Obesity, Diet, Exercise and Weight Control

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Review Article

Obesity, diet, exercise and weight control— a current review

M. K. Chin,Archie Y. S. Lo, X. H. Li, Mimi Y. M. Sham an d Yvonne W. Y. Yuan

Abstract

Obesity can be attributed to complex physiological, genetic, cultural and psychological factors. Itshould not be regarded merely as a result of weak will power or other character deficits. Thispaper attempts to provide background information on energy balance which is important vis-a-vis weight control. Weight reduction as a desirable end-point of negative energy balance is best

achieved through a combination of dietary restriction and exercise. Two alternative methods ofweight reduction are proposed and discussed. Nutritional, behavioural changes and carefulmonitoring of exercise and diet should be implemented holistically to ensure a successful weightreduction programme. Individuals also need to be aware of the many myths and misconceptionssurrounding weight control.

Keywords: Obesity; Diet; Exercise; Weight control

Introduction

Despite a growing awareness of the detrimental ef -fects of excessive body fat on health, obesity remainsa major public health problem among many Westernsocieties, and more recently, in Asian countries aswell. It has been estimated that at least 20% of theadult population in the United States are overweight,with this figure increasing to 35%-40% in adults over40 years old.

1 In a National Heart Foundation studyon Australian men and women over the age of 45,60% an d 50%, respectively, were considered over-weight.

2In a recent survey of school children in Beijing,

Sports Science Department, Hong Kong Sports Institute, Sha Tin, HongKongM. K . Chin, PhD,Mimi Y. M. Sham, BSc, Dipl Dietetics

Hong Kong Heart Centre, 40 Stubbs Road, Hong KongArchie Y. S. Lo, MD (Chicago), FRCPCDepar tment of Physiology, University of Cambridge, Downing Street,Cambridge, CB2 3EG, United KingdomX . H. Li, MDHong Kong Centre of Sports Medicine and Sports Science, The ChineseUniversity of Hong Kong, Sha Tin, Hong KongYvonne W.Y . Yuan, M ScCorrespondence to: Dr M. K. Chin

3%-5% of the children had body weight in excessof20% over the recommended range.

3Comprehensive

data are not available on obesity in the Hong Kongpopulation, but the frequency an d variety of com-mercial advertisements pertaining to weight reductionprog rammes indicate that there is strong interest inthis issue. The objective of this paper is to present thescientifically verifiable facts on diet, exercise an dweight control in relation to obesity, as opposed tosundry popular myths and misconceptions.

Definition of obesity

Obesity can be broadly defined as an excessive en -largement of the body's fa t stores. Total body fa texists in one of two forms: essential or storage fat.Essential fat is necessary fo r normal physiologicalfunctions, and can be found in varying degrees in allorgans including the central nervous system. Storagefat is deposited in the adipose tissue throughout thebody mainly under the skin. Adipose tissue serves asan efficient means of insulation and fuel storage.

Th e amount of essential fat in a person remainsfairly constant; it is primarily storage fa t that is affected

by diet or exercise.

181



182 J Hong Kong Med Assoc Vol. 44, No. 3, September 1992

While no universally accepted def ini t ion fo r obes-

it y exists, there is a general consensus tha t tota l body

f a t levels above 20% and 30% for m en and women,

respectively, would constitute obesity.4

Th e hea l th

consequences associated with obesity are numerous,

including hypertension, hypercholesterolaemia,

hyper t r ig lycer idaemia , non-insulin-dependent dia-

betes mellitus, gallstone disease (cholelithiasis), and

several forms of cancer.5

Men and women should

strive to maintain total body fa t levels at about15 %

and 25%, respectively.Obesity can also be understood in terms of the

'body mass index' (BMI). This index is der ived by

div iding body weight (W) in kilograms by he ight

squared (H2) in metres ( B M I = W/H

2). The health risk.s

associated with obesity progressively increase as the

BMI exceeds 30.6

Being above a v e r a g e weight does

no t necessarily imply that a person is too fat. Eli te

athletes and body builders have increased musclemass which, produces a raised BM I in the 'overweight'

range, but such persons do not have any abnormal

increase in body fat. Therefore, th e interpretation of

th e B M I must be carried out judiciously.

Types of obesity

There are two major categoriesof obesity: hyperplastic

and hypertrophic obesity, Hyperplastic obesity re -

sults from excess calor ic intake during critical periods

(the last trimester of pregnancy, adolescence and in-

fancy) resulting in the formation of addi t iona l fa tcells. Hypertrophic obesity is caused, by the formation

of excessively large fa t cells as a result of excess caloric

in take . This latter form is characteristic of adult-onset

obesity. It appears that once adulthood is attained,

the number of fat cells (adipocytes) is constant, The

adipocytes do not increase or decrease in number

under normal conditions; they merely expand or con-

tract.7

Obese individuals who lose weight tend to

gain it back quickly because th e abundant adipocytes

are available as vacant storage sites.

Childhood obesity

A n i m a l and human studies have demonstrated that

genetic factors can contribute to obesity. The inci-

dence of obesity in children is about 7% in those with

two lean, parents, 40% in those with one obese parent

and 80% in those with two obese parents.8

Further,

chi ldhood obesity is a significant risk factor for adult

obesity.9

Infan ts are often overfed, partly because

parents misinterprets the signals. A baby may cry

because he is wet, restless, hot, cold or lonely. It is a

common response, however, lor parents to assume

tha t the baby is hungry and hasten to feed him.

Childhood ea t ing

pe rmanen t . If poo

tha t obesitywill de

mot iv a t ed person

ha b i t s of a l i f e t i m e

Body fa t

People come in all shapes and sizes. B o d y composi-

t ion and fat d i s t r ibu t ion are s t rongly inf luenced by-

genetics, age and gender. A b d o m i n a l obesity, t yp i ca l

in men, tends to result in persons w i th 'apple' shapes.

A peripheral fa t pattern w i t h extra fat on the hips and

thighs, more commonly seen in women, resu l t s in

'pear' shapes. People a re most commonly c lassi f ied

a s 'apples' o r 'pears' using the w a i s t - t o - h i p ra t io

( WHR) . WHR is a ra tio of the c i r c umfe r enc e s at these

tw o locations, and compares f a v ou r a b ly w i th com-puted tomography of the abdominal a r e a .

l 0The WHR

reveals not only th e relative distribution of abdomi-

nal to glu tea l - femora l fat, but also th e qua n t i t y of

in t ra-abdominal o r visceral fat. Men are cons idered

upper-body obese when the WHR is greater t h a n0.95

and in women, when it exceeds 0.85." There is in-

creas ing evidence to indicate t ha t abdominal obesity

is , more so than to ta l body obesity, a serious risk

fac to r fo r coronary a r t e ry disease,11

Excess abdo mina l

f a t accelerates th e rate o f coronary artery disease in

three ways , it increases blood cholesterol levels, raises

blood pressure and decreases th e body's abi l i t y to

u se insulin effect ively, l e a d ing to i n su l in res is tance.12

Abdominal fat is, however, hyperactive, and re-

sponds well to weight reduction. This means that

abdominal fa t levels may be reduced with even a

modest reduction in body weight On the o the r hand,

fa t in the cells on the hips and thighs of females are

difficult to lose. In fact , research suggests that glu tea l -

f emora l fa t cells cling to their fa t except dur ing

lactation. 13

Energy balance-

expenditure

-intake versus

Energy balance is the relationship between energy

i n t ake and energy expenditure. When this balance is

positive, th e extra calories are stored as fa t , W h e n this

ba lance is negative, storage fat is metabolized to pro-

vide fo r energy needs. If the number of calor ies

ingested corresponds to tha t consumed in metabo-

lism, body weight does no t change except for a sma l l

intra-day variation (± 1 kg), which is mainly due to

f luc tua t ions in the body's water content. M a n y com-

plex factors affect th e rates of energy ingestion, and

caloric expenditure through exercise and metabol ic

needs.



Chin et al.: Obesity, exercise andweight control 183

Energy intake

Quanti ty

Obesity has classically been regard ed as a problem ofdisordered eating habits. Most surveys of energy in-

take, however, show tha t in general, obese individu alsdo not consume more calories than lean individu-als.

14A recent study

15of 107 males and 109 females

ranging in age from 18 to 71 years, showed that thedaily energy intakes of lean and obese adults wereidentical when expressed as kJ-kg

-1lean body weight.

Lean individuals actua lly consum ed m ore energy than

obese individuals when daily caloric intake was ex-pressed as kJ-kg

-1total body weight.

Diet compositionNutritionists previously thought that a calorie was acalorie, but we know no w that not all calories are thesame. A forced feeding study showed that prisonersona high fa t diet gained weight m ore easily than those ona low fat, high c arbo hydrate diet.

16Researchers in this

study cited two probable mechanisms for this observa-tion. Firstly, extra fa t calories co ntribute m ore to bodyf a t because dietary fat is converted to stored fa t with97% efficiency. Carbohydrates from a meal, in contrast,are converted to body fa t with only 77% efficiency.

There is, therefore, an eightfold difference in the amount

of energy wasted. Secondly, the metabolic rate followinga meal (thermic effect of a meal) is m uch higher whenthe meal is high in carbohydrates than when it is high infat. Calories expended in this way contribute to dailyenergy expenditure, rather than to increasing fa t stores.The relationships linking diet com position, energy intakeand body fat are illustrated by another study of 216adult men and women.

15The obese derived a greater

portion of their daily energy intake from fa t when com-pared w ith the lean. Therefore, one should aim for energyintake from a high carbohydrate, low fat diet, as dietcomposition m ay be as im portant as diet energy content

in the reduction ofobesity.

A comparison of a typicalChinese m enu with a low fat, high c arbohydrate samplemenu is illustrated in Table 1.

Caloric restriction

For a long time, caloric restriction has been regardedas the cornerstone of weight-loss regimens. Numer-ous low and ve ry low calorie diets have beenintroduced for the treatment of obesity.

17However,

energy-reduced dieting may not be the best weight-loss thera py because of the m any problems associatedwith reduced energy consumption. Firstly, severe re-

striction in energy intak e reduces the basal metabolicrate (BMR) by as m u c h as 30% . This m ay shift theenergy balance back in the direction of energy stor-

Table 1. Typical one day Chinese menu and isocaloric

modified low-fat, high carbohydrate diet.

Regular diet(44% of energy as fat)

Low-fat,

high carbohydrate diet(20% of energy as fat)

Breakfast

Bread: 1 slice

Margarine: 1 tbsp

Whole milk: 1/2 cup

Lunch

Stir fried chicken noodleChicken with skin: 3.5 oz

Cooking oil: 1.5 tsp

Bamboo shoot: 1/2 cup

Egg noodles: 1 cupChinese tea

Snack

Peanuts: 1/2 oz

Dinner

Stir fried marbled porkwith pineapple

Pork chop(lean and fat): 3 oz


Pineapple: 1/2 cup

Rice: 1 cupOrange: 1

Breakfast

Bread: 2 slicesJam: 1tbspSkim milk: 1 cup

Lunch

Chicken noodle in soupChicken breast: 3.5 oz

Cooking oil: 1 tsp

Corn: 1/2 cup

Egg noodles: 1 cup

Chinese tea

Snack

Crackers: 4 pieces

Dinner

Stir fried lean pork

with pineapplePork chop (lean): 3 oz


Pineapple: 1/2 cup

Rice: 2 cupsOrange: 1

age.18, 19

Since BMR accounts for 70% of total daily

expenditure, this reduction in B MR is a significantdifference. This B MR reduction m ay account in partfor the 'plateau' reached by mo st dieters when weightloss slows an d stops even when caloric intake re -m ains stable. Secondly, as much as 25% of the weightlost by dieting alone can have come from lean bodymass (LBM).

20This loss of LBM is potentially danger-

ous if the body depletes protein reserves in essentialareas of the body. The percentage of LBM lost de-creases w hen exercise is com bined with diet. Thirdly,the energy c onservation process resulting from severedieting can persist even after the dieting period isover. This causes body w eight to be regained rapidlyuntil it reaches the pre-dieting level.

21Studies in ani-

mals and humans have shown that when theserepeated cycles of weight gain and loss occur, subse-quent weight loss can be made more difficult.

22

Research ha s also shown tha t when weight is regainedafter dieting, muscle tissue tends to be replaced byfat. This has also been confirmed in a current studyon diet m anipulation in rats.

23

Energy expenditure

In the past, the focus of both health professionals an dobese individuals has been on energy intake . Research



184 J Hong Kong Me d Assoc Vol. 44. No,

has, however, increasingly demonstrated tha t the key

to effect ive therapy is to work on the expenditure

side of the equation. The average daily energy ex-

penditure in individuals between th e ages of 23 and

50 is 2,700 kcal for men and 2,100 kca l fo r women.24

Total energy expenditure is determined by three m a-

jo r components, viz. the BMR (70%), thermic effects

of food (10%) and exercise (20%). In the previous tw o

sections, we addressed th e issues of diet composition

in relation to the thermic effect of food, and diet re -

strict ion in relation t o BM R in the energy e x p e n d i t u r e

equation. In the following section, we will focus on

th e thermic effect of exercise.

C O .

50

48

46 - i

Exercise and weight control

In human beings of al l ages, inac t iv i ty ha s been asso-

ciated with obesity.25, 26

Th e addition of an exercisecomponent in a weight loss regimen appeared to im-

prove th e outcome, both init ia lly and in the long

term, by increasing th e total energy output and af-

fecting substrate utilization.2

(i ) Energy output

Exercise affects energy output in several ways.

The most obvious way is via the thermic response

to acute exercise, th e magnitude of which is de-

t e rm ined by the mode, intensity and durationof

the exercise.

27

The guidelines suggested by theAmer ican College of Sports Medicine28

state that

th e 'minimal threshold' of exercise training for

weight and fa t reduction includes continuous ex-

ercise of at least 20 to 30 minutes duration, at

moderate exercise intensity (60%~70% of maximal

heart rate) sufficient to spend 300 or more kcal

per session, with an exercise f r equency of at least

three days per week. Significant elevations in

resting energy expenditure have also been ob-

served in the post-exercise recovery period.29

A

systematic study30

on the metabolic after-effects

of exercise indicated that the resting metabolic

rate ranged f rom 7.5% to 28% higher f ou r hours

af ter exercise compared with a control day in

which no exercise was taken. The higher metabolic

rate persisted for six hours and returned to base-

line levels after eight hours as shown in Figure 1.

The investigators calculated that this elevated

post-exercise metabolism (about 40 to 50 kcal),

over and above the energy cost of the exercise

bout i tself, would result in a reduced caloric

equivalent of about 2 kg a year if individuals

exercised daily. It appears that exercise is benefi-

cial in the control of body weight, not only for the

energy loss incurred during exercise, but also be-cause a considerable additional caloric

expenditure may occur post-exercise.

Hours After Exercise

Hours After Exercise

Fig. 1, Top, BM R af ter a vigourous exercise session

compared with non-exercise control day; bottom,

BM R ranged from 6% to 17% higher after a vigorousexercise session than if was at the same time of theday on non-exercise control days. The higher BMR

lasted six hours after exercise. Modified from de

Vries andGray.30

(i i ) Subst ra te u t i l i z a t i o n

Mild to moderate in tens i fy exercise is e f fec t ive

fo r weight reduction because of the increased

utilization of free f a t t y ac ids .31

Energy for short

periodsof high intensity exercise is derived a lmost

entirely f rom stored carbohydrates in the l iver

and muscles. Mild to moderate intensity act ivi t ies

of longer duration use both carbohydrate and fat

(Fig. 2).32

These data highlight th e importance ofth e 'long slow distance' concept when ta rge t ing

body fat as the energy substrate during exercise.



Chin et al.: Obesity, exercise and weight control 185

•o100-01a >

3

„ 80-

2

•?.£t __

Ji 60 -(O

OTJ

S 40-

£"5e 20-O

oa° 0 •

_OM Fats ^o Table 2. Compariso\<^ weight.3

""""O n Carbohydrate y^a

•fj

/^^ BOlimuiii«m"" Variable

..a*"" "" CardiovascularO*** i andpulmonary

^W function

^ Nutritional\ deficiency

Tv.

^^w^ Lean body weight

\j

aRest 20 40 60 80 100 Level of HDL-C

% of ma ximum ox yge n uptake Sensitivity of insulin

Thermic effectFig. 2. Relative contribution of fat and carbohydrate as a

funct ion of exercise intensity, expressed as a Physiological and

percentage of the maximal oxygen uptake (VO 2 max). psychological stateModified from Astrand and Rodahl.32

Physical strength

Side-effect

Exercise and diet

, .. , . . , . ,. , ., , Plan of osingA negative energy balance is best achieved througha weight

combination of dietary restriction and exercise. A

n of different approaches of losing

Losing weight

only by severelimitationof

energy intake

Decrease

Occurs easily

Decrease

Decrease

?

Decrease

Under greatpressure

Decrease

Metabolic

disorder

Difficult to

maintain

Losing weight

by exercise andslight limitation

of energy intake

Increase

Generallydoes not occur

Increase or

unchanged

Increase

Increase

Increase orunchanged

Improved

Increase

Generallynone

Easy to

maintain

convenient means to partit ion a 500 k ca l/da y (3,500kcal/week) energy deficit is to reduce energy intake

by 250 kca l /day and increase energy expenditure by250 kca l /day . It is relatively easy to identify food

i tems that can be eliminated or reduced to provide a250 kc a l /day r educt ion in intake. A caloric deficit of3,500 kca l /week is equivalent to 0.5 kg weight loss.

A comparison of two alternative methods of weightreduction is i l lustrated in Table 2.

3B y com bining diet

and exercise, it is possible to achieve a deficit of 1,000calories/day, which is equivalent to approximate ly 1

kg of fat loss per week. While this m ay appear to bethe slow approach to weight loss, it is the most sensi-ble appro ach. Losses of lean body mass are minimal ,and fat loss so attained is more likely to be o f a per-

manent nature.33

Myths an d misconceptions of diet,exercise and weight control

With the increased popularity of exercise, obese indi-viduals are often confronted with exercise m yths andmisconceptions, along with gimmicks that are pro-moted as 'miracle agents' to assist in weight reduction.

Exercise and appetite

A common misconception of exercise in weight controlis that physical activity stimulates appetite, and the

resulting increased caloric intake negates the caloricexpenditure of the exercise itself. Although it is truethat increased food intake generally parallels increasedphysical activity, this relationship appears to holdonly with respect to normal act iv ity .

In a classical study,34

rats which w ere exercised dailyfor up to one hour showed a decrease in food intake andbody weight when com pared to sedentary control ani-mals. When he exercise duration wa s increased beyondone hour, food intake was increased bu t only to theextent that body weight was maintained. In contrast, atexhaustive levels of exercise (i.e. six hours), both bo dyweight and food intake decreased. The results of this

classical experimentare shown in Figure 3. Longitudinalphysical conditioning studies in hum ans also show nochange in calorie intake with m ild to m oderate intensityexercise training.

35

Rapid weight loss

Most rapid weight loss diets have one feature in com-m o n — t h e y a l low only a m o d e s t i n t a k e o fcarbohydrates . Carbohydrates const i tute approxi-m a t e l y 6 0 % o f a nor m a l m ix e d d i e t . Wh e ncarbohydrates m a k e up 10% or less of the diet, in

addition to an overall reduction in food intake, thebody starts to utilize its own carbohydrate stores in

the liver an d muscles. Since 3 g of water are stored



188J Hong Kong Med Assoc V o l .

Conclus ion

recently, among A :

as well.The associated health risks an d diseases present

a tremendous dra in to the economy and a f f e c t th e quality

of life. Obesity can be a t t r ibu t ed to complex physiologi-c a l , genetic,cultural and psychological factors. It should

y as a result of weak will power

2 4 6 8 1 0

Duration of exercise (hours)

ts . Th e most effect ive programmes fo r

losing and mainta ining a desirable body weigh t incor-

porate restrictions in calor ic intake, and increases in

caloric expenditure through exercise. Nutri t ion, behav-

ioural changes, and careful moni to r ing o f exercise and

diet should be implemented holistically to ensure a

F i g . 3. R e l a t i o n s h i p b e t w e e n food i n t a k e , e n e r g y successful weight reduction, programme. Individualsexpenditure an d body weight in laboratory rats. A, need to be aware of the many myths and misconceptionssedentary zone; B, range of proportional response surrounding weight control Most 'mi racle agents' fo r(normal activity); C , exhaustion zone. M o d i f ie d f r o m " . , ' , , *T,' • ' J r •

Mayer etal. 34 weightlossdo not haveascientificbasis.

along with 1 g of carbohydrate f rom the body stores,

there is a substantial loss of body water along withthe depletion in the stores of carbohydrates. Thus,

weight loss in. the first few weeks of dieting is essen-

tially loss of body fluid, not body fat Rapid weight

loss diets so often fail because once a desired weightis achieved, the individual typically returns to a nor-

m al diet which is high in carbohydrates. The waterlost during the diet period is rapidly regained, oftenin a matter of days. Thus, the individual's weight

l i teral ly jumps back to its previous level, and the diet

is considered a failure.

Spot reduction

Spot reduction is the attempt to reduce fat in a local-ized area of the body through exercise. It is true thatvigorous exercise and. caloric restriction will cause ageneral reduction in body fa t stores. There is , how-

ever, no conclusive scientific evidence that exercise,

massage, sauna, special skin creams, body wrappings

or pseudo-electric devices will break up or reduce fat

deposits located in specific regions, in a study com-paring th e subcutaneous tat of the act ive (playing)

and inactive arms of elite tennis players, skinfold

Acknowledgements

The authors would like to thank M r Dennis Whitby

for his valuable suggestions to the manuscript and

Miss Queenie Tam for her clerical support.

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Obesity, Diet, Exercise and Weight Control