Why We Eat (Too Much) | Andrew Jenkinson

Summary of: Why We Eat (Too Much): The New Science of Appetite
By: Andrew Jenkinson

Introduction

Embark on a fascinating journey through the history of life on Earth and our innate capacity to regulate energy intake with our summary of Andrew Jenkinson’s ‘Why We Eat (Too Much): The New Science of Appetite’. This book explores the ever-evolving relationship between energy, evolution, and human biology, while demonstrating why our metabolic system is not adapting well to the modern Western diet. Discover the concept of endosymbiosis, the influence of oxygen processing, the impact of cooking, and the role of leptin in controlling weight. Delve into the intricate tie between energy consumption, organ growth, and the human brain, and understand how our body’s negative feedback systems aim to prevent obesity.

Origins of Life Energy

Our planet starts with simple carbon-based chains of chemicals that found a formula to replicate themselves. These structures grew into increasingly complex replicants until the single-cell bacterium appeared. The bacterium’s DNA code allows it to reproduce and grow, but it needs energy. Early bacteria couldn’t process oxygen, limiting their energy generation. Then, a new kind of bacterium that could process oxygen emerged, creating a powerhouse that could generate vast amounts of energy. Older bacteria didn’t have to compete but instead, swallowed and lived with these newcomers in an arrangement called endosymbiosis. The mitochondria, the energy powerhouse inside every plant, fish, fungus, and animal’s cell, is the ancestor of these energetic bacteria. Life on Earth as we know it wouldn’t be possible without these tiny power stations known as mitochondria.

The Energy Budget of Humans

All living beings, including snakes, mushrooms, birds, roses, and humans, share a single-celled ancestor and generate energy in the same way. Mitochondria converts food into energy, and ATP stores it. Humans have big brains because they skimp on other organs. An animal’s energy budget is related to its size. Larger animals require more energy, and primates have similar energy budgets to humans. Gorillas’ gastrointestinal tracts are significantly longer because they don’t cook their food.

Fire’s Pivotal Role

Prehumans evolved larger brains due to the discovery of fire, which allowed them to transfer energy resources to their brains. The advent of fire coincided with cephalization, the evolution of larger-than-average brains. By cutting up meat and cooking it over fire, our ancestors made it easier to chew, swallow, and digest. This made the transfer of energy to the brain more efficient, freeing up energy for an ever-larger brain. The discovery of fire not only changed the way we ate but also made us who we are culturally and biologically.

Negative Feedback Systems and Survival

The book emphasizes the significance of negative feedback systems in the survival of Homo sapiens. All living organisms need negative feedback systems to keep their body functions and behaviors in check. The human body’s survival depends on timely self-correction in case of dangerous deviations. Negative feedback systems have two components: a sensor and a switch. An example of this is the kidney, which regulates hydration through two switches – thirst and urine production. The kidney senses hydration levels and sends messages to these switches accordingly. The same system is used to control energy consumption, use, and storage in the human body.

The Body’s Negative Feedback System

Our bodies have negative feedback systems for regulating various bodily functions, such as water intake and energy storage. The body can hoard energy temporarily, but overeating raises the metabolic rate, preventing excessive weight gain. The experiment by Ethan Sims in 1976 on overfeeding inmates confirmed that overfeeding can increase the metabolic rate by up to 10 percent. This finding suggests that our bodies also have negative feedback systems that protect against excessive weight gain, but it remains unclear whether the same mechanism protects against weight loss.

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