craschworks

Measuring Percentage Body Fat in Healthy Individuals
by Fiona Hayes

http://www.the-summit.co.uk/article4.htm

Justifications given

For some years obesity has been linked to increased risk for diseases such as coronary heart disease, type II diabetes, hypertension and some types of cancer. (Schull W.J. 1990; Gledhill N. 1990). Obesity has been defined as a body mass index of greater than 21 or body fat greater than 30%. Medical opinion is that to be healthy a total body fat percentage of no greater than 25% for women and no greater than 15% for men is desirable.

Over the past 20 years activity levels in the UK have fallen by an average of 800 Kcals per day and Intake has fallen by about 750 Kcals, per day (W P James: 1995; Hendler R.G. 1995). The remaining 50 Kcals causes a positive energy balance which is reflected in an increase in average adult weight. Added to this, a decrease in activity levels exacerbated by ageing causes a decrease in muscle mass, (Evans W. J. 1993; Tseng B.S. 1995; Going S.1995), which alongside the increase in weight gives a considerable rise in average total fat weight or percentage body fat.

The western world is apparently very interested in weight loss/management as witnessed by the popularity of slimming products. The U.S. National Centre for Health Statistics shows that nearly 50% of adult women are dieting to loose weight (DHSS publication 1990). It would appear therefore that loss of weight is a possible motivating factor for people to start on, or adhere to a regular exercise programme. For these reasons many health clubs and fitness centres include an estimation of percentage body fat in the battery of fitness assessments that they offer to the general public. Goals are then set for the client and these may include a target loss of body fat.

Sports coaches also often use estimations of % body fat and encourage athletes to achieve certain standards identified as desirable for elite performers in that particular sport.

Although estimations of percentage body fat are useful in collecting statistical data to identify population trends in public health, it is questionable whether the routine measurements carried out as part of fitness assessment in health clubs or as evaluation of factors leading to better sports performance are justified.

Methods
Hydrostatic Weighing

The gold standard for body fat measurement is considered to be hydrostatic weighing. This uses a model of reference man that is made up of two components. Fat and lean tissue. (lean tissue being all that is not fat.) It also assumes that the density of each component is known and that densities are constant amongst individuals. It assumes that the densities of lean tissue components are constant within and amongst individuals with a constant proportional contribution to the density of fat free mass. Finally it assumes that individuals being compared, differ only in the amount of fat when being compared to reference man (as described by Behnke and Wilmore 1974). (Behnke A. and Wilmore J.1974; Wilmore J. 1983; Skinner J. 1990).

As muscle and bone densities vary considerably between people, between male and female and between people of different ages, as well as at different body sites in the same person, the equations leading to the estimation of body fat using this method may well be inaccurate due to the assumptions made. Young and old populations tend to be overestimated whilst some athletic populations tend to underestimated. (Skinner J. 1990)

Hydrostatic weighing is expensive, uncomfortable and inconvenient and is therefore inappropriate for measuring large numbers of individuals, however it is the bench mark against which other methods of measurement of body fat are validated.

Anthropometry

One of the most common methods used for estimating body fat is skin fold measurements. This method measures folds of skin along with the underlying sub cutaneous fat at various sites on the body and then using regression equations estimates total fat from these measurements. To be close to accurate the skin fold calliper pressure should not vary by more than 2 g•mm-2 over a range of 2 to 40 mm and should be 9 to 20 g•mm-2. (Skinner J 1990), and the skin folds sites must be determined using anatomic reference points. The measurement should be read no more than two seconds after applying the full force of the calliper.

Problems occur because of error on behalf of the person measuring, difficulty in measuring obese individuals, poor quality or badly maintained callipers and assumptions made when preparing the equations used to determine % body fat from the sum of the skin fold sites. For instance the assumption is made that in young adult individuals subcutaneous fat amounts to 50% of total body fat and that distribution is consistent between people.

As ageing occurs less fat is deposited subcutaneously and more intra abdominal fat is present, thus a scale which takes into account the ageing process is used. How much of body composition changes are due to ageing and how much are due to lack of activity is at present undetermined, therefore whether this scale is accurate for very active or highly fit older individuals is questionable.

Bio Electrical Impedance

A relatively economical and increasingly popular method of estimating body fat is by use of bio electrical impedance. This is based on the concept that electric flow through hydrated fat free tissue and extra cellular water meets less resistance than through fat tissue. Thus impedance to the flow of electricity will be directly related to the amount of fatty tissue.

Because hydration affects the normal concentrations of electrolytes in the body the accuracy of this method will be affected by either over hydration or dehydration. Dehydration will decrease the impedance measure to yield a lower % fat, whilst over hydration will have the opposite affect.(McArdle Katch and Katch). This has implications when measuring female subjects who may retain large amounts of fluid during the luteal phase of the menstrual cycle.

Skin temperature may also affect readings.

Despite this, if specific reference data is collected, both BMI and bio electrical impedance may be very useful when measuring children or elderly subjects for whom skin fold measurements are inaccurate. (Lohman T.G. 1992; Chumlea W.C. 1991; Chumlea W.C. 1991)

Others

Other measurements of sub cutaneous fat include roentgenography, ultra sound and magnetic resonance imagery, however these methods are expensive and raise ethical questions such as those surrounding the use of x-rays. They do however have an advantage over skin fold measurements in that bone and muscle can be imaged and could possibly be directly measured.

Body stature and girth measurements, although often used in isolation may be especially useful when used in conjunction with sum of skin fold sites as in the Canadian Standardised Fitness Test, in which body mass index (BMI) is calculated by dividing body weight in kilograms by height in metres squared and is reviewed alongside the sum of five skin fold measurements to determine whether a high BMI is due to excess adiposity or to muscularity. The body fat distribution is then also determined using waist to hip ratio and the sum of two skin folds taken at the sites of the iliac crest and sub scapular.(Gledhill N. 1990)

What is normal

Tables showing 'Normal' or desirable body fat percentages for different ages and genders are often used to determine whether a person needs to lose body fat. Typically, an across age figure of no greater than 25% fat is quoted as desirable for females and an across age figure of no greater than 15% fat is quoted as desirable for men.

These figures are based on young active or athletic populations and do not take into account individual genotype or culture. It is thought that about 25% of the variance in fat mass can be accounted for by genetic transmission and about 30% can be accounted for by cultural transmission.(Bouchard C.1990).

Giving an individual a target fat loss based on an active young population may therefore be inappropriate. A more appropriate target would be based on an estimate of what is possible and acceptable taking into account the individual's age, genotype and cultural background.

Risk to health

As well as this, questions still remain around the effect on health of total body fat as compared to the distribution of body fat, and the negative effect of weight cycling that may result from an individual's repeated attempts to lose weight interspersed with weight gain.

Body fat content alone may not be the main risk to health. People with large partially filled adipose depots may have less risk than those with smaller but completely filled adipose depots. In animal studies restriction of energy intake in genetically obese animals increases longevity and decreases signs of ageing, even though the animals remain obese. (Abernethy R.P.1994) In humans centrally distributed body fat is associated with a higher risk of cardiovascular disease than is peripherally distributed body fat. (Bray G.A. 1988).

Weight cycling, that is repeated bouts of weight loss and weight gain, may carry a higher risk for all cause mortality and for mortality from coronary heart disease than does a body fat percentage consistently above that which is recommended for health. (Brownell K.D. 1994; Brownell K.D.1987)

Accuracy

If population studies describing health trends, especially those associated with obesity, are the reason for measuring body fat, then the measurements used need to be economical, highly reproducible and accurate.

Currently there are problems associated with all the methods used for indirect measurement of body fat and these may be amplified in particular sectors of the population. Measurement of body fat in the elderly could be used to prevent malnutrition in institutionalised elderly persons, to predict health risks and to plan and evaluate intervention strategies, to study associations among fat patterning and mortality to develop improved reference standards for the elderly. However current methods of estimating body fat in the elderly are limited by the lack of suitable reference data. (Chumlea W.C. 1989; Chumlea W.C. 1993; Kuczmarski R.J. 1989; Van Itallie T.B. 1990)

Body fat assessment in females is fraught with problems. Estimations have been largely extrapolated from male studies however, compared to men, fat regulation in women is far more elaborate with more and different sites for storage and a greater amount of essential fat. There is a larger proportion of fat distributed to the extremities thus a waist to hip ratio is less reliable in predicting health risk. The assumptions made about bone mineral density and body water to fat free mass may not hold through the reproductive cycle. In addition to this, for women involved in sport, disruptions to the menstrual cycle and hormonal changes that may occur with training may significantly alter bone mineral density and distribution of muscle mass. (Vogel J.A. 1992; Shangold M. 1988)

Target fat loss

If body fat estimations are used to provide fat loss goals for the general public, then the administrators of the tests need to be highly trained in the correct use of appropriate methods of measurement and need access to data that is appropriate for the population that they are measuring. They also need to be trained to give individual targets based not only on the figures in front of them but also on the individuals genetic and cultural background and psychological aspects of change. They should also be able to advise on appropriate methods of influencing a positive change in body composition. The author's view, based on observation, is that at present in this country most assessments are carried out by people untrained in these areas.

If target body fat percentages are used for athletic populations the sports coach should also be trained in the above areas and should be sensitive towards the athlete who has difficulty achieving or maintaining fat weights that are considered desirable for their sport. Many female distance runners, dancers and gymnasts have developed complications such as under nutrition and osteoporosis through maintaining a body weight that is unnatural for them as an individual. (Shangold M. 1988) Athletes attempting to reduce percentage body fat should be given a range of acceptable figures and should be monitored for changes in health and performance.(Hergenroeder A.C. 1990)

Health Care

Good health, whilst it is adversely influenced by being over fat is also adversely influenced by lack of exercise, which in it's turn may be a contributory factor to becoming over fat.

Trying to control fat weight and influence percentage body fat by restricting energy intake alone is not likely to improve health dramatically. In fact only 5% of patients in Canada who diet to achieve permanent weight loss succeed and reap the associated health benefits.

The implications of failed dieting include negative effects on both physical and psychological health ( Kirkland L. 1993). Thus for individuals who are overweight, assisting them to adopt an exercise programme and a healthy diet that they could maintain throughout life and that would achieve desired body composition changes with minimal lean weight loss, or even by gaining lean muscle mass, may be more appropriate than concentrating on target fat loss.(Stefanick M.L. 1993)

Conclusion

More research into accurate measurement of body fat percentage in specific populations such as females, athletes, the elderly and children is needed to develop improved methods and improved reference standards suitable for these populations.

Research into the minimum exercise dosage and types of exercise needed to improve health and positively affect body composition in different sectors of the population are needed.

Community support is necessary for people who are attempting to overcome long term problems with over fatness.

Education of those people involved in giving advice on exercise and health and in measuring fitness parameters including body composition is needed. This education should include some psychology training for those who are dealing with the sensitive issue of body fatness.

Given the inaccuracy of the measurements presently available and the lack of training of the people carrying out the measurements and giving advice on weight loss, measurement of body fat in healthy individuals is largely meaningless and may cause unnecessary concern in individuals.

With improved techniques it may prove to be a useful tool in monitoring public health in populations, and given improved training it may provide a useful motivational tool for those professionals involved in prescribing or advising on exercise programmes.

References

Abernethy R.P.1994; Black D.R. 'Is Adipose Tissue Oversold As A Health Risk?' Journal Of The American Dietetics Association. Jun 1994, 94(6) pp641-644

Behnke and Wilmore 1974 'Evaluation And Regulation Of Body Composition' Englewood Cliffs, NJ: Prentice Hall 1974.

Bouchard C.1990. 'Discussion: Heredity, Fitness and Health.' in Exercise Fitness and Health (Eds. Bouchard C., Shepherd R., Stephens T., Sutton J.R., McPherson B.D.) pp148-149. Human Kinetics Books. Champaign Illinois.

Bray G.A. 1988; Gray D.S. 'Obesity. Part I; Pathogenesis' Western Journal Of Medicine (US) Oct 1988 149(4) Pp429-441.

Brownell K.D.1987, Steen S.N. Wilmore J.H.'Weight Regulation Practices In Athletes; Analysis of Metabolic and Health effects' Med Sci Sports Exerc (US) Dec 1987 19(6) pp546-556

Brownell K.D.1994; Rodin J. ' Medical, Metabolic And Psychological Effects Of Weight Cycling'. Arch Intern Med (US) Jun 27 1994, 154(12) pp1325-1330.

Chumlea W.C 1991; Baumgartner R.N; Vellas B.P. 'Anthropometry And Body Composition In The Perspective Of Nutritional Status In The Elderly' Nutrition (US) Jan-Feb 1991 7(1) pp57-60

Chumlea W.C. 1989; Baumgartner R.N. 'Status Of Anthropometry And Body Composition Data In Elderly Subjects' American Journal of Clinical Nutrition Nov 1989 50(5 suppl) pp1158-1166

Chumlea W.C. 1993; Guo S.S.; Kuczmarski R.J.; Vellas B. 'Bioelectric and Anthropometric Assessments and Reference Data In The Elderly' Journal Of Nutrition (U.S.) Feb 1993 123(2 suppl) pp449-453

DHSS publication 1990. National Centre for Health statistics. Health. United States 1989. Hyattsville MD: Public health Service (DHSS Publication No PHS 90-1232) 1990

Evans W. J. 1993 Cambell WW. 'Sarcopenia And Age Related Changes In Body Composition And Functional Capacity' . Journal Of Nutrition (Us) Feb 1993 123(2 suppl) P 465-8

Fitness and Health (Eds. Bouchard C., Shepherd R., Stephens T., Sutton J.R., McPherson B.D.) pp109-112. Human Kinetics Books. Champaign Illinois.

Gledhill N. 1990 'Discussion. Assessment of Fitness' in Exercise Fitness and Health (Eds. Bouchard C., Shepherd R., Stephens T., Sutton J.R., McPherson B.D.) pp122. Human Kinetics Books. Champaign Illinois.

Going S. 1995, Williams D. And Lohman T. 'ageing And Body Composition; Biological Changes And Methodological Issues' Exerc Sports Sci Review (US) 23 Pp411-458 1995

Hendler R.G. 1995, Welle S L.,Statt M. C., Barnard R., Amatruda J.M. 'The Effects Of Weight Reduction To Ideal Body Weight On Body Fat Distribution' Metabolism Clinical And Experimental. (USA) 1995 44(11) pp1413-1416

Hergenroeder A.C. 1990; Klish W.J. 'Body Composition In Adolescent Athletes' Paed Clin North Am (US Oct 1990, 37(5) pp1057-1083

Kirkland L. 1993; Anderson R; 'Achieving Healthy Weights' Canadian Family Physician Jan 1993 39 pp157-158

Kuczmarski R.J. 1989; 'Need For Body Composition In Elderly Subjects' American Journal of Clinical Nutrition Nov 1989 50(5 suppl) pp1150-1157

Lohman T.G. 1992; 'Exercise Training and Body Composition in Childhood' Canadian Journal of Sports Science Dec 1992 17(4) 284-287

McArdle Katch and Katch .'Exercise Physiology' third edition Lea and Febiger 1991 pp623

Schull W.J. 1990. 'Heredity, Fitness and Health' in Exercise Fitness and Health (Eds. Bouchard C., Shepherd R., Stephens T., Sutton J.R., McPherson B.D.) pp137-138. Human Kinetics Books. Champaign Illinois.

Shangold M. 1988; Mirkin G. In 'Women And Exercise . Physiology and Sports Medicine' F.A. Davis Company. Philadelphia.

Skinner J. S. 1990, Baldini F. D., Gardener A.W. 'Assessment of Fitness' in Exercise

Stefanick M.L. 1993. 'Exercise and Weight Control'; Exercise and Sports Science Review (US) 1993 21 pp363-396

Tseng B.S. 1995; Marsh D.R.; Hamilton M.T. ;Booth F.W. 'strength And Aerobic Training Attenuate Muscle Wasting And Improve Resistance To the Development Of Disability With Ageing' Journal Of Gerontology And Biological Sci And Med Sci (US)

Van Itallie T.B. 1990, Lew E.A. 'Health Implications of Overweight In The Elderly' Prog Clin Biol Res (US) 1990 326 pp89-108

Vogel J.A. 1992; Friedl K.E. 'Body fat Assessment In Women; Special Considerations' Sports Medicine (New Zealand) April 1992, 13(4) pp245-269

W P James: 1995. 'A Public Health Approach To The Problem Of Obesity' International Journal of Obesity Related Disorders. Sept. 1995 19 Suppl 3 pp37-45

Wilmore J 1983. 'body Composition In Sport And Exercise: Directions For Future Research.' Med. Sci. Sports Ex. 15: pp21-33 1983

© Copyright Fiona Hayes 1998