Fasted vs. Fed State Exercise

Fasted vs. Fed State Exercise for Cardiovascular Health and Weight Loss

Although many medications exist for both heart disease and obesity, cost, lack of access for all people, side effects and the desire for a more natural solution have left many people seeking lifestyle treatments such as exercise. Scientists know that exercise is highly beneficial for heart health. When exercise also produces weight loss, these benefits are much improved. Although using exercise to treat or prevent heart disease / obesity is recommended, not all people respond well. Some see significant weight loss and health improvements while others see little changes. For these reasons, new strategies surrounding the use and design of an exercise program are needed. One such strategy could be performing aerobic exercise before breakfast (fasted exercise). When exercising fasted, food/energy stores are low, and one relies on stored body fat for energy. This may help heart health and weight loss. This has never been tested in a program long enough to see such changes. This study will, for the first time, assess the effects of a 16-week aerobic exercise program performed fasted compared to after eating. Outcomes will include blood fats, blood pressure, fat-burning abilities and weight loss.

Starting an exercise program can also make people to eat more. This limits the success of exercise. The study will also evaluate ways fasted exercise could change eating, as it possible that fasted exercise could also cause people to eat more, which would limit weight loss and health improvements.

Study Overview

• Status: Recruiting
• Conditions: Obesity; Weight Loss; Exercise
• Intervention / Treatment: Behavioral: 16 week exercise intervention

Detailed Description

This study will be the first to evaluate a long-term (16-week) aerobic exercise intervention performed in the fasted state (compared to fed state) at a guidelines-based dose. Primary outcomes for Aim 1 will include changes in fat & fat-free mass (DXA), energy compensation, blood pressure & lipids, aerobic fitness, and substrate oxidation (respiratory quotient, RQ) at rest and during activity.

It is also important to understand sources of response variability to an exercise program. Individuals tend to compensate for the energy they expend during exercise, primarily by increasing energy intake (EI). Such compensatory eating behaviors likely stem from a series of evolutionarily conserved responses, ensuring energy is available for vital organ function and reproduction when faced with an energy deficit. This proposal will be the first to evaluate how fasted exercise training influences (Aim 2 outcomes): physiological hunger (hormonal responses to a standardized meal) and behavioral constructs shown to influence EI and weight status (food reinforcement and attentional bias towards food cues). The overall hypothesis is that fasted state exercise will result in greater energy compensation, attenuating weight loss compared to an identical dose of exercise performed in the post-prandial state. This study will further hypothesize an attenuated weight loss with fasted exercise training will negate beneficial cardiovascular adaptations stemming from improvements in oxidative metabolism commonly associated with fasted exercise. Adults (aged 18-59 years, BMI: 25-45 kg/m2) will be randomized to a 16-week supervised aerobic exercise intervention (progressing to a guidelines-based dose of 1600 kcal/wk). Exercise sessions will be performed between 0500h and 1100h, 4 days per week in either the fasted state (FAST, 8-12 hour fast) or post-prandially (FED, within 3 hours of eating at least 300 kcal).

• Study Type: Interventional
• Enrollment (Estimated): 40
• Phase: Phase 2

Contacts and Locations

• Study Contact: Name: Kyle D Flack, PhD; Phone Number: (479) 434-4019; Email: kyle.flack@achehealth.edu
• Study Contact Backup: Name: Blake Metcalf, DCN; Phone Number: 479-434-4003; Email: blake.metcalf@achehealth.edu

Study Locations

• United States
  • Arkansas
    • Fort Smith, Arkansas, United States, 72916
      • Recruiting
      • Arkansas Colleges of Health Education Research Institure Health and Wellness Center
      • Contact: Kyle D Flack, PhD; Phone Number: (479) 434-4019; Email: kyle.flack@achehealth.edu
      • Contact: Blake Metcalf, DCN; Phone Number: 4794344003; Email: blake.metcalf@achehealth.edu

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: Yes

Description

Inclusion Criteria:

• Aged 18-59
• BMI 25-45
• Healthy enough to exercise

Exclusion Criteria:

• Taking medications or supplements that are known to influence energy expenditure,
• Currently exercising more than once per week
• Currently dieting for weight loss
• Currently taking weight loss drugs
• Have had a previous weight loss surgery
• Currently diagnosed with Diabetes
• Currently diagnosed with heart disease (Heart failure, uncontrolled hypertension, uncontrolled hypercholesterolemia, Coronary heart disease)

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: Randomized
• Interventional Model: Parallel Assignment
• Masking: None (Open Label)

Number of Arms

2

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Fasted group; Complete all exercise sessions of intervention before breakfast- fasted at least 8 hours	Behavioral: 16 week exercise intervention; Both groups will receive a 16-week supervised aerobic exercise program progressing to 1,600 kcal of EE per wk (4 sessions/week) at moderate intensity (40-50% heart rate reserve, HRR).
Experimental: Fed exercise group; Complete all exercise sessions of intervention after breakfast- within 3 hours of eating at least 300 kcal	Behavioral: 16 week exercise intervention; Both groups will receive a 16-week supervised aerobic exercise program progressing to 1,600 kcal of EE per wk (4 sessions/week) at moderate intensity (40-50% heart rate reserve, HRR).

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
body composition	kg of fat free and fat mass via DXA	Baseline (week 0) and post-intervention (week 25)

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Total and acylated ghrelin	Total and acylated ghrelin (pg/mL in plasma) will be assessed in the fasted state and response to a test meal via blood sampling at 0 minutes (pre meal), 15, 30, 45, 60, 90, and 120 minutes post-meal.	Baseline (week 0) and post-intervention (week 25)
GLP-1	Glucagon-like peptide 1 (GLP-1, Pmol/L in plasma) will be assessed in the fasted state and response to a test meal via blood sampling at 0 minutes (pre meal), 15, 30, 45, 60, 90, and 120 minutes post-meal.	Baseline (week 0) and post-intervention (week 25)
PYY	Peptide YY (PYY, pmol/L plasma) will be assessed in the fasted state and response to a test meal via blood sampling at 0 minutes (pre meal), 15, 30, 45, 60, 90, and 120 minutes post-meal.	Baseline (week 0) and post-intervention (week 25)
Leptin	Leptin (ng/mL in plasma) will be assessed in the fasted state and response to a test meal via blood sampling at 0 minutes (pre meal), 15, 30, 45, 60, 90, and 120 minutes post-meal.	Baseline (week 0) and post-intervention (week 25)
Food reinforcement	amount of work one is willing to do for a snack food	Baseline (week 0) and post-intervention (week 25)
Attentional bias for food cues	percentage of time fixated on food cues during a dot-probe task, assessed by eye tracking	Baseline (week 0) and post-intervention (week 25)
Skeletal muscle efficiency	kcal expended per kg per watt during a graded cycle ergometer test	Baseline (week 0) and post-intervention (week 25)
walking ecconomy	Gross energetic cost of movement (J/kg/m) will be assessed during a graded walking test with indirect calorimetry.	Baseline (week 0) and post-intervention (week 25)
resting metabolic rate	Resting metabolic rate assessed via indirect calorimetry	Baseline (week 0) and post-intervention (week 25)
muscle strength	Peak torque and work per repetition (Foot-Pounds) will be assessed during an isokinetic and isometric task	Baseline (week 0) and post-intervention (week 25)
muscle power	Average power (watts) will be assessed during an isokinetic and isometric task	Baseline (week 0) and post-intervention (week 25)
skeletal muscle mass	The D3Cr dilution technique will be used to determine kg of skeletal muscle mass	Baseline (week 0) and post-intervention (week 25)

Collaborators and Investigators

• Sponsor: Arkansas Colleges of Health Education

Study record dates

Study Major Dates

• Study Start (Actual): January 5, 2026
• Primary Completion (Estimated): July 1, 2027
• Study Completion (Estimated): December 1, 2027

Study Registration Dates

• First Submitted: March 13, 2026
• First Submitted That Met QC Criteria: March 17, 2026
• First Posted (Actual): March 23, 2026

Study Record Updates

• Last Update Posted (Actual): March 23, 2026
• Last Update Submitted That Met QC Criteria: March 17, 2026
• Last Verified: March 1, 2026

More Information

Terms related to this study

• Keywords: Exercise; obesity; weight loss
• Additional Relevant MeSH Terms: Nutrition Disorders; Overnutrition; Body Weight; Body Weight Changes; Overweight; Pathological Conditions, Signs and Symptoms; Behavior; Nutritional and Metabolic Diseases; Signs and Symptoms; Obesity; Weight Loss; Motor Activity
• Other Study ID Numbers: 479-401-6011

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: UNDECIDED

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No