Hormonal Nutrition

The answer

Leptin

Leptin therapy only works for true leptin deficiency — not common obesity.

Leptin is your fat tissue's status report to your brain: more fat, more leptin. In theory that should curb overeating, and it does for the handful of people born unable to make it. But in ordinary obesity leptin is already high and the brain tunes it out, so a leptin shot won't melt fat. It is the hormone behind the idea of a body-weight set point, not a weight-loss drug.

The answer

Leptin resistance

The more fat you carry, the more leptin you make — but chronically high leptin trains the brain to ignore it, and less of it even reaches the brain in the first place. That is why "boosting leptin" is the wrong goal. No supplement or diet reliably resets leptin sensitivity; the one lever the biology supports is gradually losing fat, which lowers leptin itself.

The answer

Falling leptin

Leptin is not only a "you have enough fat" signal — its drop during a deficit is what tells your body to conserve. In mice, keeping leptin from falling blocked most of the starvation-mode changes. In people this helps explain why hunger climbs and metabolism dips as you lean out. Bear in mind this is animal work: the direction is well supported, but the exact human numbers aren't settled here.

The answer

Ghrelin

Fat suppresses ghrelin poorly; protein and carbs quiet it better. Weight loss pushes ghrelin up.

Ghrelin is why you feel hungry on schedule — it surges before habitual mealtimes and falls after eating. When you lose weight it rises, part of why keeping weight off feels like fighting your own biology. One practical wrinkle: fatty meals don't shut ghrelin down as well as protein- or carb-rich ones, so an all-fat snack can leave you hungrier than expected.

The answer

Yes protein is more filling

Only 5 trials met the strict pooling bar; 28 pointed the same way.

Anchoring meals with protein does tend to leave you fuller for a few hours than the same calories with less protein. But the evidence base is thinner than it looks — only a handful of trials were rigorous enough to pool, and the authors wrote the paper partly to warn against treating such meta-analyses as the last word. Treat protein-for-satiety as a well-supported habit, not a precise dose.

The answer

Gut hormones GLP-1 + PYY

Food intake fell ~35% after surgery; blocking both hormones together added back ~20%.

A smaller stomach is only half the story of why bypass surgery curbs hunger. The surgery makes the gut release far more GLP-1 and PYY after meals — the same satiety hormones your body naturally produces from protein- and fibre-rich foods. Researchers had to block both at once to restore appetite; either alone was covered by the other. Appetite is hormonal, not just mechanical.

The answer

150 mcg/day

Pregnancy: 250 mcg/day. Main sources: iodised salt, dairy, seafood.

Aim for about 150 mcg of iodine a day (250 if pregnant). Most people get there through iodised salt, dairy and seafood; cut all three and you may fall short. You don't need to megadose — more isn't better, and very high intakes can disturb the thyroid too. Raw cruciferous vegetables have mild goitrogens, but you'd have to eat huge amounts uncooked for it to matter.

The answer

Yes enables T4→T3

RDA 55 mcg/day (one Brazil nut ≈ 70–90 mcg). In autoimmune thyroiditis, supplementation lowers thyroid antibodies.

Selenium lets your body convert storage-form T4 into the active T3 your cells use, so a deficiency can blunt thyroid signalling. Most people hit the 55 mcg target easily — a single Brazil nut can cover a day. In Hashimoto's, selenium modestly lowers thyroid antibodies, but don't megadose: chronically high selenium is itself harmful.

The answer

Lower T3

Only active T3 fell — T4, reverse-T3 and TSH were unchanged.

When you sustain an energy deficit, your body trims active thyroid hormone (T3) so it burns less — a normal adaptation, not thyroid disease. Here it appeared even in lean, long-term calorie-restricted people, and tracked with how much they ate rather than their body-fat level. Practically: expect some metabolic slow-down on a prolonged diet, and know that eating at maintenance again lets intake — and T3 — come back up.

The answer

Yes restriction raises cortisol

Counting calories didn't raise cortisol — but it did raise perceived stress.

Simply eating less nudged the stress hormone cortisol up over three weeks, and it was the calorie restriction, not the calorie-counting, that did it. Chronically elevated cortisol can chip away at muscle, worsen sleep and drive cravings — one reason aggressive crash diets tend to backfire. The practical read: keep deficits moderate rather than extreme, and don't stack a harsh cut on top of high life stress.

The answer

Yes — if you're a big reactor

High reactors ate more only under stress; they also preferred sweets across both days.

Stress doesn't push everyone to eat — it mainly moves the people whose cortisol jumps most in response. If that's you, expect stronger pulls toward food, especially sweets, on high-stress days. It's a small lab study, so treat it as a pattern worth noticing in yourself rather than a precise effect. Managing the stressor is more useful than white-knuckling the cravings.