What is a Personal Fat Threshold?
The personal fat threshold (PFT) is the maximum amount of body fat an individual can store before developing metabolic dysfunction, particularly type 2 diabetes, and this threshold varies between individuals independent of BMI. 1
Core Concept
The PFT hypothesis explains why some people develop type 2 diabetes at normal BMI while others remain metabolically healthy despite obesity. 1 Each person has a genetically determined capacity to safely store fat in subcutaneous depots, particularly in the lower body. 2 Once this personal threshold is exceeded, fat accumulates in ectopic locations (liver, pancreas, muscle) and visceral depots, triggering metabolic dysfunction including insulin resistance and beta-cell failure. 1
Key Mechanistic Features
Individual variability: The threshold is highly personal—some individuals develop diabetes at BMI 22 kg/m² while others remain healthy at BMI 35 kg/m². 1
Subcutaneous fat capacity: The ability to expand healthy subcutaneous fat, especially in the lower body (gluteofemoral region), determines metabolic health. 2 When this capacity is exhausted, fat spills over into harmful depots. 2
Ectopic fat accumulation: Exceeding the PFT leads to fat deposition in the liver, pancreas, and skeletal muscle, directly impairing insulin secretion and action. 1
Visceral adiposity: Central fat accumulation is a marker of exceeded PFT and strongly predicts cardiometabolic disease. 3, 2
Clinical Evidence Supporting PFT
The UKPDS cohort demonstrated that one-third of people diagnosed with type 2 diabetes had BMI less than 25 kg/m², with a median BMI of only 28 kg/m². 1 These individuals responded to substantial weight loss with diabetes remission, despite remaining at "normal" or "overweight" BMI levels. 1
Body composition studies show that total body fat and visceral fat excess—not BMI alone—drive glucose intolerance, beta-cell dysfunction, and cardiovascular risk even in normoglycemic individuals. 4 Conversely, lower-body subcutaneous fat is associated with favorable glycemic profiles. 5
Ethnic Considerations
Asian populations demonstrate lower PFT compared to Caucasians, developing metabolic disease at BMI 2-3 kg/m² lower for the same body fat percentage. 6 South Asians show insulin resistance even when lean, with higher visceral adiposity at any given BMI. 6 This explains why obesity thresholds are defined at BMI ≥25 kg/m² for Asian populations versus ≥30 kg/m² for Caucasians. 6
Clinical Implications
Weight loss targets: Individuals with type 2 diabetes or metabolic dysfunction should aim for weight reduction sufficient to drop below their personal threshold, regardless of whether they meet traditional obesity criteria by BMI. 1
Assessment beyond BMI: Waist circumference (≥88 cm for women, ≥102 cm for men in Caucasians; ≥80 cm for women, ≥90 cm for men in Asians) identifies those who have exceeded their PFT. 6
Fat distribution matters: Central adiposity (android fat, truncal-to-leg fat ratio, android-to-gynoid ratio) predicts poor metabolic control, while lower-body fat is protective. 5
Common Pitfalls
Do not dismiss metabolic disease risk in normal-weight individuals based solely on BMI—they may have exceeded their personal threshold. 1 Conversely, do not assume all obese individuals require identical interventions; some may remain below their threshold and metabolically healthy. 1 Always assess body fat distribution using waist circumference alongside BMI for accurate risk stratification. 6, 3