Conference Coverage

Weight Loss Through Dieting Increases Insulin Sensitivity



HOUSTON – Diet-induced weight loss with or without an accompanying exercise training program improved insulin sensitivity and other key cardiometabolic risk factors in an obese elderly population, a randomized trial showed.

However, exercise training alone in the absence of weight loss had no effect on insulin sensitivity in the 52-week-long clinical trial.

"This is actually a novel finding in this population of obese older adults, and it suggests a distinct complementary effect of regular exercise only in the setting of prerequisite weight loss," observed Dr. Matthew F. Bouchonville of the University of New Mexico, Albuquerque.

He reported on 107 obese subjects with a mean body mass index of 37 kg/m2, all of whom were at least 65 years old. Sixty percent were women. Participants were randomized to one of four groups: a 52-week supervised dietary intervention with the goal of a 10% loss in body weight at 6 months and maintenance of that slimmed-down weight during the following 6 months; an exercise program; a combined diet-and-exercise intervention; or a control group. Essentially the study compared the metabolic effects of weight loss without exercise, versus exercise without weight loss, versus both interventions.

The primary outcome was change in insulin sensitivity index (ISI) over 1 year as measured via a 75-g oral glucose tolerance test. At 6 months, there was nearly a 40% increase in ISI in both weight-loss interventions – that is, the diet-only and diet-plus-exercise groups – with no significant difference between the two. Moreover, the exercise-only intervention had no effect on ISI; it was identical to that in the control group. Thus, at that intermediate 6-month time point there didn’t seem to be any added value for an exercise program in terms of enhancement of insulin sensitivity, Dr. Bouchonville explained.

But that changed as patients were followed from the 6-month mark out to 12 months. During that period, insulin sensitivity continued to improve in the diet-only group such that at 1 year their ISI was 70% better than at baseline, while the ISI in the diet-plus-exercise group showed an even more robust improvement: an 86% gain over baseline. The exercise training–only group still showed no change in insulin sensitivity at 12 months.

"The combination of these interventions is associated with an even greater improvement in insulin sensitivity," Dr. Bouchonville said. "This lends support to the recommendation that lifestyle interventions directed at this population incorporate both diet-induced weight loss and also regular exercise."

That recommendation was made on the basis of an earlier analysis of the data showing that the combination of weight loss and exercise training provided greater improvement in physical function and reduction in physical frailty than did either intervention alone (N. Engl. J. Med. 2011;364:1218-29).

This new analysis of the randomized trial data focused on change in insulin sensitivity because insulin resistance has been implicated as the main driving force behind the metabolic syndrome, the physician continued.

The same pattern seen with regard to change in insulin sensitivity recurred for the other cardiometabolic risk factors serving as secondary outcomes in the study: that is, no effect for exercise alone, but significant improvements noted in both the diet and diet-plus-exercise groups. For example, abdominal adiposity as measured by MRI decreased by an average of nearly 800 cc and C-reactive protein dropped on average by nearly 2 mg/dL in the combined intervention group, while triglyceride levels declined by 25-30 mg/dL in both of the weight loss interventions. Blood pressure also improved significantly, but again, only in the weight-loss interventions, not with exercise alone.

Audience members expressed surprise that the exercise training program alone did not have a significant impact on insulin sensitivity or the other cardiometabolic risk factors. They wondered if the exercise was not sufficiently intensive. Dr. Bouchonville replied that all indications are that it was. The program entailed three 90-minute group workouts per week led by a physical therapist. Each session included aerobic exercise, resistance training, and balance and flexibility exercises. Participants gradually reached 70%-85% of their peak heart rate. Their peak oxygen consumption improved significantly over time, as did their physical function scores, although the improvements on these measures were even greater in the combined diet-plus-exercise arm.

The diet intervention was pretty intensive. Patients met weekly with a dietician who prescribed a balanced diet that included 1 g of high-quality protein per kilo of body weight while maintaining an energy deficit of 500-750 kcal per day. They kept food diaries, and there were weekly weigh-ins. Body weight fell by 10% in the diet-only group and 9% in the diet-plus-exercise group but did not decrease in the exercise or control groups.


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