Menopause Live (20 August, 2012) From IMS

Can any new information be added to the question of insulin resistance after menopause? Yes, as it is not clear whether there is any benefit from moderate-to-vigorous aerobic exercise in postmenopausal women that are unsuccessful in losing weight. Do older women benefit from exercise? The study of Mason and colleagues [1] investigated the independent and combined effects of dietary weight loss and exercise on insulin sensitivity and restoration of normal fasting glucose in middle-aged and older women. The Nutrition and Exercise in Women (NEW) study was a 12-month, randomized, controlled trial, conducted from 2005 to 2009 on 439 inactive, overweight, postmenopausal women. Women were randomized to dietary weight loss, moderate-to-vigorous intensity aerobic exercise, combined diet and exercise, or no intervention. They attended weekly group meetings in the first 6 months, followed by monthly meetings, in addition to biweekly phone or e-mail contacts. Body mass index, body fat, waist circumference, VO2max, pedometer steps and average energy consumed were monitored. Insulin resistance was assessed at base line and after 12 months of intervention through insulin, C-peptide, fasting plasma glucose levels and calculated HOMA-IR model. At 12 months, the greatest weight loss was achieved in the diet + exercise group, followed by the diet group. Women in the diet and diet + exercise groups experienced significant reductions in insulin, C-peptide, HOMA-IR and fasting plasma glucose levels, when compared to the exercise-alone and control groups. This reduced the 1-year incidence of developing impaired fasting glucose. However, moderate-to-vigorous exercise was most effective in reverting from impaired fasting to normal glucose levels, independent of weight loss. The authors concluded that dietary weight loss, with or without exercise, significantly improved insulin resistance in both younger and older postmenopausal women.

Comment
It is well known that insulin resistance increases during the menopause transition, leading to the development of metabolic syndrome [2]. Insulin resistance may be hepatic and peripheral. Increased hepatic glucose production, especially during the night, is associated with an increase in fasting glucose levels. Insulin resistance in the skeletal muscles leads to lower utilization of glucose and increase in postprandial glucose levels. Muscles are less sensitive to insulin than liver. Glucose uptake into muscles requires three to four times the amount of insulin needed to suppress hepatic glucose output. Accumulation of visceral fat also increases insulin resistance, menopause being the most dangerous time, with a transition from a gynoid to an android body fat distribution [3]. 

Physical activity and weight loss help the body respond better to insulin. The Diabetes Prevention Program (DPP) and other large studies [4,5] have shown that losing just 5–7% of body weight prevents or delays diabetes by nearly 60%. Walking 30 minutes a day for 5 days a week, for people aged 60 or older, lowered their chances of developing diabetes by 70%. Whether dietary weight loss influences more hepatic or peripheral insulin resistance is unknown. However, it is logical to assume that moderate-to-vigorous physical exercise would greatly influence insulin resistance in skeletal muscles. The study of Mason and colleagues confirms this assumption, showing that added aerobic exercise for 12 months led to regression from impaired to normal fasting glucose, independent of weight loss. Dieting and exercise, on the other hand, were most effective in preventing the development of impaired fasting glucose. Unfortunately, glucose tolerance testing and HbA1c were not measured in this study, to further elucidate the effect of diet and exercise on the two types of insulin resistance. 

Could these results lead to clinical implications? It seems that overweight postmenopausal women with impaired fasting glucose and difficulty in losing weight should be encouraged to exercise. These women would benefit from moderate-to-vigorous aerobic exercise added to the 30 minutes walking/day, for 5 days a week. Older women benefit from diet + exercise. It is never too late to start exercising, preferably in groups, which seems to be more relaxing and less stressful.

Teodora Beljic Zivkovic
Faculty of Medicine, University of Belgrade, ’Zvezdara’ University Medical Center, Belgrade, Serbia

References
1. Mason C, Foster-Schubert KE, Imayama I, et al. Dietary weight loss and exercise effects on insulin resistance in postmenopausal women. Am J Prev Med 2011;41:366-75.
http://www.ncbi.nlm.nih.gov/pubmed/21961463
2. Janssen I, Powell LH, Crawford S, et al. Menopause and the metabolic syndrome: the Study of Women’s Health Across the Nation. Arch Intern Med 2008;168:1568–75.
http://www.ncbi.nlm.nih.gov/pubmed/18663170
3. Lee CG, Carr MC, Murdoch SJ, et al. Adipokines, inflammation, and visceral adiposity across the menopausal transition: a prospective study. J Clin Endocrinol Metab 2009;94:1104-10.
http://www.ncbi.nlm.nih.gov/pubmed/19126626
4. Diabetes Prevention Program Research Group; Knowler WC, Fowler SE, Hamman RF, et al. 10-year follow-up of diabetes incidence and weight loss in the Diabetes Prevention Program Outcomes Study. Lancet 2009;374:1677–86.
http://www.ncbi.nlm.nih.gov/pubmed/19878986
5. Tuomilehto J, et al. Programme for prevention of type 2 diabetes in Finland 2003-2010.
http://www.diabetes.fi/files/1108/Programme_for_the_Prevention_of_Type_2_Diabetes_in_Finland_2003-2010.pdf