Dissecting the Glycemic Index

Posted on Feb 01, 2019

One thing we’ve not touched on too much so far is the glycemic index, or GI.

GI is a pretty big deal in the general world of dieting, and there are all manner of cook books and weight loss diets based on the premise of GI. Health authorities and nutritionists are always telling us to go for low GI foods, and that anything high GI should be kept to an absolute minimum, as this can spike blood sugar and lead to weight gain.

As you’ve probably guessed, we’ve got a fairly middle ground view of GI, and while it’s not totally redundant, you really don’t need to worry about it as much as many people believe.


What is the Glycemic Index?

The glycemic index is a scale which measures how quickly foods are broken down into sugar in your body once you eat them. Each food is given a score of up to 100. (Pure sugar (glucose) scores 100.) Within this, foods that have a score of 55 or less are considered low-GI, between 56 and 69 is medium-GI and 70 and above is high-GI.

The idea is that by picking mostly low-GI foods (and some medium) that you reduce spikes in blood sugar and insulin, which keeps your risk of diabetes, over-eating and weight gain to a minimum.

You could have probably guessed this, but the foods that come in low on the GI scale are things like rolled oatmeal, beans, fibrous vegetables, whole-wheat pasta and so on, while high-GI foods are white bread, sweets/ candy, white bagels, pretzels and some high-sugar fruits like pineapple. In between you get your medium-GI foods – stuff like different types of rice, instant oats and wholemeal bread.


Why You Needn’t Worry About GI

On the face of it, GI seems a sensible system – after all, it makes sense to try and keep spikes in blood sugar low for the most part, but there are several flaws that mean GI really isn’t worth bothering about.

For starters, in the initial GI trials, foods were tested in isolation, meaning that when the researchers examined the effects of pasta on participants’ blood sugar, the participants ONLY ate pasta. That’s plain pasta – no sauce, no meet, no cheese and no veggies. It was the same for bread, beans, bagels – everything. Think about it - how often do you do that?

As soon as you add another macronutrient into the mix, you change the GI, as protein and fats will slow digestion, and decrease the speed of the food breaking down, so your high-GI white pasta suddenly turns into a medium or low-GI meal once you pour that tomato sauce with extra lean beef on, and sprinkle some cheese over the top.

Additionally, in the initial trials, researchers scored GI based on 50 grams of carbohydrate from each food. For a food like rice, that’s not too much, as 50 grams of carbohydrate comes in at around 70g or 1/3 cup (raw weight.) That’s not too big a serving size, but to get 50 grams of carbs from broccoli, you’re looking at almost a kilo – good luck eating that!

A better system would be to base GI off the standard serving size of a food, which is where glycemic load (GL) came in. While this is a little more accurate, the same issue still arises with the fact it measures foods in isolation.


It’s Only Carbs

Typically, the foods you see labeled with a GI are those that are predominantly carbohydrate-based. This is okay, but there are other foods that have an impact on blood sugar too.

Low-fat dairy products and whey protein actually have a significant effect on blood sugar levels, yet don’t make the GI list.

With that in mind too, it’s clear to see that GI isn’t a measure of how “healthy” a food is at all. Whether clean eating or flexible dieting, we’d all say that foods like cottage cheese, watermelon and whey protein are pretty healthy, yet going by GI, all these score highly and could therefore be seen as ‘bad’.


No Ranking for Satiety

One of the supposed benefits of GI is that lower-GI foods keep you feeling full, due to the slower digestion and (sometimes) higher fibre content.

This is fine in theory, but take a food like white potatoes – they score as a high GI, but also rank as one of the most satiating foods out there.


Is GI Defunct?

Pretty much.

For diabetics, it can serve some purpose, but considering that most of us eat mixed meals (containing at least protein and carbs, if not protein, carbs and fats) GI won’t really make much difference, as digestion speed and food breakdown will be altered depending on the composition of the meal.

On the whole, low-GI foods do tend to be more nutrient-dense, higher in fibre and protein, plus may help with a more sustained energy release, but that definitely doesn’t mean you should discount high-GI foods.

Not only are they perfectly fine to include in your diet, some actually have a whole host of health benefits. What matters more is context:

Is your diet balanced, are you hitting macros, feeling full and enjoying what you eat? If so, you’re doing it right and don’t need to worry about GI.

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