A study that attempted to tease out the effects of fasting insulin levels on RQ (Twenty-Four-Hour Respiratory Quotient: The Role of Diet and Familial Resemblance. Søren Toubro, Thorkild I. A. Sørensen, Charlotte Hindsberger, Niels, Juel Christensen, Arne Astrup. The Journal of Clinical Endocrinology & Metabolism, Volume 83, Issue 8, 1 August 1998, Pages 2758–2764). They
…studied the familial correlation of both 24-h respiratory quotient (RQ), an index of the ratio of fat to carbohydrate oxidation, and the possible influence of dietary macronutrient composition expressed by the food quotient (FQ), i.e. the theoretical RQ produced by the diet. We measured the habitual FQ of the 7 days diet by weighed food records, followed by measurement of 24-h RQ in respiration chambers in 71 healthy Caucasian siblings from 31 families.
After adjustment for age, gender, and 24-h energy balance, 24-h RQ correlated in families as indicated by an intraclass correlation coefficient (ri) of 0.31 (P = 0.03). FQ, adjusted for age and gender, was also a familial trait for the two days immediately preceding diet (ri = 0.32, P < 0.01). The familial effect on 24-h RQ, adjusted for age, gender, and 24-h energy balance, remained after adjustment for the FQ of the two days preceding diet (ri = 0.27, P < 0.05) and was reduced but not abolished after further adjustment for fasting plasma insulin plus free fatty acids (ri = 0.24, P < 0.09).
We conclude that substrate oxidation rates measured by RQ exhibit familial correlation after proper adjustment for confounders such as energy balance, gender, and age, and that this effect could not be fully explained by preceding diet composition, fasting plasma insulin, and free fatty acids.
A higher RQ is a measure of propensity to gain fat mass (Obesity (2010) 18, 2255–2259. Respiratory Quotient Predicts Fat Mass Gain in Premenopausal Women. Amy C. Ellis, Tanya C. Hyatt, Gary R. Hunter and Barbara A. Gower.).
This observation suggests that low postprandial fat oxidation may uniquely predispose obesity-prone individuals to accrual of adipose tissue.
A third study (Sb Lek. 2000;101(1):99-104. Respiratory quotient in obesity: its association with an ability to retain weight loss and with parental obesity. Hainer V1, Kunesová M, Parízková J, Stich V, Mikulová R, Slabá S.):
A high fasting respiratory quotient (RQ) was observed during the treatment by very low calorie diet (VLCD) in obese patients who regained weight at two-year follow-up (weight regainers) or in those who exhibited repeated cycles of weight loss with a subsequent weight regain (weight cyclers).
In contrast obese patients who succeeded to retain the weight loss achieved initially by the VLCD at 2-yr follow-up (weight losers) or those who did not exhibit weight fluctuations (weight noncyclers) were characterized by a significantly lower RQ.
Therefore a high fasting RQ during the VLCD treatment should be considered predictive of body weight gain. Resting metabolic rate (RMR) expressed per kg fat free mass (FFM) did not influence body weight changes.
A high RQ revealed in obese subjects reporting parental obesity and a low fasting RQ observed in those obese without family history of obesity suggest a role of hereditary factors in the ability to oxidize fat in severely obese subjects. In contrast, parental history of obesity did not affect RMR in severely obese individuals.