Energy Balance

Energy Intake          -           Energy Expenditure            =                Weight Gain/Loss

                               food                                                    BMR*                                     
                                       drink                                                  exercise

               growth & development

*BMR is your Basal Metabolic Rate. This is the amount of energy (calculated in kcal) that you would expend on a daily basis without undertaking any movement of exercise. This varies according to your age and weight.

Energy expenditure can be averaged by taking the BMR and multiplying it by an estimated Physical Activity Level (PAL), which is as follows:



Light Moderate Heavy
Sedentary 1.4 1.6 1.7
Moderately Active 1.5 1.7 1.8
Very Active 1.6 1.8 1.9

If the amount of calories taken in exceed that of the expenditure, then weight gain will occur. If the amount of calories expended exceeds that taken in then weight loss will occur. We need nutrients in varying quantities, a healthy diet for a non-athlete should consist of around 50 - 60% carbohydrate, 15 - 20% protein and 25 - 30% fat, with a good intake of water as well as vitamins and minerals from fresh fruit and vegetables. Too much of any one of these nutrients can cause the body some problems, in varying degrees.
On the whole, excess vitamins and minerals are discarded by the body via the kidneys, however a few nutrients do have a toxicity, which means that an excess can cause the body harm. There are not many vitamins and minerals that have this, and generally toxicities will only occur when vitamin and mineral tablets are being taken. The best sources of vitamins and minerals are from fresh foods, the body will absorb them much easier than from tablets and the foods that they are in will often have nutrients which aid absorption as well as being generally healthy and good for you.

Body Mass Index

Body mass index, or BMI as it is more commonly known, is a general tool for judging the weight status of the general public. BMI is calculated by the following equation:

BMI = weight (kg)

Guidelines from the Department of Health give indications on weight status according to BMI, they are as follows:


18.5 - 25 healthy weight
25 - 30 overweight
30 - 35 obese
>35 morbidly obese
>40 extremely obese



Department of Health 2006

BMI is a relatively good, simple indicator of weight status amongst a population. It is not advisable to use this for athletes though as BMI does not take into account muscle mass and fat free mass in comparison to fat mass. Many athletes, due to the muscle mass they have will appear overweight or obese, when this is not the case. The best way to measure an athlete's body composition is by body fat testing, which can either be undertaken by a bioelectrical impedance test of by using skinfold measurements, which can be very accurate if undertaken properly. These measurements will then give a more accurate indication of the weight status and body composition of the athlete. It is important to note, however, that body fat testing should be undertaken as part of a training programme and should be monitored over a period of time, rather than scrutinised. Younger athletes, especially females can become too concerned over body fat, which can lead to further problems. Body fat testing should be mainly used for fully developed athletes as changes during development in younger children and adolescents can change constantly, giving confusing results. This is not to say that testing shouldn't be undertaken, although caution should be used when interpreting  the results.

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