exercise and the development of diabetes

there are many studies on the relationship between exercise and the development of diabetes. the studies for diabetes prevention have been somewhat conflicting about the intensity and amount of time doing exercise, with some suggesting that doing low-intensity exercise for longer was as good as high-intensity exercise for a shorter period of time. this study in the Annals of Internal Medicine addressed this issue, looking at men and women with abdominal obesity and therefore higher likelihood of developing diabetes, though none with diabetes (see exercise and glucose intolerance obesity AIM 2015 in dropbox, or Ann Intern Med. 2015;162:325-334​). in brief:

--300 abdominally obese adults were assigned to one of three 24-week interventions from 2009-2013, of which 217 completed the study. mean age 51.4, BMI 33.4 and waist circumference 110.6 cm (43.5 inches). ​fasting glucose mean was 5.4 mmol/L (97 mg/dL), 2 hr pp glucose mean of 7.3 mmol/L (132 mg/dL). 

--all were given 5 weekly sessions. control group had no intervention. groups:

    --low-amount, low-intensity exercise (LALI): 180 and 300 kcal/session for women and men, respectively, at 50% of maximum oxygen consumption (eg, routine walking). mean time per session was 31 minutes

    --high-amount, low-intensity exercise (HALI): 360 and 600 kcal/session at 50% of max oxygen consumption (eg, routine walking). mean time per session was 58 minutes

    --high-amount, high-intensity exercise (HAHI): 360 and 600 kcal/session, at 75% of max oxygen consumption (brisk walking/light jogging). mean time per session was 40 minutes

    --no difference between groups in unsupervised additional daily activity or sedentary time

results, controlling for age and sex:

    --waist circumference changes:

        --LALI: -3.9 cm [-5.6 to -2.3], p<0.001

        --HALI: -4.6 cm [-6.2 to 3.0], p<0.001

        --HAHI: -4.6 cm [-6.3 to -2.9], p<0.001

        --no statistical difference between the exercise groups

    --reduction in 2-hour glucose levels

        --adjusting for covariates, only the HAHI group reached significant difference from controls: -0.7 mmol/L (-12.5 gm/dL), with CI of -1.3 to -0.1 mmol/L (-23.5 to -1.5 mg/dL), and p=0.027.

conclusions: not much difference between different exercise interventions in abdominal obesity, but HAHI had lower sugar levels.

so, I have seen at least 6-8 studies looking at lifestyle interventions in delaying the development of diabetes in high risk people, typically either in those with genetic high risk -- eg, those who have 2 parents with diabetes or those from specific high risk groups (eg Pima Indians), or in those with prediabetes (eg the Diabetes Prevention Project, DPP). In general, these studies show that diet and exercise put off the development of diabetes by about 10 years. ​the largest trial was DPP a 2.8 year trial comparing standard of care with an intensive lifestyle intervention vs metformin in nondiabetics with high fasting glucose, impaired 2-hr postload glucose and BMI>24, with the perhaps the surprising results that lifestyle change was dramatically better than metformin (diabetes incidence rates were 4.8 cases/100 with lifestyle intervention, 7.8/100 with metformin, and 11.0 in placebo group). 10-year followup (5.7 years after the trial ended) had 2766 participants, finding those in the original lifestyle group regained some weight (though the modest weight loss with metformin continued) but that the diabetes incidence was reduced by 34% with lifestyle and 18% with metformin as compared to placebo, indicating pretty long-term persistence of the effect of the interventions (there was some continued intervention:  lifestyle sessions were offered to all, those in the intensive lifestyle group were also offered 2 group classes of 4 session/year, those on metformin were offered to continue at 850mg bid if tolerated) -- see dm DPP 10yr followup lancet 2009 in dropbox, or Lancet 2009; 374: 1677–86​.  

so, bottom line, lifestyle changes are really helpful. this study unexpectedly had 2 findings: that waist circumference seemed to decrease equivalently with exercise but independent of the intensity and even at the lower level of 150 min/week. but blood sugar decreased only in the high intensity group at 200 minutes/week (this does differ from the American Diabetes Assn guidelines, but I should add that it is unclear what the clinical significance of this is in a non-diabetic population).