Full mechanism, in text

What the carb-insulin model claims

1 · Simple model · CICO (calories in, calories out)

CICO is right about thermodynamics but fails as behavioral guidance, because intake and output influence each other: eat less, and output drops too.The simplest model: weight change = intake − output. Eat more → gain, eat less → lose. The first law of thermodynamics holds — energy doesn't appear or disappear.

But CICO as behavioral guidance fails because it assumes 'intake' and 'output' are independent variables. In reality they influence each other: eat less → output automatically drops; eat more → NEAT (non-exercise activity thermogenesis) automatically rises.

2 · Dynamic system · the body is not a calculator

Eat 500 kcal less and BMR, NEAT and TEF all drop, so the real deficit is far smaller than 500 kcal; this is adaptive thermogenesis.Actual energy expenditure includes:
BMR (basal): the largest single block of daily expenditure, shaped by weight, body composition, hormones, ageTEF (thermic effect of food): about 5–15% of daily expenditure for a mixed diet; by macronutrient, protein 20–30% > carbs 5–10% > fat 0–3%EAT (exercise activity thermogenesis): deliberate exerciseNEAT (non-exercise activity thermogenesis): walking, fidgeting, posture — most overlooked and most variable, and it shifts when energy balance is experimentally changed
Eat 500 kcal less: BMR drops (less weight + metabolic adaptation), NEAT drops (you unconsciously move less), TEF drops (less food). The actual deficit is far less than 500 kcal — this is adaptive thermogenesis.

How stubborn it is: six years after The Biggest Loser competition, resting metabolic rate was still about 704 kcal/day below baseline, and after adjusting for body composition and age the residual metabolic adaptation was still about −499 kcal/day.

3 · Carb-insulin hypothesis (CIM) · why it's seductive

The carb-insulin hypothesis blames obesity entirely on insulin, but several of its logical consequences failed when tested in tightly controlled inpatient feeding studies.CIM narrative: eat carbs → insulin ↑ → fat cells 'lock in' fat → body 'thinks' it's starving → overeat → obesity. It sounds mechanistic and blames insulin entirely.

Problems:
Protein also raises insulin (sometimes more than carbs) but doesn't cause obesitySeveral logical consequences of CIM were tested directly in a pair of tightly controlled inpatient feeding studies and failed — Hall's 2017 review concludes that important parts of the model have been experimentally falsified and that it is too simplistic'Insulin locks fat' oversimplifies: lipolysis is continuous; insulin regulates net fluxMetabolic-ward directly testing CIM (Hall 2016, isocaloric keto vs high-carb): keto increased fat oxidation early but body fat loss was not faster

4 · The real model · multi-directional feedback network

Real energy balance is a two-way feedback network: food shapes hormones, hormones shape expenditure and appetite, and expenditure and weight shape how much you eat next.Real energy balance is a bi-directional feedback network:

Food → hormones → expenditure → food (loop):
Diet composition affects hormones (insulin/leptin/ghrelin/)Hormones affect energy expenditure and appetiteExpenditure and weight affect how much you eat next mealSleep/stress/microbiome/drugs all influence the loop
Practical implications:
You don't need to count calories, but understand satiety and food quality are more reliable regulators than willpowerProtein + fiber + whole foods → high satiety → automatically eat lessSleep deprivation → ghrelin ↑/leptin ↓, heightened food-reward sensitivity, and lower NEAT → you eat more and move less without noticingLong-term sustainability > short-term extremes

Full mechanism, in text

1 · Simple model · CICO (calories in, calories out)

2 · Dynamic system · the body is not a calculator

3 · Carb-insulin hypothesis (CIM) · why it's seductive

4 · The real model · multi-directional feedback network

Energy balance · a dynamic feedback network

Full mechanism, in text

1 · Simple model · CICO (calories in, calories out)

2 · Dynamic system · the body is not a calculator

3 · Carb-insulin hypothesis (CIM) · why it's seductive

4 · The real model · multi-directional feedback network

Energy balance · a dynamic feedback network