Should We Only Eat Low GI Foods?
Here is what they don’t want you to know.
There are a lot of myths in the health and fitness industry and one of them is avoiding foods based on their GI, otherwise known as Glycemic Index.
Due to these misconceptions about GI it has become a great marketing ploy for companies to tick consumers into thinking their product is superior by often relating it to lowering blood sugar levels and insulin. This has also been used by personal trainers in a lazy way to get their clients to eat less calories, instead of educating then in how to have an effective and sustainable diet. So let’s look at the research to see if we really need to worry about GI.
WHAT IS GI?
The Glycemic Index (GI) is a relative ranking of a food's ability to raise blood glucose. Foods are categories as Low, Medium or High based on their GI number.
Low GI foods are options like oats, sourdough rye, whilst high GI are foods like donuts and white bread, with glucose ranked as 100.
HOW IS GI MEASURED?
GI is measured in a FASTED state, with carbohydrates consumed ALONE (1). In practical terms that translates to waking up in the morning after eating nothing for 6-10hours and then eating carbs only to see the effects on your blood sugar levels over the next 2 hours.
This doesn't really translate into the real world and how people actually eat.
Most people eat a mixture of food sources together, not just carbs alone. Toast with butter (carbs and fats together), oats with milk (carbs and protein together), bacon & eggs on toast (carbs, fats and protein together).
The point is, no one in a fasted state consumes carbohydrates alone.
DOES MIXING FOOD EFFECT GI?
YES! Protein, fat and fibre, all LOWER the glycemic response of a food (1).
So in the morning if you want an egg & spinach omelette on white toast, and you start to feel bad because you should have Low GI wholewheat brown bread, just remember that the fibre from the spinach and the fat and protein from the eggs, has lowered the GI of the meal.
The point is, don’t worry about the GI of a single ingredient, because mixing food sources changes the GI of the whole meal.
FULLER FOR LONGER WITH LOW GI?
That statement is probably the first line of defence for the Low GI activists. Whilst there might be some anecdotal evidence supporting this claim, it’s not concrete and in fact it’s conflicting.
One study (2) over a 30 day period looked at men eating a diet with the same macronutrient (carbs, fats, protein) breakdown, but one group ate High GI foods whilst the other didn’t. They found that the High GI group where able to stay full enough not to get cravings to over eat.
But i think the nail in the coffin is the research (3) on the Satiety Index (how much food keeps you feeling full).
White potatoes and white rice are demonised as High GI foods but actually rank highest on the Satiety Index! Meaning they keep you fuller for longer.
The point is, the GI numbers don't translate into feeling full.
WEIGHT LOSS WITH LOW GI?
The media and marketing campaigns will argue that low GI foods are better for weight loss.
But research shows (4) that low GI foods have no added benefit to high GI foods for weight loss.
Here is an extract from the research:
"In summary, lowering the glycemic load and glycemic index of weight reduction diets does not provide any added benefit to energy restriction in promoting weight loss ..."
The title of another research paper (5) basically spells it out in black and white:
“Should obese patients be counselled to follow a low-glycemic index diet? No.”
As we should know that calories are what determine weight loss or gain. So providing you're in a calorie deficit - GI will make ZERO difference to fat gain.
To take this point to the extreme a professor in the USA, dubbed the "Twinkie Professor" (6), ate only high GI Twinkies and “junk food” but making sure to stay in a calorie deficit and lost just over 12 kgs.
INSULIN SPIKES WITH HIGH GI?
Many people will have you believe that high GI carbs are more likely to store body fat because of the rapid insulin spike. Little do these people know that GI and Insulin are not always related, and that even that protein powder they are chugging down on will spike their insulin.
One study examined the insulin response to a fixed amount (239 calories) of different foods over 2 hours, following a 10 hour overnight fast (7).
Check out this table below:
As you can see even yoghurt (with a Low/Mid GI) spikes insulin more than white rice!
A WORD ON DIABETES
High GI foods are a concern for Diabetics due to the increase in blood sugar levels. But as discussed above, no one eats High GI foods on there own; it’s always mixed with other food sources that lower the GI of the meal.
Diabetics should be more concerned about the amount of carbohydrates they eat, not the GI. Even eating large amount of Low GI foods can raise blood sugar levels that can negatively affect a diabetic.
So you’re probably thinking of all the High GI carbs your going to eat for the rest of our lives, and forget the low GI types.
Again, this is by no way recommending that approach. It is simply setting straight the misconception and alarmist of High GI foods and helping people understand that there is nothing wrong with eating white bread, or food of that nature.
When you're eating protein, fat and fibre together with your chosen High GI carbohydrate source - the GI scale is irrelevant.
So don't stress anymore about high and low GI. Eat the foods you enjoy and keep your diet sustainable.
(1) Aragon A. Elements challenging the Glycemic Index. Alan's Vault. 2006.
(2) Kiens B, Richter EA. Types of carbohydrate in an ordinary diet affect insulin action and muscle substrates in humans. Am J Clin Nutr 1996;63:47-53.
(3) Holt SH, Miller JC. A satiety index of common foods. Eur J Clin Nutr 1995 Sep;49(9):675-90.
(4) Raatz SK, et al. Reduced glycemic index and glycemic load diets do not increase the effects of energy restriction on weight loss and insulin sensitivity in obese men and women. J Nutr. 2005 Oct;135(10):2387-91.
(5) Raben A. Should obese patients be counselled to follow a low-glycaemic index diet? No. Obes Rev. 2002 Nov;3(4):245-56.
(6) Park M. "Twinkie diet helps nutrition professor lose 27 pounds." CNN News. 2010 Nov 8.
(7) Holt, S.H., Miller, J.C., & Petocz, P. (1997). An insulin index of foods: the insulin demand generated by 1000-kJ portions of common foods. American Journal of Clinical Nutrition. 66, 1264-1276