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The importance of physical activity to good health

Samantha Stear
PhD MSc BSc RPHNutr
Science Director
The Sugar Bureau
Duncan House
Dolphin Square
London
SW1V 3PW
W:www.sugar-bureau.co.uk
Member
Scientific Advisory Committee
National Osteoporosis Society

We are all becoming more aware of the physiological and psychological rewards of being physically active. Physical inactivity is recognised as a significant, common and preventable risk factor for NCD (noncommunicable diseases), which accounts for almost 60% of global deaths and 43% of the global burden of disease.(1) Maintaining regular physical activity helps avoid weight gain and obesity. Physical activity reduces the risk of developing heart disease, type II diabetes, osteoporosis and certain forms of cancer.(2) Physical activity also plays a role in a person's wellbeing by reducing stress, anxiety and feelings of depression. Therefore, the recommendation that everyone should accumulate 30 minutes or more of moderate-intensity physical activity on at least 5 days of the week is fully justified.(3) This includes activities such as brisk walking or cycling as well as sports or structured exercise.
However, despite the known health benefits of physical activity and the fact that it is potentially accessible to all, it is estimated that over 60% of the world's population are not active enough.(1)
In 1997 the Institute of European Food Studies conducted a pan-EU survey of consumer attitudes towards physical activity, body weight and health, in 15,339 adults from 15 member states. The majority of participants were unaware of the additional health benefits of physical activity beyond those related to weight loss/maintenance. Therefore there is huge scope for increasing awareness of the well-established benefits of exercise, such as reduced blood pressure, improved lipid profile and improved insulin function.

Obesity
Achieving and maintaining a healthy body weight through diet and physical activity is important for all of us. Excess body weight increases the risk of heart disease, diabetes and also several cancers including colon, breast (postmenopause), endometrial, oeso-phageal and renal cancer. Maintenance of body weight is dependent on both dietary energy intake and energy expenditure. The FAO/WHO (Food and Agriculture Organization of the UN/World Health Organization) Expert Consultation recommended that the optimal combination to avoid weight gain and obesity was a high-carbohydrate diet and regular physical activity.(4) There is an increasing realisation that the emerging epidemic of obesity cannot simply be attributed to dietary factors.(5) One of the clearest indications to support this derives from the fact that in general energy intakes are declining while average body weight is increasing. This indicates that physical activity levels are probably declining even faster, possibly as a consequence of increasing mechanisation such as elevators, escalators, remote controls, motorised transport and energy-saving appliances that displace physically arduous tasks.(5)
Exercise is important in the treatment of obesity, particularly in the long-term maintenance of weight loss. Physical activity is associated with improved motivation and therefore with better dietary compliance, increased lean body mass and an amelioration of the usual suppression of metabolic rate that accompanies weight loss. The first step for people who are obese is simply to modify their lifestyle to build in more physical activity. Simply moving around is difficult for someone who is very obese, but it does expend a lot of energy.
 
Diabetes
Physical activity protects against the development of type II diabetes.(6) Regular moderate-intensity exercise is associated with a reduced risk of developing diabetes, and this still applies in overweight individuals. Physical activity improves insulin sensitivity and acutely lowers blood glucose, favourably influences lipid profiles, facilitates weight control and maintains muscle mass.
People with diabetes should be encouraged to engage in moderate-intensity physical activity for at least 30 minutes most days of the week. Moy et al showed a threefold reduction in mortality over 7 years in patients with type 1 diabetes who were physically active compared with sedentary patients.(7) Some types of exercise will mean that additional carbohydrate is required to prevent hypoglycaemia in individuals with diabetes.

Cardiovascular disease
Heart disease accounts for a third of all global deaths. Regular physical activity decreases the risk of cardiovascular disease mortality in general and of coronary heart disease (CHD) mortality in particular, yet only a minority of adults take sufficient exercise to benefit their health.(8) In fact, physically inactive people have about double the risk of developing CHD. Physical exercise can help to maintain desirable body weight and has beneficial effects on blood pressure, insulin sensitivity and possibly blood coagulation mechanisms.(8) Habitual physical activity also reduces the risk of arterial hypertension, particularly among those who are overweight, and therefore can be a useful adjunct to pharmacological treatment.
To confer a benefit to the cardiovascular system, physical activity does not need to be carried out at a high intensity. Gentle exercise such as walking, cycling and swimming can be effective in reducing the risk of CHD,(8) can contribute to the maintenance of a desirable body weight and can be modified to suit most age groups and abilities. Even after a heart attack, physical activity has a key role to play in improving survival.

Osteoporosis
Physical activity is important for bone health and helps protect against the risk of fracture by maintaining and improving bone density and neuromuscular competency. There is evidence that a lack of physical activity plays a major role in the deterioration of bone quality that accompanies osteoporosis. The loading of bone either from gravitational forces or from muscular tension influences its functional strength, particularly at the loaded regions of the skeleton. Both arise through weight-bearing activities such as running, jumping and climbing stairs, whereas activities such as weight training and swimming involve muscular tension alone.(9) Although there is unlikely to be any improvement in bone density from low-impact activities such as walking at a normal pace, they may contribute to improved balance and coordination, which in turn might help prevent the falls that precipitate fractures.
Participation for about 30 minutes in varied physical activities with a weight-bearing component should be encouraged to promote stronger bones in all ages;(9) however, the activities need to be carried out at an intensity that is appropriate for both the age and capability of the individual.

Cancer
Due to the relationship between physical activity and energy expenditure, obesity, changes in sex hormone levels and age at menarche, there are certain cancers for which it is relevant to consider the role of physical activity. It appears that about 30 minutes a day of moderate to vigorous activity would be useful in protecting against cancer.(10) In particular, regular exercise has been shown to help reduce the risk of cancers of the colon, breast and endometrius. Active persons have been shown to have a 30-40% reduction in risk of colon cancer, and active women a 20-30% reduction in risk of breast cancer compared with sedentary individuals. No significant association has been found between physical activity and rectal cancer, and the data for prostate cancer are equivocal. The data are suggestive of a 20% reduction in risk of lung cancer in active persons compared with sedentary individuals, but it is difficult to separate out the overwhelming effect of smoking on lung cancer risk.

Advice on exercise
The recommendation that everyone should accumulate 30 minutes or more physical activity over the course of most days of the week is fully justified.(11) Simple lifestyle changes involve becoming less sedentary - so, first, we need to decrease the amount of time spent watching television and on the computer. The next stage is to become more active: for example, park further away from the shops, get off the bus a stop earlier or walk to the shops. The aim is to gradually build up to 30-40 minutes of sustained exercise, such as brisk walking, cycling or swimming, at least 5 days a week. However, gradual is the key, so try three lots of 10 minutes to start with and take it from there. It is important to remember to fuel up when increasing physical activity, otherwise it will be difficult to keep being active.

Dietary considerations
A healthy, balanced diet is essential for good health. The key to making a diet healthy and balanced is simply "everything in moderation", plus extra carbohydrates if exercising. But why the emphasis on carbohydrates? The preferred energy fuel for the muscles is glucose, especially as the amount and intensity of physical activity increases. Glucose is formed from the breakdown of carbohydrates - the sugars and starches in the diet - and is stored as glycogen. However, the body can store only a limited amount of glycogen, so the stores need to be topped up to avoid fatigue. Consequently, a lack of carbohydrates in the diet often causes people to give up their exercise programme. No matter what type of exercise, the body will always use some glucose for energy, and the more glucose it uses, the more carbohydrates need to be consumed to replenish the stores.
Therefore, physically active people need to consume a diet where more than half is made up of carbohydrate foods.(4,8) The bulk of carbohydrate intake should come from starchy sources such as bread, rice, potatoes and pasta, and the remaining can come from the more sugary sources such as sugar, fruit and juices. However, most carbohydrate foods, for example pasta or sugars, are eventually broken down into glucose, and therefore one type is not necessarily better than the other.
Although 2-3 hours after a large meal are needed before exercising, a high-carbohydrate snack within 30 minutes of sustained exercise has several benefits. Eating 25-50g of rapidly absorbed carbohydrate just before exercise will not only improve performance but also help maintain blood sugar levels and prevent the feeling of lightheadedness. There are plenty of portable high- carbohydrate snacks to choose from - Jaffa cakes, jelly beans, bagels, honey or jam sandwiches, cereal bars, bananas, watermelon, dried fruit, juice or sports drinks.

Summary
Taking part in regular physical activity helps reduce the risk of developing heart disease, diabetes, osteoporosis and certain forms of cancer. The best way to lose weight or avoid weight gain is to increase physical activity levels and to reduce dietary fat intake, which in turn can be achieved by increasing dietary intake of starchy and sugary carbohydrates. Even if there is no weight loss but the individual becomes fitter, it would help avoid the many health complications of being overweight and so increase life quality and expectancy.
The greatest health benefits will be gained by encouraging people who are currently sedentary to get involved in some form of physical activity. However, it's also important to encourage those who are already active to remain active and possibly to increase their activity levels, in terms of time spent, frequency or intensity. Finally, it's essential that the diet contains adequate carbohydrates as this will not only help reduce dietary fat levels but also provide the energy to fuel activity and thereby reap the benefits of long-term good health.

References

  1. World Health Organization; 2003. Available from URL: http://who.int/en
  2. World Health Organization. Obesity: preventing and managing the global epidemic. Report of a WHO consultation on obesity. Geneva: WHO; 1998.
  3. Blair SN, Connelly JC. How much physical activity should we do? The case for moderate amounts and intensities of physical activity. In: Killoran A, et al, editors. Moving on: international perspectives in promoting physical activity. London: HEA; 1995.
  4. FAO/WHO. Report of a Joint Expert Consultation. Carbohydrates in human nutrition. FAO Food and Nutrition Paper No. 66. Rome: FAO; 1998.
  5. Prentice AM, Jebb SA. Obesity in Britain: gluttony or sloth? BMJ 1995;311:437-9.
  6. Wei M, Gibbons LW, Mitchell TL, Kampert JB, Lee CD, Blair SN. The association between cardiorespiratory fitness and impaired fasting glucose and type 2 diabetes mellitus in men. Ann Intern Med 1999;130:89-96.
  7. Moy CS, Songer TJ, LaPorte, et al. Insulin-dependent diabetes mellitus, physical activity, and death. Am J Epidemiol 1993;137:74-81.
  8. Department of Health. Nutritional aspects of cardiovascular disease. Committee on Medical Aspects of Food Policy. Report on Health and Social Subjects No. 46. London: HMSO; 1994.
  9. Department of Health. Nutrition and bone health. Committee on Medical Aspects of Food Policy. Report on Health and Social Subjects No. 49. London: HMSO; 1998.
  10. Department of Health and Social Security. Nutritional aspects of the development of cancer. Committee on Medical Aspects of Food Policy. Report on Health and Social Subjects No. 48. London: HMSO; 1998.
  11. Blair SN, Jackson AS. Physical fitness and activity as separate heart disease risk factors: a meta analysis. Med Sci Sports Exer 2001;33:762-4.

Resources
Diabetes UK
W:www.diabetes uk.co.uk
British Heart Foundation
W:www.bhf.org.uk
National Osteoporosis Society
W:www.nos.org.uk
Health Development Agency
W:www.hda.nhs.uk