The Definition of Obese People:
It’s Way More Interesting Than You Think

What is the definition of obese people?

Definition of Obese People
Before we can fix obesity, we first must understand what it is.

According to the Centers for Disease Control and Prevention, an adult who has a “Body Mass Index” (BMI) of 30.0 or higher is obese. BMI is calculated by comparing a person’s height and weight. It is a messy definition, since it doesn’t measure body fat per se. It doesn’t take into account body shape or type. And it doesn’t tell us anything about what causes the problem.

A second definition of obese people

A second definition is far more illuminating. We quote author Steven O'Rahilly of the University of Cambridge Metabolic Research Laboratories' Institute of Medical Science, who, in the November 19, 2009 issue of Nature wrote:

“obesity is most simply defined as a state in which the total amount of triglycerides stored in adipose tissue is abnormally increased.”

Let’s break this down. What are triglycerides? And what is “adipose tissue”?

  • Triglycerides are a form of fat. A triglyceride is three fatty acids chemically tied together with a molecule of glycerol. Triglycerides are bigger than fatty acids.
  • Adipose tissue is a fancy science-y name for fat tissue.

So what the O'Rahilly definition of obese people tells us is that, at a fundamental level, someone who is obese has too much of this bigger kind of fat in their fat tissue.

Implications of this definition of obese people

Let's ask ourselves: what might cause fat tissue to store too many triglycerides? The answer, it turns out, is interesting. A well-established biochemical pathway shows that a molecule called alpha-glycerol phosphate (or glycerol-3-phosphate as it’s sometimes known) plays an incredibly important role.

As science writer Gary Taubes has pointed out, when you have alpha-glycerol phosphate floating around in the fat cells, an excess amount of triglycerides will get stuck in the fat tissue.

In other words, high levels of alpha-glycerol phosphate in the fat cells cause obesity, as it is defined by O'Rahilly.

So what controls alpha-glycerol phosphate?

As Taubes and other have pointed out, we make alpha-glycerol phosphate in response to burning blood sugar. When you burn glucose in the fat cells, this creates alpha-glycerol phosphate as a byproduct.

How does glucose get into the fat cells to begin with?

The most typical pathway involves the hormone insulin. Insulin pulls blood sugar into fat cells so that the sugar can be burned for fuel.

How do we make insulin?

Again, complicated answer. But one key driver of insulin is the sugar and carbohydrate in our diets. When we eat excessive amounts of sugar and/or carbs (particularly refined carbs that are easy to digest), this spikes our insulin levels.

So what does all this tell us?

Working backwards, we see that carbohydrates and sugar must be implicated in obesity. To summarize:

1. When you eat carbs and sugar...

2. This drives the pancreas to secrete insulin...

3. Insulin pulls blood sugar into the fat cells (also known as adipocytes)...

4. The blood sugar inside the fat cells is oxidized for fuel...

5. This reaction produces alpha-glycerol phosphate...

6. Alpha-glycerol phosphate binds more free fatty acids into triglycerides than normal...

7. Triglycerides are too big to escape the fat cells and thus get stuck inside...

8. So an abnormal amount of triglyceride gets trapped in the fat tissue...

9. This, by the definition cited above, is obesity.

Challenge any obesity researcher about this chain of cause and effect.

Go ahead. Notice that nowhere did we mention words like “calories” or “over eating” or “exercise.” All we talked about was the biochemistry of how sugar impacts the fat tissue. And this clearly implicates carbs as the primary cause of overweight and obesity.

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