Volume 89, Issue 3, March (2003), pp. 365-374 © The Author 2003
doi:10.1079/BJN2002789

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Carbohydrate-induced manipulation of insulin sensitivity independently of intramyocellular lipids

Gary S. Frost^1,2,CA, Louise M. Goff², Gavin Hamilton², E. Louise Thomas², Waljit S. Dhillo², Anne Dornhorst² and Jimmy D. Bell^2
1 MRC MRI Unit, Clinical Sciences Centre, Department of Nutrition & Dietetics, and Department of Metabolic Medicine, Division of Investigative Science, Hammersmith Hospital, Imperial College School of Medicine, London W12 0HS, UK
² MRC MRI Unit, Clinical Sciences Centre, Department of Nutrition & Dietetics, and Department of Metabolic Medicine, Division of Investigative Science, Hammersmith Hospital, Imperial College School of Medicine, London W12 0HS, UK

 (Received 6 February 2002–Revised 9 October 2002–Accepted 21 October 2002)

Subjects with insulin resistance have been shown to have higher storage levels of intramyocellular lipid (IMCL) than their insulin-sensitive counterparts. It has been proposed that elevated IMCL stores may be the main cause of insulin resistance. The aim of the present study was to ascertain whether there is a causal relationship between IMCL storage and insulin resistance. IMCL storage was assessed using magnetic resonance spectroscopy and insulin sensitivity was assessed by performing an oral glucose tolerance test. A 4-week intervention of reduction of dietary glycaemic index was used to manipulate insulin sensitivity in a cohort of healthy volunteers; the effects of this intervention on IMCL were measured after 4 weeks of intervention. Significant improvements in the insulin sensitivity index occurred following the dietary intervention (baseline 7·8 (SEM 1·11) v. post-intervention 9·7 (SEM 1·11), P=0·02). However, there were no changes in IMCL storage levels, suggesting that insulin sensitivity can be manipulated independently of IMCL. This suggests that in healthy volunteers, insulin sensitivity is independent of IMCL storage and the high storage levels that have been found in insulin-resistant subjects may occur as a consequence rather than a cause of insulin resistance.

Abbreviations: GI; glycaemic index; iAUC; incremental area under the curve; IMCL; intramyocellular lipid; NEFA; non-esterified fatty acid; OGTT; oral glucose tolerance test

Keywords:
Intramyocellular lipids, Insulin resistance, Insulin sensitivity, Magnetic resonance spectroscopy, Glycaemic index, Carbohydrate