Updated 11 February 2013

Signs of a diet fanatic

Fanaticism in any form is generally not a good idea, and the same applies to dieting and exercise.

Fanaticism in any form is generally not a good idea, and the same applies to dieting and exercise. Unfortunately, many people can be classified as diet fanatics. Let’s have a look at some of the manifestations of diet and exercise fanaticism and why they should be avoided.

There are no absolutes

Firstly it helps to keep in mind that all the biological sciences, including nutrition and medicine, are based on complex biological systems, such as the human body, and that it is impossible to define absolute values for most parameters. The pure sciences, like physics and chemistry, can state without fear of contradiction that a water molecule consists of two atoms of hydrogen and one atom of oxygen.

However, when we define most of the parameters applied in nutrition, we are working with broad guidelines, not absolute values. You will, therefore, understand that anyone who tries to work out their energy intake or expenditure to the last kJ, is attempting the impossible.

Obsession with absolute values

As mentioned above, readers who insist on working out their energy intake or output to the last  kJ, are really wasting their time.

Let’s take the energy value of commonly eaten foods as an example. The energy content of foods is influenced by so many different factors that it is impossible to say exactly how many kJ these foods contain.

The energy content of an apple is determined by the carbohydrate, protein, fat, dietary fibre, ash, and water content of the apple, plus where it was grown, what time of year it was picked, how ripe it is when you eat it, if it has been processed (e.g. canned), if other nutrients have been added (e.g. sugar), how much it weighs, if you eat the peel with the flesh, and how you serve it (raw, cooked etc.).

One can, therefore, say that a medium-sized unpeeled, raw apple weighing 80g contains approximately 196 kJ, but this is a rough estimate based on averages, not an absolute value

For your own sake and sanity, it is much more sensible to stop being obsessed about the kJ value of foods and to use the nutrient values purely as guidelines.

Obsession with body weight

Human weight varies over a 24-hour period, from day to day and from month to month. Variations in body weight of up to 3 kg per day are perfectly possible and most people are not even aware of the fact that they weigh 2-3 kg more in the evening than when they got up in the morning.

But those of you who jump onto a scale once day or even more often, are going to expose yourself to unnecessary stress. If you are trying to lose weight and discover that you suddenly weigh 2-3 kg more that yesterday, you are going to get agitated. You will think that your efforts to lose weight are not succeeding and resort to some other obsessive behaviour, such as purging or starving yourself, or doubling up on your exercise routine, or rushing out to buy pills and potions to ‘correct’ this change in your weight.

Body weight is particularly sensitive to water balance and anything that affects your water intake or excretion can affect your body weight. Unfortunately many women are prone to water retention caused by fluctuations in female hormone levels.

Some women gain appreciable amounts of weight before, during or just after menstruation, due to water retention. Once the hormones have settled down, this weight ‘disappears’, and in some cases it may be a good idea to ask your doctor to prescribe a mild diuretic for those times of the month when you retain water.

Conversely those of you who ‘lose’ weight by inducing diarrhoea with laxatives are fooling yourselves. When you start drinking liquids again, that weight will reappear and while you are dehydrated you may be doing your body harm.

The golden rule when slimming is to weigh yourself only once a week at more or less the same time, wearing more or less the same clothes. This simple rule will save you a great deal of anxiety and give you a more balanced picture of your progress.

Obsession with exercise

Other readers are obsessed about how many kcal or kJ they have used up during exercise. Once again there are no absolute values - the amount of energy you use up during a gym session depends on many factors, such as how vigorously you have exercised, how long you exercise, what type of exercise you have done, the ambient temperature, the physiological response of your body to exercise, your body build and many other factors.

The energy values used to determine how much energy an individual uses during exercise are, therefore, also not absolute values and should be regarded as simple guidelines.

Always keep in mind that exercise has longer lasting effects on the human body, such as an increase in the basic metabolic rate for up to 24 hours after a session, and that these effects are not included in kJ value of an activity such as cycling for 30 minutes. Use exercise to assist your weight loss, but don’t get frantic about how many kJ you have used up while exercising, otherwise you will get even more stressed.

The basic principles of nutrient intake, weight loss and exercise are all based on approximate values, not absolute ones, and you need to use moderation in your approach to these values. Diet fanaticism is a self-defeating pursuit. Nothing is written in stone.

Any questions? Ask DietDoc

Dr Ingrid van Heerden is a registered dietician and holds a doctoral degree in Nutrition and Biochemistry. She believes that "we are what we eat" and offers free nutrition and weight loss advice via her DietDoc service on Read more of her articles.


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