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Does Caffeine Increase Fat Metabolism? A Systematic Review and Meta-Analysis

Scott A. Conger, Lara M. Tuthill, and Mindy L. Millard-Stafford

metabolism; although, this does not rule out the possibility that fat metabolism is augmented with CAF. A recent meta-analysis on 19 studies ( Collado-Mateo et al., 2020 ) indicated CAF increased fat metabolism during exercise based on whole-body gas exchange variables (e.g., respiratory exchange ratio [RER

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Impact of Polarized Versus Threshold Training on Fat Metabolism and Neuromuscular Variables in Ultrarunners

Andrés Pérez, Domingo J. Ramos-Campo, Cristian Marín-Pagan, Francisco J. Martínez-Noguera, Linda H. Chung, and Pedro E. Alcaraz

Interestingly, POL has shown to improve VO 2 peak, anaerobic threshold, aerobic efficiency, time to exhaustion during an incremental test, 14 finishing time in 10-km races, 13 and running economy in ultrarunners. 9 In addition, fat metabolism has a key role in endurance events. 15 The maximal fat oxidation

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Amino Acid Mixture Enriched With Arginine, Alanine, and Phenylalanine Stimulates Fat Metabolism During Exercise

Keisuke Ueda, Yutaka Nakamura, Makoto Yamaguchi, Takeshi Mori, Masayuki Uchida, and Satoshi Fujita

Although there have been many investigations of the beneficial effects of both exercise and amino acids (AAs), little is known about their combined effects on the single-dose ingestion of AAs for lipid metabolism during exercise. We hypothesize that taking a specific combination of AAs implicated in glucagon secretion during exercise may increase fat metabolism. We recently developed a new mixture, d–AA mixture (D-mix), that contains arginine, alanine, and phenylalanine to investigate fat oxidation. In a double-blind, placebo-controlled crossover study, 10 healthy male volunteers were randomized to ingest either D-mix (3 g/dose) or placebo. Subjects in each condition subsequently performed a physical task that included workload trials on a cycle ergometer at 50% of maximal oxygen consumption for 1 hr. After oral intake of D-mix, maximum serum concentrations of glycerol (9.32 ± 6.29 mg/L and 5.22 ± 2.22 mg/L, respectively; p = .028), free fatty acid level (0.77 ± 0.26 mEq/L and 0.63 ± 0.28 mEq/L, respectively; p = .022), and acetoacetic acid levels (37.9 ± 17.7 μmol/L and 30.3 ± 13.9 μmol/L, respectively; p = .040) were significantly higher than in the placebo groups. The area under the curve for glucagon during recovery was numerically higher than placebo (6.61 ± 1.33 μg/L • min and 6.06 ± 1.23 μg/L • min, respectively; p = .099). These results suggest that preexercise ingestion of D-mix may stimulate fat metabolism. Combined with exercise, the administration of AA mixtures could prove to be a useful nutritional strategy to maximize fat metabolism.

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Metabolic Flexibility During Exercise in Children with Overweight/Obesity Versus Children who are Lean

Brandon Dykstra, Dillon Kuszmaul, and Anthony D. Mahon

inflexibility has been associated with insulin resistance, type II diabetes, dyslipidemia, and obesity ( 18 , 19 ) and, thus, presents an area of health concern. Specifically, obesity has been shown to lead to impairments in MF with respect to both carbohydrate and fat metabolism ( 43 ). Different approaches

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The Acute Effects of Dairy Calcium Intake on Fat Metabolism during Exercise and Endurance Exercise Performance

Kimberly M. White, Roseann M. Lyle, Michael G. Flynn, Dorothy Teegarden, and Shawn S. Donkin

The purpose of this study was to test the effect of acute dairy calcium intake on exercise energy metabolism and endurance performance. Trained female runners completed two trials. Each trial consisted of a 90-min glycogen depletion run followed by a self-paced 10K time trial, conducted one hour after consumption of a high dairy (500 mg Ca+2) or low dairy (80 mg Ca+2) meal. During the 90-min run, blood samples and respiratory gases were collected. No treatment main effects of acute dairy intake were found for respiratory exchange ratio (RER), calculated fat oxidation, lactate, glycerol, or 10K time. Following this protocol, acute dairy calcium intake did not alter fat utilization or endurance performance in trained female runners.

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Carbohydrate, Protein, and Fat Metabolism during Exercise after Oral Carnitine Supplementation in Humans

Elizabeth M. Broad, Ronald J. Maughan, and Stuart D.R Galloway

Twenty nonvegetarian active males were pair-matched and randomly assigned to receive 2 g of L-carnitine L-tartrate (LC) or placebo per day for 2 wk. Participants exercised for 90 min at 70% VO2max after 2 days of a prescribed diet (M ±SD: 13.6 ± 1.6 MJ, 57% carbohydrate, 15% protein, 26% fat, 2% alcohol) before and after supplementation. Results indicated no change in carbohydrate oxidation, nitrogen excretion, branched-chain amino acid oxidation, or plasma urea during exercise between the beginning and end of supplementation in either group. After 2 wk of LC supplementation the plasma ammonia response to exercise tended to be suppressed (0 vs. 2 wk at 60 min exercise, 97 ± 26 vs. 80 ± 9, and 90 min exercise, 116 ± 47 vs. 87 ± 25 μmol/L), with no change in the placebo group. The data indicate that 2 wk of LC supplementation does not affect fat, carbohydrate, and protein contribution to metabolism during prolonged moderate-intensity cycling exercise. The tendency toward suppressed ammonia accumulation, however, indicates that oral LC supplementation might have the potential to reduce the metabolic stress of exercise or alter ammonia production or removal, which warrants further investigation.

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Aerobic Exercise Alters Postprandial Lipemia in African American versus White Women

Keith A. Shannon, Robynn M. Shannon, John N. Clore, Chris Gennings, Beverly J. Warren, and Jeffrey A. Potteiger


To determine whether ethnicity influences postprandial lipemia after a bout of aerobic exercise.


Randomized crossover design. Healthy White (W; n = 6) and African American (AA; n = 6) women (age, W 27.0 ± 3.3 yr, AA 21.6 ± 1.4 yr; body-mass index, W 25.0 ± 0.93 kg/m2, AA 25.8 ± 0.79 kg/m2) participated in 2 treatments (control and exercise), each conducted over 2 d. On d 1, participants rested (control) or walked at 60% of maximal oxygen uptake for 90 min (exercise) and then consumed a meal. On d 2, after a 12-hr overnight fast, participants consumed an oral fat-tolerance test (OFTT) meal of 1.7 g fat, 1.65 g carbohydrate, and 0.25 g protein per kg fat-free mass. Blood was collected premeal and at 0.5, 1, 2, 3, 4, 5, and 6 hr post-OFTT and analyzed for triacylglycerol (TAG), glucose, and insulin. Areas under the curve (AUCs) were calculated for each blood variable.


A significantly lower TAG AUC was observed for AA (0.86 ± 0.24 mmol · L−1 · 6 hr−1) after exercise than for W (2.25 ± .50 mmol · L−1 · 6 hr−1). Insulin AUC was significantly higher for AA after exercise (366.2 ± 19.9 mmol · L−1 · 6 hr−1) than for the control (248.1 ± 29.2 mmol · L−1 · 6 hr−1).


The data indicate that exercise performed ~13 hr before an OFTT significantly reduces postprandial lipemia in AA compared with W. It appears that AA women have an increased ability to dispose of TAG after exercise and a high-fat meal.

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Increased Meal Frequency With Exercise Mitigates Postprandial Triacylglycerol

Jesudas E. Menon, David J. Stensel, Keith Tolfrey, and Stephen F. Burns

Purpose: This study examined how manipulating meal frequency, with and without exercise, affects postprandial triacylglycerol (TAG). Methods: Fourteen sedentary men completed four 2-day trials in a noncounterbalanced random cross-over order: (1) consumption of 1 large high-fat milkshake without exercise (1-CON), (2) consumption of 2 smaller high-fat milkshakes without exercise (2-CON), (3) consumption of 1 large high-fat milkshake with exercise (1-EX), and (4) consumption of 2 small high-fat milkshakes with exercise (2-EX)—total energy intake was standardized across trials. On day 1, participants rested (1-CON and 2-CON) or walked briskly for 60 minutes (1-EX and 2-EX). On day 2, participants consumed either a single large high-fat milkshake (75% fat; 1-CON and 1-EX) for breakfast or 2 smaller isoenergetic milkshakes (2-CON and 2-EX) for breakfast and lunch. Plasma TAG were measured fasting and for 7 hours after breakfast. Results: Peak incremental TAG was 30% lower on 2-EX than 1-CON (P = .04, d = 0.38). Postprandial TAG increased more rapidly in the first 4 hours in 1-CON than other trials; but at 6 hours, TAG was exaggerated in 2-CON compared with 1-CON. Conclusions: Increasing meal frequency after exercise, without altering overall fat intake, attenuates postprandial TAG.

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Multiple Bouts of Resistance Exercise and Postprandial Triacylglycerol and Serum C-Reactive-Protein Concentrations

Stephen F. Burns, Masashi Miyashita, Chihoko Ueda, and David J. Stensel

The present study examined how multiple bouts of resistance exercise, performed over 1 d, influence 2 risk factors—postprandial triacylglycerol (TAG) and serum C-reactive-protein (CRP) concentrations—associated with coronary heart disease. Twenty-four men age 23.5 (SD 3.4) y completed two 2-d trials, exercise and control, at least 1 wk apart in a counterbalanced randomized design. On day 1 of the exercise trials participants completed 20 sets of 15 repetitions of 5 different resistance exercises divided into five 45-min bouts of exercise—100 sets and 1500 repetitions in total for all exercises. Exercises were performed at 30–40% of 1-repetition maximum. Blood samples were taken before and after exercise. On day 1 of the control trial participants were inactive, with blood samples taken at time points corresponding to the exercise trial. On day 2 of both trials participants consumed a test meal (0.89 g fat, 1.23 g carbohydrate, 0.4 g protein, 60 kJ per kg body mass). Blood samples were obtained fasted and for 6 h post prandially. Total area under the postprandial TAG concentration versus time curve was 12% lower in the exercise than in the control trial (8.76 [3.54] vs. 9.94 [4.31] mmol·L-1·6 h, respectively; P = 0.037). Serum CRP concentrations did not change over the 2 d in the control trial but increased in the exercise trial: trial × time interaction (P = 0.028). Multiple bouts of resistance exercise reduce postprandial TAG concentrations but increase serum CRP concentrations. The extent to which these findings are clinically relevant requires further study.

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Effects of Medium-Chain Triacylglycerol Ingested With Carbohydrate on Metabolism and Exercise Performance

Julia H. Goedecke, Richard Elmer, Steven C. Dennis, Ingrid Schloss, Timothy D. Noakes, and Estelle V. Lambert

The effects of ingesting different amounts of medium-chain triacylglycerol (MCT) and carbohydrate (CHO) on gastric symptoms, fuel metabolism, and exercise performance were measured in 9 endurance-trained cyclists. Participants, 2 hr after a standardized lunch, cycled for 2 hr at 63% of peak oxygen consumption and then performed a simulated 40-km time trial (T trial). During the rides, participants ingested either 10% 14C-glucose (GLU), 10% 14C-GLU + 1.72%MCT(LO-MCT), or 10% l4C-GLU + 3.44%MCT(HI-MCT) solutions: 400 ml at the start of exercise and then 100 ml every lOmin.MCTingestiondid not affect gastrointestinal symptoms. It only raised serum free fatty acid (FFA) and ß-hydroxybutyrate concentrations. Higher FFA and ß-hydroxybutyrate concentrations with MCT ingestion did not affect fuel oxidation or T-trial performance. The high CHO content of the pretrial lunch increased starting plasma insulin levels, which may have promoted CHO oxidation despite elevated circulating FFA concentrations with MCT ingestion.