98: Cortisol & Insulin Resistance: How Cortisol Drives Fat Gain & Carb Cravings with Dr. Ben Bikman

From the lecture: the type 1 diabetes example demonstrates that even severe cortisol excess cannot cause fat storage in the absence of insulin. Diabulimia patients who deliberately underdose insulin lose fat despite high cortisol. Cortisol promotes visceral fat uptake and subcutaneous fat breakdown, but net fat gain requires insulin to activate LPL and inhibit HSL broadly. Bikman's argument is that insulin is the 'how much' and cortisol is the 'where'. By keeping insulin low, one can mitigate the fat-accumulating potential of cortisol, even if fat distribution may still shift slightly. This aligns with low-carb or ketogenic strategies that naturally lower insulin.

Bikman explains that cortisol peaks in the morning to help mobilize glucose for the day and should fall in the afternoon to evening. Chronic stress flattens this rhythm, leaving cortisol high when it should be low. This late-day elevation can stimulate gluconeogenesis, cause insulin resistance through ceramides, and drive carb cravings at night, all of which disrupt sleep and metabolism. Maintaining a robust rhythm helps confine cortisol's catabolic effects to the active period, reducing metabolic harm.

Bikman cites multiple studies showing that high cortisol predicts cravings for carbohydrates and starches. In Cushing's patients, cravings for sweet and savory carb-rich foods diminished after cortisol was normalized. The mechanism: hypothalamic NPY/AgRP stimulate appetite, while amygdala dopamine makes high-carb foods feel rewarding. Eating those foods raises insulin, which further promotes insulin resistance and fat storage, creating a positive feedback loop. Recognizing the stress-craving link allows for pre-emptive strategies.

Bikman describes diabulimia, where patients deliberately underdose insulin to stay thin. Cortisol spikes as a stress response to uncontrolled hyperglycemia and ketosis, yet the complete absence of insulin prevents any fat storage, leading to wasting, organ damage, and high mortality. His point is to illustrate insulin's dominance over cortisol, but the clinical warning is clear: this is a devastating practice and must be avoided.

Bikman explains that cortisol activates enzymes that produce ceramides, which then inhibit Akt. He remarks that ceramides are a common intracellular cause of insulin resistance. While he doesn't prescribe a ceramide-reducing protocol here, his other work suggests low-carb diets, exercise, and time-restricted feeding can lower ceramide levels. This entry is speculative but rooted in his lecture's emphasis that ceramide accumulation is the key molecular event linking cortisol to insulin resistance.

Bikman explains that cortisol, upon binding the glucocorticoid receptor, upregulates genes involved in sphingolipid synthesis, specifically ceramide production. Ceramides are enigmatic sphingolipids that accumulate and then activate protein phosphatase 2A (PP2A). PP2A dephosphorylates and thereby inactivates Akt, a critical kinase in the insulin signaling cascade. Without active Akt, GLUT4 translocation is impaired, so muscle and fat cells cannot take up glucose, creating systemic insulin resistance. This is compounded by cortisol simultaneously driving hepatic glucose production and muscle proteolysis, flooding the bloodstream with glucose and amino acids while tissues are insulin resistant. Bikman cites colleagues Will Holland and Scott Summers as key researchers in this area.

Bikman describes that visceral adipose tissue has higher activity of 11β-HSD1, which converts inactive cortisone to active cortisol, amplifying the hormone's local effect. Cortisol then upregulates lipoprotein lipase (LPL) to pull fatty acids into visceral fat cells and inhibits hormone-sensitive lipase (HSL), preventing fat breakdown there. In subcutaneous fat, cortisol does the opposite: it upregulates HSL and ATGL, promoting lipolysis, which mobilizes stored fat and depletes limb fat. This creates a ‘redistribution’ of fat from the periphery to the trunk. The net result is a more central, apple-shaped obesity that is strongly linked to metabolic disease. Bikman emphasizes that this depot-specific effect does not mean cortisol controls total fat mass—that remains insulin's domain.

Bikman references a 1988 study by Dunger et al. on newly diagnosed untreated type 1 diabetic children. These children had extremely high cortisol levels (multiples above normal), were eating voraciously, yet were experiencing rapid fat loss and wasting. This occurs because insulin is required for LPL activation across adipose tissue and for inhibiting HSL; without insulin, fat cells cannot trap triglycerides. Cortisol can influence the location of fat storage but is utterly insufficient to cause net fat gain on its own. Bikman uses this to assert that insulin is the ‘reigning’ hormone for fat storage, while cortisol is a ‘location’ hormone. This insight is crucial for people who fear that stress alone makes them fat; the real problem is the insulin response to stress eating.

Bikman details that cortisol crosses the blood-brain barrier and binds glucocorticoid receptors in the hypothalamus and amygdala. In the hypothalamus, it activates neuropeptide Y (NPY) and agouti-related protein (AgRP), potent orexigenic signals that stimulate hunger. Simultaneously, it blunts leptin signaling, reducing satiety. In the amygdala, cortisol increases dopamine release, linking stress to reward-seeking behavior and making high-carb, high-fat foods more appealing. He cites several human studies: Ciao 2017 found baseline cortisol predicted craving for starches; Logo 2019 showed food-induced cortisol surges correlated with carb cravings; Geer 2016 in Cushing’s patients showed that high cortisol increased cravings for sweet and savory carb-rich foods, and these cravings diminished when cortisol was normalized. This creates a vicious cycle: stress raises cortisol, which drives carb cravings, which spikes insulin, exacerbating insulin resistance and weight gain.

Bikman notes that cortisol is one of the most potently circadian hormones. Its morning peak is thought to prepare the body for activity by ensuring blood glucose availability. In a healthy pattern, levels fall through the afternoon and evening. When chronic stress disrupts this rhythm, cortisol can remain elevated at times when it should be low, perpetuating gluconeogenesis, insulin resistance, and cravings into the night. This disruption may shift the body's fat storage patterns and amplify metabolic harm. Although Bikman doesn't prescribe a specific protocol, the lesson is that supporting a normal circadian rhythm (light exposure, meal timing, stress management) could help keep cortisol in its physiological window.