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Nutrition and your body as you age

Thanks to advances in medicine, improved diet and better living conditions, the percentage of Australians who live to a ripe old age is growing exponentially. Between 1991 and 2011, the proportion of Australia's population aged 65 years and over has increased from 11.3% to 13.7%, the Australian Bureau of Statistics (www.abs.gov.au) reports. During the same time, the proportion of the population aged 85 years and over has more than doubled from 0.9% to 1.8% of the total population. 

We investigated the physiological changes that occur with ageing – all of which can have a drastic effect on your diet and nutrition.

a) Impaired digestion
This may include the following changes:

• The deterioration of digestive-enzyme production and efficiency in your body. This includes, for example, a decrease in the amount of lactase enzyme, which is required for the digestion of lactose. This could hamper digestion of dairy products, decrease calcium intake and absorption, ultimately resulting in osteoporosis.

• A decrease in the production of stomach acid – a condition termed “hypochlorhydria”. This occurs in up to 30% of older people, leading to lower absorption of vitamin B12. This, in turn, can lead to pernicious anaemia or bacterial overgrowth in the small bowel, which may cause nutrient malabsorption.

• Constipation. This is a common affliction in the senior years and is most often linked to inadequate liquid and fibre intake, and a sedentary lifestyle. Certain medications can also contribute to the problem.

b) Oral health problems
These may include:

• Dry mouth (also known as “xerostomia”). An inadequate production of saliva affects more than 70% of the senior population and has a significant negative effect on food and nutrient intake. Xerostomia makes chewing and swallowing difficult and leads to avoidance of dry, crunchy or sticky foods.

• Loss of teeth and ill-fitting dentures. This can seriously affect an older person’s ability to chew food. In fact, people who wear dentures are known to chew up to 85% less efficiently than those who still have their own teeth. Lack of dentition can also lead to the avoidance of meat, fresh fruit and vegetables which causes energy, iron, vitamin C and beta-carotene deficiencies.

c) Loss of sensory perception
Changes are typically as follows:

• Reduced taste perception (this is called “dysgeusia”) and impaired ability to smell (called “hyposmia”) are both quite common in elderly people. It’s often the result of factors such as Alzheimer’s disease, medication, surgery, radiation therapy and the normal ageing process. Because seniors have an impaired ability to taste and smell their food, they get less pleasure from eating, which can reduce food and nutrient intake. It can also expose them to food poisoning – simply because they’re not able to taste or smell when food is spoiled. The lack of these two senses also blunts the metabolic responses of the body, which react to the stimulation of taste and smell. This includes the secretion of saliva, gastric acid, pancreas enzymes and insulin.

• Deterioration or loss of sight may also negatively affect food intake – part of the pleasure of eating is associated with the visual appeal of foods.

d) Altered metabolism
As you age, your metabolism may be affected in the following ways:

• Reduced glucose tolerance
With each decade of life, your blood glucose levels increase by 1.5 mg/dL, leading to reduced glucose tolerance. In some people, this change may lead to type 2 diabetes – a condition with significant consequences in terms of nutrition.

• Reduced resting metabolic rate (RMR)
As you age and become less physically active, your RMR can decrease by up to 20%. This refers to the energy your body uses to fuel processes like breathing, digestion and blood circulation. As a result, your energy requirements will become less as you grow older. If you continue to eat as much as you always did, the excess energy will be stored in the form of fat, causing overweight and obesity.

• Deterioration of cardiovascular function
Older people, particularly women, are more prone to hypertension (or “high blood pressure”), because their blood vessels become less elastic with age. Raised cholesterol levels are also common, leading to heart disease and heart failure. Factors such as obesity, alcohol intake, smoking and diabetes contribute significantly to an increased risk for cardiovascular disease in seniors.

• Reduced kidney function
The deterioration of kidney function in older people can be quite severe, with up to 60% of normal renal function being lost between the ages of 60 and 80 years. For this reason, older people are less responsive to changes in fluid status and the so-called acid-base balance of the body. High protein intakes may overburden the renal system and cause a build-up of protein waste products and electrolytes (e.g. potassium and sodium).

• Reduced lean body mass, increased body fat
The loss of lean body mass (muscle tissue) and an increase in body fat is one of the greatest challenges older people face. This loss of muscle tissue amounts to a decrease of 2 to 3% per decade and contributes to a deterioration in physical function. On the other hand, the body fat percentage in men tends to increase from 15% in youth to 25% at the age of 60 years. In women the increase is even greater – from 18-23% in youth to 32% in 60-year-olds. These changes in body composition are due to hormonal changes (lower testosterone production in men and menopause in women), and a reduction in physical activity.

References:
(Mahan LK, Escott-Stump S. 2000. Krause’s Food, Nutrition & Diet Therapy. 10th Ed. WB Saunders Co, Philadelphia; Charlton KE et al, 2001. Poor nutritional status in older black South Africans. Asia Pacific Journal of Clinical Nutrition, Vol 10(1):31-38).

- (Dr Ingrid van Heerden, registered dietician)

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