Uploaded July 2026 | Updated September 2026, 1 week ago
Is insulin the real cause of weight gain? Of every objection to Calories in, Calories out, the carbohydrate-insulin model is the only one that tries to break the equation instead of dodging it, so in this segment from our Calories in, Calories out episode we test it the hardest, three ways. In a metabolic ward at equal Calories, cutting fat lost more body fat than cutting carbs, 89 grams a day against 53, the opposite of what the insulin model predicts. Fasting insulin barely predicts who gains weight; in one adult cohort, doubling it predicted less weight gain, not more. And your after-meal insulin is mostly a measure of how much food just showed up, a passenger that looks like a driver.
Then the part almost nobody arguing about insulin online has clocked: GLP-1 drugs like semaglutide and tirzepatide raise your insulin response to a meal on purpose, and they still produce the largest weight loss of any obesity medication we have ever approved, around 15 and 20 percent of body weight. Insulin up, food down, weight down. The mechanism is appetite, start to finish. We close with the whole list, claim by claim, and what actually tends to work once you accept that the inputs are not really a matter of willpower.
Timestamps:
0:00 Claim 4: it's not Calories, it's insulin
0:12 The carbohydrate-insulin model, stated fairly
1:00 Test 1: the metabolic ward
1:51 Test 2: does insulin even predict weight gain?
3:03 The post-meal insulin card
4:16 How science is supposed to work
4:40 Test 3: the GLP-1 drugs that should end it
5:56 Insulin up, food down, weight down
6:36 The mechanism is appetite
7:22 The whole list, claim by claim
8:41 What to actually do
9:30 Next week: are GLP-1s cheating?
Resources
Barbell Medicine coaching and templates: barbellmedicine.com
Plus podcast subscription: barbellmedicine.com/shop/subscriptions/plus-podcast-subscription
Barbell Medicine Premium: barbellmedicine.com/shop/subscriptions/barbell-medicine-premium
Signal (book pre-order): barbellmedicine.com/shop/learning/signal
Hall et al., Cell Metabolism 2015. doi.org/10.1016/j.cmet.2015.07.021
Wilding et al., New England Journal of Medicine 2021 (STEP 1). doi.org/10.1056/NEJMoa2032183
Jastreboff et al., New England Journal of Medicine 2022 (SURMOUNT-1). doi.org/10.1056/NEJMoa2206038
Is insulin the real cause of weight gain? Of every objection to Calories in, Calories out, the carbohydrate-insulin model is the only one that tries to break the equation instead of dodging it, so in this segment from our Calories in, Calories out episode we test it the hardest, three ways. In a metabolic ward at equal Calories, cutting fat lost more body fat than cutting carbs, 89 grams a day against 53, the opposite of what the insulin model predicts. Fasting insulin barely predicts who gains weight; in one adult cohort, doubling it predicted less weight gain, not more. And your after-meal insulin is mostly a measure of how much food just showed up, a passenger that looks like a driver.
Then the part almost nobody arguing about insulin online has clocked: GLP-1 drugs like semaglutide and tirzepatide raise your insulin response to a meal on purpose, and they still produce the largest weight loss of any obesity medication we have ever approved, around 15 and 20 percent of body weight. Insulin up, food down, weight down. The mechanism is appetite, start to finish. We close with the whole list, claim by claim, and what actually tends to work once you accept that the inputs are not really a matter of willpower.
Timestamps:
0:00 Claim 4: it's not Calories, it's insulin
0:12 The carbohydrate-insulin model, stated fairly
1:00 Test 1: the metabolic ward
1:51 Test 2: does insulin even predict weight gain?
3:03 The post-meal insulin card
4:16 How science is supposed to work
4:40 Test 3: the GLP-1 drugs that should end it
5:56 Insulin up, food down, weight down
6:36 The mechanism is appetite
7:22 The whole list, claim by claim
8:41 What to actually do
9:30 Next week: are GLP-1s cheating?
Resources
Barbell Medicine coaching and templates: barbellmedicine.com
Plus podcast subscription: barbellmedicine.com/shop/subscriptions/plus-podcast-subscription
Barbell Medicine Premium: barbellmedicine.com/shop/subscriptions/barbell-medicine-premium
Signal (book pre-order): barbellmedicine.com/shop/learning/signal
Hall et al., Cell Metabolism 2015. doi.org/10.1016/j.cmet.2015.07.021
Wilding et al., New England Journal of Medicine 2021 (STEP 1). doi.org/10.1056/NEJMoa2032183
Jastreboff et al., New England Journal of Medicine 2022 (SURMOUNT-1). doi.org/10.1056/NEJMoa2206038
