Title: Obesity review - Causes and implications of excess body fat

Key words: Obesity, overweight, Body Mass Index, diet, physical activity, genetic factors, thyroid, brown fat, adipose tissue, familial obesity, breast feeding, lifestyle, socio-economic status, health implications, education,

Date: June 2001

Category: Weight management

Type: Article

Author: Dr M Draper


Obesity Review

The Causes And Health Implications Of Excess Body Fat.

Obesity, the term applied to people who are overweight and/or have excess body fat, is one of the commonest problems in the Western or Developed world. Obesity is a rapidly increasing nutritional disorder which has both short and long term health implications. It is both normal and desirable to have some reserves of fat in the body. In lean men about 16 per cent of body weight is fat at age 25, increasing to 24 per cent by age 65. In lean woman, about 30 per cent of body weight is fat at age 25, increasing to about 36 per cent by age 65. (1).

How are overweight and obesity defined?

Overweight is usually defined as body weight that is 10 to 20 per cent greater than the ideal range. Obesity is the term used when body weight is greater than 20 per cent above the ideal weight.

The World Health Organisation defines overweight using body mass index (BMI , which is body weight in kg divided by height in metres squared. An acceptable range for BMI is 18.5-24.9 kg/m2. Values below 20 are associated with undernutrition, while a BMI between 25-29.9 indicates overweight. Those with figures > 30 are classified as obese. For Waist Circumference and Skinfold Thickness measurements see Appendix One.

Aetiology of excess body fat.

The causes of overweight and obesity is often simplified into the following three components that govern energy balance: diet, physical activity and genetic factors which determine individual predisposition by effects on appetite and metabolism. The interaction of these three factors leads to an individual becoming overweight.

The changing pattern of excess body fat in Britain (see Table1) is a cause for concern and perhaps indicates that the main factors are diet and lack of physical exercise because the genetic makeup is unlikely to have changed dramatically between 1980 and 1991 when the number of people classified as obese have doubled. Populations with food provision in excess of requirements , with >30 % dietary energy from fat and low levels of physical activity are those with the highest prevalence of overweight people. It does seem that in the vast majority of cases obesity is caused by consuming more calories than are needed to maintain normal weight.

Certain diseases such as an underactive thyroid are an occasional cause of obesity. Some overweight people strongly believe that they consume the same amount or even less food than do their thin counterparts and recent research has shown this to be true. (2). There may be genetic and nutritional factors that influence a persons basal metabolic rate and this could partly explain why some people gain weight more easily than others.

One theory to explain this maybe variations in the amount of brown adipose tissue. There appears to be two types of body fat , the ordinary subcutaneous fat which is mainly an energy store when excess calories are consumed and a different type of fat which is more metabolically active and is found between the shoulder blades and around the kidneys. The brown fat appears to have the ability to burn up excess energy and appears to be linked to thermogenesis.

Obese people may have less brown fat or have brown fat which is less active (3a & 3b). Some researchers suspect this may be one of the causes of familial obesity. It is possible that a number of nutritional factors including the balance of vitamins, minerals and essential fatty acids may influence the activity and metabolism of brown fat.

Obesity often starts in childhood and a recent study by von Kries et al (4) reports some interesting findings on the relationship beween breast feeding and obesity. Using data from 9357 of the 134,577 children examined for the 1997 school entry health examination in Bavaria, they found that the risk of obesity at age 5 or 6 years could be reduced by 35% if children had been exclusively breast fed for 3 to 5 months. the risk can be reduced even further if children are breast fed for longer than 5 months. Preventing childhood obesity and its consequences may be important arguments in the drive to promote breast feeding in industrialised countries.

A recent study by Reilly et al (5) in 1999 showed there has been an increase in the prevalence of overweight and obese children in preschool British children. The value of these estimates is to alert those involved in preventive medicine that there is a need for measures to be taken in our own population.

A study in Japan by Takahashi et al (6) used data from Toyama local government health check ups to try to elucidate the relationship between obesity and lifesyle in 3-year-old children. Their conclusions suggested several factors influenced the developement of obesity in Japanese children and these included overweight parents, overweight at birth as host factors , physical inactivity and snacking irregularity as behavoural factors and the mother's job as an environmental factor.

A study on a Native Community in Canada (7) with a high incidence of non insulin dependent diabetes mellitus in Mohawk adults showed in a 3 year study that between the age of 9 and 10 years old there was increased weight, height, BMI, skin fold thickness : decreased fitness; and increased television watching.

In adults it has been previously demonstrated that obesity is common among women with low socioeconomic status and a recent Swedish study by Wamala et al (8) in 1997 concluded that reproductive history, unhealthy dietary habits and psychosocial stress accounted for the association between low socioeconomic status and obesity in middle aged women.

The eating patterns of elderly Greeks was studied by Walqvist et al (9) and they concluded that adherence to a traditional Greek eating pattern may be protective against obesity and appears to promote greater food variety.

An interesting theory put forward by Groves (10) for the increase in obesity seen in civilised populations is the increase in our diets of carbohydrates especially those derived from wheat and sugar. His arguments are based on archeological and anthropological data. He believes that during our evolution Homo erectus lived some 500,000 years ago was mainly meat eating and only when meat was in short supply did our ancestors eat nuts, berries and fruits. He uses anthropological data from modern tribes to show that when Eskimo in Greenland increase their intake of preserved food , dried potatoes, canned foods and cereals they develop the diseases of civilisation.

A similiar trend occurs when Masai in Africa eat less meat and replace it with maize and beans. He says the health of Kikuyu improved when they stopped being wholly vegetarian and started eating meat.

The health trend we have all been encouraging is to reduce animal fats, increase carbohydrates and maintain protein, perhaps we need to look in a more complex way and remind ourselves that our present eating habits were influenced by the demands placed on agriculture by the industrial revolution and the need to produce food that could feed urban populations with food that did not perish. The present low levels of Omega 3 essential oils may be partly due to the fact that these oils do not store well and the popularity of white flour may be because even the weevils will not eat it!

The eating of wholefoods (meats, nuts, seeds, vegetables and fruit) that have not been processed and modified may be a move in the right direction because the ratios of carbohydrate, protein, fats and oils tends to more closely parallel that which is considered healthy. In the developed world, we seem to overproduce poor quality food. A return to organic methods, lower pesticide residues and increased mineral and vitamin intake may help to reduce the overall calorie intake, increase satiety and reduce body weight, as some observational studies are suggesting (unpublished data ).

The health implications of excess body fat.

The adverse effects of obesity are well documented and include:

There are a few benefits to being obese and these include a reduced risk of osteoporosis and an increased tolerance of cold weather.

The importance of reducing childhood obesity cannot be over emphasised because of the link between childhood obesity and adult coronary heart disease and diabetes. The eating and lifestyle patterns of the obese adult can obviously influence the growing child and the present increase in prevalence could pass from one generation to the next unless educational programs can influence the children and young adults who are starting to become overweight (11).

Perhaps we should try to identify how the eating and lifestyle patterns of one subgroup who do not gain weight differs from that of another that gains weight given similiar environmental circumstances. This evidence-based advice might be better accepted by those who need to make a change in their eating patterns.

How are overweight and obesity defined?

Overweight is generally defined by an individual's weight being 10 to 20 per cent greater than the ideal range. Obesity is the term used when weight is greater than 20 per cent above the ideal weight.

The World Health Organisation defines overweight using body mass index (BMI, which is body weight in kg divided by height in metres squared. An acceptable range for BMI is 18.5-24.9 kg/m2. Values below 20 are associated with undernutrition, while BMI between 25-29.9 indicates overweight and those with figures > 30 are classified as obese.

Waist circumference is a simple measurement which indicates the need for weight management and reflects coronary risk related to both overweight and central fat distribution. A healthy waist measurement, reflecting low coronary risk is below 94 cm /37 inches for men and 88cm/35 inches in woman. Those with waist measurements greater than 102cm/40 inches in men and 88cm/35inches in woman have the greatest health risks and should seek professional help.

The most widely used technique for estimating body fat reserves is measurement of skinfold thickness of subcutaneous adipose tissue using standardised calipers that exert a moderate pressure (10gm per mm2 over an area of 20-40mm2) and therefore cause temporary discomfort. The mean of the skin fold thickness at the following four sites should be calculated to give the most precise measurement: (Triceps, Biceps, Subscapular and Supra-iliac) and the desirable ranges are 3-10mm for men and 10-22mm for woman. The precise relationship between skinfold thickness and percentage of body fat varies with age and gender and is not a simple linear relationship(1).

Table 1

%age of People Classified as Overweight or Obese in Britain


Overweight (BMI > 25)

Obese (BMI > 30)






















Table 2:

Excess mortality with overweight and obesity


Body weight as %age of mean




Cause of death







All causes







Diabetes mellitus







Digestive diseases







Coronary heart disease







Cerebral vascular lesions







Cancer, all sites







Colorectal cancer







Prosatate cancer







Endometrial cancer







All uterine cancer







Cervical cancer







Gall bladder cancer







Breast cancer







Figures show mortality relative to that for people between 90 and 110 per cent of average weight. From data reported by Lew, E. A. and Garfinkel, L (1979) Variation in mortality by weight among 750 000 men and women. Journal of Chronic Diseases, 12, 563-76; and Garfinkel, L. (1886) Overweight and mortality.

Cancer, 58, 1826-9.

The following books are recommended for their interesting and unusual perspectives on weight loss and diet. There are however questions being asked about the long term use of high protein diets, especially in women, because of the link with osteoporosis. If you have any queries, just email us at:


Recommended Diet Books1. ATKINS, R.C. - Dr Atkins New Diet Revolution (1992)Vermillion ISBN 0 09 186783 5. GROVES, B. - The Calorie Fallacy (1999)Bookmarque

ISBN 1-870519-29-9

3. HOLFORD, P. - The 30 day Fat Burner Diet (1999)Piatkus

ISBN 0 7499 1920 5

4. D'ADAMO, P. WHITNEY,C. - The Eat Right Diet (1998)Century.London

ISBN 0 7126 7784 4




REFERENCES/FURTHER READING1. BENDER, D.A.(1997) Introduction to Nutrition and Metabolism

p179-196 Taylor & Francis.

2. ROSE, G.A, WILLIAMS, R.T. (1961) Metabolic studies on large

eaters and small eaters. Br J Nutr. 15:188.

3a. JUNG, R.T, et al. (1979) Reduced thermogenesis in obesity. Nature


3b. HIMMS-HAGEN, J. (1979) Obesity may be due to a malfunctioning

of brown fat. Can.Med.Assn J. 121: 1361.

4. VON KRIES, R. et al. (1999) Breast feeding seems to reduce the risk

of obesity in children - British Medical Journal 319:147-150

5. REILLY, J.J., DOROSTY, A.R., EMMETT, P.M. (1999) Prevalence

of overweight and obesity in British Children: cohort study - British

Medical Journal 319:1039-1039

6. TAKAHASHI, E. et al (1999) Influence Factors on the Development

of Obesity in 3-Year-Old Children Based on the Toyanma Study -

Preventive Medicine v 28 n 3p.293-296 American Health Foundation

and Academic Press.

7. MACAULAY, A.C. et al (1997) The Kahnawake Schools Diabetes

Prevention Project: Intervention, Evaluation, and Baseline Results of a

Diabetes Primary Prevention Program with a Native Community in

Canada -Preventive Medicine v 26 n6 p779-790 - Academic Press.

8. WAMALA, S.P., WOLK,A., ORTH-GOMER,K. (1997)

Determinants of Obesity in Relation to Socioeconomic Status among

Middle-Aged Swedish Women - Preventive Medicine v 26 n 5 p.734-

744 Academic Press.


WATTANAPENPAIBOON, N. (1999) The Significance of Eating

Patterns: An Elderly Greek Case Study - Appetite, v 32 n 1 p.23-32

Academic Press.

10. GROVES, B. (1999) The Calorie Fallacy p. 20-34 - Bookmarque

11. WILLIAMS, C.L. et al (1998) Healthy Start: A Comprehensive

Health Education Program for Preschool Children - Preventive Medicine, v 27 n 2 p216-223. Academic Press.