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1 From the Departments of Pulmonology and Dietetics, University Hospital Maastricht, Maastricht, Netherlands, and Numico Research, Wageningen, Netherlands.
2 Address correspondence to MAP Vermeeren, Department of Pulmonology, University Hospital Maastricht, PO Box 5800, 6202 AZ Maastricht, Netherlands. E-mail: mverm{at}bze5.azm.nl..
ABSTRACT
Background: Use of nutritional supplements in depleted patients with chronic obstructive pulmonary disease (COPD) requires optimization between positive effects on outcome and potential acute adverse effects on metabolism and exercise performance.
Objective: The aim of this study was to investigate the acute effects of nutritional supplements on metabolism and exercise capacity in stable COPD patients.
Design: In part 1, the effects of 3 different energy loads (placebo, 1046 kJ, and 2092 kJ) with a normal distribution of macronutrients were investigated in 14 COPD patients. In part 2, the effects of a fat-rich compared with a carbohydrate-rich supplement (both 1046 kJ) were studied in 11 COPD patients. The study was performed in a randomized, double-blind, crossover fashion. Metabolic and ventilatory variables were measured postprandially and during a submaximal cycle endurance exercise test.
Results: Overall, no immediate negative effects of the supplements were found in part 1. A slight but significant postprandial increase in respiratory quotient was found after the 1046-kJ and 2092-kJ supplements compared with placebo. There was no significant difference in metabolism or exercise capacity after a fat-rich or carbohydrate-rich supplement. Surprisingly, the change in shortness of breath (postprandial compared with preprandial) was significantly greater after the fat-rich supplement.
Conclusions: An energy load up to 2092 kJ had no adverse immediate effect in COPD patients compared with placebo. The subjects who consumed the fat-rich supplement experienced more shortness of breath than did the subjects who consumed the carbohydrate-rich supplement.
Key Words: Nutrition • exercise • COPD • metabolism • chronic obstructive pulmonary disease • nutritional supplement
INTRODUCTION
The association between weight loss and chronic obstructive pulmonary disease (COPD) has long been recognized. In the 1960s, several studies reported that a low body weight and weight loss were negatively associated with survival in COPD (1). Adverse effects of weight loss and, in particular, loss of the fat-free-mass component on skeletal muscle function and exercise capacity were reported extensively (2). Weight loss results from an imbalance between dietary intake and energy expenditure. An elevated resting energy expenditure (3) is reported in COPD, as well as an elevated total daily energy expenditure (4). The latter is related to the increased oxygen cost of breathing and possibly also to a decreased mechanical and metabolic efficiency (5). Therefore, patients with COPD can lose weight despite an apparently normal dietary intake. Besides, symptoms that occur frequently, such as dyspnea and fatigue, as well as an elevated systemic inflammatory response, are reported in relation to a decreased appetite and dietary intake (6, 7). So when optimal adaptation of dietary habits fails to improve dietary intake to preserve body weight, nutritional supplements are commonly indicated. To improve functional capacity, nutritional support should be combined with an anabolic stimulus. Indeed, nutritional support as an integrated part of a pulmonary rehabilitation program results in improvements in muscle function, exercise capacity, and health status (8).
In supplemented COPD patients, potential adverse effects on the ventilatory system of the nutritional support strategy also have to be considered. Nutrition and ventilation are intrinsically related because oxygen is required for optimal energy exchange. Meal-related dyspnea and limited ventilatory reserves may restrict the quantity and composition of nutritional support in patients with respiratory disease.
It was suggested that carbohydrate-rich supplements would induce greater ventilation as a result of a higher respiratory quotient (RQ). In clinically stable patients with COPD, 3 studies (9–11) compared the acute effects of high-energy (3849 kJ) nutritional supplements with high and low carbohydrate contents, respectively, on immediate postprandial energy metabolism at rest and during exercise. For instance, Efthimiou et al (9) found adverse effects of supplements on exercise performance. However, the energy content of the supplements was even higher than that of a normal meal and would therefore be difficult to incorporate into the daily pattern of meal consumption without affecting spontaneous food intake.
It is important in daily clinical practice to find out the optimal disease-related nutritional support strategy that improves muscle function but interferes minimally with symptoms and activity patterns. The first aim of the present study was therefore to examine the effects of liquid oral nutritional supplements with different, but clinically applicable, energy contents on symptoms and exercise capacity. The second aim was to compare the effects of a carbohydrate-rich with a fat-rich supplement, at the most optimal energy load, on symptoms and exercise capacity in patients with COPD.
SUBJECTS AND METHODS
Study population
The study group consisted of patients with COPD participating in an inpatient pulmonary rehabilitation program. The patients were in clinically stable condition; patients with signs of an airway infection were excluded. Other exclusion criteria were cardiovascular, neurologic, or endocrine diseases or locomotor limitations and a resting arterial oxygen tension <7.3 kPa, or the need for oxygen supplementation. In part 1, 14 patients (10 men) and in part 2, 11 patients (9 men) participated in and completed the study. Patient characteristics are summarized in Table 1. No subject participated in both studies. All subjects were fully informed of the aims and the procedures of the study and gave written informed consent. The ethical committee of Maastricht University approved the study. The procedures followed were in accord with the Helsinki Declaration of 1977, as revised in 1983.
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TABLE 1. Physiologic, pulmonary, and metabolic characteristics of the study group1
Study design
The first aim of the study was to test the effects of 2 different clinically applicable energy loads (1046 and 2092 kJ compared with placebo) on symptoms, lung function, and exercise capacity (part 1). Second, the effects of a high-carbohydrate compared with a high-fat supplement on symptoms, lung function, and exercise capacity were investigated at the most optimal energy load (1046 kJ) (part 2). The nutritional supplements were administered in a randomized, double-blind, crossover fashion. The composition of the nutritional supplements, which were given as drinks with an equal volume of 200 mL, are shown in Table 2. The placebo was a mixture of coffee creamer and lemon syrup with an energy load of 209 kJ. There was not more than 1 d between the study days. The measurements were done within 2 wk after the patients completed an incremental bicycle ergometer test. The administration of medication was standardized on the study days. Also, a breakfast with the same composition was given every study day at the same time (0730). The study design for both studies is shown in Figure 1.
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TABLE 2. Energy profile and composition of the different supplements
FIGURE 1. . Study design. VAS, visual analogue scale;
Part 1
The experiment started 2 h after breakfast at 0930. Patients had to ingest the supplement in 15 min. Fifteen minutes after the supplement was consumed pulmonary function was measured and 30 min after the supplement was finished the exercise test began.
Part 2
The procedure followed in part 2 was exactly the same as that in part 1, except that blood glucose was analyzed as well. Furthermore, the patients had to ingest the supplement in 5 min because differences in gastric emptying might have influenced the results if patients drank the supplements at different speeds.
Assessments
Pulmonary function
The flow-volume curve was measured by using a flow screen (Masterlab; Jaeger, Wurzburg, Germany). Forced expiratory volume in 1 s, inspiratory vital capacity, forced vital capacity, mean expiratory flow, and peak expiratory flow were calculated from the flow-volume curve. The highest value of 3 measurements was used for analysis. The values were expressed as a percentage of the reference value (12).
Symptoms
Using a visual analogue scale, the patients reported the following symptoms: shortness of breath, satiety, and pain in the legs. The severity of the symptoms was assessed before and after administration of the supplements and before and after the exercise test. The symptom of pain in the legs was scored only before and after the exercise test.
Oxygen saturation
During the study, transcutaneous oxygen saturation was measured with a pulse oxymeter. The electrode was placed around a finger of the left hand of the subject. Measurements were done with an SaO2 monitor (Fastrac; Sensormedics, Anaheim, CA), which is attached to a printer that automatically registers the lowest measured oxygen saturation value every minute.
Submaximal cycle ergometer test
Submaximal exercise testing was performed on an electrically braked cycle ergometer (Examiner 400; Lode, Groningen, Netherlands). Patients began to exercise at 50% of the maximal cycled load (Wmax) for 10 min. When the patients had performed this exercise, the workload was increased to 70% of Wmax (13). The patient cycled as long as possible but for a maximum of 30 min. Mechanical efficiency was calculated by using this submaximal exercise testing protocol. The maximal endurance time was also noted. The mean values of oxygen consumption (
Metabolic and ventilatory variables were measured in expired air by using a breathing mask (Oxycon Beta; Jaeger, Wurzburg, Germany). The device was calibrated before each test. Simultaneously, heart rate was registered every minute by using a sport tester (PE 3000; Polar Electro Oy, Kempele, Finland).
Biochemical variables
A venous blood sample was taken to measure plasma lactate concentration. Blood was collected in a vacuum tube (Vacutainer; Becton Dickinson, Franklin Lakes, NJ). The blood samples were stored on ice (4°C) and centrifuged for 5 min at 3120 x g (Sigma 2-15; Lameris, Breukelen, Netherlands). Plasma lactate concentration was determined by an enzymatic method with use of an automated system (Cobas Mira; Roche, Basel, Switzerland). Plasma lactate was measured at rest, every 2 min during exercise, and once during recovery (2 min after completion of the test). In part 2, a venous catheter was placed in the forearm to obtain venous blood samples. These venous blood samples were analyzed for glucose concentration to monitor gastric emptying and lactate concentration indirectly.
Statistics
The data were analyzed to evaluate the effects of the nutritional supplements on pulmonary function and to examine the endurance and the metabolic, cardiovascular, and subjective responses to exercise. The mean response of
RESULTS
Part 1
Comparison of lung function before and after supplement ingestion showed no negative effects on pulmonary function (data not shown). The time course of
FIGURE 2. . Mean (±SEM) response of oxygen consumption (
There was a clear effect of the different energy loads on RQ. At rest at 60 min postingestion, RQ was significantly higher after the 1046-kJ and 2092-kJ supplements than after the placebo (0.87 ± 0.05, 0.89 ± 0.05, and 0.84 ± 0.04, respectively). During exercise, RQ remained significantly elevated after the 1046-kJ and 2092-kJ supplements compared with the placebo. At 50% of Wmax, RQ after the 2092-kJ supplement was significantly higher than the RQ after the 1046-kJ supplement, as shown in Figure 2.
The effect on VE was less apparent, but after 50 min, VE was significantly elevated after the 2092-kJ supplement compared with the placebo (14.1 ± 2.1 and 12.7 ± 2.4 L/min, respectively; P = 0.01). During exercise, however, there was no difference in VE among the 3 supplements. The heart rate after the 2092-kJ supplement was significantly different from that after the placebo at 40 and 50 min postingestion, as shown in Figure 2. There were no significant differences during the exercise test.
The changes in oxygen saturation were small, but significant, at 10 and 30 min after ingestion of the 1046-kJ (93.8 ± 1.9% and 94.1 ± 1.6%; P < 0.05) and 2092-kJ (93.6 ± 1.6%; P < 0.01; 94.2 ± 1.4%; P < 0.05) supplements, respectively, compared with placebo. There were no differences in lactate concentrations during the experiment among the 3 supplements. Also, the relative increase in lactate was not significantly different among the placebo, and 1046-kJ and 2092-kJ supplements (107 ± 73%, 104 ± 89%, and 108 ± 95%, respectively).
From the symptoms assessed by visual analogue scale, the change in satiety after the supplements was significantly different for the 2092-kJ supplement than after the placebo, as shown in Figure 3. The symptoms shortness of breath, fatigue, and pain in the legs did not change during the experiment.
FIGURE 3. . Difference between the mean (±SEM) post- and preprandial satiety score on a visual analogue scale (VAS) 30 and 60 min after consumption of placebo (), a 1046-kJ supplement (), and a 2092-kJ supplement (). n = 14. 2092-kJ supplement significantly different from placebo at 30 min, P < 0.05 (ANOVA with postprandial value as the dependent variable, with treatment and period as fixed factors, and with patient as a random factor; the Tukey test was performed post hoc.)
The differences in the mean duration of the exercise test after the 3 supplements were small and insignificant. There were insignificant differences in mechanical efficiency after the 3 supplements.
There were 3 patients who were not able to cycle 5 min at 50% of Wmax after the 2092-kJ supplement. The endurance time was dramatically lower in these outliers than in the other 11 patients, as shown in Figure 4. A low body mass index (18.9 ± 1.7), low fat-free-mass index (fat-free mass divided by height2: 14.7 ± 0.5), low maximal exercise performance (49 ± 3 W), and low mechanical efficiency characterized these patients.
FIGURE 4. . Kaplan-Meier plot of endurance time during submaximal cycle ergometry after consumption of placebo (solid line), a 1046-kJ supplement (dashed line), and a 2092-kJ supplement (dotted line). Upper panel: total group - outliers (n = 11); lower panel: outliers (n = 3).
Part 2
Pulmonary function before and after ingestion of the supplements is shown in Table 3. Comparable with part 1, there were no negative effects of the supplements on pulmonary function. Peak expiratory flow increased significantly after the carbohydrate-rich supplement compared with baseline and compared with after the fat-rich supplement.
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TABLE 3. Pulmonary function before and after consumption of the supplements in part 2 of the study1
The courses of
FIGURE 5. . Mean (±SEM) response of oxygen consumption (
There were no significant differences in heart rate after the carbohydrate-rich and fat-rich supplements. Blood saturation seemed slightly lower after the carbohydrate-rich supplement, and was significantly so 10 and 15 min after ingestion (P < 0.05). However, on average, the slightly lower saturation after the carbohydrate-rich supplement was not clinically significant (ie, a drop in oxygen saturation >4%).
Lactate concentration was significantly different at the start of the exercise test between patients consuming the carbohydrate-rich and fat-rich supplements: 1.7 ± 0.3 and 1.3 ± 0.2 mmol/L, respectively (P < 0.05). The relative increase in lactate was not significantly different after the 2 supplements.
Blood glucose concentration was measured during the whole experiment. At rest, blood glucose increased significantly after ingestion of the carbohydrate-rich supplement. The highest blood glucose value was at 30 min after ingestion ( glucose: 2.6 mmol/L, range: -0.2 to 5.5 mmol/L). At the start of the exercise test, blood glucose was not significantly different between subjects who consumed the carbohydrate-rich and the fat-rich supplement (5.7 ± 1.3 and 5.3 ± 0.7 mmol/L, respectively). During the exercise test, blood glucose concentration was not significantly different for the 2 supplements.
There were no significant differences in the mean duration of the exercise test after the carbohydrate-rich and fat-rich supplements (12.6 ± 7.2 and 13.1 ± 7.1 min, respectively). Also, the mechanical efficiency after the 2 supplements was not significantly different (20.0 ± 5.8% and 19.8 ± 5.9%, respectively).
The symptoms satiety, fatigue, and pain in the legs did not change significantly during the experiment after ingestion of the supplement. Only the symptom shortness of breath changed: there was a significantly greater increase in dyspnea after ingestion of the fat-rich supplement than after the carbohydrate-rich supplement, as shown in Figure 6.
FIGURE 6. . Difference between mean (±SEM) post- and preprandial shortness of breath score on a visual analogue scale (VAS) 30 and 60 min after consumption of a fat-rich () and a carbohydrate-rich () supplement. n = 11. ANOVA with postprandial value as the dependent variable, with treatment and period as fixed factors, and with patient as a random factor.
DISCUSSION
Nutritional supplements are needed in some COPD patients to reverse weight loss or to improve nutritional status. In contrast with a long-held belief, the present investigation did not show significant adverse effects of the studied nutritional supplements on the ventilatory system. Remarkably, there were even positive effects of a carbohydrate-rich supplement relative to those of a fat-rich one at a relatively low energy content, as will be discussed below.
In the first part of the study, we evaluated the most optimal energy load to be given as a supplement between regular meals. As expected, relative to the 1046-kJ supplement, the metabolic and ventilatory response at rest was significantly higher after the 2092-kJ supplement. During exercise, this difference was eliminated. For the total group, there were no differences in exercise endurance capacity. Satiety, however, was clearly greater after the 2092-kJ supplement, which might interfere with a normal meal pattern. Another remarkable observation was the strikingly reduced endurance capacity of 3 patients after the 2092-kJ supplement, whereas no difference was seen between the placebo and the 1046-kJ supplement. Although this phenomenon was observed in only a few patients, these results are important to consider because this subgroup was characterized by a low body mass index and fat-free-mass index, low maximal exercise capacity, and low mechanical efficiency. One potential cause could be an increased oxygen cost of breathing because Mannix et al (15) recently reported a significant inverse relation between body mass index and the oxygen cost of breathing in COPD. Furthermore, we showed in a previous study a significantly elevated ratio of VE to
The RQ was indeed higher after the carbohydrate-rich supplement, but this was not due to an increased
The absence of adverse effects of nutritional supplements was also indirectly confirmed in previous studies that showed positive effects of 2–3 nutritional supplements (1046 kJ) as an integrated part of pulmonary rehabilitation on weight, fat-free mass, muscle function, and exercise capacity. Future studies using nuclear magnetic resonance or muscle biopsies might investigate the suggested specific effects of carbohydrates alone or combined with specific bioactive nutrients on oxidative muscle metabolism.
In conclusion, a liquid oral nutritional supplement with an energy content of 1046 kJ is preferable to an energy load of 2092 kJ because after the smaller load there was a better metabolic and ventilatory response and less satiety. Also, the carbohydrate-rich supplement was preferable to the fat-rich supplement because lung function increased and there was less shortness of breath.
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