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Cover of The Obesity Code by Jason Fung, MD

Metabolic health · fasting

The Obesity Code

by Jason Fung, MD

Jason Fung argues that body weight is regulated by hormones and food timing as well as calories. The book is most useful as a challenge to simplistic blame-and-willpower explanations of obesity.

01

The big ideas

  • Obesity is a chronic, biologically regulated condition—not a character flaw.
  • Insulin, food quality, sleep, stress, and meal timing can influence hunger and energy storage.
  • Frequent restriction followed by regain is common because the body adapts to weight loss.
02

What you can try

  • Reduce highly refined carbohydrates and ultra-processed foods.
  • Build meals around protein, fiber-rich plants, and minimally processed foods.
  • If appropriate, discuss a consistent eating window rather than grazing throughout the day.
03

Read critically

  • The book treats insulin as a more complete explanation of obesity than current evidence supports.
  • Fasting is not appropriate for everyone, including some people using diabetes medicines, pregnant patients, and those with eating-disorder histories.
  • Calories still matter even when hormones affect appetite and expenditure.
04

Questions to discuss

  • Would time-restricted eating be safe with my medicines and conditions?
  • What is a realistic first weight or waist goal for me?
  • Could sleep, stress, or a medication be affecting my weight?
About this summary

This is an original, AI-assisted overview prepared for patient education. It is not a substitute for the book, medical advice, or an individualized treatment plan.