Perceptions and beliefs Barriers to increasing physical activity include time constraints, usually linked to domestic or work commitments, health status, age, performance expecta- tions and lack of will power.
The emphasis should be on adapting advice to fit in with the individual’s lifestyle and avoiding prescriptive advice, which may fail to address the individual’s perceptions and beliefs.
People with Type 2 diabetes who wish to increase their levels of general activity will need encouragement, motivation and the choice of a physical activity or sport which matches their individual needs.
For the majority of this
DIABETES AND PHYSICAL ACTIVITY 25
middle-aged sedentary population, an increase in gentle exercise, e.g. walking, can be safely recommended. Exercise at this level has been shown to have health benefits for people with Type 2 diabetes (27). It is feasible for people with Type 2 to increase physical activity at a higher intensity, but recommendations should include checking with their physician before beginning a programme of vigorous exercise and exercising under supervision.
Type, Intensity, Frequency and Duration Advice to people with diabetes will depend upon the type of exercise they wish to do.
Gentle exercise at light or moderate intensity does not place the same demands upon diabetes management as that caused by vigorous exercise.
People with Type 1 diabetes may be at risk of hypoglycaemia and it is important to consider the effect of the type, intensity, frequency and duration of exercise and its effect on blood glucose.
Timing of meals and sessions of physical activity should be planned wherever possible and exercise should avoid the peak action of insulin as this has been shown to precipitate hypoglycaemia.
The majority of people with Type 1 who take exercise find that they may have to adjust their insulin, their carbohydrate intake or a combination of both.
People who are taking part in competitive sports or who wish to take part in endurance races or increase their activity to a vigorous level are strongly recommended to consult a specialist diabetes professional.
Medication People with Type 2 diabetes who are controlled by diet alone, or who take metformin or acarbose, are able to exercise without risk of hypoglycaemia.
They do not need to make any adjustment to their medication when increasing physical activity.
Those taking insulin or oral hypoglycaemic agents will need to time exercise sessions to avoid peak action of agents and may need to take extra carbohydrate during training to prevent hypoglycaemia.
It is difficult to adjust insulin for exercise in people taking an insulin mixture twice daily and in Type 2 diabetes this is further complicated by an inability to measure accurately insulin resistance.
Because of the action of increasing insulin sensitivity, people with Type 2 diabetes who increase their physical activity may find that their insulin requirements decrease over time and that they may need less insulin.
This is best measured on an individual basis and should be monitored by frequent blood glucose tests.
People with Type 1 diabetes will need to plan ahead for exercise and make appropriate insulin adjustment.
One study has shown that moderately intensive exercise sessions lasting 45 min can lead to hypoglycaemia and this was effectively overcome by a reduction in insulin by 30, 50% before exercise (28).
The effects of exercise are mediated by the timing of exercise (pre- or post-
26 NUTRITIONAL MANAGEMENT OF DIABETES MELLITUS
prandial) and the blood glucose levels at the start of exercise.
It is impossible to formulate precise guidelines for insulin adjustment for those with Type 1 wishing to exercise, but consultation and experimentation accompanied by frequent blood glucose tests can help to identify the most effective strategies in individuals with Type 1 diabetes.
The absorption of insulin injected subcutaneously can be accelerated by exercise and may precipitate hypoglycaemia.
To prevent this, it is advised that insulin is injected away from the site of exercising muscle, e.g. into the abdomen in the case of runners and cyclists, and that exercise does not take place at the time of peak insulin action.
Contraindications to Exercise Although the health benefits of exercise are well established, there are certain areas where caution must be observed.
Encouragement to increase physical activity for people with diabetes will be affected by some underlying features and physical exercise is not without risk in diabetes.
All people with diabetes are advised to have a medical examination prior to beginning an exercise programme to identify any complications which may be adversely affected by exercise.
Those wishing to take part in strenuous activity will find the following are relative contraindications: poor glycaemic control, the presence of ketones, proliferative retinopathy, microangiopathy, neuropathy, nephropathy and cardiovascular disease.
Although strenuous activity may be contraindicated, some individuals may be able to increase general everyday physical activity.
Practical implications of increasing physical activity include consideration of possible damage to the soft tissues and joints, especially in the feet, and it is recommended that those with diabetes consult a podiatrist and purchase good, supportive footwear.
Precipitation of cardiac events is possible, especially in those with Type 2 diabetes, and exercise should not be encouraged without giving the following guidelines: avoid irregular, strenuous exercise, do not exercise when unwell and stop exercise immediately if any pain, especially chest pain, is experienced.
It is also important to warm up and cool down thoroughly before and after exercise sessions.
DIETARY ADVICE FOR EXERCISE
PRACTICAL MANAGEMENT Dietary advice to people with diabetes wishing to increase physical activity is individual and will depend upon many factors including medication, type, frequency and duration of exercise and for many people it is a process of experimentation. For those taking insulin, there is more than one way to
DIABETES AND PHYSICAL ACTIVITY 27
regulate blood sugar levels during exercise either by reducing insulin, increasing carbohydrate intake or a combination of the two. Advice should be tailored to the individual depending upon the following: . Dietary intake . Insulin regime . Blood glucose levels . Type of activity . Timing of activity
Dietary Intake It is now universally accepted that the best diet for maximising exercise tolerance and performance is one that is high in carbohydrate (50, 60% energy from carbohydrate).
Athletes routinely use high-carbohydrate diets when training.
The Diabetes UK recommendations for all people with diabetes encourage a high-carbohydrate diet and this should apply whether people are exercising or not.
This diet should help protect against the risk of hypoglycaemia during periods of increased physical activity.
There is some discussion about the type and amount of carbohydrate.
The glycaemic index (GI) of carbohydrate foods has been shown to be a useful tool in maximising performance in athletes and sportsmen and women and there may be a role for it in people with diabetes who exercise at a strenuous level for more than 60 min (29).
It is recommended that low GI foods are consumed at the meal or snack before exercise takes place and that high GI foods are consumed during endurance events and after exercise to replenish glycogen stores.
Examples of low GI foods, which can be eaten before an exercise session and high GI foods/drinks, which can be taken during or after an event, are given in Table 2.2.
Table 2.2 Examples of high and low GI carbohydrate foods
GI Examples of food Timing
Low Pasta, Basmati rice, couscous, instant noodles, 2, 3 h before exercise, barley, wholegrain products, porridge, muesli, especially endurance All-Bran, oat-based cereal bars, lentils and events pulses including baked beans, chick peas and kidney beans, dried apricots High Isotonic sports drinks, fruit juice, ordinary squash, During an exercise jelly beans, ripe bananas, honey sandwich session (if required) High Corn Flakes, Rice Krispies, sugared cereals, white Within 30, 60 mins of bread, rice (other than Basmati), potatoes completing an exercise session
28 NUTRITIONAL MANAGEMENT OF DIABETES MELLITUS
It is recommended that people with diabetes eat before exercising and that they should exercise approximately 3 h after a large meal to ensure digestion and absorption of food.
Additional carbohydrate may be needed immediately before exercise, during exercise and after exercise to replenish glycogen stores.
The amount of carbohydrate will depend upon blood glucose levels.
Intake of sufficient fluid should be advised to avoid dehydration.
Water, sugar-free squashes and sugar-free sports drinks are suitable for rehydration if fluid only is required.
Fruit juice, ordinary squash and isotonic sports drinks are useful for replenishing fluid and carbohydrate.
Hypertonic drinks, e.g.
Lucozade, are not suitable for rehydration and should be used only to treat hypoglycaemia.
Fizzy drinks and sodas may cause problems with bloating and wind and are best avoided.
Insulin Regime For those who are on a basal/prandial regimen it may be necessary to reduce insulin by 30, 50% before strenuous activity.
Extra carbohydrate should be taken when engaging in unplanned activity where it is impossible to reduce insulin.
It is advisable that people avoid periods of strenuous physical activity when short-acting insulin is peaking, i.e. within 2 h of use.
People with Type 1 diabetes may find they can reduce their insulin after an endurance event, e.g. marathon running, and that it may take several days before they return to their pre-race insulin dose.
This process should be supported by frequent blood glucose tests.
Blood Glucose Levels It is recommended that people with diabetes monitor their blood glucose levels before, during and after exercise.
Optimum blood glucose levels are those between 6, 13 mmol/l before exercise begins.
If blood glucose levels are 5 6 mmol/l, people should be advised to take some carbohydrate with a high glycaemic index, e.g. isotonic sports drinks, ripe bananas.
If blood glucose levels are above 13 mmol/l, then exercise should be delayed until blood glucose falls to the acceptable levels.
If blood glucose drops below 5 mmol/l during exercise, fast-acting carbohydrate should be taken immediately to prevent hypoglycaemia.
Type of Activity The amount of carbohydrate to be taken during exercise depends upon the type of activity. People with Type 2 diabetes who are increasing physical activity at low/moderate intensity by going for a walk often need to make no change to their medication or dietary intake. However, if they take insulin and are