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NCT Number: NCT06134258

Mechanisms of Fasting Induced Reduction in Energy Expenditure

Fasting reduces the energy consumption of the human body. The extent of this adaptation varies significantly between different individuals. The aim of this research project is to investigate how this adaptation of the metabolism is regulated by the body. For this purpose, we will first measure how the so-called basal metabolic rate of the body reacts to a short-term fasting of 24 h in a preliminary study. Those subjects with a particularly pronounced and those subjects with an only slightly pronounced reaction of the basal metabolic rate will be invited to the main study.

Here, in random order (24 h fasting vs. 8 h fasting), the following is compared

* how the basal metabolic rate of the body reacts to the reduced energy intake. * how the energy metabolism increases after a test meal * what role in particular the thyroid hormones play in this adaptation. In addition, a sample of the subcutaneous adipose tissue is taken in each case and it is examined how the regulation of metabolic processes at the cellular level.

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Key information

Conditions

Fasting Behavior Feeding Behavior

Age range

18 year–40 year

Sex eligibility

All sexes

Study type

Interventional

Phase

Not applicable

Primary location

About this study

The extent of this adaptation varies significantly between different individuals. The aim of this research project is to investigate how this adaptation of the metabolism is regulated by the body. For this purpose, we will first measure how the so-called basal metabolic rate of the body reacts to a short-term fasting of 24 h in a preliminary study. Those subjects with a particularly pronounced and those subjects with an only slightly pronounced reaction of the basal metabolic rate will be invited to the main study.

Who can participate

Healthy volunteers accepted: Yes

Only the study team can determine whether someone qualifies for participation.

Inclusion criteria

  • Age: 18 to 40 years
  • Body mass index 18.0 to 27.0 kg/m²
  • Exclusion Criteria:
  • Chronic conditions necessitating medical treatment (e.g., renal failure, hepatic dysfunction, cardiovascular disease, diabetes mellitus),
  • Known or suspected non-compliance, drug or alcohol abuse,
  • Inability to follow the procedures of the study
  • Participation in another study with investigational drug within the 30 days preceding and during the present study,
  • Previous enrolment into the current study,
  • Enrolment of the investigator, his/her family members, employees and other dependent persons,
  • Hypothyroidism or hyperthyroidism
  • Pregnant, breastfeeding and menopausal women

Treatment and study plan

Mixed meal test

Other

mixed meal test after fasting

Primary outcomes

  1. change of energy expenditure (EE) determined by indirect calorimetry (kcal per 24h)

    Time frame: 60 minutes after ingestion of test meal

    Difference of EE (determined by indirect calorimetry) between baseline and 60 minutes after ingestion of the liquid test meal. Both measurements will be performed after an overnight fasting period.

Secondary outcomes

  1. Level of free thyroxine

    Time frame: after 24 hours and after 12 hours of fasting

    The thyroid hormone (TH) system is an important regulator of EE. We hypothesize that levels of TH are higher in the "spendthrift" than in the "thrifty" group.

  2. Level of free triiodothyronine

    Time frame: after 24 hours and after 12 hours of fasting

    The thyroid hormone (TH) system is an important regulator of EE. We hypothesize that levels of TH are higher in the "spendthrift" than in the "thrifty" group.

  3. Respiratory quotient (RQ)

    Time frame: after 24 hours and after 12 hours of fasting

    We hypothesize that the participants in the "thrifty" group have a lower proportion of fatty acid metabolism and therefore a higher RQ.

Study contacts

Contact information is provided by the study sponsor or research team.

Matthias Betz

CONTACT

[email protected]

0041 61 265 2525

Rahel Loeliger

CONTACT

[email protected]

0041 61 265 2525

Sponsors and collaborators

Lead sponsor

ETH Zurich

Other

Collaborators

  • University Hospital, Basel, Switzerland

Registry information

Official study title

Mechanisms of Fasting Induced Reduction in Energy Expenditure - FIRE Trial

Acronym: FIRE

Important dates

Study start
2023
Primary completion
2026
Study completion
2026
First posted
Nov 18, 2023
Registry last updated
May 30, 2025

OpenTrials presents study information sourced from ClinicalTrials.gov. The official registry record should be consulted for the latest information.

View the official ClinicalTrials.gov record (opens in a new tab)

This listing is for discovery and informational purposes only. It is not medical advice, does not guarantee that a study is recruiting, and does not determine eligibility. Contact the study team and a qualified healthcare professional when considering participation.

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