greater than expected total body fat, or if a woman is 30% greater than expected body fat, the person is over fat.

It should also be noted that a person can be overweight without being over fat and vice versa, but a man with body fat equal to or greater than 25%, or a woman with body fat equal to or greater than 32% may be both over fat and obese according to some reports.²³ The ratio of body fat to lean tissue is a better determinant of health and fitness than weight alone that is measured on a bath scale or other methods. Lean tissue however decreases due to inactivity and ageing. Ageing leads to decrease in basal metabolic rate (BMR) and decreased lean tissue but increase in body fat. Physical activity increases BMR and also increases lean tissue and tends to slow the ageing process. This is why participation in various physical activities, exercise and fitness programs as well as good nutrition is necessary for better ageing.

Essential body fat: Fat is an important body component with several functions. It should be noted that not all fat is bad. Certain fat known as 'essential body fat' is necessary for adequate body physiology and for good health and such fat is stored in muscles, organs, bones and central nervous system. Men require about 2-4 % essential fat while women require 8-12% essential fat. Essential fat is higher in women to enable them maintain hormonal and reproductive processes and to stay in good health. The rest of the body fat that is not needed for vital functions is non essential fat, which also have other purposes in the body such as insulation, serving as protective padding, storing excess energy for use during starvation, etc. Non essential fat is stored throughout the body around organs, inside body cavities like abdomen, and even under the skin. A regular/average man may have 12-20% total body fat while a regular/average woman may have 18-25% total body fat according to a report by the American Council on Exercise [24]. It is best to keep the level of non essential fat at a healthy level through weight loss or weight maintenance to prevent overweight and obesity.

Underweight: An underweight person is one whose BMI is less than 18.5. If the underweight condition is sustained for a long time, the person may be at risk of developing serious conditions and may be prone to falls, poor stamina, anaemia, malnutrition, poor wound healing and various illnesses.¹⁹

Obesity: A person living with obesity is one whose BMI value is 30.0 or higher. Obesity has 3 sub-classes based on the severity of the problem, class 1, or mild obesity (BMI at 30.0-34.9), class II or moderate obesity(BMI at 35.0-39.9) & class III or extreme/morbid obesity(BMI at 40.0 and above) as shown for the general populations in Table 1a. Obesity has many medical and quality of life consequences and health risks. The general classification of BMI values and weight status has been published in literature.^25,26

The BMI value cut-offs: The BMI cut offs for healthy weight, overweight and obesity statuses are different for Asian populations.^27,28 Asians have a higher tendency to develop metabolic syndrome, so their BMI cut-off for obesity is revised downwards to less than 30.0 according to published reports.²⁷ One study states that BMI for Asians (especially Japanese) is set at 25.0, while BMI of 23.0 to 24.9 is designated as overweight, and BMI of 30.0 is designated as obesity class II for Japanese or other Asians.²⁷ Other studies have put BMI of 27 or higher as obesity cut off for Asians and Asian Americans.^27,28 Thus a BMI considered normal or low for a non Asian may place Asians at risk. Table 1b, modified from the Joslin Diabetes Center,²⁹ compares Asian and non- Asian BMI cut offs.

BMI limitations: Although high BMI usually correlates with high body fat, there are some exceptions in that some high BMI levels can be observed in situations not involving fatness, while low BMI values can be observed in people who carry ample amount of fat tissue.

For example, athletes and weight lifters, people with increase in muscle and bone mass due to body building, or people born naturally big as well as people with edema or ascites, have high body weight and high BMI values but these conditions do not reflect fatness.

Body builders have increased muscle and bone mass through body building, weight lifting and rigorous walk outs and this increases their total muscle mass , bone strength and body weight which can result in high BMI. Similarly, high BMI values are observed in people who are born big naturally because of genetics. Such people naturally have heavy bones and big muscles and consequently high body weight.

The BMI value is also high in people living with edema and ascites. Edema is abnormal accumulation of fluid in various parts of the body especially at the extremities such as hands, arms and wrists or legs, feet and ankles. Ascites is an abnormal condition in which serous fluid accumulates mostly in the peritoneum or abdominal cavity and other body regions. Fluid accumulation can arise from different causes such as liver disease, cancer, bacterial peritonitis, alco