1 September 2009

Making the Most of GI News

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Neville said...

Apples and bloating of the stomach.
For the last 70 years I have always eaten several apples a day and always have had good health. However, a couple of years back I started getting bad bloating several hours after eating apples. Researching on the web I found a study that linked certain apples to this problem but could not find which apples were the cause. Do you have any information on the link between certain apples and bloat?

GI Group said...

Hi Neville, We have asked Karen to comment on this and will post her reply as soon as possible.

ministaren@gmail.com said...

I have a question:

Is it true that the starches in cooked potatoes turn into insoluble fibres when cooled down? And if so, wouldn't that lower the GI significantly?

Thanks in advance.

Unknown said...

I am looking for a high GI fruit snack to enjoy post exercise and that I don't have to worry about keeping fresh. Fruit Roll-Ups and their high GI has caught my eye, but the list of ingrediencts makes me balk. What about similar snack products like Fruitabu which are actually made of fruit? Is it the process of making the roll or the ingredients that give Fruit Roll-Ups their high GI?


GI Group said...

Hi Kevin, We haven't tested Fruitabu so can't really comment. However, here's what Dr Emma Stevenson writes about the highs and lows of GI and recovery in The Low GI Handbook:

'Post-exercise recovery is a critical challenge for athletes and recreational exercisers, and one that’s all too often overlooked. Good nutrition between training sessions is vital for rapid and effective recovery. This is the time when you need to top up your muscle and liver glycogen stores. And if you are an athlete who trains or competes twice a day, you really need to replenish your glycogen stores fast.

How? Well, you can achieve this by increasing both insulin and glucose concentrations in the blood stream rapidly during the immediate post-exercise period. Did you know that during the first 30–60 minutes after exercise, your muscles are particularly sensitive to increases in insulin and there is increased activity of a glycogen-storing enzyme called glycogen synthase. This means that when you eat or drink something, the glucose virtually ‘speeds’ into the muscle cells and is converted to glycogen. Consuming high GI carbs as soon as possible means you can really make the most of this ‘window of opportunity’.

What does this mean in practical terms? It means having 50–75 grams of carbs within the first 30 minutes after exercise and then a further 50–70 grams every two hours until you have consumed a total of 500 grams, or until you have eaten a high carb meal.

If your recovery period is longer than a few hours or restoring muscle glycogen after exercise is not your goal, then you don’t need to eat large amounts of high GI carbs straight after exercise.

Dr Stevenson and her colleagues ran a trial in which they asked athletes to run on a treadmill for 90 minutes at 70 per cent of their maximum capacity (to reduce their muscle glycogen stores). Then over the following 24-hour period, they gave the athletes a high GI or low GI diet consisting of 8 grams of carbohydrate per kilogram of body mass in mixed meals that would typically form part of an athlete’s diet. Back at the lab the following morning, they asked the athletes to run to exhaustion on a treadmill at 70 per cent of their maximum capacity.

What they found was that the athletes’ endurance capacity was significantly improved after a low GI recovery diet compared with a high GI diet. In the low GI trial, the athletes used more fat as a fuel source which meant they ‘spared’ their muscle glycogen stores for later in the exercise session.

But, when they repeated this trial with intermittent exercise (typical of soccer, hockey, netball and rugby) rather than an intense exercise session, they found no differences in recovery of endurance capacity between high GI and low GI diets.

However, if you are exercising primarily for your health and fitness or for weight loss, a low GI post-exercise meal may help your body maintain a higher rate of fat burning (oxidation).

Here’s what happens. Your body’s fat oxidation (a technical term that means fat burning) will be elevated post-exercise but will be rapidly suppressed if you eat high GI carbohydrates. This is because your body’s higher insulin response to the blood glucose spike after a high GI meal
or snack suppresses enzymes that oxidise fat. This basically means you burn less fat and more carbohydrate.

Your body’s lesser insulin response after a low GI carb meal or snack suppresses fat oxidation to a lesser extent. What’s the benefit? It means your body continues using fat as an energy source long after you have finished exercising. Because weight gain tends to creep up on most of us, every little bit counts!

If you are exercising primarily for your health and fitness or for weight loss, a low GI post-exercise meal may help your body maintain a higher rate of fat burning (oxidation).'

Anonymous said...

"What’s the benefit? It means your body continues using fat as an energy source long after you have finished exercising. Because weight gain tends to creep up on most of us, every little bit counts!"

You're not suggesting a kjoule is not a kjoule are you? Energy is energy; burn fat, burn glucose, it doesn't matter for weight loss when the metabolic accountant sorts it out.

Susie said...

I was excited to find this site this morning while sipping my coffee! My son is on the low glycemic index therapy diet for the treatment of epilepsy given through Dr. Elizabeth Thiele/ Heidi Pfieffer at the Massachusetts General Hospital in Boston. It will be a great resource for me. Thank you!

GI Group said...

Hi Susie,

Thank you for your post. It really does make our day when we get comments like these.

Please keep us posted as to your son's progress on the diet and perhaps send us your story down the track for our 'success stories' section.

We would also be interested to hear if there are topics (re carbs and GI) you would like us to follow up that you think would be of special interest to people following this diet.