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Obesity epidemic
For more than 2000 years, the relation between overweight and morbidity and mortality was well-known, as the ancient Greek physician Hippocrates once said that naturally fat people have higher chances for sudden death more than people who are naturally lean. Just like hypertension and atherosclerosis, obesity is considered as a disease. The actual reason behind obesity is due to an imbalance between energy intake from food and energy expenditure. Fat cells store this excess energy and enlarge in size. Therefore, the main pathological lesions that cause obesity are hyperplasia and hypertrophy.8
The enlarged fat cells could lead to obesity-related clinical complications either due to having extra weight or mass of the enlarged fats or due to the increased free fatty acids secretions. The diverse medical, social and psychological disabilities involves plenty of medical and behavioral problems. Each disease of that is either resulted from the enlarged fat size or the excess fat cells. Enlarged fat size can lead to osteoarthritis and sleep apnea. However, excess fat cells causes the serious complications of obesity which is diabetes mellitus, cardiovascular disease, hypertension and gallbladder disease and some types of cancer that are associated with excess body weight (Figure 1)8.
Figure 1: Illustrative chart showing causes of obesity and obesity-related health complications8
The fat cell can be considered as an endocrine cell, and the fat tissue as an endocrine organ. Leptin is one of most significant type of adipokines that are secreted from fat cells and that makes the fat cell an endocrine cell and the fat tissue an endocrine organ. However, pathophysiologically, the free fatty acids are the most significant secretions of fat cells that give these cells its endocrinological properties. Notwithstanding that, the distribution of fat is the determent of the body response to the endocrine secretions and elevated visceral fats promotes insulin resistance related to obesity and hyperinsulinemia.8
Surprisingly, the literature statistics stated that obesity has nearly – globally – doubled over the last three decades.6 Specifically, adulthood obesity has been increasing in all countries. Furthermore, the prevalence of obesity is increasing rapidly reaching an epidemic rate that is both in the industrial world and worldwide.21
In 2014, 39% of adults aged 18 years and older (38% of men and 40% of women) were overweight. In the state of Qatar, the total population is 2,144,101 individuals; 1,597,403 are males and 546,698 are females.22 The statistics shows that obesity and diabetes are the most prevelant co-morbidities in Qatar which shows the need for serious proactive preventive actions for obese people at risk of diabetes.11

Body fat percent
BF% is defined as the proportion of a person’s fat mass over body weight. A study showed that BF% can better indicates cardiac function, arterial status, glucose, blood pressure and lipids than other anthropemtric indices such as BMI. The analysis of this study revealed that BF% is positevly accosiated with triglyceride blood levels, LDL cholesterol and negatively associated with HDL cholesterol. Therefore, it has the ability to detect glucose disturbances, risk of cariovascular diseases and cardiometabolic diseases in addition to its ability to estimate breast cancer survival rate. However, race plays a role in invidualizing the BF% results giving different values among different ethnic individuals.9

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DEXA as an alternative absorptiometry technique to other body composition measurements
Dual-energy X-ray absorptionometry (DEXA, DXA) is the leading method in measuring BF% of the entire body regions as well as specific sub-reginonal parts of the body. DEXA is a very accurate and percise technique – comparing to other body composition techniques – to be used in clinical settings in addition to drug trials. It is a non-invasive and rapid tool that conducts the measurements with minmal radiation exposure. Moreover,it is convenant be used on children and adults. This technique represents an efficient tehcnique in the management or treatment of diseases that can influence the relative amount of lean and fat tissues. Due to its technical advantages and its availabilty, DEXA is an effective subsitution to the other classical body composition screening techniques. DEXA has the capability to detect bone mineral content, bone mineral denity as well as lean and fat parts of the entire body or certain regions such as arms, legs, trunk and abdemen.12

Age, gender and ethnic differences in body fat percent among adults
Several studies have proved that BF% differs from ethnicitity to another and among different age goups and different genders. One meta-anylsis study indicated that there is a remarkable variance in BF% between American Caucasians and the European Caucasians with the European having 3.8% higher BF% notwithstanding having the same BMI as the Americans. The study contributed this difference to the variance in energy intake, energy expenditure and/or body build among both Caucasian populations. Moreover, the study reported that African Nigerian blacks have low BF% in comparison with the other Black populations.1 It is revealed in the literature that among the factors that contribute to the differnces of BF% among the ethnicities are body fat distribution, musculaity, bone mass and leg length as well.2 A study conducted measuring BF% of women and men found that the BF% was significantly higher in Pacific, Maori and Asian Indians than Europians.3 Another study demonstrated that Caucasian men have lower BF% but higher BMI than their Chinese counterparts who have high BF% with body tendency to store fat in the central part of body (Abdomen) and the study contributed that difference to the diversity in both populations body fat distribution.7 On the hand, a study stated that women by their body nature has higher BF% comparing to men as well as more adiposity in hips and thighs and this fat distribution in females – independent of BF% – protects againist metabolic disorders, such as type 2 diabetes and atherosclerosis. Moreover, subcutanues fats have special structure and metabolic profiles and vary in size and function from gender to another. In addiotion to that, intraabdominal fats including visceral fats that are related to digestive organs accounts for 6 – 20% of the total body fat and exist in high percentage in men more than women.4 On the other side, age can affect fat accumlation in the body in both genders in terms of the impact of cortisol in the body, the decrease in the growth hormone and the alternations in testosterone levels with age.17 Specifically, BF% appears to increase with age till reaching middle age and then it declines later in life.4

Validity of DEXA compared with other body composition screening
Few researches have studied the effectiveniess of DEXA comparing to other anthropemtric indices such as waist circuferance (WC) and body mass index (BMI). However, it has been been found that DEXA is a much practical tool than these methods in measuring body fatness giving a high resultion imaging, thus a high quality and accurate results. Validation studies have found similarities between DEXA and computered tomography (CT) in their ability to measure body fats, highlighting that DEXA can be used in epdemiological studies as a refereance tool. While DEXA is being extensively used in large surveys such as the National Health and Nutrition Examination Survey (NHANES), other anthropmetric measurements such as BMI and WC are still the most widely used tools of adiposity mesurements in epedimiolgical studies because they are simple to use. However, these measurements do not defferentiate between fat mass and lean mass which is why their validity in measuring the body fatness has been always doubted.13
Notwithstanding all of these advantages of DEXA, it has some shortcomings that can be summarized by being a costly technique, in addition to the need for trained staff, the exposure of people to radiation as well as inability of the machine to move from place to place.18 All of these restrictions limit the use of DEXA in clinical settings as well as in private medical health centers.14
Among several methods for adiposity screening, recently developed screening assessment, such as computed tomography (CT) and magnetic resonance imaging (MRI), can produce a very precise results of the locations and amount of fat tissues in the different body parts. However, the use of these screening tools is limited due to being expensive, complicated and the lack of protability.15
Another anthropometric measurement that measures body fat – indirectly – is BMI. It measures height and weight only which is why the precision of it – in detecting obesity – is limited, especially for older adults, who have decreased BF% and declined muscle mass or the opposite such as an elderly having portly body but low muscle mass, therefore BMI can overestimate some individuals and underestimate others. Another people who can be overestimated in body fatness by BMI are lean people who have muscular bodies such as sports people, therefore, they may have misleading results of BMI.16
Another fat assessment tool to measure body fat is the skinfold thickness, which is a technique that uses a caliper to measure fat at one or more body places. Applying skinfold thickness tool gives reliable estimate of body fat, particularly if measurements are taken from various sites. However, the result can differ when the measurements is repeated by different people or if the indivaual taking the measurements is not trained.14
In addition to these techniques of BF measurements, body fat could be detected by bioelectrical empedance which is a technique based on the principle that lean mass attracts electricidal current more than fat mass as well as taking height and weight into consideration in calculating BF%. However, results can differ depending on the body water content in addition to the positions where the electrodes are positioned.20

Research question
What are the body fat percent cut-off values specific for the different age groups of both genders of Qatari adults?

Summary
Obesity is considered a disease that is caused by excess weight or enlargement of fat cells and that could lead to diverse obesity-related complications. BF% is an anthropometric parameter that can be effectivity determine the risk of cardiovascular diseases as well as cardiometabolic disease. However, it can be affected by age, gender and ethnicity which several studies have shown and proved. BF% can be measured accurately and precisely by DEXA which represents the one of the best current screening tools in detecting body fats invasively and conveniently.
Objectives
The aim of this research is to create a well-studied and Qatari-adults-specific cut-off values of BF% for different age-gender groups that can be used as a reference for determining obesity-related health risks.

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