This paper reports the final 24-month outcomes of a randomized controlled trial evaluating the effect of additional therapeutic contact (ATC) as an adjunct to a community-based weight-management program for overweight and obese 13-16-year-olds. ATC involved telephone coaching or short-message-service and/or email communication once per fortnight. Adolescents were randomized to receive the Loozit group program-a two-phase behavioral lifestyle intervention with (n=73), or without (n=78), ATC in Phase 2. Adolescents/parents separately attended seven weekly group sessions (Phase 1), followed by quarterly adolescent sessions (Phase 2). Assessor-blinded, 24-month changes in anthropometry and metabolic health included primary outcomes body mass index (BMI) z-score and waist:height ratio (WHtR). Secondary outcomes were self-reported psychosocial and lifestyle changes. By 24 months, 17 adolescents had formally withdrawn. Relative to the Loozit program alone, ATC largely had no impact on outcomes. Secondary pre-post assessment of the Loozit group program showed mean (95% CI) reductions in BMI z-score (-0.13 (-0.20, -0.06)) and WHtR (-0.02 (-0.03, -0.01)) in both arms, with several metabolic and psychosocial improvements. Adjunctive ATC did not provide further benefits to the Loozit group program. We recommend that further work is needed to optimize technological support for adolescents in weight-loss maintenance. Australian New Zealand Clinical Trials Registry Number ACTRNO12606000175572.

Skeletal muscle plays a major role in insulin-stimulated glucose disposal. This paper reviews the range of evidence in humans and experimental animals demonstrating close associations between insulin action and two major aspects of muscle morphology: fatty acid composition of the major structural lipid (phospholipid) in muscle cell membranes and relative proportions of major muscle fiber types. Work in vitro and in vivo in both rats and humans has shown that incorporation of more unsaturated fatty acids into muscle membrane phospholipid is associated with improved insulin action. As the corollary, a higher proportion of saturated fats is linked to impairment of insulin action (insulin resistance). Studies in vitro suggest a causal relationship. Among polyunsaturated fatty acids (PUFA) there is some, but not conclusive, evidence that omega-3 (n-3) PUFA may play a particular role in improving insulin action; certainly a high n-6/n-3 ratio appears deleterious. In relation to fiber type, the more highly oxidative, insulin-sensitive type 1 and type 2a fibers have a higher percentage of unsaturated fatty acids, particularly n-3, in their membrane phospholipid, compared to the insulin-resistant, glycolytic, type 2b fibers. These variables, however, can be separated and may act in synergy to modulate insulin action. It remains to establish whether lifestyle (e.g., dietary fatty acid profile and physical activity), genetic predisposition, or a combination are the prime determinants of muscle morphology (particularly membrane lipid profile) and hence insulin action.

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