Last partial update: July 2017 - Please read disclaimer before proceeding

 

Obesity is a complex problem that is different for each individual

Obesity is a complex problem that is centres around the interplay of numerous genetic, dietary, gastrointestinal (e.g. gut bacterial flora) and physical activity factors. Many of the problems relate to poor eating and exercise habits that are psychologically and emotionally based and solutions often need to be psychologically based. For this reason, the cause of each case of obesity is specific to the individual and that person's treatment needs to be tailored to their particular situation.

Below is a discussion of the dietary and exercise dynamics involved in determining body fat levels. The psychology of poor eating behavious is discussed in the trreatment section.

Processed foods and gut bacterial flora

The role of gut bacterial flora is only just starting to be discovered and to date research in this area has not revealed any specific factors that could be used to influence a person's weight. It is very likely, however, that such factors will be found and that they will add to the energy restricting and exercise increasing solutions for reducing weight that we currently have. One fact that is worthwhile mentioning is that processed food does alter the bacterial flora in the gut and it has been shown that even comsuming such foods for only a few days a week is just as harmful to gut bacteria as consuming it every day. Thus you really need to have a consistently good diet.

 

The balance between body enegry intake and use - The determining factor in weight gain

For body weight to remain unchanged, energy intake in the diet must equal energy expended by the body. If the energy intake is greater than the energy expended, then the excess energy is stored in the body, mostly as fat. Often this difference is only slight and thus the fat gain is commonly a very gradual one. (The person just puts on a kilo or so per year; but the years keep mounting up.) On the other hand, if energy intake is less than energy expenditure, then the body uses stored energy (i.e. fat) to make up the difference.

Most of the body’s energy stores are in the form of fat (triglycerides), although glucose is also an important form of stored energy. (Glucose is stored as glycogen in the liver and muscle.)

The body uses energy, either from diet or its stores, in three different ways; normal functioning at rest, exercise and eating.

To keep the body functioning normally:

Approximately 70 per cent of the energy expended by the body is used to keep the body functioning in its resting state; that is when not exercising or eating. The amount of energy used when resting during the day is termed the resting metabolic rate (RMR). (It is very similar the basal metabolic rate (BMR), which is measured a night while sleeping.) RMR levels vary from person to person and thus, while resting, some people will burn up more energy than others. (This partially explains why some people gain weight more easily and find it more difficult to lose weight.) While resting, muscle consumes only 20 per cent of the energy used. (The liver, brain and heart use 29, 19 and 10 per cent respectively.) During exercise however, muscle energy use can rise by 50 times or more.

Most of the factors that determine RMR cannot be changed. These include the person’s genetic make-up, height, age, illness, and the level of some hormones. (Unfortunately a person’s RMR decreases with age, especially around the 40s and 50s, which helps explain why weight is often put on at this time.) Some factors, however, can be changed. The most important of these is lean body mass; that is, body weight without any excess fat. People with more muscle have a higher lean body mass and a higher RMR, and therefore use up more energy. Increasing physical activity can increase body muscle mass resulting in an increase in RMR of up to ten per cent. This results in a large increase in the body’s energy consumption and can result in significant weight loss. On the other hand, very low energy diets can reduce muscle mass and thus reduce RMR. This lessens the achieved weight loss from the diet.

Drugs such as caffeine and nicotine increase RMR slightly, which is one reason why people gain weight when reducing their intake.

It is worthwhile mentioning that if a person attempts to lose weight through diet alone, the weight lost will mostly be fat (at least 75%); but some will also be muscle. Losing muscle is not good as it decreases the body’s RMR (making weight loss harder) and decreases fitness levels. If muscle loss is to be avoided when reducing dietary energy intake, physical activity levels need to be increased at the same time.

2.   Physical activity:
Physical activity usually accounts for about 20 per cent of energy expenditure.
However, there is considerable individual variability in energy used in physical activity and increasing physical activity is the major way a person can increase their body’s energy use.

3.   Digestion:
About ten per cent of energy intake goes into digestion.

 

Energy functions of food groups - What foods increase body fat?

Most food groups provide energy to the body. However, the energy content and the way it is used by the body differ greatly with each group. The table below shows the energy content of each major nutrient group and states how it is used by the body. This is important when considering fat storage and thus obesity.

 

Function and energy content of nutrient groups

 

 Nutrient

Foods

Energy content

Function / use

Cal per gram

kJ per gram

Fat

Fatty acids

Mainly animal sources and vegetable oils.

9

37

Mostly stored as fat for later energy use by the body when needed. Also an integral part of cell membranes.

Fat

Cholesterol

Lambs brains, liver, eggs and some seafood.

Synthesis of body compounds including cell membranes and body chemicals, such as steroid  hormones.

Alcohol

Alcoholic beverages

7

29

Used for energy. Alcohol is not converted to fat but is metabolized to provide energy before fat and thus reduces the rate of fat breakdown.

Protein

Meats, fish, poultry, eggs, milk products,  cereals, nuts and legumes, including soy beans, lentils, beans and peas

4

17

Mostly used in the synthesis of body components. Only rarely used as an energy source, such as in starvation.

Carbohydrate

Starches (complex carbohydrates)

Pasta, potato, breads, cereals, fruit, legumes

4

16

Provides energy for the body’s functions and some energy storage. It is usually stored as glycogen in the liver (and the muscle) but may be converted to fat if consumed in excess. (Glycogen is just many glucose molecules joined together.) The sugar that circulates in the blood and provides energy for the body is glucose. The brain relies almost solely on this glucose for energy and thus it is very important for blood glucose levels to be maintained.

Carbohydrate

Simple sugars  (sucrose, glucose, fructose, lactose)

Fruit, honey and other sweet syrups

Fibre

Bread, cereals, vegetables, fruit.

0

0

Fibre keeps the bowel functioning normally and has a role in protection of the bowel from cancer causing substances. Soluble fibre can reduce blood cholesterol levels.

Vitamins and minerals

A wide variety of foods is needed, especially vegetables, fruit, low-fat dairy and lean meat.

0

0

They are essential for the synthesis of many body components, especially enzymes. These nutrients have no significant energy function. Some are also important antioxidants.

Water

Fluids, fruit and vegetables

0

0

70% of the body is composed of water.

 

The main cause of excess fat storage in the body is excess energy in the diet. By weight, fat and alcohol provide significantly more energy than carbohydrates and protein. Thus, they are often very important sources of excess dietary energy. Reducing fat and alcohol intake is imperative if a person is to restrict dietary energy intake to levels that will maintain a healthy weight. All people need some fats in their diets as there are a few fats that we need that we cannot make and we do need some energy from fat. About 15 per cent of dietary energy from fat is sufficient.  However, most Western diets have more than twice the amount of fat that is needed for the body to function well and thus reducing fat intake will generally not cause any harm. It is important to recognise that a variety of fats are needed in the diet and getting the right balance is important. Excess dietary saturated fat is common in Australia and is especially harmful as it also increases cardiovascular disease and its reduction should be a priority; although everyone still needs some. On the other hand, many people have a diet relatively low in omega-3 fats and these should be increased in most people’s diets. (They are mainly provided by fish.) This topic is discussed further in the chapter What’s in your food?

Body fat stores mostly originate from dietary fat or from dietary carbohydrates that are converted to fat. However, the body prefers to store fat as fat. The main reason for this is that the process of storing carbohydrates as fat is an inefficient use of dietary energy. Storing carbohydrate as fat consumes about 25 per cent of the carbohydrate’s energy content whereas storing fat as fat only uses about 3 per cent of the fat’s energy content. For this reason, carbohydrates are only stored as fat if dietary energy intake from carbohydrates is considerably excessive.

The problem of taking a short term view - Healthy weight loss is a slow process.

Healthy weight loss is usually slow, with weight losses of 0.5 to 1.0 kilograms per month or waist size losses of 1 to 2 cm per month being desirable / normal. (Women often lose weight slower than men.) A weight loss of 5 to 10 per cent over six to twelve months is good progress and will give significant health benefits. Remember that by keeping to a long-term weight loss strategy, people are losing actual body fat permanently. One kilogram of fat lost is equivalent to two 500 mg tubs of margarine.

An example demonstrating why fat loss is slow


Let us assume that a person’s weight is stable on a diet with an energy content of 8000kJ per day and the person initially plans to decrease their dietary energy intake to 7000kJ per day, a reduction of 1000kJ or 12.5 per cent of energy intake. As the person still weighs the same, he or she will initially still need to use 8000kJ and the extra 1000kJs of energy will need to be come from burning body fat. It takes an overall energy deficit of about 32,000kJ to lose one kilogram of body fat. Thus, at this rate, it would take about 32 days to lose one kilogram of body fat. However, as your body gradually loses weight, its energy requirements also gradually reduce and this already slow rate of fat loss will gradually become even slower. Eventually a new equilibrium will be set up where the person’s reduced 7000kJ energy intake is the correct amount to maintain a new lower weight and no further weight loss will occur. This new equilibrium is likely to take months to achieve and thus the person’s initial dietary change will continue giving weight (fat) loss benefits over this time. This is a very simplistic calculation, but it does give an idea of why fat loss is a slow process. This slow change does have one benefit; it also means an occasional ‘night out’ will not suddenly increase body fat stores.

It is worth noting that muscle weighs more than fat and the increased body muscle mass that occurs with increased exercise may slow perceived weight loss even further. However, muscle actually takes up less space than fat (i.e, it is denser) and while people may not notice much weight loss, they will notice their body volume decreasing, often by clothes / belts fitting better. (i.e. people will still appear thinner). Thus, waist measurement is often a better guide to progress than weight loss early on in an exercise / dietary program.

Early weight loss in quick fix diets is due to changes in body water content (that occurs when body glucose stores are used up) rather than loss of body fat and is quickly (in a matter of days) replaced when normal eating patterns are resumed and glucose stores (and water that is stored with it) are replaced.

 

'Energy density' of foods

For most people, only a certain volume of food can be eaten at any one sitting before they feel full and wish to stop eating. One good way of reducing the amount of energy that is consumed is to try to mostly consume foods with a low energy density. This means choosing foods with relatively few kilojoules per gram of food. Most foods available for purchase in Australia are required to have the energy density on the packaging; it is displayed as the number of kJ in 100g of the product. The table below displays the APPROXIMATE energy density of many foods commonly consumed in our society and there are a few things that are worthwhile pointing out.

Table of energy densities of foods appears at the end of this section (Click here.)

 

Factors that alter the body’s healthy energy balance

An increase in body fat can be due to an increase in the size of fat cells, which occurs in almost all obese people, and / or an increase in fat cell number, which is common in most forms of severe childhood obesity. Obesity has numerous and varied causes and there are usually several factors operating.

Most cases are due to poor dietary and exercise behaviours with genetic susceptibility also playing a role. Poor eating and exercise habits ususally develop during childhood and this explains why parental attention to diet and exercise is so important. As mentioned above, they often have psychological / emotional component and based are much easier to avoid than fix!

Diet

Poor eating behaviours are a very important cause of obesity and are dealt with below. They include:

Other key dietary factors include:

Physical activity
We have also become an increasingly sedentary society, relying on cars etc for transport rather than walking and spending far too much time doing activities that require staring at a screen. It has been estimated that 50 years ago Australians used to walk about 17 kilometres per day just doing their normal daily activities. Today it is more like three kilometres!! And watching over three hours of TV per day (the Australian average) does not help matters!!

In general, men tend to care less about health issues, including becoming overweight, than women, and their rate of obesity is, not surprisingly, higher.  

Genetic susceptibility
Genetic factors are complex in nature and involve multiple genes that ultimately act by enhancing the storage of fat. (Five genes that influence obesity have so far been found.) These genes act by altering factors such as appetite and satiety levels and by controlling the proportion of energy from the diet that is stored rather than expended (i.e. altering the person’s metabolic rate). This is done through the complex interaction of numerous body hormones and other compounds originating primarily in the brain and fat tissue. Overall, genetic susceptibility is an important factor in somewhere between 40% and 70% of obese patients.

The body’s usual weight is ‘actively defended’ by body hormones and its response to weight loss is to increase hormones that:

This is an important contributing factor in the failure of weight loss programs by most who attempt them and a very important reason for encouraging both children and adults not to become overweight in the first place. Prevention is much better than cure!

A few rare genetic abnormalities, such as Prader-Willi, Ahlstrom’s, Cohen’s and Carpenter’s Syndromes, are associated with obesity.

Other factors
Hormonal (or endocrine) diseases causing obesity include injury to the hypothalamus, Cushing’s disease, polycystic ovarian disease, hypothyroidism, hyperinsulinaemia, acromegaly and hyperprolactinaemia.

The principal drugs that can cause obesity are phenothiazines, tricyclic anti-depressants, Epilim, Tegretol, and steroid drugs. Oral contraceptives (‘the pill’) can also slightly increase weight. Hormone replacement therapy for menopausal women has also been implicated but there is good evidence it does not contribute to obesity.

Drugs and hormonal diseases are responsible for a small fraction of the obesity problem and these should be dealt with through consultation with a GP. The environmental factors of poor diet and lack of physical activity are by far the most important causes.

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Approximate 'energy density' of common foods

(Please note that serving sizes often vary greatly and more be considerably more or less than 100g)

Food

 

Energy density

Fat content

Food

 

Energy density

Fat content

kJ per

100g of food

g of fat  per 100g of food

kJ per

100g of food

g of fat  per 100g of food

Fruit (fresh)

Vegetables (Steamed or boiled unless stated)

Apple

180

0.1

Avocado

879

22.6

Banana

360

0.1

Beans (long green)

87

0.2

Grapes

260

0.1

Broccoli

24

0.3

Mango

236

0.2

Capsicum

75 to 100

1.6

Pear

200

 

Carrot

103

0.8

Rockmelon

90

0.1

Lettuce

27

0.1

Pineapple (fresh)

160

0.1

Peas

250

0.4

Pawpaw

120

0.1

Potato (boiled)

260

0.1

Plum

150

0.1

Potato chips (hot)

1030

14.0

Peach

132

0.1

Pumpkin (boiled)

200

0.7

Prunes

780

0.4

Sweet potato (boiled)

270

0.1

Raisins / Saltanas

1200 to 1300

0.5 to 0.9

Tomato

56

0.1

 

 

 

Zucchini

60

0.3

 

 

 

Canned beans (drained)

308 to 360

0.6

 

Drinks

kJ per 100mL

g per 100g

Dairy

kJ per 100g

g per 100g

Soft drinks,  lemonade, cola

175

0.0

Cheese

1200 to 1700

22.0 to 37.0

Apple juice

176

0.0

Cheese spread / dip

1200 to 1440

25.0 to 33.0

Orange juice

150

0.0

Yoghurt, natural 

360 (normal)

250 (low fat)

4.4 (normal)

0.2 (low fat)

Pineapple juice

160

0.1

Yoghurt, fruit

370 (normal)

315 (low fat)

2.1 (normal)

0.2 (low fat)

Water

0

0.0

Ice cream

830

11.2

Beer

145

 

Milk (regular)

270

3.8

Beer (Low alcohol)

100

0.0

Milk (reduced fat)

225

1.8

Wine (red or while)

280

0.0

Milk (skimmed)

145

0.1

Fruit drinks (tropical, apple, orange etc)

160

0.0

Custard

390

3.0

Milk (See dairy)

 

 

Milk, sweetened condensed

1370

9.2

 

Meat

kJ per 100g

g per 100g

Spreads / oils

kJ per 100g

g per 100g

Blade steak (grilled)

740 to 860

6.8 to 10.6

Butter

3000

81.4

Rump steak (grilled)

800 to 1140

6.7 to 16.8

Margarine

3000

83.5

Mince

900 to 1200

12.0 to 22.0

Margarine, reduced fat

1500

40.0

Leg of lamb (baked)

740 to 940

5.6 to 11.9

Cream

1400

35.6

Fillet steak (grilled)

860 to 970

9.6 to 13.2

Olive oil

3700

100.0

Lamb chop (loin)

740 to 1530

7.2 to 31.4

Peanut butter

2640

54.4

Chicken breast (baked)

660 (no skin)

910  (with skin)

4.8 (no skin)

12.7 (with skin)

Honey

1400

0.0

Beef sausage (grilled)

1070

18.2

Vegetable oil

3400

92.0

Ham, leg

450 to 585

3.6 to 7.6

Jams

1100

0.0

Salami

1800

36.0

 

 

 

Egg (Poaged boiled, scrambled)

630 to 680

11.0 to 13.5

 

 

 

Egg (fried)

1070

21.3

 

 

 

 

Treats / takeaway food

Carbohydrate foods

Apple pie

960 to 1300

13.4 to 20.0

Pasta (boiled weight)

500 to 550

0.4 to 0.8

Danish pastry

1290

15.5

Rice (boiled weight)

520 to 630

0.2 to 1.0

Pizza

1000 to 1100

9.0 to 10.6

Bread (white)

970 to 1250

2.0 to 3.0

Garlic bread

1700

17.4

Bread (wholemeal)

940 to 1130

2.6 to 3.8

Cake

1200 to 1600

7.0 to 19.0

Other biscuits

1700 to 2200

3.8 to 30.0

Doughnut (iced)

1780

24.1

Cracker biscuits / crispbreads

1340 to 2000

2.5 to 24.0

Ice cream

830

11.2

Breakfast cereals

1100 to 1700

1.0 to 16.6

Chocolate

2150

28.0

Pizza

1000 to 1100

9.0 to 10.6

Sweet biscuits

1700 to 2200

3.8 to 30.0

Garlic bread

1700

17.4

Hot chips

1100

8.0 to 14.0

Pancake / picklet

1200

15.0

Potato crisps

2250

35.0

 

 

 

Cheese cake

1420

22.2

 

 

 

 

Notes:

  • Foods marked in pink have either a high energy density or high fat content and consideration should be given to restricting their consumption.
  • The energy contents mentioned in the table relate to 100g (or 100mL) of the food. Often the actual serving will be considerably more or considerably less. For example, the average serving of fruit juice would be 200mL to 250mL, while the average serving of peanut butter would be more like 5g.
  • The values for energy density and fat content for meats depend on how much fat is removed. The lowest levels are where all visible fat has been removed.
  • Many take away foods have a energy density due to their high fat / sugar content and are better avoided or consumed very sparingly. Luckily, many of these tasty foods can be made at home with a reduced energy content by using little oil / sugar. Good examples are home made pasta, pizzas and hamburgers

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