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5. Effects of refeeding or supplementation on respiratory quotients and substrate oxidation rates of CED subjects

When CED subjects were refed by providing energy supplements of 800 kcal (3.35 MJ) per day (15 g protein, 35 g fat and 105 g carbohydrate) over a period of 12 weeks, there was an overall increase in body weight (+ 1.9 kg) of which 1 kg was the increase in fat mass over this period of time (SOARES et al., 1992). Nearly 70% of the total increase in body weight occurred within the first 3 weeks. The basal fasted RQs were significantly elevated (with values > 1.0) and so was the BMR both in absolute terms and when expressed per kg FFM. The maximal rise in RQ was seen in the first 6 weeks of supplementation, which was also the period of maximal increase in fat mass (Figure 2). RQs and the substrate oxidation rates, both in the fasted and the fed state, are summarised in Table 6. They show that there was a predominant increase in carbohydrate oxidation, both in the fasted and fed state, and the changes in RQ provided evidence of de novo lipogenesis during this phase (ELLA and LIVESEY, 1988). Massive increases in carbohydrate intake are known to result in high RQs (> 1.15), with up to 25 % increase in BMR due to the cost of de novo lipogenesis, even in the post-absorptive state (SCHUTZ et al., 1982). Smaller rises in RQs during rehabilitation have been documented in the Minnesota study and in other refeeding studies of undernourished subjects (RAMANAMURTHI et al., 1962).

Table 6. Non-protein respiratory quotients (NPRQ) and substrate oxidation rates (SOR) in the fasted and fed state before and after 12 weeks supplementation in CED subjects

































* Mean of 6 hours post-prandial.
** Negative fat oxidation is indicative of net lipogenesis.

From PIERS et al., 1992c.

In conclusion, it may be stated that the chronically energy deficient or undernourished state is in many ways metabolically different from the normal, well-nourished situation. There is a predominant reliance on carbohydrate as metabolic fuel, even 12 hours after the last meal. This selective utilisation of carbohydrate as substrate has possible metabolic advantages. The preference for carbohydrate utilisation as fuel is seen also in the fed state and during refeeding or energy supplementation and is associated with de novo lipogenesis which may contribute to the enhanced thermic effect of diets in these subjects.


I am grateful to Dr. M. Elia for critical comments on the manuscript and Mr. J. Stubbs for helpful discussion.


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