Open Access Research

Fasting substrate oxidation in relation to habitual dietary fat intake and insulin resistance in non-diabetic women: a case for metabolic flexibility?

Madelaine T Carstens1, Julia H Goedecke14, Lara Dugas2, Juliet Evans1, Jacolene Kroff1, Naomi S Levitt3 and Estelle V Lambert1*

Author Affiliations

1 MRC/UCT Research Unit for Exercise Science and Sports Medicine, Department of Human Biology, Faculty of Health Sciences, University of Cape Town, PO BOX 115, , Newlands, Cape Town, 7725, South Africa

2 Department of Preventive Medicine and Epidemiology, Strict School of Medicine, Maywood, IL, USA

3 Division of Endocrinology & Diabetic Medicine, Department of Medicine, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa

4 South African Medical Research Council, Parow, Cape Town, South Africa

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Nutrition & Metabolism 2013, 10:8  doi:10.1186/1743-7075-10-8

Published: 14 January 2013



Metabolic flexibility described as “the capacity of the body to match fuel oxidation to fuel availability” has been implicated in insulin resistance. We examined fasting substrate oxidation in relation to dietary macronutrient intake, and markers of insulin resistance in otherwise healthy women, with and without a family history of diabetes mellitus (FH DM).


We measured body composition (dual x-ray absorptiometry), visceral and subcutaneous adipose tissue area (VAT, SAT, using Computerised Tomography), fasting [glucose], [insulin], [free fatty acids], [blood lipids], insulin resistance (HOMA-IR), resting energy expenditure (REE), respiratory exchange ratio(RER) and self-reported physical activity in a convenience sample of 180 women (18-45 yrs). A food frequency questionnaire was used to assess energy intake (EI) and calculate the RER: Food Quotient (FQ) ratio. Only those with EI:REE (1.05 -2.28) were included (N=140). Insulin resistance was defined HOMA-IR (>1.95).


The Insulin Resistant (IR) group had higher energy, carbohydrate and protein intakes (p < 0.05) and lower PA levels than Insulin Sensitive (IS) group (P < 0.001), but there were no differences in RER or RER:FQ between groups. However, nearly 50% of the variance in HOMA-IR was explained by age, body fat %, VAT, RER:FQ and FH DM (adjusted R2 = 0.50, p < 0.0001). Insulin-resistant women, and those with FH DM had a higher RER:FQ than their counterparts (p < 0.01), independent of body fat % or distribution.


In these apparently healthy, weight-stable women, insulin resistance and FH DM were associated with lower fat oxidation in relation to dietary fat intake, suggesting lower metabolic flexibility.

HOMA-IR; Insulin-sensitivity; Dietary fat intake