Effects of a Single Dose of BURN-XT™ on Resting Metabolic Rate, Substrate Oxidation, and Various Indices of Affect

Introduction: Many consumers use dietary supplements in the hopes of increasing energy and burning more calories, which if sustained over time may help accelerate weight loss. The purpose of this clinical trial was to investigate the effects of an over-the-counter thermogenic supplement called Burn-XT™ (BXT) on metabolic rate, substrate oxidation, and various psychometric indices of affect that impact weight management. Methods: Using a double-blind, placebo-controlled, cross-over design, 16 women and 10 men (29.3 ± 7.3 yr, 169.4 ± 8.6 cm, 75.5 ± 14.3 kg) underwent two testing sessions: placebo (PL) and BXT. Seated metabolic rate and substrate oxidation, vital signs, and anchored visual analogue scale (VAS) assessments of energy, mood, motivation, focus, fatigue, concentration, and appetite were made before supplementation and hourly for three hours post-ingestion. Two-factor (2x4) factorial ANOVAs and paired sample t-tests (corrected for multiple comparisons) were used for analyses. Results: Significant increases in metabolic rate (oxygen consumption) were noted at 60 minutes in BXT (+11.9 mL O2/min) vs. PL (-2.5 mL O2/min), p = 0.004, d = -0.74. Only BXT increased metabolic rate compared to baseline at 60 minutes (+11.9 mL O2/min, p = 0.021, d = -0.53) and 120 minutes (+12.1 mL O2/min, p = 0.019, d = -0.54). The AUC for resting energy expenditure increased more in BXT vs. PL (p = 0.007, d = -0.57). VAS detected significant improvements in energy, mood, focus, and concentration for BXT vs. PL at 120 and 180 minutes (all p < 0.05, d = -0.58 to -0.68). In all cases, within-group changes from baseline for these VAS parameters were significant (all p < 0.05, d = -0.76 to -1.38) in BXT but not in PL. No within or between group differences in appetite, substrate oxidation, or heart rate were noted. Small (~3-4 mm Hg), but statistically significant (p < 0.05, d = -0.51 to -0.69) increases in diastolic blood pressure were noted in BXT at 60, 120, and 180 min vs. PL; and in systolic blood pressure at 60 min vs. PL. In all cases, values remained within normal clinical hemodynamic ranges. Conclusions: A single dose of BXT safely increased metabolic rate, energy, mood, focus, and concentration. Given that these factors are known to favorably impact weight management, future studies should determine whether daily supplementation with BXT reduces body weight and improves body composition.

Influence of fat-free mass and resting metabolic rate on increased food reinforcement after exercise training

Purpose Models of appetite control have been largely based on negative feedback from gut and adipose signaling to central appetite centers. However, contemporary models posit that fat-free mass (FFM) or the energy demand of FFM [i.e., resting metabolic rate (RMR)] may play a primary role in the motivational drive for food intake (i.e., food reinforcement). The relative reinforcing value of food (RRVfood) is associated with energy intake (EI) and increases with an acute energy deficit. Chronic exercise-induced energy deficits lead to alterations in fat mass (FM), FFM, and RMR and provide an opportunity to test whether change in (∆) FM, ∆FFM, ∆usual EI, or ∆RMR are associated with ∆RRVfood. Methods Participants (n = 29, BMI = 25–35 kg/m2) engaged in aerobic exercise expending 300 or 600 kcal, 5 days/weeks for 12 weeks. The reinforcing value of food (PMaxfood) was measured via a computer-based operant responding task and RRVfood was calculated as the reinforcing value of food relative to non-eating sedentary behaviors. RMR was determined by indirect calorimetry and body composition by DXA. Results Post-training FFM correlated with usual post-training EI (rs = 0.41, p < 0.05), PMaxfood (rs=0.52, p < 0.01), and RMR (rs = 0.85, p < 0.0001). ∆RMR negatively correlated with ∆PMaxfood (rs = − 0.38, p < 0.05) and with ∆RRVfood (rs = − 0.37, p < 0.05). ∆PMaxfood and ∆RRVfood were not associated with ∆FFM (p = 0.71, p = 0.57, respectively). Conclusions Reductions in RMR with weight loss may increase food reinforcement as means of restoring FFM and RMR to pre-weight loss amounts. Limiting reductions in RMR during weight loss may benefit weight maintenance by restricting increases in food reinforcement after weight loss.

Efficient Evaporative Cooling and Pronounced Heat Tolerance in an Eagle-Owl, a Thick-Knee and a Sandgrouse

Avian evaporative cooling and the maintenance of body temperature (Tb) below lethal limits during heat exposure has received more attention in small species compared to larger-bodied taxa. Here, we examined thermoregulation at air temperatures (Tair) approaching and exceeding normothermic Tb in three larger birds that use gular flutter, thought to provide the basis for pronounced evaporative cooling capacity and heat tolerance. We quantified Tb, evaporative water loss (EWL) and resting metabolic rate (RMR) in the ∼170-g Namaqua sandgrouse (Pterocles namaqua), ∼430-g spotted thick-knee (Burhinus capensis) and ∼670-g spotted eagle-owl (Bubo africanus), using flow-through respirometry and a stepped Tair profile with very low chamber humidities. All three species tolerated Tair of 56–60°C before the onset of severe hyperthermia, with maximum Tb of 43.2°C, 44.3°C, and 44.2°C in sandgrouse, thick-knees and eagle-owls, respectively. Evaporative scope (i.e., maximum EWL/minimum thermoneutral EWL) was 7.4 in sandgrouse, 12.9 in thick-knees and 7.8 in eagle-owls. The relationship between RMR and Tair varied substantially among species: whereas thick-knees and eagle-owls showed clear upper critical limits of thermoneutrality above which RMR increased rapidly and linearly, sandgrouse did not. Maximum evaporative heat loss/metabolic heat production ranged from 2.8 (eagle-owls) to 5.5 (sandgrouse), the latter the highest avian value yet reported. Our data reveal some larger species with gular flutter possess pronounced evaporative cooling capacity and heat tolerance and, when taken together with published data, show thermoregulatory performance varies widely among species larger than 250 g. Our data for Namaqua sandgrouse reveal unexpectedly pronounced variation in the metabolic costs of evaporative cooling within the genus Pterocles.

The Effects of Omega-3 Supplementation on Resting Metabolic Rate: A Systematic Review and Meta-Analysis of Clinical Trials

Background. It is uncertain if omega-3 polyunsaturated fatty acids are associated with increase in resting metabolic rate (RMR) in adults. Objective. The aim of the present study was to evaluate the overall effects of omega-3 on RMR. Methods. Both PubMed and Scopus libraries were searched up to April 2021. Study quality was assessed using the Jadad scale. Random- and fixed-effects models were utilized in order to obtain pooled estimates of omega-3 supplementation impacts on RMR, using weight mean difference (WMD). Results. Seven studies including a total of 245 participants were included. There was significantly higher FFM-adjusted RMR in the intervention group than the control group (WMD: 26.666 kcal/kg/day, 95% CI: 9.010 to 44.322, p = 0.003 ). Study quality showed that four of seven included studies were of high quality. However, there was no significant difference in results in the subgroup analysis according to the quality of studies. Subgroup analyses revealed significant changes for sex (for women: WMD = 151.793 kcal/day, 95% CI = 62.249 to 241.337, p = 0.001 ) and BMI (for BMI > 25: WMD = 82.208 kcal/day, 95% CI = 0.937 to 163.480, p = 0.047 ). Influence analysis indicated no outlier among inclusions. Conclusion. The current study depicted that omega-3 polyunsaturated acids can significantly increase RMR in adults. However, further assessments of omega-3 supplementation therapy are critical to monitor its long-term outcomes and potential clinical application.

Reliability of resting metabolic rate between and within day measurements using the Vyntus CPX system and comparison against predictive formulas

Background: To detect longitudinal changes of resting metabolic rate (RMR) resulting from the effects of energetic stress, reliable RMR measurements are crucial. The Vyntus CPX is a new automated indirect calorimetry system for which RMR reliability has not been determined. Additionally, its agreement with common predictive RMR formulas is unknown. Aim: To determine the within and between-day reliability of RMR measurements using the Vyntus CPX system and its agreement with predictive RMR formulas. Methods: Young (31 ± 7 years) healthy participants (n = 26, 12 females, 14 males) completed three measurements of RMR, two consecutive measures on the same day, one the day before/after, all under standardised conditions. Reliability was assessed with pairwise comparisons of between-day at the same time (BDST), within day consecutive measurements (WDCM) and between-day different time (BDDT), for parameters of reliability (mean change (MC), intraclass correlation (ICC) and typical error of measurement (TEM)). Measured RMR values (kcal/day) were compared against predictive values of 4 common formulas. Results: Parameters of reliability (mean, (95% confidence interval)) were: -BDST: MC, 0.2(-2.3—2.7)% (p = 0.67); ICC, 0.92(0.84—0.97); TEM, 4.5(3.5—6.2)%. -WDCM: MC, −2.5(-6.2—1.3)% (p = 0.21); ICC, 0.88(0.74—0.88); TEM, 7.0(5.4—9.8)%. -BDDT: MC, −1.5(-4.8—1.9)% (p = 0.57); ICC, 0.90(0.76—0.95); TEM, 6.1(4.8—8.5)%. RMRratios (measured/predicted) were: 1.04 ± 0.14 (Nelson, p = 0.13), 1.03 ± 0.10 (Mifflin, p = 0.21), 0.98 ± 0.09 (Harris-benedict, p = 0.30), 0.95 ± 0.11 (Cunningham1980, p = 0.01), 1.00 ± 0.12 (Cunningham1991, p = 0.90) and 0.96 ± 0.13 (DXA, p = 0.03). Conclusions: The Vyntus CPX is reliable and measured RMR values agreed with four predictive formulas but are lower than Cunningham1980 and DXA RMR estimates for this population.

The Association of Gut Microbiota with Resting Metabolic Rate in Overweight/Obese Women: A Case-Control Study

Purpose Low Resting Metabolic Rate (RMR), as a risk factor for obesity, can be affected by many factors. Indeed, genetic and environmental factors are variables taken into account when predicting RMR, and may contribute to a high inter-individual variance. Besides the well-known causes of obesity, researchers have demonstrated the contribution of gut microflora in obesity and energy expenditure. Therefore, the goal of the current study was to compare the Firmicutes/Bacteroidetes ratio and the relative abundance of, Prevotellaceae, Faecalibacterium prausnitzii, bifidobactrium spp, lactobacillus spp, Akkermansia muciniphila, Bacteroides fragilis, and Escherichia coli in two groups of people with normal and low RMR in overweigh/obese women in Iran. Results The abundance of F. prausnitzii (p>0.001), B. fragilis (P= 0.02), and Firmicutes phylum (P= 0.02) were significantly higher in the controls compared to the cases, and showed significant positive association with RMR, (β = 1.29 ×10−5, P=0.01), (β = 4.13 ×10−6, p= 0.04), and (β = 7.76 ×10−1, p= 0.01), respectively. Regarding Lactobacilus, the results showed a significant positive association with RMR (β = 1.73 ×10−4, p= 0.01). Conclusion Intestinal microbiota may be associated with host metabolism. Therefore, future work should investigate, using clinical trials, the impact of manipulating gut microflora to positively influence energy expenditure.

Association of major dietary patterns with resting metabolic rate and body fatness in middle-aged men and women: Results from a cross-sectional study

Background: The association of dietary patterns and resting metabolic rate is still unclear. Aim: To study the relationship between the major dietary patterns, resting metabolic rate, and adiposity measures in Iranian adults. Methods: This is a cross-sectional study of 270 adults aged between 18–45 years old who lived in Tehran. Dietary intakes were achieved using food frequency questionnaire. Resting metabolic rate was measured using indirect calorimetry. Anthropometric measures were recorded using body composition analyzer. Results: Three major dietary patterns were identified by factor analysis labeled as healthy pattern (vegetables, fruits, and fruits juices, legumes, poultry, nuts, fish, egg, low fat dairy product, olive, and olive oil), mixed pattern (non-refined cereals, vegetables, vegetable oils, mayonnaise, high fat dairy product and, pickles), Western pattern (refined cereals, red or processed meat, soft drinks, sweets and desserts, Tea and coffee, salty snacks and French fries). After adjusting for covariates higher score of the Western dietary pattern was associated with lower resting metabolic rate ( p = 0.023). There was significant decreasing difference in means for fat free mass across tertiles of mixed pattern when the first tertile was compared to the third tertile ( p = 0.046). Higher adherence to healthy pattern was associated with lower body weight ( p = 0.034), body mass index ( p = 0.021), and higher resting metabolic rate ( p = 0.033). Conclusions: Higher adherence to the Western dietary pattern was associated with a lower amount of resting metabolic rate. Also higher adherence to the healthy dietary pattern was associated with higher resting metabolic rate and lower body weight and body mass index. Further studies are required to examine the causal relationship between dietary patterns and resting metabolic rate.

Correlation between Metabolic Rate and Salinity Tolerance and Metabolic Response to Salinity in Grass Carp (Ctenopharyngodon idella)

The metabolic rate could be one of the factors affecting the salinity tolerance capacity of fish. Experiment I tested whether metabolic rates correlate with the upper salinity tolerance limit among individual grass carp by daily increasing salinity (1 g kg−1 day−1). The feeding dropped sharply as the salinity reached 10 g kg−1 and ceased when salinities exceeded 11 g kg−1. The ventilation frequency decreased weakly as salinity increased from 0 to 12 g kg−1 and then increased rapidly as salinity reached 14 g kg−1. The fish survived at salinities lower than 14 g kg−1, and all fish died when salinity reached 17 g kg−1. The upper salinity tolerance limit was not correlated with metabolic rates. Therefore, a lower metabolic rate may not necessarily allow for better salinity tolerance capacity. Experiment II tested how different salinities (0, 0.375, 0.75, 1.5, 3, and 6 g kg−1 for 2 weeks) affect the metabolic parameters of grass carp. The changes in the resting metabolic rate with increasing salinity could be explained by the relative changes in interlamellar cell mass and protruding lamellae. The maximum metabolic rate remained constant, suggesting that the salinity-induced changes in the gill surface had a minor effect on oxygen uptake capacity.