by Greg McKenzie © Copyright 2016
Hi GI, Bye GI!
Greg's articles

Hi GI, Bye GI!

I’m back on the warpath, and the Glycemic Index (GI) is my enemy. I have critiqued it in previous posts, so you may want to browse them first, or simply hang on tight while I take you into its mysteries, inconsistencies and sheer madness here.

I’ve come back to this topic for three reasons. Firstly, ageing healthily means keeping weight off and the GI has been held up both by scientists and popular diet book authors as the most powerful tool available to facilitate this.

Secondly, I have just completed a weight-loss course to re-certify as a personal trainer. It was authored by a researcher in this area who, though warning us that the GI is considered controversial, nonetheless plunged into its use as a tool for weight loss as if its unproven hypothesies were medical fact.

Thirdly, I have just sat in the sun having my usual lunch of tuna, avocado, and mashed chickpeas on lovely flat, wholemeal Middle Eastern bread. In between nibbling at the really great part of the meal – the mound of pickled onions on the side, I mused that this meal has been important in facilitating the 8-kilo weight loss I have achieved over the last 6 months or more.

I further thought about the amount of wheat, rice and other high GI no-nos I have consumed daily while steadily dropping weight. I thought about the red Heart Foundation tick on the package the bread came in – endorsing it as healthy heart food – and the vigorous, healthy peoples this style of bread has nurtured for thousands of years.

Shouldn’t my radical glycemic response to high GI foods have scuppered my weight loss? Shouldn’t I be steadily creeping towards obesity, diabetes, heart disease and cancer as GI pundits predict I will if I continue to eat high GI foods?

Let’s step back a bit and look at the Glycemic Index, it’s history, methodology and validity as a stand-alone guide to eating for weight-loss and disease prevention.

In 1980-81 Dr David J Jenkins and fellow researchers at the University of Toronto looked at carbohydrate foods and tested the principle that complex carbs were digested more slowly than simple carbs and therefore their digestion should result in lower blood glucose response. This was not the case and because their research was aimed at providing dietary guidelines for diabetics they developed a methodology for examining the effect on blood sugar of a variety of carbohydrate foods.

This is where the whole GI thing begins to come unstuck because their methods do not stand up to rigorous scientific standards. Subjects  fasted for 12 hours then ate foods containing 50g of carbohydrate. Their blood sugar levels were tested over a 2-hour period and compared to levels after eating 50g of glucose or white bread. The result was the Glycemic Index where foods are rated for their blood glucose response compared to a standard (white bread or glucose) given an arbitrary rating of 100.

All well and good, except that one of the criticisms of this method was that diabetics take up to 4 hours after eating for blood glucose level (BGL) to stabilize. Critics say the test should be conducted over 4 hours.

The Toronto team were not trying to extrapolate their findings and classification of foods in the GI to the general population. They were simply trying to find a way for diabetics to manipulate their diet for the best outcomes. Diabetics and others with diseases were excluded from the study.

The problem lies with both the diet industry and the GI industry itself which has used the GI to make some pretty extravagant and unproven claims. It goes like this: eating high GI foods shoots up blood sugar and insulin levels which in turn leads to obesity, heart disease, diabetes and cancer. Wow! That’s a dramatic claim, unsupported by long-term studies yet governments, communities and individuals have seized upon GI as THE tool to solve so much of society’s dietary-related health malaise.

Interestingly, the American Diabetes Association cautiously supports GI but maintains it’s the total carbohydrate in foods consumed that is important for diabetics and that individuals should determine the methods that work best for them. The American Institute for Cancer Research (AICR) “cautions the public not to make dietary changes based solely on this interesting but still unproven concept.”

Why did I just complete an accredited course that based its entire weight-loss strategy on the GI after warning us that the nutrition community is deeply divided over its efficacy? Why have so many people sworn off nutritious, low-calorie foods like wholemeal bread and potatoes (both high-GI) while sugar remains a moderate GI food?

Hysteria, and a belief that it’s not the amount of food eaten but the type eaten that counts underscores the way GI has spread like a wildfire. It continues to burn beyond its supply of fuel, namely better research. People do not want to be told to cut down on fatty foods and eat a bit less. They want to be told it’s the mysterious effects of carbohydrate and strange goings on in their pancreas that are to blame for weight gain and a failure to get it off, let alone keep it off.

It’s tough to lose weight as you age and your metabolism slows but believe me the rules have not changed.

For me, the fundamental problem of the GI is that it does not dwell in the real world. Critics have pointed out that many foods have not been tested for practical reasons and averages and estimates are used to determine their GI. You’d need to eat a kilo of carrots and 20 cups of broccoli to ingest the equivalent of 50g of glucose.

Who eats like this? We eat mixed meals which vary digestion and glucose response times.

Many other factors determine the rate at which BGLs go up. The type of starch, for instance. Amylose content goes up in potatoes cooked and allowed to cool before eating, so according to the GI it’s ok to eat potato salad but not a baked potato. Come on, that’s ridiculous. Eating high GI foods with protein or fat (as you do) slows glucose response. Interestingly, non-GI research shows adding protein or fat to carbohydrate foods sends up insulin but BGLs actually go down.

The GI pundits scrambled on these inconsistencies and came up with the Glycemic Load (GL) in order to apply the GI to everyday meals. You multiply the GI rating of a food by the amount of carbs in the serving, then divide by 100. Critics point out the obvious fact that this just compounds an already imprecise calculation.(GI)

Is your head spinning yet? It gets worse. Organic acids and their salts slow the rate of stomach emptying and so affect BGLs. Adding vinegar, lemon juice or even a piece of sourdough bread (Verboten!) to a meal lowers its GI value. Fibre content of foods slows digestion and in turn lowers GI ratings.

Alcohol is low-GI in general and beer in particular only moderate. Drinking alcohol before a meal lowers its GI by 15%. Low-GI foos include chocolate cake (38), ice cream (37) and pure fructose(19). Sugar has a moderate GI of 68. Remember glucose is GI 100 so adding the more complex sugar of sucrose to high-GI foods should lower GI but it doesn’t. Potatoes and rice have high-GI ratings of over 70 but are eaten heavily in countries where rates of diabetes are low.

There is huge variation in the ripeness, processing, length of storage, and cooking methods of foods that affects their GI rating. Even within vegetable varieties, like white potatoes there is a range of moderate to high GI. Peaches rate 42 GI but that is an average of two studies – Italian peaches rate 56, Canadian varieties rate 28.

The GI was formulated under experimental conditions following 12 hours fasting. In the real world the composition of the previous meal affects glycemic response. GI subjects were tested in the morning, critics point out that GI measured in the afternoon results in much less difference between foods.

A 2006 study in the British Journal of Nutrition tried to unravel some of these inconsistencies and link both GI and Glycemic Load to everyday eating with inconclusive results, especially for the link between GI/GL and the incidence of diabetes. They didn’t muck around, either. They started with 1255 adults and tested 813 returnees to the study 5 years later. They concluded that “the present results call into question the utility of GI and GL to reflect glycemic response to food adequately, when used in the context of usual diet.”

The GI does not factor in insulin response, which varies in individuals, yet claims high-GI foods lead to high BGL and insulin, which in turn leads to weight gain.

The cutoffs between low, medium and high GI foods are arbitrary and subject to change. Early research, using only 5 subjects, concluded carrots had a GI of 92 (not sure how they got them to consume a kilo of them) and found there was a large variation in individual glucose response. Later testing used 10 subjects (wow) and calibrated carrots’ GI down to 47. It’s commendable that research into the GI of foods is ongoing but using two standards (both white bread and glucose) leads to large variations in GI outcomes.

The whole insulin bogeyman is irresponsible. Animal studies show that when insulin is up, food intake goes down and appetite is supressed. Further, normal insulin rise after eating did not lead to weight gain.

I started this entry to clarify GI for you, show it’s shortcomings and question why we have accepted its precepts so uncritically but I have probably just befuddled and confused you. So be it. The GI IS befuddling and confusing. There is no conclusive evidence from studies that low-GI foods reduce hunger or promote fullness for weight loss but this tantalising morsel is held as its main pillar.

It’s a happy coincidence that many low-GI foods are healthy and will help you feel fuller and lose weight but that is due to many factors besides the rapidity (or not) of their rise as blood sugar after digestion. It is not certain that high insulin levels follow the consumption of high GI foods for weight gain but this unproven hypothesis is another sacred tenet of the GI.

Low GI diets DO help diabetics control blood sugar but other interventions, like calculating total carbohydrate may be more effective. As for using GI for prevention of cancer and heart disease there is simply not enough evidence despite the hype from those on the bandwagon.

AICR concludes “until more definitive data, including controlled trials are available, basing dietary decisions on a food’s glycemic index is not warranted.”

I would add that while 100 Australians die each week from bowel cancer it is criminal that over-application of the GI scares people away from healthy, fibre-rich foods like wholemeal bread and potatoes.

To lose weight, maintain a healthy, well-balanced diet high in plant foods (fruit and vegetables, grains and legumes) and low in fat and gradually reduce serving sizes over time until the weight comes off. Forget the GI as a guide – it is inconsistent, confusing, contradictory and not practical in the real world. Useless and dangerous, in fact.

Be prepared for your body to fight back as your energy consumption goes down. You may feel fatigue and hunger as your body tries to force you to eat more and move less. Do not starve but embrace mild hunger between meals as a friend. Your system will adjust to less food as you go along and hunger will diminish as energy returns.

Losing even 5 kilos will have a marked effect on your health. Good luck.