An interventional study of Intermittent Fasting with Energy Restriction and Energy Restriction without Intermittent Fasting in Intermittent Fasting, Body Weight, and Body Composition, sponsored by Masaryk University. Completed at 1 site in Czechia. Open to participants aged 18 Years and older, including healthy volunteers. Per ClinicalTrials.gov, last updated 2026-11-03.
Sponsored by Masaryk University · Not applicable, Interventional, and Treatment
This study examined whether intermittent fasting helps people lose weight and body fat, and whether it affects muscle mass. The researchers compared intermittent fasting with a diet that reduced daily energy intake without limiting meal times.
The study included healthy adult volunteers aged over 18 years. Researchers randomly assigned 95 participants to one of three groups. The dietary intervention lasted three weeks, and 75 participants completed it.
Participants followed one of these eating plans:
Intermittent fasting with reduced energy intake: Participants ate 25% less energy than their estimated daily needs. They ate all their meals within a six-hour period each day.
Reduced energy intake without intermittent fasting: Participants ate 25% less energy than their estimated daily needs. They could eat throughout the day without a fixed eating window.
Intermittent fasting without reduced energy intake: Participants ate enough energy to meet their estimated daily needs. They ate all their meals within a six-hour period each day.
Researchers measured body weight and body composition before and after the intervention. They used a body composition analyzer to estimate body fat, muscle mass, and other body tissues. They also contacted participants weekly to monitor their progress and any problems related to the diet.
After three weeks, participants in the first group lost an average of 2.3 kilograms of body weight. Those in the second group lost 2.2 kilograms. The difference between these groups was not statistically significant. Participants in the third group lost an average of 1.1 kilograms, which was significantly less than in the other two groups.
All three groups lost some body fat. However, the differences in body fat loss between the groups were not statistically significant. The group combining intermittent fasting with reduced energy intake showed a greater loss of fat-free mass than the group practicing intermittent fasting without reducing energy intake.
The results suggest that reducing daily energy intake was more important for short-term weight loss than limiting meal times alone. Longer studies are needed to determine the lasting effects of these eating patterns on body weight and body composition.
Intermittent fasting is an eating pattern in which people consume food only during a defined period of the day. It may help with weight loss, but it is unclear whether limiting eating hours provides additional benefits when daily energy intake is reduced. Another concern is whether intermittent fasting leads to a greater loss of muscle mass during weight loss.
The aim of this study was to compare intermittent fasting with continuous energy restriction. The researchers examined changes in body weight and body composition. They also investigated the effects of intermittent fasting without a prescribed reduction in daily energy intake.
This randomized controlled study included three dietary intervention groups. A total of 95 participants were randomly assigned to the groups, and 75 completed the three-week intervention. Participants were healthy adult volunteers older than 18 years. People with medical conditions that could make participation unsafe or affect the results were excluded.
Study groups and dietary interventions
Participants received an individual meal plan based on their estimated daily energy needs and usual physical activity.
Intermittent fasting with energy restriction: Participants consumed 75% of their estimated daily energy needs within a six-hour eating window. They fasted for the remaining 18 hours.
Continuous energy restriction: Participants consumed 75% of their estimated daily energy needs without a prescribed eating window.
Intermittent fasting without energy restriction: Participants consumed 100% of their estimated daily energy needs within a six-hour eating window. They fasted for the remaining 18 hours.
Participants selected the start of their six-hour eating window according to their daily routine. All groups followed meal plans designed to provide adequate nutrients. The plans emphasized sufficient protein and dietary fiber, along with vegetables, fruit, whole grains, dairy products, and other sources of protein. Participants could drink water, unsweetened tea, and unsweetened coffee. They were instructed to leave at least three hours between their last food intake and bedtime.
Researchers contacted participants by telephone during the intervention to monitor adherence to the meal plans and identify possible adverse events.
Measurements and outcomes
Researchers measured body weight, height, waist circumference, and other body measurements before and after the intervention. They assessed body composition using multifrequency bioelectrical impedance analysis. This method estimates body fat, fat-free mass, skeletal muscle mass, and other body compartments by measuring the body's response to a weak electrical current.
The main outcomes were changes in body weight and body composition after three weeks. Researchers also recorded adverse events, including fatigue, hunger, headaches, difficulties with concentration, and uncomfortable fullness after meals.
Main findings
Participants who followed intermittent fasting with energy restriction lost an average of 2.3 kilograms. Participants who followed continuous energy restriction lost an average of 2.2 kilograms. The difference between these groups was not statistically significant.
Participants who followed intermittent fasting without energy restriction lost an average of 1.1 kilograms. Their weight loss was significantly smaller than that of the other two groups.
The groups did not differ significantly in the amount of body fat lost. The group combining intermittent fasting with energy restriction lost more fat-free mass than the group practicing intermittent fasting without energy restriction. The difference between these groups was statistically significant. However, the study did not find a statistically significant difference in fat-free mass loss between intermittent fasting with energy restriction and continuous energy restriction.
No serious adverse events were reported. Fatigue was more frequent in the group combining intermittent fasting with energy restriction than in the continuous energy restriction group. Uncomfortable fullness or overeating was more frequent in the group practicing intermittent fasting without energy restriction than in the continuous energy restriction group.
Conclusion
The study found that intermittent fasting combined with reduced energy intake did not lead to significantly greater weight loss or body fat loss than continuous energy restriction over three weeks. Limiting eating hours without reducing prescribed energy intake resulted in less weight loss. The findings suggest that both energy intake and diet quality are important when considering changes in body weight and body composition.
The study was limited by its short duration and relatively small number of participants. Body composition was assessed using bioelectrical impedance analysis rather than dual-energy X-ray absorptiometry. Further research is needed to determine the long-term effects of these eating patterns.
333 studies on the registry are indexed under Intermittent Fasting; 99 are open to participants now.
This study's enrollment of 95 is above the median of 50 across 320 interventional studies indexed under Intermittent Fasting.
Browse Intermittent Fasting studies →Masaryk University is the lead sponsor of 47 studies on the registry; 20 are open to participants now.
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Go through the criteria one by one — yes, no or not sure — and take the list to your doctor or the study team. Kept in this browser only.
Adults aged over 18 years. Interest in and willingness to spend time preparing and consuming meals according to the prescribed dietary plan.
Exclusion Criteria:
Pregnancy or breastfeeding. Presence of a pacemaker or insulin pump. Underweight ( \< 18.5 kg/m²). Cancer, gout, severe gastrointestinal disease, kidney disease, diabetes mellitus, disease, thyroid disease, or eating disorders.
History of organ transplantation. Use of warfarin. Inability to consume the prescribed foods, including adherence to a vegan diet.
Underlined terms in the criteria open these too. Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
A condition in which the immune system attacks the body’s own tissues, such as rheumatoid arthritis, lupus, psoriasis, type 1 diabetes or inflammatory bowel disease.
Immunotherapy studies often leave out active autoimmune disease, and some name exceptions, such as thyroid disease on replacement hormone. Check the exceptions this study lists.
BMI (body mass index)
Weight in kilograms divided by height in metres squared. Example: 70 kg and 1.75 m gives 70 ÷ (1.75 × 1.75) ≈ 22.9.
What counts as overweight or obesity differs between countries (some use lower cut-offs), so go by the range the study states.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Autoimmune disease
A condition in which the immune system attacks the body’s own tissues, such as rheumatoid arthritis, lupus, psoriasis, type 1 diabetes or inflammatory bowel disease.
Immunotherapy studies often leave out active autoimmune disease, and some name exceptions, such as thyroid disease on replacement hormone. Check the exceptions this study lists.
Explained by clinicaltrials.gg, not part of the registry record. The study team decides who can take part.
Participants followed a six-hour daily eating window and consumed 75% of their estimated daily energy requirements for three weeks.
Behavioral: Intermittent Fasting with Energy Restriction
Participants consumed 75% of their estimated daily energy requirements for three weeks, without a prescribed six-hour eating window.
Behavioral: Energy Restriction without Intermittent Fasting
Participants followed a six-hour daily eating window and consumed 100% of their estimated daily energy requirements for three weeks.
Behavioral: Intermittent Fasting without Energy Restriction
Participants followed a six-hour daily eating window and consumed 75% of their estimated daily energy requirements for three weeks.
Participants consumed 75% of their estimated daily energy requirements for three weeks, without a prescribed six-hour eating window.
Participants followed a six-hour daily eating window and consumed 100% of their estimated daily energy requirements for three weeks.
Change in Body Weight
Change in body weight (kg) from baseline to the end of the three-week dietary intervention. Body weight was measured before and after the intervention, and the changes were compared between the three intervention groups.
Time frame: Baseline and after 3 weeks of dietary intervention
Plan to share: No
From the registry record's own update history. This site started tracking changes on Sep 25, 2026; for anything earlier, see the record history on ClinicalTrials.gov ↗
This study is completed, as verified in Oct 2026. You cannot join it, but the record below documents what was studied.
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Masaryk University