Why do we get fat

Chapter 19 Fat: Where did it come from and where is it going? (1)
The time has come to roll up your sleeves, start tackling obesity, and go big.What we need to know is: what are the physiological factors that regulate the amount of fat in tissues.Specifically, knowing how our diet affects this regulation allows us to know what we are doing wrong and how to correct it.We also need to understand what exactly determines the "innate" tendency to become fat or stay lean, and what nutrients, diet and lifestyle can be used to change this tendency and combat obesity.

I'm going to start with a little bit of basic physiology and endocrinology, which, understandably, you may find difficult to understand.All I can promise is that if you pay attention, you'll eventually know everything you should know—why people get fat and what exactly we can do to fix it.

A simple question: why do we store fat?

Well, let me explain.Some of the fat in our bodies provides insulation, keeping us warm; others guard the periphery of our organs, protecting our more delicate internal organs; so what is the rest of the fat used for?For example, fat around the waist?

Often, the expert view is that fat storage is like a kind of long-term savings account — a retirement account that is only tapped in times of dire need.Meaning, you take in excess calories and stash them as fat in your body, which stays in adipose tissue until one day, your body realizes you haven't eaten enough (either dieting, or exercising, or maybe stranded in starvation. Island), will use the fat, as emergency fuel.

Fat is continuously shed from fat cells and circulates in the body for fuel.Fat goes back into fat cells if it is not being burned as fuel by other tissues.This cycle continues regardless of whether we have eaten or exercised recently. In 1948, Ernst Wertheimer, a German biochemist who emigrated to Israel and arguably the father of the study of fat metabolism, wrote: "The mobilization and deposition of fat occur continuously and alternately with the animal's Nutritional status is irrelevant."

The statement "independent of the nutritional status of the animal" is often cited in academic discussions of adipose tissue regulation.This means that even when a person or other animal eats fewer calories than it expends—in what Gene Mayer calls a "semi-starved" state—they still store calories as fat.As I pointed out earlier, this statement alone explains the coexistence of obese mothers and starving children in poor societies.

Most of the fat shed from fat cells is used as fuel throughout the 24 hours of the day, which the cells burn for energy.Nutritionists might think (and like to tell us) that sugar is, in a way, the body's go-to fuel.Because cells burn sugar before burning fat (unfortunately, this is a low-level misleading).Here's the premise: If your diet is high in sugar (and most people's diets are), your cells will burn a lot of sugar before you burn fat.

Imagine that you are eating a meal, and like most meals, this meal contains both sugar and fat.When fat is digested, it is sent directly to fat cells for storage.With sugars, the body requires more direct action.When sugar is digested, it appears in the blood as glucose, the "sugar" in blood sugar.Cells throughout the body use the glucose in the blood as fuel.But cells can't grab and use glucose directly on their own unless they're helped by some other partner in the body.

This helping partner is insulin.Insulin has many roles in the body, but one of the most important roles is controlling blood sugar.Your pancreas starts to secrete insulin before you start eating.In fact, whenever you think about eating, your pancreas is stimulated by your brain.This reflex also occurs without conscious thought.Insulin actually prepares your body for eating.When you take your first bite of a meal, more insulin is secreted.As the glucose from the meal begins to enter the bloodstream, more insulin is secreted.

Insulin then signals cells throughout the body to increase the rate at which they "take" glucose from the blood.These cells use some of the glucose they eat as immediate energy and some as backup.Muscle cells store glucose in the form of a molecule called muscle glycogen, liver cells store some glucose as liver glycogen, and some glucose is converted into fat.Fat cells, of course, store glucose in the form of fat.

As your blood sugar starts to drop, and with it your insulin levels, more and more of the fat stored at mealtimes is released from adipose tissue, taking up the vacant part of the blood for energy.The longer the time elapses after a meal, the more fat is burned (released more) and the less glucose is used (used up).The reason why you can sleep soundly at night and don't need to get up every few hours to open the refrigerator to find food is that the fat shed from the adipose tissue ensures that when you don't eat, all the tissue cells work normally until breakfast tomorrow.

So perhaps adipose tissue is more of a wallet than a savings card or retirement account.You keep putting fat in and taking fat out.During or after each meal, you gain a tiny bit more (more fat goes into the fat cells than comes out), and then after the meal digests, you lose a tiny bit more (the opposite happens).You also stay slim while you sleep.In an ideal country where you don’t get fat at all, the fat stored after eating during the day will be released at night and when you don’t eat, and will be completely consumed.

Fat cells are like an energy buffer, providing a place to store calories that you absorb at meals but don't use right away.When you need calories, fat cells put them back into circulation.It’s as if your wallet provides you with a place to store money from an ATM that you can use throughout the day.Only when your fat reserves hit their lowest point will you feel hungry again and be motivated to eat again.It's as if we like to set a minimum amount of cash in our wallets, at which point we head to the ATM to "restock".

However, the fact that fat moves in and out of our fat cells throughout the day doesn't explain how the cells decide which fats go in and which go out, and which fats have no choice but to be locked up inside the cells.The cell's decision is fairly simple: look at the size of the fat.

The fat in our body exists in two different forms with completely different purposes.The fat that gets in and out of cells is called a fatty acid, and it's this form of fat that we burn for fuel.The fats that have to be stored are called triglycerides, which consist of three fatty acids linked by glycerol.

The reason for this role assignment is super simple: triglycerides are too large to pass through the cell membranes surrounding fat cells, while fatty acids are small enough to slip through with relative ease.Fatty acids pass in and out of cells throughout the day and are burned as fuel when needed.Triglycerides are stashed away for emergencies.

When a fatty acid enters a fat cell, it links with a glycerol molecule and two other fatty acids to form a brand new triglyceride.So it got bigger in size, and now it can't get out freely through the cell membrane.So now these three fatty acids are trapped inside the fat cells until the triglycerides are broken down or destroyed before they can flow out of the cells again and back into the blood circulation.To put it vividly, people who bought large pieces of furniture found that the furniture was too large to enter when they passed the door.You have to take the furniture apart into small parts, move the pieces into the door, and put them back together inside.If you're moving and you want to bring a particular piece of furniture with you to your new home, you'll have to take it apart inside, put it back together outside, and repeat the process.

The upshot is that anything that increases the flow of fatty acids into fat cells, where they can be linked into triglycerides, helps store fat and eventually makes you fat.Anything that breaks down these triglycerides into fatty acid molecules, allowing the fatty acids to escape from fat cells, helps you lose weight.

It's actually very simple.As Edwin Astorwood pointed out half a century ago, there are dozens of hormones and enzymes that play a role in these processes, and it's easy to speculate how they could be disturbed so that too much fat comes in , too little going out.

Only one hormone dominates this activity, though, and that's insulin. Astorwood made this point 50 years ago, and it remains uncontroversial.As I said, the insulin you secrete first responds to dietary sugar, and the main purpose of doing so is blood sugar control.However, insulin is also responsible for coordinating the storage and use of fat and protein.For example, it ensures that your muscle cells get enough protein to do the necessary rebuilding and repair work, and it also ensures that you can store enough fuel (glucose, fat, and protein) to function properly between meals.Where we store our backup fuel is adipose tissue, and insulin is the master regulator of fat metabolism.This was discovered in 1965 by two scientists, Salomon Berson and Rosalyn Yalow.They invented the key technology for measuring blood hormone levels, and Jarlow later won the Nobel Prize for this work.Bosang could of course also share in this honor, but unfortunately he passed away before the award was presented.

Insulin does this primarily through two enzymes.The first is lipoprotein lipase, often shortened to LPL.I mentioned this enzyme earlier when we talked about how ovariectomized mice gain weight. LPL is an enzyme that pokes out of the membranes of different cells and pulls fat out of the blood and into the cells.

If LPL is on the surface of muscle cells, it pulls fat into the muscle, where it is used as fuel.If it is on the surface of fat cells, it will make the fat content of fat cells higher.As I said before, women's estrogen suppresses the activity of LPL on fat cells, so less fat is accumulated.

LPL simply answered many of the questions I had about where and when to gain weight.Why do men and women gain weight differently?Because the distribution of LPL is different, the influence of sex hormones on LPL is also different.

The LPL activity in the visceral adipose tissue of men is relatively high, so the viscera of men are more likely to obtain fat, while the LPL activity in the adipose tissue below the waist is relatively low.One of the reasons men gain weight from the waist up as they age is that they produce less testosterone, an androgen, which suppresses LPL activity in abdominal fat cells.Less testosterone means more LPL activity on visceral fat cells, which leads to more fat.

(End of this chapter)