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Health Sense: Calorie-restriction diets and the endocrinology of aging
If we live long enough, all of us will eventually experience some changes to our bodies
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If we live long enough, all of us will eventually experience some changes to our bodies. If you look around you, you will notice that the majority of people fall into two camps as they grow older. One group is old and frail, while another group is overweight or even downright obese.
Both outcomes lead to poor health. Those who are frail tend to suffer from injuries easily, especially fractures resulting from falls, with disastrous consequences as morbidity and mortality are high after fractures.
Meanwhile, those who are overweight are more likely to end up suffering from diabetes, heart disease or strokes, again with a higher mortality rate.
We do not become frail or obese all of a sudden.
Of course, some people are disadvantaged by the curse of genetics. For instance, many are overweight from their youth because most of their family members are similarly obese.
On the other hand, frailty may also be passed on, as people whose parents have suffered from a fragility fracture are more likely to suffer a fracture themselves when they grow older.
But apart from heredity, a number of bodily changes begin to occur in all of us after the age of 30 ' slowly at first but becoming more pronounced in middle-age ' especially after the onset of menopause in women.
You may notice that you are not able to eat as much as before when you are past 40. That is because your gut, or intestinal, hormones, which promote satiety (sensation of fullness) are enhanced with increasing age.
As a result, our energy intake becomes lesser and lesser as we grow older.
This phenomenon has been termed the anorexia of ageing. Some authorities believe that this is a natural adaptation to aging, because we tend to slow down as we grow older and, therefore, we do not need to eat so much, e.g., we have a reduced energy intake.
This is all fine and good ' provided energy intake is balanced against energy expenditure. However, in some susceptible persons, the decline in calorie intake is greater than energy expenditure. Over time, the relative anorexia in such persons will cause them to lose muscle mass (sarcopenia).
It is not surprising that, over many years, these people become frail in their old age.
Our hormonal systems also undergo a steady decline in function as we grow older. Thyroid hormone production drops, and about 10 percent of people are deficient in thyroid hormone by the time they reach the age of 80.
Tiredness, weight gain, mental decline, depression and heart failure are common consequences.
Similarly, pancreatic function also declines. About 50 percent of people above 80 years old are diabetic.
Postmenopausal women are beset by osteoporosis, while men will experience a steady decline in the sex hormone testosterone that continues even beyond old age (andropause).Low testosterone leads to sexual dysfunction, loss of muscle bulk and muscular strength, rapid weight gain, tiredness and loss of stamina.
Coupled with concurrent growth hormone decline in both sexes, it is little wonder that many older men and women experience a considerably poorer quality of life. Low testosterone and growth hormone causes accumulation of fat mass and a decline in muscle bulk, causing people who are already overweight to become even more obese.
So what can a person do in order to age better and avoid these pitfalls?
The Japanese in Okinawa are renowned for their longevity, with many living beyond 100 years.
It turns out that their 'secret' is rather simple. From their youth, they practice a daily habit of calorie restriction, eating until they are only about 80 percent full.
They also exercise regularly to maintain their fitness and muscular strength, they avoid smoking and they drink only moderate quantities of alcohol. When these people were tested, they were found to have robust levels of sex hormones, calcium and Vitamin D, with very low levels of systemic inflammation. There was no need to resort to expensive supplements.
Calorie restriction (CR), in particular, has been shown in long term studies involving primates (the nearest example to human beings) to contribute toward longevity. As the term implies, CR is simply consuming less calories, fewer by 30 to 40 percent than usual.
This creates a low level of stress that that is actually protective. In a very long-running study of over 25 to 30 years that has just been published in Nature, a group of primates that were calorie-restricted by 30 percent lived longer and were healthier at the end of the study period compared with another group that was unrestricted.
Older adults who can maintain good physical activity have been shown to have lower death rates, better quality of life and health status and better preservation of muscular strength, stability and mental cognition.
Naturally, it would be best if CR, combined with regular exercise and physical activity, is started early enough in life such that its benefits may be reaped by the time one enters middle age.
The writer, a physician, is an endocrinologist at the Gleneagles Medical Center and a past president of the Endocrine & Metabolic Society of Singapore. For more information, visit klinikdiabetessingapura.com.
