Why some women stay thin without dieting: science investigates

Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.

Inclusion Criteria: * BMI ≤ 17.5 kg/m2 * 20 kg/m2 ≤ BMI ≤ 25 kg/m2 Exclusion Criteria: * For women with Constitutional thinness : * Women under guardianship or deprived of their liberty by judicial or administrative decision * Women who are pregnant, breastfeeding, or likely to become pregnant * Women who engage in intense physical activity (more than 3 sessions of physical activity per week) * Abnormal levels of IGF-1, estradiol, free T3, cortisol, and leptin * For the MC group specifically: cases of thinness due to a suspected organic cause. This includes Marfan syndrome, identifiable by: personal or family history of degenerative aortic disease (aneurysm, dissection), ligamentous hyperlaxity, arachnodactyly * History or presence of a systemic condition likely to interfere with the physiological and metabolic parameters measured (e.g., diabetes, endocrine or metabolic disease) * Any acute or chronic disease that may influence the results (e.g., infections, tumors, inflammatory diseases) * Medical or surgical history deemed by the investigator to be incompatible with this study (e.g., muscular, neurological, or joint disorders, or contraindications to the application of a magnetic field, etc.) Presence of diabetes, and any other condition limiting the application of either strategy under trial * Use of medications that may interfere with the study results * Cardiovascular conditions (history of cardiovascular and/or neurovascular disease, as well as the presence of cardiovascular and/or neurovascular risk factors other than obesity/overweight, such as: high blood pressure, high cholesterol, diabetes, heart rhythm disorder, known carotid atherosclerosis, thrombophilia) * Surgery within the previous 3 months * Women excluded from another study * Regular tobacco or alcohol consumption * Specific diets likely to impact metabolism, influence biological parameters (FT3, cortisol in particular) or skew results (deficiencies, low calorie intake). This includes vegan, mono, ketogenic, and low-calorie diets, intermittent fasting, or diets requiring specific supplementation that may interfere with the endocrine system. For women Normal-Weighted Women * Women under guardianship or deprived of their liberty by judicial or administrative decision * Women who are pregnant, breastfeeding, or likely to become pregnant. * Women who engage in intense physical activity (more than 3 sessions of physical activity per week) * History or presence of a systemic condition likely to interfere with the physiological and metabolic parameters measured (e.g., diabetes, endocrine or metabolic disorders) * Any acute or chronic disease that may influence the results (e.g., infections, tumors, inflammatory diseases) * Medical or surgical history deemed by the investigator to be incompatible with this study (e.g., muscular, neurological, or joint disorders, or contraindications to the application of a magnetic field, etc.) * Presence of diabetes or any other condition limiting the application of either strategy under investigation * Taking medications that may interfere with the study results * Cardiovascular conditions (history of cardiovascular and/or neurovascular disease, as well as the presence of cardiovascular and/or neurovascular risk factors other than obesity/overweight, such as: high blood pressure, high cholesterol, diabetes, heart rhythm disorder, known carotid atherosclerosis, thrombophilia) * Surgery within the previous 3 months * Women excluded from another study * Regular tobacco or alcohol consumption * Specific diets likely to impact metabolism, influence biological parameters, or skew results (deficiencies, low calorie intake). This includes vegan, mono, ketogenic, and low-calorie diets, intermittent fasting, or diets requiring specific supplementation that may interfere with the endocrine system.