Thermic effect of a meal. 2. Role in chronic undernutrition

Changes in energy expenditure associated with ingestion of high protein, high fat versus high protein, low fat meals among underweight, normal weight, and overweight females

Background

Metabolic rate is known to rise above basal levels after eating, especially following protein consumption. Yet, this postprandial rise in metabolism appears to vary among individuals. This study examined changes in energy expenditure in response to ingestion of a high protein, high fat (HPHF) meal versus an isocaloric high protein, low fat (HPLF) meal in underweight, normal weight, or overweight females (n = 21) aged 19–28 years.

Methods

Energy expenditure, measured using indirect calorimetry, was assessed before and every 30 minutes for 3.5 hours following consumption of the meals on two separate occasions. Height and weight were measured using standard techniques. Body composition was measured using bioelectrical impedance analysis.

Results

Significant positive correlations were found between body mass index (BMI) and baseline metabolic rate (MR) (r = 0.539; p = 0.017), between body weight and baseline MR (r = 0.567; p = 0.011), between BMI and average total change in MR (r = 0.591; p = 0.008), and between body weight and average total change in MR (r = 0.464; p = 0.045). Metabolic rate (kcal/min) was significantly higher in the overweight group than the normal weight group, which was significantly higher than the underweight group across all times and treatments. However, when metabolic rate was expressed per kg fat free mass (ffm), no significant difference was found in postprandial energy expenditure between the overweight and normal groups. Changes in MR (kcal/min and kcal/min/kg ffm) from the baseline rate did not significantly differ in the underweight (n = 3) or in the overweight subjects (n = 5) following consumption of either meal at any time. Changes in MR (kcal/min and kcal/min/kg ffm) from baseline were significantly higher in normal weight subjects (n = 11) across all times following consumption of the HPHF meal versus the HPLF meal.

Conclusion

There is no diet-induced thermogenic advantage between the HPHF and HPLF meals in overweight and underweight subjects. In contrast, in normal weight subjects, ingestion of a HPHF meal significantly increases MR (69.3 kcal/3.5 hr) versus consumption of a HPLF meal and provides a short-term metabolic advantage.

Consequences of inadequate food energy and negative energy balance in humans

Energy deficiency is probably best measured in adults by the body mass index (BMI). Acute energy deficiency (AED) is associated with body weight loss, along with changes in body composition, as well as a reduced BMR and physical activity. Chronic energy deficiency (CED) is an inadequacy in food to which individuals adapt, at some cost. Individuals with this have never 'lost' weight: they have simply grown less. They adapt to the decreased food energy by reductions in their total energy expenditure (TEE), linked mainly to a lower body size, and to their physical activity. It seems unlikely that enhanced metabolic efficiency contributes substantially to energy saving in CED. Supplementation of energy deficient individuals is accompanied by significant fat deposition; this may have deleterious consequences. Women in many developing countries achieve a successful outcome to pregnancy in spite of being chronically undernourished. Reductions in basal metabolism and behavioural changes in the form of diminished physical activity could meet most of the extra energy needed for pregnancy. Milk energy output is maintained within the expected range in undernourished lactating mothers. Energy deficiency in children is best measured by height-for-age for stunting, and weight-for-height for wasting. Deficits in behavioural and functional parameters in children exist with undernutrition, and can be reduced by early nutritional supplementation along with the appropriate environment.

Fasting in healthy individuals and adaption to undernutrition during chronic disease

During long-term fasting, gluconeogenesis from amino acids was thought to lessen, when ketone bodies from lipolysis became a major fuel source. Thus, muscle mass is conserved. However, recent studies show that this adaptation does not occur in chronic undernourishment. In cancer, chronic undernutrition without disease, and HIV infection, carbohydrate utilization is high. Enhanced hepatic glucose production occurs in active inflammatory bowel disease and in underweight cancer patients. Repletion of tissue after undernutrition is energetically inefficient because of enhanced diet induced thermogenesis (following anorexia nervosa) and decreased fat, and increased protein, oxidation (in tuberculosis).

Dynamic aspects of oxygen consumption and carbon dioxide production in swine

A model is proposed that allows study of the short-term dynamics of gas exchanges (and heat production) in large open-circuit respiration chambers. The model describes changes in [O2] and [CO2] in the respiration chamber by a series of differential equations based on animal metabolism and physical characteristics of gas exchange. The model structure was similar for O2 and CO2, although model parameters differed. A constant level of O2 consumption (and CO2 production) was assumed for resting animals which was different for fed and fasted animals. The adaptation from a fed to a fasting state was described as a first-order process. Physical activity (standing or sitting) was recorded and was included in the model as a constant. Thermic effect of feed comprised the O2 consumption and CO2 production related to several relatively rapidly occurring processes after ingestion of a meal (e.g. ingestion, digestion or absorption). In the model, these processes were pooled into a single phenomenon. Model parameters were obtained statistically by comparing model predictions (based on the numerically integrated differential equations) with the observed [O2] and [CO2]. The model was evaluated by studying gas exchanges in growing pigs that were fasted for 31 h and re-fed a single meal thereafter. The model fitted the data well over the 47 h measurement range-Traditional methods in which heat production is calculated suffer from noisy data when the interval between observations becomes too short. The proposed method circumvents this by modelling the observed concentration of gases in the respiration chamber rather than the calculated heat production.

Adaptive changes in energy expenditure during mild and severe feed restriction in the rat

Using a new-generation open-circuit calorimeter capable of monitoring the cost of activity, and thereby both the real thermic effect of feeding (TEF) and basal metabolism in free-moving freely-feeding rats, we have reassessed the proposal that when food intake is restricted an adaptative reduction in energy expenditure participates in the achievement of energy balance. Total energy expenditure, energy expenditure due to spontaneous activity, TEF, basal energy expenditure and respiratory quotient (RQ) were computed by indirect calorimetry in rats given either a mildly restricted (MR) feed intake for 20-30 d (17 g feed/d) or a severely restricted (SR) feed intake for 1-10 d (4 g feed/d). In MR rats no significant changes in any of the measured variables were observed. In contrast, SR rats exhibited an adaptative reduction in energy expenditure due to a reduced spontaneous activity and probably also due to a reduced basal energy expenditure. On the other hand none of the animals fed on a restricted feed intake showed an adaptative TEF decrease, suggesting that TEF under ad lib. feeding is rather an obligatory process that does not include an adaptative component. Taken together, these results point out that under restricted feeding most of the decrease in energy expenditure is associated with simple passive mechanisms, such as body weight loss, and with the reduced feed intake per se. Only under severe feed restriction can some additional energetic economy be obtained from a possible reduction of basal metabolism, and to some extent from reduced activity.

Energy balance in stable malnourished patients with chronic obstructive pulmonary disease

We have measured caloric intake, energy expenditure, and the thermogenic effect of food in ten patients with stable COPD who had a history of involuntary weight loss over several years and were malnourished (< 85 percent ideal body weight). Each patient completed a 7-day food record. Indirect calorimetry was performed in the resting postabsorptive state. After placement of a nasoenteric tube, patients were randomly assigned to be refed or sham-fed (mean +/- SD, 16 +/- 3 days), following which, metabolic measurements were repeated. Indirect calorimetry was also performed before and after a large meal in each patient. Home caloric intake was 135 +/- 23 percent of resting energy expenditure. Resting energy expenditure was 94 +/- 16 percent of that predicted by the Harris-Benedict equation and did not change significantly during inpatient refeeding. Refeeding resulted in weight gain (2.4 +/- 1.9 kg, p < 0.02). A large meal caused substantial increases in energy expenditure (24 +/- 18 percent), carbon dioxide production (39 +/- 18 percent), and oxygen consumption (23 +/- 16 percent). We conclude that stable malnourished COPD patients consume adequate calories to meet average energy requirements and are not hypermetabolic. Inpatient refeeding by nocturnal nasoenteric infusion is well tolerated and results in weight gain, but the thermogenic effect of a large meal poses a considerable metabolic and ventilatory load that could precipitate acute respiratory failure.

Energy supplementation reverses changes in the basal metabolic rates of chronically undernourished individuals

The objective of the present study was to examine the influence of energy supplementation and its cessation thereafter on the basal metabolic rates (BMR) of chronically undernourished individuals. Seven apparently healthy males were supplemented daily with 3.35 MJ (15 g protein, 35 g fat, 105 g carbohydrate) for 12 weeks. The average gain in body-weight was 1.9 kg (body fat, 58%; fat-free mass (FFM), 42%). The rise in BMR exceeded that accounted for by the increases in FFM during the 12 weeks of supplementation and was attributed to increases in the amount and activity of the visceral tissue as well as to an added cost of lipogenesis. At 12 weeks after cessation of the supplement, body-weights and FFM had decreased to presupplementation levels. BMR at this stage were significantly lower than at the 12th week of supplementation, when expressed per kg FFM or when adjusted for FFM using an analysis of covariance. These results suggest an increase in the metabolic efficiency during this negative energy balance period. The study demonstrates that, in the chronically undernourished, the changes in BMR are reversible and, hence, physiologically important to the process of adaptation to low-energy intakes.

Thermic effect of a meal. 3. Effect of dietary supplementation in chronically undernourished human subjects

Five apparently healthy, chronically undernourished (UN) male volunteers aged between 18 and 30 years were studied before and after 12 weeks of dietary supplementation. The thermic effect of a meal (TEM) was measured over a period of 6 h using a ventilated-hood system. Results indicated a significant increase in body-weight after supplementation due to increases in body fat and fat-free mass (FFM) in the proportion of 69% and 31% respectively. The basal metabolic rates (BMR) measured post supplementation were significantly higher in absolute terms, with a trend towards higher values when adjusted for the changes in FFM. TEM responses measured after 12 weeks of supplementation were significantly lower when expressed either in absolute terms (presupplementation 227.0 kJ v. post supplementation 193.5 kJ), or as a percentage of the energy density of the meal (9.1% v. 7.7%). This lower TEM was reciprocal to the changes in the BMR (r -0.86). The post-meal total energy output (PMTEO) was, however, not significantly different after 12 weeks of dietary supplementation. The unchanged PMTEO would indicate an unaltered 'thermogenic capacity', following supplementation, in these chronically undernourished subjects. These results confirm our earlier conclusion that, in chronic undernutrition, the thermic response to a meal may not contribute to any energy saving.