Abstract

Introduction The rising trend in diabesity in the Kingdom is alarming and the medical costs associated with these trends are anticipated to be in the billions of dollars. Beside this significant economic burden, diabesity is highly associated with cardiovascular morbidities and mortalities due to perturbations or loss of heart rate variability. This can be improved by the restoration of the sympathovagal (S/V) balance. Most weight reduction interventions aim to reduce body weight by 5 to 10% within a 6 month period. This magnitude of weight loss translates into beneficial blood pressure adaptations. However, it is neither easy to achieve nor maintain. Hypothesis: A 2% decrease in body weight will significantly and favorably modify sympathovagal balance, systolic blood pressure and baroreceptor sensitivity. Methods Study Design: This study will be a longitudinal, single blind, cross-over and counter balanced (to prevent an order effect) design. Subjects: Subjects will be nonhypertensive and nondiabetic between the ages of 18 and 25 years. They will be obese, nonsmokers, healthy, free of known cardiovascular and respiratory diseases, and not using prescription or over-the-counter medications. Weight loss intervention: Our proposed investigation will use caloric restriction (dieting) as an intervention to achieve weight loss. Body weight measurements will be made prior to and following the treatments. Measurements: The study will collect recordings of arterial blood pressure and the electrical activity of the heart. Sympathetic and parasympathetic components will be derived from these measurements. Statistical Analysis: A repeated measures analysis of variance (RANOVA) will be used. Statistical significance will be set at P < 0.05. Discussion Obesity and the cardiac autonomic nervous system are intrinsically related. A 10% increase in body weight is associated with a decline in parasympathetic tone, accompanied by a rise in mean heart rate. Conversely, obese subjects undergoing 10% weight loss were found to have improved autonomic cardiac modulation, reflected in decreased heart rate and increased HRV, mainly through an increase in the cardiac parasympathetic modulation. (Poirier et al. 2003, Nature) A meta-analysis of 25 studies concluded that a 1 kg loss of body weight was associated with an approximate 1 mmHg drop in blood pressure (Neter et al. 2003, Hypertension). So a 5 to 10% body weight loss translates into substantially beneficial blood pressure adaptations. An analysis by the Trials of Hypertension Prevention Research Group, showed that those who lost at least 4.5 kg and sustained this loss continued to maintain a substantial reduction in blood pressure through 36 months compared to the control group. The study concluded that sustained weight loss is a key factor in long term reduction in risk for cardiovascular disease. (Annals of Intern Med. 2001). However, it is neither easy to achieve nor maintain, and most subjects return to their original body weight. (Byrne 2003, International Journal of Obesity). Conclusion Obesity is strongly associated with a lot of health problems. Unfortunately, efforts to reduce obesity have been less successful than desired. Part of the problem being that a 5-10% weight loss is not realistic enough for some patients to achieve and maintain. We hope to investigate a more modest 2% weight change to see if patients will still experience some of the benefits.