Exercise and Weight Loss in Diabetes and Coronary Artery Disease

Andrew Heilbrunn

Biokinetics Department, Centre for Diabetes and Endocrinology, Johannesburg

In the last five decades, there has been numerous diabetes, exercise and weight loss related research. The majority of researchers have shown that exercise and decreased total and visceral body fat play an extremely important role in both the prevention and the treatment of Type 2 Diabetes and Coronary artery disease.

Traditionally the preferred approach to weight loss was calorie restriction.  Exercise was seen as a means of maintaining weight lost. In fact, studies suggest that it is easier to maintain ones goal weight through regular exercise than through continued calorie restriction.

The overweight population were of the opinion that it was necessary to lose a significant amount of body weight in order to bring about healthy, physiological adaptations. However a 5 to 7% reduction in visceral and total body fat may be associated with lower blood pressure, lower cholesterol and lower blood glucose levels. (Movsas S, 2008)

Exercise, Diabetes and Coronary Artery Disease

Between 1960 and 2000, Paffenbarger and Blair initiated longitudinal, follow up physical activity studies on more than 80 000 subjects. They compared the “active” to the “non-active” and the “fit” to the “unfit” subjects and observed the relationship between activity patterns and the risk of developing cardiovascular disease, obesity, diabetes and other chronic illnesses. Their findings contributed enormously to establishing a relationship between physical activity and reduction in risk of mortality from certain chronic illnesses, in particular cardiovascular disease.  Subjects categorised as” unfit”, had the highest Coronary Artery and Cerebrovascular disease death rates.  The risk of being “unfit” appeared to be a higher risk for coronary artery disease than high blood pressure, high cholesterol and obesity.

Eighty to ninety percent of patients with type 2 diabetes are overweight or obese. A personal and a familial history of obesity, caused by poor eating habits and a sedentary lifestyle and compounded by weight gain related to Sulphonylurea and Insulin utilization, mean that many struggle with weight loss. In light of the above, Blair and Paffenbarger’s findings suggested that as long as you were “relatively fit”, even if you were overweight, you would have a lower risk of coronary artery disease.

How much exercise is necessary to bring about weight loss and physiological changes to decrease mortality?

The amount of exercise necessary to bring about healthy adaptations is somewhat controversial.  Paffenbarger suggests that people should try to burn 1500 to 2500 calories per week, which equates to approximately 60-90 minutes of brisk walking per day.  Blair concluded that one would benefit from exercise (5-7 times per week) at 60-85% aerobic capacity (duration 30-60 min). The American College of Sports Medicine (ACSM) advocated 30-60 minutes per day of moderate intensity physical activity, (A brisk walk) was sufficient. The latest literature suggests that in order to bring about weight loss through exercise alone, one would have to exercise for more than 60 minutes per day. Based on the results of our own research, as well as the work of researchers such as Blair, Paffenbarger, Sigal and Eves we recommend a combination of moderate calorie reduction and 3 to 5 weekly exercise sessions of 45 to 60 minutes duration performed at a moderate to high intensity (i.e. brisk walking and / or a moderate intensity, resistance-training circuit). In addition, we suggest participating in informal activity such as stair climbing, gardening, shopping or housework daily.

Moderate physical activities performed throughout the day, adding up to a total of 60 minutes of activity by the end of the day, appear to have the same physiological health benefits as one continuous bout of exercise lasting 60 minutes. This may come as a surprise to the sedentary person who views exercise as a daunting and demanding task.  Small, regular and progressive activities taken throughout the day can combine to offer the same rewards as 30-60 minutes in a fitness centre.

Which type s of exercise should people participate in, in order to reduce body-fat percentage?

There are generally 2 modes of exercise people can participate in:

1.       Endurance exercise such as walking, cycling, jogging and swimming.  These are activities which involve low intensity exercise carried out continuously for a long period of time.

2.       Resistance or interval type exercise which involves a higher intensity type of exercise carried out in short bursts with rest intervals, such as a resistance training circuit or most types of ball sports.

There is some controversy surrounding the mode of exercise that people should participate in, in order to bring about visceral and total body-fat loss.  Endurance activities at a low to moderate intensity (60% of ones theoretical heart rate maximum) were traditionally seen as the best way to utilize fat as a primary energy source; however, recent findings suggest that this low intensity utilized a negligible amount of fat in 60 minutes.  In reality one would have to cycle, walk or jog at 60% VO2 max for 2-3 hours per day in order to bring about significant fat percentage reduction.  On the other hand, higher intensity interval or intermittent exercise for 60 minutes, 3 to 4 times per week increases ones basal metabolic rate for a longer period than low intensity endurance training and this may be more beneficial in body-fat percentage reduction.

In an exercise and Type 2 diabetes research concluded in 2007, the combination of endurance and resistance type activities seemed to improve blood glucose control and reduce visceral adiposity more significantly than endurance or intermittent type activities individually. (Sigal RJ, 2007).  One of the explanations for this positive result was a better exercise compliance with a combination of exercises.  Furthermore, in a meta-analysis of exercise and Type 2 diabetes studies, involving 377 subjects, exercise significantly improved visceral adiposity, glycemic control and triglycerides, even in the absence of significant weight loss (Sojung, L, 2007)

In a recent study comparing people participating in a Weight Watchers programme to those participating in regular activity at commercial fitness centres, weight loss was more significant in the Weight Watchers group.  However, when the data was analysed, it was clear that the majority of weight lost in the Weight Watchers group was lean tissue and not fat. Although the fitness centre group lost less weight, intra-abdominal fat was significantly lower than the Weight Watchers group.  Intra-abdominal fat, which is more predictive of Cardiovascular disease was measured with Computer Tomography (CT scans).  These results suggest that exercise, without significant weight loss may have a positive influence on the Metabolic Syndrome (Ball S, 2008).

Exercise Prescription and barriers to exercise

Various medical and physical concerns will govern the type, intensity and duration of exercise an individual is capable of performing safely.  Several lifestyle and socio-economic issues such as motivation, personal goals and preferences, stage of change and cultural influences will also affect the type of exercise intervention developed and its implementation.  Written exercise instructions may help with adherence to an exercise programme.  However, of more importance is the level of support the Physician, Educator and exercise physiologist gives the patient regarding the uptake of activity.  Physician support, patient consultation, specific advice regarding the type, time and intensity of the exercise programme and the setting of appropriate and realistic goals appear to be the strongest predictors of adherence. Furthermore exercising in a group environment or under personal supervision has been shown to improve long term exercise compliance. (Penny B, 2007).

Conclusion

Exercise and calorie restriction have their pros and cons, however the combination may produce the best physiological results. Comprehensive lifestyle therapies, involving nutritional therapy, daily exercise, and behavioural modification, can lead to a 5-7% reduction in visceral and total body fat percentage over 10 to 20 weeks.

Exercise can play a key role in the prevention and management of obesity and diabetes.  It can improve glycaemic control, reduce adiposity, reduce cardiovascular risk and improve quality of life.  Both Endurance and Resistance training modalities should form the cornerstone of any exercise programme.  Prescribed correctly and with adequate considerations of the barriers, motivators and medical concerns facing people with diabetes, exercise can be an extremely safe and effective treatment strategy.