Thursday, 25 October 2012

The glycaemic index: Broken down (pun not intended)

I hope you have your learning pants on, because today we’re going to get scientific.

I go on a lot about glycaemic index (GI) and low GI meals. One might say I am obsessed with it. One might be right. So for the purposes of clarity and doing my job for generalised nutrition education, I’m going to do a short explanation of the concept, why it’s so important to me, and why it should be important to you.

For those of you too lazy to read my three pages of hard work, I made this:

Infographic on Glycaemic Index by An Unlikely Dietitian
For a larger image, or to download, click here.
You’re welcome.

For the wonderful nerds who are still here, let’s get started.
What is glycaemic index?

Simply put, glycaemic index describes how quickly the carbohydrates from your meal enter into your blood. 

What is the difference between low GI and high GI?

A high glycaemic index means the carbohydrates from your meal enter your blood quickly (thus causing a blood glucose spike). A low glycaemic index means the carbohydrates from a meal are released into your blood slowly (meaning you have a steady blood glucose for a few hours after your meal).

Let’s quickly talk about what happens when we eat carbohydrate.

When you eat carbohydrates, and those carbohydrates enter your blood, your body releases insulin into your blood. Insulin’s most fundamental role is to remove glucose from the blood and shift it in your cells. Once it is in your cells, the glucose can be used for energy.

Insulin is good. Without it we would die. But if we have an insulin spike (which happens after a blood glucose spike), things start going awry.

So the problem with high GI foods is what exactly?

· Insulin spikes promote formation of fat tissue and inhibits breakdown of fat.

· Insulin spikes cause your blood glucose to dip too low (insulin doesn’t really have a great sense of moderation and balance) which then causes you to be hungry sooner.

· Blood glucose spikes and insulin spikes damage your pancreas, increasing risk of diabetes type 2.

· High GI meals mess with your cholesterol (reducing HDL, “good fats”, and raising triglycerides, “bad fats”).

· High GI meals increase inflammatory markers, with increases risk for many inflammatory diseases such as diabetes, heart disease, osteoarthritis, and polycystic ovarian syndrome.

· High GI meals leave your gastro-intestinal tract faster, which leaves your stomach empty and growling for something more.

And as anybody who has ever met me knows: I am always hungry as it is. I don’t need that to be worsened by a high GI diet.

So low GI foods…

· Delay hunger and keep you fuller for longer, thereby preventing obesity.

· Protect your pancreas and prevent diabetes type 2.

· Prevent inflammation and therefore diseases such as diabetes, heart disease, osteoarthritis, and polycystic ovarian syndrome.

· Improve your blood cholesterol and therefore reduce risk of heart disease.

· Improve your body’s blood clotting and therefore reduce risk of heart disease.

So how do we know what foods are high GI and low GI?

Glycaemic index of a carb is measured on humans, and is given a value of:

- Below 55 (low GI)
- 55-70 (medium GI)
- Above 70 (high GI)

But I tend to ignore these because (1) what you eat with the carbohydrate changes the GI anyway (unless you're one for eating a big bowl of plain pasta by itself), and (2) I don't have time or the energy to sit and check the GI of every food I eat.

If you are curious, you could check the GI of a food using this website, or download a list of low/high GI foods. But I prefer to just use a general guide when I put my meals and snacks together, to bring the GI lower and keep me going for longer.

The guidelines are...

1. Protein lowers the GI of a meal.
Include lean meats, fish, legumes, an egg, low fat dairy or peanut butter with your meals.

2. Fat lowers the GI of a meal.
Include a small amount of canola oil, olive oil, soft margarine, olives or avocado in your meals.

3. Fibre lowers the GI of a meal (especially when the carbohydrates are trapped within the fibre).
High fibre foods include whole fruits and whole vegetables, oats, legumes, pasta and wholegrain foods such as wholewheat bread. Bran cereals are a good example of starch being trapped within a "fibre shells", whereas cereals such as cornflakes have no fibre surroundings.

4. Acidity will lower the GI of a meal.
Try adding some vinegar or lemon juice to your salad or avocado sandwich, or have a citrus fruit with your snack.

5. Processed starches or fruit will raise the GI of a meal.
Choose whole pasta or oats instead of instant noodles or instant oats. Choose whole foods instead of mashed or pureed foods.

6. Cooking starches and fruit will raise the GI of the meal.
Avoid overcooking starch – for example, cook your pasta until al dente and no further. Cooling your starch slightly before eating will also reduce its GI.

7. Overripe fruit have a higher GI than underripe or ripe fruit
Try avoid bananas when they’re nearly liquid. Slightly green bananas are even better.

8. There are two kinds of starch: Amylose and amylopectin. Amylose is more difficult to break down and therefore is absorbed more slowly. Most starchy foods have both kinds, but the starches with more amylose will have a lower GI.
Include wholegrain cereals (such as whole-wheat, oats, bulgur and barley),  long grain or wild rice, legumes, sweet potatoes and russet potatoes, which all have high amylose contents.

9. Phytochemicals (phytic acid, polyphenols, lectins) inhibit starch digestion and lower the GI of your meal.
Eat legumes, excellent sources of phytochemicals, at least 3 times a week.

These of course are guidelines to keep in the back of your mind. Guidelines, not rules. So please don't go out there and start emptying bottles of vinegar over your sandwiches, or eating your potatoes raw. A balanced, healthy, delicious diet is the aim here.

Since starting this, I have realised this will have to be first of a series of posts. I need to write about why we need carbohydrates and must never, ever, ever, ever, ever, ever eat carb-free diets. Ever. I also need to chat about the new kid on the block, glycaemic load (GL).

So stay tuned dear readers! And remember to...

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