The Glycemic Index And Insulin

Understand the basics to make an informed decision.

There are two “new” bad boys in the nutrition bubble: carbohydrate and insulin. The carbohydrate-insulin-hypothesis claims that carbs are noxious for your health because they raise blood sugar and, as a consequence, insulin, inherently making you fat. In the light of this, insulin gets a bad reputation for being the hormone driving adiposity. The glycemic index of foods is rediscovered in a desperate attempt to keep blood glucose as low as possible. But is this even necessary? Let’s take a look!

Under normal conditions glucose concentration in the blood must be precisely controlled to keep all bodily processes functioning smoothly. Why? Glucose is a very reactive molecule and can damage several tissues if its blood concentration is too high. If you want to know what this looks like, just look at the symptoms associated with diabetes mellitus (blindness, necrotic tissue, neuropathies…). On the counterpart, if blood glucose is too low, you start getting dizzy, further you fall into coma and in the worst case you die. Your body certainly doesn’t want that to happen!

The Glycemic Index

Although practically all carbohydrates end up as glucose in your blood, different carb sources can affect the rate at which glucose appears in your blood. This is the foundation on which the glycemic index (GI) was built.

The glycemic index is a ranking of carbohydrates on a scale from 0 to 100 according to the extent to which they raise blood sugar levels after eating. Foods with a high GI are those which are rapidly digested and absorbed and result in larger fluctuations in blood sugar levels. Low GI foods, due to their their slow digestion and absorption, produce slower rises in blood sugar
and insulin levels.

Surely you have heard about blood sugar “peaking” and then “crashing”, which (supposedly) leads to all kinds of problems: tiredness, hunger etc. However, these blood sugar fluctuations are more likely akin to gentle waves on the coastline of your blood vessels. Why? There are only around 4 grams total of glucose in your blood at any time point and blood glucose levels are maintained within a narrow range (homeostasis) [Source]. Again, the idea that our body can’t handle blood sugar fluctuations alone stems from diabetes patients, where there is a pathologic disturbance of the blood glucose homeostasis.

Is this even useful?

Remember that the GI is a tool to manage blood glucose levels and was “invented” to help diabetes patients. These individuals suffer from a disregulated glucose metabolism, so they need to worry about it, but healthy individuals really don’t

The arbitrary simple vs. complex carbohydrates classification through the GI does not work as a fat loss tool neither. Calorie per calorie simple and complex carbohydrates have the same impact on body composition. Therefore, the use of these terms on food labels has little nutritional or physiological impact.

The glycemic indices of various foods, depending on whether white bread or glucose is used as the
reference food. You’ll find significant variation in these values due to differences in methodology, as even the temperature of food impacts its GI. If you are healthy, you can forget about this!

Taking this even further, the GI isn’t even a very reliable measure. People’s blood sugar responses are highly individual, even in the same individual at different times of the day [Source]! In addition, the GI is based on each food being consumed in isolation, not within a meal. Other nutrients in a meal can greatly change the digestion and absorption rates. And as you probably know, each meal should include not only carbs, but also a serious amount of protein and some fats, each of which impact the GI of a meal.

Body Composition and the GI

Does the GI of a diet determine its effects on your body composition?

No. Research comparing weight loss diets with the same energy content and macronutrient composition but a different GI consistently fail to find changes in muscle retention or fat loss between groups [Source]. In addition, the glycemic load (grams of carb x GI) of the diets didn’t affect appetite as measured by perceived hunger, fullness, compliance and ad libitum food intake. Even markers of health were unaffected.

Note that if you are on a fat loss diet, you often have no other means as to reduce carbs to lower energy intake. Protein and fat both need to cover a certain base and therefore stay relatively the same, but with carbs you can go as low as you need to. This doesn’t mean that you can’t lose weight while eating carbs. It’s just a matter of energy balance.

Chantal’s competition diet. Carbs had to be cut down to 80 grams at the end to maintain a deficit that allowed her to cut significant amounts of body fat. Protein and fat also got lowered, but had to cover a “health-threshold”. Nobody ever cared for the GI or insulin.

If you’re worried that the above may not apply to bulking, these results were replicated in a study of weight gain instead of loss [Source].

Possible Advantages of low GI diets

A meta-analysis and systematic review [Source] found that the effects of the GI on health markers are dependent on the health markers’ initial values. Therefore low glycemic load diets are good for your health if you’re initially unhealthy (like obese or diabetic), but in healthy populations there was no effect.

This is an example of a ceiling effect, a phenomenon you’ll find plenty of in physiology, but people constantly fail to understand: more of a good thing isn’t necessarily better! You can’t fix what isn’t broken, so if you’re already healthy, eating “healthy” foods plateaus at some point to make you even healthier. You still need to have a solid base, but you have the wiggle room for your favorite treats.

Long story short: you don’t need to worry about the GI. Your body already has blood sugar well under control if you’re healthy. If the homeostatic mechanisms of blood sugar do not function properly as in diabetes, than the GI or glycemic load of your food possibly becomes relevant.

The Carbohydrate/Insulin Hypothesis

I guess you may have heard that carbs and/or insulin are per se fattening. This is called the carbohydrate-insulin-hypothesis which claims that carb intake spikes our blood glucose levels, which in turn triggers insulin to get released, which causes your body to store blood glucose as fat.

The problem with this hypothesis is that it uses several half-truths to prevaricate an otherwise glaring weakness (or even logical error): energy balance.

Insulin – facts

Blood glucose management is hormonally regulated, primarily by the antagonistic pancreatic hormones insulin (glucose storage) and glucagon (glucose release). When blood glucose levels are elevated, insulin is released by the β-cells of the pancreas and release of its rival hormone glucagon is reduced. Glucose is then either used directly to generate energy or stored mainly as glycogen in liver and muscle tissue. If enough fatty acids are around and glycogen storages are full (which is mostly the case when you are in a caloric surplus), synthesis of fat tissue is initiated. This is a neat regulate mechanism working 24/7 to keep us alive. Fluctuations in insulin levels are not bad, they are completely normal.

Why should carbs even be problematic for our bodies? Evolution has made sure our bodies can deal with carbs, because it is found in many of the world’s most nutritious foods: fruits. Fruit is in fact one of the foods humans have consumed for the longest period of our genetic existence. Fruit has been a staple in the human diet ever since we were still monkeys living in the jungle. There are a very small percentage of humans, for example the Inuits, that can’t deal that well with carbs, but for most of us the regulation of carb intake by insulin release works just fine.

In other words, it’s not as simple as “more insulin means more fat storage”. Insulin is indeed a storage hormone, but it cannot store what isn’t there and it stores nutrients not just in fat tissue but also muscle tissue. Insulin is our friend, certainly not our foe!

Closing words

Carbs are perfectly safe to eat. Fluctuations in blood glucose and therefore insulin production are normal and necessary. Metabolically healthy individuals don’t need to worry about the GI, blood glucose levels or insulin.

All of this may sound too good to be true, but sometimes you really literally can have your cake and eat it too. You can get shredded without limiting your carb intake. Even sugary foods are okay for dieting, as long as they fit in your calories. And you certainly shouldn’t avoid eating fruit or dairy because too much fructose or lactose will make you fat. That’s exactly the kind of broscience that drives people into following obsessive and monotone diets that aren’t healthy in psychological or nutritional terms.

Now before you go tell everyone it’s ok to stuff yourself with candy, please remember this article only deals with carbs in the light of “are they okay to consume”. Different carb sources contain different macros (fat and protein) and different types of carbs and fibre, but lots of other substances as well, notably micronutrients. This cannot be emphasized enough. Calories from
sugar may not differ from calories from sweet potatoes, but sugar still contains empty calories, whereas sweet potatoes are packed with other stuff that’s good for your health. This makes it important to have a good baseline nutrition with plenty of fruits, legumes and vegetables as your staple carb sources to make sure you cover your health-needs. Beyond that you are free to “supplement” with other carbs as you fancy.

Are you struggling with a boring diet or are you not enjoying your training anymore? Contact us and let us talk how we can reach your body composition or strength goals and let training and eating be fun again!

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