139: Why Some Thin People Get Diabetes and Ethnicity’s Impact with Dr. Ben Bikman

Bikman spends considerable time on the inverse relationship between insulin and free fatty acids under normal physiology, and how hypertrophic fat cells break this rule. He illustrates that the liver, when confronted with both high free fatty acids and high insulin, is forced to store rather than burn fat, causing ectopic liver fat and setting the stage for hepatic insulin resistance. The Adipo‑IR index mathematically captures this break, making it the ‘most beloved’ marker. He also touches on sex differences: women have higher basal free fatty acids because their smaller adipocytes are more lipolytically active, thus they have a higher normal Adipo‑IR (around 5.9 vs men’s <4). He encourages clinicians and patients to use it, even though free fatty acid testing is not standard.

Bikman cites that researchers have argued waist circumference or waist-to-hip ratio outperforms BMI across ethnic groups, a sentiment he ‘agrees with completely.’ He ties this to the biology of visceral fat: it inevitably grows by hypertrophy, making it inherently more metabolically damaging than subcutaneous fat that can grow through hyperplasia. While he doesn’t give specific waist cutoff numbers, he implies that clinicians should be paying more attention to the tape measure than the scale.

Bikman presents the adiponectin/leptin ratio as a clinically useful marker that ‘correlates meaningfully with insulin sensitivity, visceral fat accumulation, and all the markers of the metabolic syndrome.’ He acknowledges that it’s not widely used because these tests are still ‘a little obscure,’ but he strongly encourages patients to discuss it with their clinicians. He positions it alongside the Adipo‑IR index as a way to infer fat cell size without a biopsy, making the science of adipocyte biology accessible.

Bikman explains that white adipose tissue expands by hypertrophy (existing fat cells ballooning) or hyperplasia (forming new small cells). Hypertrophic cells exceed a critical size where they become insulin resistant, failing to suppress lipolysis even when insulin is high, resulting in simultaneous high insulin and high free fatty acids—a metabolically toxic duet that forces the liver to store ectopic fat. At the same time, enlarged cells endure hypoxia, activating HIF-1α, which stimulates angiogenesis but also triggers a cascade of pro-inflammatory cytokines like TNF-α and IL-6. This local inflammation spills systemically, exacerbating insulin resistance. In contrast, hyperplastic expansion maintains small, well-vascularized fat cells that secrete adiponectin and respond normally to insulin. The ‘adipose expandability hypothesis’ posits that each individual has a finite capacity for safe hyperplasia; exceed it and hypertrophy takes over. This cellular lens explains why some people with high BMI remain metabolically healthy (they store fat hyperplastically) while others with modest weight gain develop diabetes because their fat cells hit the hypertrophic threshold early. Thus, the relevant question is not ‘how much fat?’ but ‘how big are the fat cells?’.

Bikman highlights a landmark Lancet study that calculated ethnic‑specific BMI equivalents for diabetes risk. For South Asians, the BMI threshold matching a European’s BMI 30 was just 23; for Chinese and Arab populations it was 26. Additional analyses showed Singapore Chinese women needed a BMI of only 25 to equal the diabetes risk of a white European woman at BMI 40. The biological basis: South and East Asians have a lower personal fat threshold because their subcutaneous tissue has limited capacity for hyperplasia, so adipocytes rapidly enter hypertrophic, insulin‑resistant states at lower total fat mass. Even at birth, Asian Indian newborns have higher total adiposity and more visceral fat than European newborns, proving a genetic predisposition. Bikman argues that this is not a minor nuance but a fundamental revision of the relationship between weight and metabolic risk; continued use of universal cutoffs means that early‑stage disease is ignored in millions. He explicitly advocates that clinicians should adopt ethnicity‑adjusted thresholds and move toward metrics like waist circumference that capture central adiposity.

Bikman elaborates that the personal fat threshold varies enormously—one person may exceed it at a BMI of 22, another at 35—because it is set by genetics (and hence ethnicity), early‑life programming, and the innate ability of subcutaneous tissue to produce new small fat cells. Crucially, below the threshold, fat accumulation can remain metabolically neutral, even if total body fat is high. South Asians and East Asians, on average, have a lower threshold, which is why they develop fatty liver and insulin resistance at BMIs that would be considered healthy for a white European. This reframes the clinical question: instead of asking whether a patient is obese by population standards, the physician should assess whether that individual has exceeded their own storage capacity—manifested by rising waist circumference, elevated free fatty acids, and eventually hyperglycemia. The concept also explains why some obese individuals are metabolically healthy: they have a high personal fat threshold and store excess energy through hyperplasia.

Bikman describes the adiponectin/leptin ratio: adiponectin is secreted by small, healthy adipocytes and promotes insulin sensitivity; leptin rises with total fat mass, especially from enlarged cells. In hypertrophic obesity, adiponectin falls and leptin rises, causing the ratio to plummet, correlating with insulin resistance and visceral fat accumulation. Although no standard cutoffs exist, he suggests tracking the ratio over time if one can persuade a clinician to order the tests. The Adipo‑IR index, his self‑described favorite, is simply fasting insulin multiplied by fasting free fatty acids. In healthy adipose, insulin suppresses lipolysis, keeping free fatty acids low. When adipocytes become insulin resistant, the brake fails, and the product of high insulin and high free fatty acids quantifies the degree of adipose insulin resistance. He provides sex‑specific normal ranges: for women ~5.9, for men less than 4 (mid‑3s), because women naturally have higher baseline free fatty acids and thus a higher normal Adipo‑IR. Both markers tell you about fat cell size and function without a biopsy.