Adaptation of Human Brown Adipose Tissue to Calorie Restriction

Inclusion criteria

• Body mass index (BMI) of 27-40 kg/m², with a body fat percentage (determined by DXA, Hologic Wi) exceeding 25% in men and 30% in women.
• Reported stable body weight over the preceding 3 months (body weight changes of less than 3%).
• Laboratory safety test results (general biochemistry and complete blood count) within the normal reference range or with abnormalities deemed clinically insignificant by the medical research team and not requiring pharmacological treatment.
• Adequate venous access for blood sampling required by the procedures described in this protocol and absence of needle, blood, or medical procedure phobia.
• Readiness and ability to consume all foods included in the assessments and dietary intervention.
• Ability to understand and comply with study procedures, as assessed by the research team.
• Availability to participate in the study.
• Commitment to completing the study regardless of the assigned group.

Exclusion criteria

• Diagnosis or presence of signs or symptoms that, in the opinion of the research team, may contraindicate the dietary intervention or any of the procedures included in the study.
• Diagnosis or history of metabolic (including any type of diabetes mellitus), hematologic, pulmonary, cardiovascular, gastrointestinal, neurological, immune, hepatic, renal, urologic, or psychiatric diseases that could interfere with study outcomes or protocol adherence.
• History of any surgical procedure that, in the opinion of the research team, could alter energy metabolism or digestive function during the course of the study.
• Having been exposed to medical procedures involving an estimated radiation dose exceeding 5 mSv in the past 5 years or 10 mSv over a lifetime.
• Use of medications or supplements that are known to alter body weight or appetite.
• Weight loss exceeding 10% in the past two years or more than 5% in the past six months, unless completed weight recovery has occurred.
• Adherence to unconventional dietary patterns, such as vegan or fasting diets, or inability to tolerate the foods provided during the study.
• Pregnancy, plans to become pregnant within the next two years, postpartum period (within 12 months after delivery), or lactation.
• Perimenopausal status, defined as the presence of irregular menstrual cycles, hormonal changes indicative of perimenopause, or menopausal symptoms.
• Participation in any type of nutritional intervention or treatment within the past three months.
• Diagnosis or risk factors for the development of an eating disorder.
• Frequent disruptions in the sleep-wake cycle.
• Clinically significant abnormalities in gastric emptying, current diagnosis of any form of diabetes, blood pressure exceeding 160/90 mmHg, or resting heart rate below 50 or above 100 beats per minute (while seated), regardless of stable antihypertensive medication use.
• Active or untreated malignant disease or remission from a clinically significant malignant disease for less than five years prior to the evaluation.
• History of drug or alcohol abuse or a positive drug test, unless due to a medication prescribed by a healthcare professional.
• Smoking, vaping, or habitual use of tobacco products, unless abstinent for at least 72 consecutive hours during the past four weeks.
• Habitual caffeine consumption exceeding the equivalent of three espresso coffees per day (225 mg/day).
• Being a direct relative or household member of the research team personnel.
• Any other condition that, in the opinion of the research team, contraindicates study participation.