In Food Today 37, attention was drawn to the fact that maintaining body weight in the normal range improves health; that the proportion of the population that is overweight or obese is now substantial; that a hundred million years of heredity benefited, during famine, those who accumulated fat in times of plenty; that losing weight is consequently difficult for most people and that fad diets and nostrums have no place in weight loss. How then should one reduce weight?

The only way to lose weight is to ensure, on a regular basis, that the food intake provides substantially less energy (expressed in terms of kilocalories or kilo joules) than that used for body warming, normal activity and exercise. When food intake is reduced, the rate of metabolism falls by a factor of about 15%. Hence the margin between the energy used and that provided by the diet must be at least 25% and preferably 40%. If a woman who normally utilises 2000 kcal diets with 1500 kcal, the margin between her reduced utilisation (i.e. 2000-15%) and her intake is only 200 kcal a day. This would mean that she would take over 5 weeks to lose 1kg, in practice, an unacceptably slow rate of weight reduction. Consequently, if there is an inadequate energy gap, the weight loss is so slow that motivation is lost.

The natural energy use of most women, unless they exercise strenuously on a regular basis, is of the order of 2000 kcals per day. Excess weight increases this level but because the excess weight also has the effect of retarding exercise it is wise to accept the figure of 2000 kcals as the useful baseline. In men the output figures are higher, but ignoring this is beneficial. It means that with the same diet men will normally lose weight more rapidly, an advantage, because men are normally less patient about the rate of weight loss.

When weight is lost by any diet, recent studies have confirmed, that the body tissue lost (after the first week, when the loss is 20% stored carbohydrate and 80% water) is always about 75% fat and 25% other body constituents (including protein). Hence the loss of 1 kilo in weight requires a cumulative loss of just about 7000 kcals. On this basis it is possible to demonstrate that with a food intake of say

• 1200 kcals a day (a common level for diets), the weight loss is about 0.3 – 0.7 kilos per week, at
• 800 kcals intake a day it is about 0.7 – 1.4 kilos per week and at
• 500 kcals intake it is between 1.5 – 2.5 kilos per week.

Is there then a perfect diet?

Unfortunately the answer is a resounding “No”. A person who could define one would be a multi-millionaire within the year. Each person has his/her own food preferences. Thus many of us who work in the field accept that the availability of various diets is an advantage, providing always that the principles which ensure safety, even on prolonged use are adopted. What then are these safety requirements?

• The minimum daily intake of protein should be 50g. The actual minimum is less but international expert opinion is that the extra margin is important.
• The minimum fat intake is about 7g/day to ensure adequate essential fatty acid intake and to stimulate bile flow.
• At an intake below about 1400 kcals per day it is virtually impossible to ensure long term maintenance of the body economy of vitamins and particularly minerals with a diet based on normal foods. Thus diets should either include a vitamin/mineral supplement or include a compounded food replacement to provide the minimum needs for the vital components (particularly protein, vitamins and minerals).
• Because a substantial amount of water is lost during dieting, the non-calorie containing fluid intake should be high.

With these few simple principles, is dieting easy? Again the answer is “No”. It is a fight to stick to the diet, but the following aspects help:

• Do not pitch the target weight too low initially. A loss of even 5-10% weight reduces many medical problems. Take the weight down in sensible steps.
• The will and drive to succeed is paramount.
• Many people find that sympathetic group or individual encouragement helps.
• Regular serious exercise helps substantially. Unfortunately many of those with excess weight find it difficult to exercise sufficiently to make any real difference. They should still be encouraged to do so.

Above all, realise that whatever weight is taken off must be kept off. But this will be a topic for a further article.

References

Further reading: Marks J & Schrijver, J (2001). Available at: www.europa.eu.int/comm/food/fs/scoop/7.3_en.pdf

FOOD TODAY 06/2003