• Allison Fahrenbach

Insulin, Carbs & Fat Gain

"Insulin is bad."

“Insulin makes you fat."

“Carbs spike insulin.”

"Therefore avoiding carbs leads to fat loss.”

By now I'm sure most of you have heard statements like this, statements based on the idea that the consumption of certain foods (like carbs) will cause your blood sugar to spike and consequently cause your pancreas to release more insulin. This insulin then shuttles that sugar into your fat cells and as a result, you gain weight.

Like many things in diet and fitness- these over-simplified, generalized statements are both true and not true.

What's true:

1- Some foods can influence a spike in blood sugar. There is no doubt that certain foods are digested at different rates and along different pathways in the body. Any basic knowledge of human digestion will simply point out that some foods break down and digest faster than others. It is also true that simple carbs and sugars break down faster, enter the bloodstream faster, and therefore raise your blood sugar faster.

But this oversimplified statement is problematic because this is only typically the case of foods consumed singularly. A single banana for instance.

However, we rarely consume singular foods. A banana consumed with peanut butter for example, or a banana eaten with a protein shake, has a much DIFFERENT impact on your blood sugar than just a banana by itself.

2- Certain foods do digest faster and may cause you to become hungry again much quicker. Since it is true that certain foods digest and break down quicker it’s also true that some foods have less sticking power in terms of helping you to feel full for a longer period of time. For example a handful of chips is going to have far less of an impact on your satiety (fullness factor) then a bowl of oatmeal. Simple, processed carbs, in other words, tend to NOT help you feel full because they digest quickly.

The "insulin makes you fat" statement is based on the fact that eating these faster digesting foods causes a rapid rise and fall in blood sugar, which leads you to over-eat since you never feel full. This leads to weight gain.

But it's really NOT that simple.

What's NOT true:

1- Insulin is not a fat storage hormone.

This is a total fallacy. Insulin is in fact not a fat storage hormone but a sugar storage hormone. Just think about it, all of the statements about insulin are related to sugar in food, sugar in the digestive system and sugar in the bloodstream. Therefore insulin is not about fat storage but rather sugar storage.

2 -Sugar isn’t always stored as fat.

While it is true that insulin shuttles sugar out of your bloodstream it’s not true that it’s automatically then stored as fat. Your body has two other options for storage- the liver and muscles- that are first filled with sugar in the form of glycogen. Insulin pulls the sugar from your bloodstream and primarily fills these two other storage tanks first. If those two are already full then it may resort to filling your fat cells.

Let’s look at two people- one who is sedentary and one who does intense strength training daily. People who strength train tend to burn more glygocen (stored sugar) which helps deplete your glycogen levels and ensures that you have room to accommodate any incoming carbs (sugar), therefore preventing it from being stored as fat.

A sedentary person on the other hand is far more likely to store incoming carbs as fat.

3-Your blood sugar is going to fluctuate regardless of what your diet and exercise habits look like. The theory that controlling your blood sugar will help you control your weight has some credibility. If blood sugar levels are stable it helps create less rises and falls in appetite, and therefore tends to prevent overeating. However it’s almost impossible to keep your blood sugar level all the time. That would be like trying to never feel too hot or too cold or too sleepy or too energetic.

Your blood sugar levels are actually designed to fluctuate and your body is appropriately equipped to handle these fluctuations on its own. If you notice you feel dramatic rises and falls in energy then it might be worthwhile to examine your food choices and ensure you're selecting nutrient dense foods that will help promote a sense of satiety and help even out your blood sugar levels.

But aside from that you don't need to resort to any sort of restrictive dietary measures unless you have some sort of physical condition that influences your ability to regulate blood sugar on your own.

4- Eating carbs doesn't guarantee a spike in your insulin. While carbs (particularly simple carbs) in the diet are the closest linkage to an increase in blood sugar levels there is no guarantee that eating carbs will cause blood sugar to spike.You have to remember that the rate of digestion is just ONE of the things that influences a spike in blood sugar. It's not the only thing.

This is why many people fall into the trap of believing that whole grain, complex, low glycemic carbs are far superior to other carb sources. This mindset is build on the premise that even though these carbs ultimately end up as sugar, because they take longer to breakdown and digest, the increase in your blood sugar is slower and the insulin spike is subdued.

But, as I mentioned earlier, the glycemic index is the measure of SINGULAR foods. And rarely do foods get consumed singularly.

For example eating a higher glycemic food alongside some fat and protein will slow down the digestion and thus the insulin response.

In this way, you can effectively adjust the glycemic index of any carb by consuming it with some fat or a protein source.

And even then, there is often an insulin response from foods that aren't even carbohydrate based.

Red meat and whey protein are good examples. Both have been shown to cause a high insulin response. It's not really known why this is the case, but it does lend itself to the credibility that carbs are not the only food source that triggers an insulin response in the body.

Lastly, it’s important to keep in mind that the amount of sugar your body has to deal with is always highly influenced by portion control. It's all about NOT eating foods in amounts beyond what the body can handle.

Eating a smaller portion of a simple carb (like a couple of pieces of candy) won’t have nearly as much of an impact on your blood sugar levels as say eating a big bowl of fruit salad.

Even though the fruit has more fiber and a slower rate of digestion, the little bit of candy won’t have that much of a spike in blood sugar simply because there isn’t that much to begin with.

In other words- higher portions of a traditional low glycemic or slower digesting carb food can elevate your insulin response more than a small portion of a high glycemic fast digesting carb.

5- You don’t need insulin to store fat.

Insulin does not hold the monopoly on fat storage. You can, and do, store fat without an insulin response. No matter what you do and no matter what your diet looks like, it’s virtually impossible to prevent fat storage from happening. For example, the body primarily stores triglycerides (fat) in fat cells called adipocytes. These fat calls can expand, if needed, to hold excess fat, but they do have a limit on how much they can expand. When they reach their limit of expansion the body synthesizes new fat cells. This creates seemingly endless space for fat storage, whether it originated as dietary fats or carbs.


Yes, blood sugar levels and insulin do play a role in your diet, eating habits, and overall body weight.

Yes, eating foods that help you feel full longer will help you eat less over the long term and possibly give you more energy to fuel physical activity.

Yes, if you’re someone who doesn’t get much physical activity it’s probably a good idea to avoid a lot of simple sugary substances since you’re not burning off that much sugar in your system to begin with.

With that said, it’s still important to understand that trying to control your body fat levels by way of controlling blood sugar and insulin is a limited process that cannot guarantee weight-loss nor will it promise protection against weight gain. There are LOTS of factors that contribute to your body fat levels and how your body stores incoming food- and MOST of them are completely unrelated to insulin.

Lastly- insulin is not "bad". It's not some demon hormone. It's actually CRUCIAL. Insulin’s job is a very important one: when you eat food, it’s broken down into basic nutrients which make their way into the bloodstream. These nutrients must then be moved from the blood into muscle and fat cells for use or storage, and that’s where insulin comes into play: it helps shuttle the nutrients into cells by “telling” the cells to open up and absorb them.

So, whenever you eat food, your pancreas releases insulin into the blood. As the nutrients are slowly absorbed into cells, insulin levels drop, until finally all the nutrients are absorbed, and insulin levels then remain steady at a low, “baseline” level. This cycle occurs every time you eat food and it's a crucial process. Just because one of insulin's roles pertains to fat storage does not mean it's only role is fat storage.

If you’re overweight and sedentary, and you happen to eat a lot of processed, simple, sugary carbs then yes, it's going to cause problems with weight management. Over time your body is going to have more and more trouble dealing with insulin, which can develop into Type 2 diabetes and place you at a greater risk of heart disease.

HOWEVER if you are lean, train regularly and eat a sensibly healthy diet, you won't have these problems and likely don't need to freak out over the occasional higher glycemic carb and how it impacts your insulin.

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