Title: Obesity and Health

Key words: Obesity, diet, physical activity, genetic factors, brown fat, socio-economic factors, excess mortality

Date: July 2000

Category: 9. Weight Management

Type: Article

Author: Dr M Draper

Obesity and Health

The Aetiology And Health Implications Of Excess Body Fat


Obesity is a term applied to people who are overweight and have excess body fat. It is one of the most common problems in the developed world. Obesity is a rapidly increasing nutritional disorder that has short- and long-term health implications.

However, it is 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 women, about 30 per cent of body weight is fat at age 25, increasing to about 36 per cent by age 651.

Aetiology of excess body fat

The causes of overweight and obesity are often simplified into the following three components:

·        diet

·        physical activity

·        genetic factors (which determine individual predisposition by effects on appetite and metabolism)

·        These factors govern energy balance and the interaction between them can lead to an individual becoming overweight.


·        The changing pattern of excess body fat in Britain is a cause for concern (see Table1). It may, perhaps, indicate that the main factors are diet and lack of physical exercise because the genetic makeup of the population is unlikely to have changed dramatically between 1980 and 1991 when the number of people classified as obese has doubled.

%age of People Classified as Overweight or Obese in Britain


Overweight (BMI > 25)

Obese (BMI > 30)





















Populations with food provision in excess of requirements, with >30% dietary energy derived from fat and with 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 slimmer counterparts and recent research has shown this to be true2. There may be genetic and nutritional factors that influence a person’s basal metabolic rate. This could partly explain why some people gain weight more easily than others. One theory to explain this may be variations in the amount of brown adipose tissue. There appear to be two types of body fat:

·        Ordinary subcutaneous fat - which is mainly used to store energy when excess calories are consumed

·        Brown fat - which is more metabolically active and is found between the shoulder blades and around the kidneys.

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 that is less active3,4. Some researchers suspect this may be one of the causes of familial obesity. 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. A recent study by von Kries et al.5 reports some interesting findings on the relationship between 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 could be reduced still further if children were 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.6 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 al7 used data from Toyama local government health check ups to try to elucidate the relationship between obesity and lifestyle in 3-year-old children. Their conclusions suggested several factors influenced the development of obesity in Japanese children. These included:

·        host factors - overweight parents and overweight at birth

·        behavioural factors - physical inactivity and snacking

·        environmental factor - the mother's job


·        A study on a Native Community in Canada8 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 and skin fold thickness alongside decreased fitness and increased television watching.

In adults it has been previously demonstrated that obesity is common among women with low socio-economic status. A recent Swedish study by Wamala et al.9 in 1997 concluded that reproductive history, unhealthy dietary habits and psychosocial stress accounted for the association between low socio-economic status and obesity in middle-aged women.

The eating patterns of elderly Greeks were studied by Walqvist et al10. 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 Groves11 for the increase in obesity seen in civilised populations is the increase in our intake of carbohydrates, especially those derived from wheat and sugar. His arguments are based on archaeological and anthropological data. He believes that during our evolution, Homo erectus who lived some 500,000 years ago, was mainly meat eating. 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 Eskimos in Greenland increase their intake of preserved food, dried potatoes, canned foods and cereals they develop the ‘diseases of civilisation’3.

A similar trend occurs when Masai in Africa eat less meat and replace it with maize and beans. He says the health of the 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. This created the need to produce food that could feed urban populations with foods that did not perish. The present low levels of Omega 3 essential oils in our diets may be partly due to the fact that these oils do not keep. The popularity of white flour may be because even the weevils will not eat it!

The eating of whole foods (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 apparently overproduce poor quality food. A return to organic methods, with lower pesticide residues and an increase in 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:

·        reduced life expectancy

·        increased blood pressure

·        increased risk of coronary heart disease

·        elevated blood fats (cholesterol)

·        a reduced ability to take exercise

·        an increase in gallstones

·        diabetes

·        varicose veins

·        hiatus hernia

·        constipation

·        post-operative infections

·        poor wound healing

·        osteoarthritis

For women in particular there is an increased risk of irregular periods and period pains, hairiness and cancers of the breast and womb. Smoking also carries an increased risk in obese individuals.

Table 2 represents the excess mortality with overweight and obesity expressed as a ratio of that condition as a cause of death in obese people: the expected rate in lean people.

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





Prostate 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.

There are a few benefits to being obese. 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. The present increase in prevalence could be passed from one generation to the next unless educational programs can influence the child or adult who is starting to become overweight12. Perhaps we should try to identify how the eating and lifestyle patterns of a subsection who do not gain weight differ from those who do gain weight, given similar environmental circumstances. This evidence-based advice might be accepted by those who need to make a change in their eating patterns.


How are overweight and obesity defined?

The definition of overweight is 10 to 20 per cent greater than the acceptable range. Obesity is when weight is more than 20 per cent greater than the acceptable range.

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

Other measures

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 skin fold thickness of subcutaneous adipose tissue using standardised callipers 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, Sub-scapular and Supra-iliac.

The desirable ranges are 3-10mm for men and 10-22mm for woman. The precise relationship between skin fold thickness and percentage of body fat varies with age and gender and is not a simple linear relationship1.


1.      Bender, D.A. Introduction to Nutrition and Metabolism. 1997; p179-196 Taylor & Francis.

2.      Rose, G.A, Williams, R.T.  Metabolic studies on large eaters and small eaters. Br. J. Nutr. 1961; 15:188.

3.       Jung, R.T, et al. Reduced thermogenesis in obesity. Nature. 1979; 279:323.

4.      Himms-Hagen, J. Obesity may be due to a malfunctioning of brown fat.  Can. Med. Assn. J. 1979; 121: 1361.

5.      Von Kries, R. et al. Breast feeding seems to reduce the risk of obesity in children. B.M.J. 1999;  319:147-150.

6.      Reilly, J.J., Dorosty, A.R., Emmett, P.M. Prevalence of overweight and obesity in British Children: cohort study. B.M.J. 1999;  319:1039-1039.

7.      Takahashi, E. et al.  Influence Factors on the Development of Obesity in 3-Year-Old Children Based on the Toyanma Study. Preventive Medicine. 1999; 28 (3) p.293-296 American Health Foundation and Academic Press.

8.      Macaulay, A.C. et al.  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. 1997; 26 (6) p779-790 - Academic Press.

9.      Wamala, S.P., Wolk, A., Orth-Gomer, K. Determinants of Obesity in Relation to Socioeconomic Status among Middle-Aged Swedish Women. Preventive Medicine 1997; 26 (5) p.734- 744  Academic Press.

10.  Wahlqvist, M. L., Kouris-Blazos, A., Wattanapenpaiboon, N. The Significance of Eating Patterns: An Elderly Greek Case Study. Appetite. 1999; 32 (1) p.23-32 Academic Press.

11.   Groves, B. The Calorie Fallacy 1999; p. 20-34. Bookmarque.

12.  Williams, C.L. et al.  Healthy Start: A Comprehensive Health Education Program for Preschool Children. Preventive Medicine. 1998; 27 (2) p216-223.  Academic Press.