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Understanding Insulin

Junk food

Confused about insulin? Tired of seeing it blamed for everything from obesity to acne without knowing exactly what it is? Here’s a quick explanation in plain English.

A lot of people have two big misconceptions about insulin:

Both of these statements are incomplete at best, and by the end of this article, you should understand why.

What is Insulin?

Insulin is a hormone produced in the pancreas. In healthy, non-diabetic, non-obese people, insulin is responsible for important things like…

That’s how insulin works in healthy people. Many people in the US today have diabetes or some degree of impaired insulin metabolism, and for those people, insulin metabolism is very different. In diabetes, the pancreas either don’t produce insulin at all (Type 1 Diabetes) or the rest of the body doesn’t respond properly to the insulin they do produce (Type 2 Diabetes/metabolic syndrome). This obviously means that insulin works differently in diabetes, but diabetes is not what this particular article is about.

So with that said, here’s a look at how insulin works, what insulin sensitivity and insulin resistance are, what they have to do with body weight, and why metabolic health doesn’t necessarily mean keeping insulin as low as possible. A lot of the evidence is taken from this review and this one, both free for anyone to read.

Insulin and Fat Storage

There’s a very common oversimplification that “insulin causes fat storage,” but it’s much more complicated than that.

In healthy people, insulin shows up after a meal to stabilize blood sugar. Yes, as part of this stabilization, it does store some energy as fat, but here’s the thing: a healthy person then burns that stored fat for energy in between meals. Just after a meal, you’re in “fat-storing” mode: insulin levels are high, glucose is being stored, and glucose production in the liver is turned down. But then between meals, you switch to running off that stored fuel: insulin levels are low, the stored glucose is being burned and more glucose is being produced in the liver.

When insulin is working this way, its fat-storage function isn’t “bad.” In fact, it’s good: it gives you a steady supply of energy throughout the day, so you don’t have to walk around with a nutrient drip attached to your arm all the time. And it also helps regulate appetite and let you know when your body is full. One of the major reasons why fructose may be more obesogenic than glucose is that it doesn’t raise insulin as much.

The technical name for this happy state of affairs is insulin sensitivity. In insulin-sensitive people, insulin shows up when it’s needed after a meal, does its job, and then packs up and goes home without a fuss. The person changes smoothly from “fat-storing” to “fat-burning” mode throughout the day, and the net result is that their weight stays stable.

In other words, available evidence does not show that insulin is “bad” or that it “causes obesity.” Healthy people have insulin highs and lows throughout the day, and don’t gain weight. So then what is the problem with insulin?

When Insulin Metabolism Goes Wrong

The opposite of insulin sensitivity is insulin resistance. In insulin resistance, your body produces insulin normally, but doesn’t use it properly, and the whole delicate balance of blood sugar regulation, fat storage, and fat burning breaks down. This causes all kinds of problems, including chronically high insulin, and it can cause weight gain because “fat-storing” mode is always on, and “fat-burning” mode is always off.

This is what most people are probably thinking of when they say things like “high insulin levels cause weight gain,” but insulin resistance is not the way insulin works in healthy people. It’s a very complicated problem, with many different causes. Just to name a few:

(Also, just as a note, it’s commonly repeated that eating saturated fat causes insulin resistance. This may be true in rats, but it doesn’t pan out in human trials. You can read an explanation here.)

Insulin and Carbs: What’s the Deal?

The list above should make it very clear that carbs are far from the only thing affecting insulin levels. In fact, they’re not even the only macronutrient that spikes insulin: protein will do it, too. The effect that carbohydrates have on your insulin levels depends on many different factors:

It’s true that a lot of people today are already insulin resistant; those people might truly benefit from a lower-carb diet to restore insulin sensitivity. But this is a therapeutic diet for a disease state; that doesn’t make it a requirement for the entire population.

Summing it Up

Insulin is a hormone that affects fat storage and appetite; in healthy people, it naturally rises and falls over the course of a day. Many people do have chronically elevated insulin, and that really is a problem, but it doesn’t make insulin itself the bad guy. Let’s go back for a minute to the two big misconceptions about insulin from the beginning:

That’s not true. Insulin exists to keep you alive and regulate energy storage. Chronically elevated insulin levels are dangerous, but fluctuations throughout the day are completely normal.

That’s not true, either. In healthy people, eating carbohydrates from whole foods does not cause unhealthy insulin levels, and maintaining insulin sensitivity doesn’t have to mean eliminating carbs. Also, all kinds of other things affect insulin metabolism (sleep and exercise, for example).

Again, this all gets a lot more complicated when you start talking about diabetes. But it’s worth at least understanding how insulin works in healthy people – not everyone is a diabetic, and not everyone needs to eat like one!