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Why do we gain weight when we age?

It’s a well-known fact that as we get older, most of us put on weight. It is only the few who move into middle age can comfortably get into dresses and trousers we wore in our 20s. In fact across the UK population, on average there is a gradual increase in body weight of 3–5 kg (7-12lbs) per decade between the ages of 30 and 50 – the dreaded middle-age spread!

Why is this?

A major factor is that for most of us, after the age of 30 our general level of physiological function begins to slow down. We become less active and our aerobic fitness level decreases by around 5% per decade. Reactions slow, lung efficiency decreases, heart and circulation become less efficient, muscles lose strength (we actually lose muscle fibres (sarcopenia) as we age. On average we lose around 40-50% of our muscle mass between 30 and 65 years of age with a similar loss of bone mass. Since muscle (lean tissue) is a key calorie burner, our metabolism slows by as much as 5-10% per decade after 30. Not surprisingly therefore, if our eating habits remain the same, we become fat storers rather than fat burners – and we put on weight. Unfortunately, there is not an age-related decline in appetite!

But look at the graph below which demonstrates the remarkable effects of keeping fit and physically active.  Even from early childhood there is a marked difference in general physiological function between sedentary and active individuals. During the optimal timeslot in our 20s, there is a 20-25% difference in the way our bodies work – and this extends well into our older years. In fact an active 65 year-old can have the physiology of a person more than 20 years younger!

Staying fit and active maintains muscle mass which helps prevent the lowering of metabolic rate, which in turn helps prevent the age-related weight loss so commonly seen in our society.

 

Whilst the most common method of weight loss is dieting, the long-term success rate of this method is quite poor. Only about 10-20% of those who lose weight by reducing calories maintain their full weight loss over the longer term Taking exercise is strongly associated with better long-term weight control than dieting alone.

A study recently published in the International Journal of Obesity surveyed of over 5,000 middle-aged men and women compared improvements in aerobic fitness – measured by the time walked on a treadmill with the gradient increasing every minute – with changes in body weight over an 8-year period. Even those who only marginally improved their aerobic fitness level (i.e. a one-minute improvement in treadmill time) gained on average only 0.6 kilograms (1.3lbs) compared to those who showed no improvement in fitness who gained on average almost 5kgs (11lbs) over the 8 years.

Each one-minute improvement in treadmill time reduced the chance of a 6kg (1stone) weight gain by 15% in men and by 10% in women and the chance of a 10kg (3 stones) gain by 21 percent in both men and women.

 

It should be noted, however, that improvements in fitness level were necessary to minimize weight gain; simply maintaining a given fitness level was not sufficient to ward off the slow increase in body weight through middle age. Indeed, these and other recent findings suggest that increasing amounts of physical activity may be necessary to effectively maintain a constant body weight with increasing age.

Thus, it seems that increased physical activity and fitness play more of a role in minimizing age-related weight gain and preventing significant weight gain than in promoting weight loss. Many of the chronic and disabling diseases now prevalent in our society may be in part attributed to an increase in age-related weight gain.

The message is clear. For long-term weight control, regular exercise is a must.


 

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