Tossing and Turning?
A small study by Sydney University PhD student, Ahmad Afaghi, reported in The Australian found a high-GI meal eaten four hours before bedtime cut the time needed to get to sleep. Afaghi presented his results at the Australasian Sleep Association Conference in October 2005. He found that the average was nine minutes for people who had eaten a high-GI meal, but 17.5 minutes for those who ate a comparable meal. ‘It makes sense from a physiological point of view,’ says Prof Jennie Brand-Miller. ‘Glucose levels affect the level of trytophan in the blood and therefore serotonin in the brain.’ However, it’s very early days and needs to be confirmed by larger, long-term studies before recommending people with sleep problems start experimenting with high GI meals.
GI and Weight Loss Benefits: Boost or Boast?
Researchers from the University of Minnesota set out to test whether reducing the glycemic index of a diet already low in calories would have any further weight loss benefit for obese adults. The small study reported in the Journal of Nutrition confirmed the benefit of lowering glycemic index on insulin sensitivity but not for additional weight loss.
The researchers randomly allocated a group of 29 obese adults to a high GI, low GI or high fat diet (there were about 9 or 10 people in each group). The kilojoule-restricted diet provided ~3000 kJ less than estimated energy needs. The team gave the 29 participants their food for the first 12-week phase and instructions (22 participants at this stage) for the second 24-week, ‘free-living’ part of the trial. At 12 weeks, they found significant weight changes from baseline in all groups, but no difference among groups, with weight loss ranging from 8.4 to 9.9 kg. All groups had improved insulin sensitivity. During the free-living phase, all groups maintained initial weight loss and continued to show improved insulin sensitivity, with both parameters independent of diet composition. The researchers conclude: ‘lowering the glycemic load and glycemic index of weight reduction diets does not provide any added benefit to energy restriction in promoting weight loss in obese subjects.’
—Journal of Nutrition, 135:2387-91
GI Group: What about fat loss? The study reports fat mass change (extrapolated from skinfold changes) for the first phase. People on the high GI diet lost 4.5 ± 1.9 kg (mean ± SEM) fat mass over 12 weeks; those on the low GI diet lost 6.9 ± 0.9 kg. If you are wondering why that's not significantly different, it's because they have only 9 or 10 subjects in each group. So the study was underpowered. Had they had more subjects and the difference was similar, it would be significant. To date, eight intervention studies have compared high and low GI diets for weight loss. All favour the low GI diet in one way or another, but in some cases (like the above study), the differences do not reach statistical significance. A meta-analysis can overcome these limitations.
A Little Resistance Goes a Long Way
Supplementing foods with resistant starch has the potential to improve insulin sensitivity—a crucial factor in the development of diabetes, report Keith Frayn and his colleagues from the Oxford Centre for Diabetes and INSERM-INRA in France in the September issue of the American Journal of Clinical Nutrition. Over four weeks, they gave ten volunteers 30 grams resistant starch, compared with a placebo. They say ‘Insulin sensitivity was higher after resistant starch supplementation than after placebo treatment,’ making the point that further studies in insulin-resistant people are needed.
—American Journal of Clinical Nutrition, 2005; 82 559–567
So, What is Resistant Starch? Most starches are digested and absorbed into the body through the small intestine. Low GI carbs, for example, are digested and absorbed slowly. Some carbs, however, are not absorbed at all. They resist digestion and make their way to the large bowel. Good bacteria in the large bowel ferment the resistant starch and in the process enhance your protection against bowel cancer. This type of starch is called resistant starch. Under-ripe bananas, cold cooked potato, pasta and legumes such as baked beans are all natural sources of resistant starch.
GI? GL? GR? IL? GGE? Getting the Measure
Where the end-game is about the multiple health benefits of improved insulin management and insulin sensitivity, should we be talking GI (glycemic index), GL (glycemic load), GR (glucose response), II (insulin index), GGE (glycemic glucose equivalents or something else? Azmina Govindji (co-author of The Gi Plan with Nina Puddefoot) explores the most accurate way of describing the glycaemic effect of carbohydrates in the summer 2005 issue of The Nutrition Practitioner. She concludes:
‘From the emerging evidence, it appears that the crucial element is the choice of slowly digested carbohydrates over those that are more rapidly digested. It is about the quality of carbohydrate, not quantity. GI refers to the rate of digestion; it is an intrinsic property of the food, reflecting its quality. GL is analysed from the original GI and reflects the quantity of carbohydrate in particular. Since the key is to choose low glycaemic carbohydrates, a low GL diet may not necessarily offer the glycaemic benefits of a low GI diet. For example, a low GL meal of a normal portion of pasta (a classic low GI food) could have the same GL as a small serving of mashed potato (a high GI food). However, small amounts of mashed potato have not been shown to offer the glycaemic benefits of low glycemic carbohydrate foods.
‘While GI is not a perfect measure and should not be used in isolation, it is currently the most familiar term with UK consumers and the use of an alternative term could cause confusion in the whole glycaemic concept. The science behind the benefits of lower GI is robust and means that this is not a short-term fad. As part of a balanced diet (that is low in sugar and saturates), GI can help consumers make more informed choices.
‘Here is the opportunity for healthcare professionals to fully make use of the media who, lets face it, have more impact on our patients than we could ever hope to achieve. In time, hopefully we will develop the best and most full explanation and terminology. But for now, it makes sense to work with what we have and indeed to take advantage of it. The time has come for us to distinguish between carbohydrates as we currently do for fat. It's about slow carbs, not low carbs. Carbs are fine, but it's the good carbs that really matter.’
—The Nutrition Practitioner (Vol 6 Issue 2, summer 2005)
‘Wholegrain’ and Low GI Are Not the Same
For most consumers, ‘wholegrains’ mean eating grains in nature’s packaging—or close to it—traditional rolled oats, cracked wheat, brown rice and pearl barley, for example. There are countless reasons to include more whole cereal grains in your diet, but it’s hard to go past the fact that you are getting all the benefits of their vitamins, minerals, protein, dietary fibre and protective anti-oxidants. Studies around the world show that eating plenty of wholegrain cereals reduces the risk of certain types of cancer, heart disease and type 2 diabetes. A higher fibre intake, especially from whole cereal grains, is linked to a lower risk of cancer of the large bowel, breast, stomach and mouth.
Photo: Scott Dickinson
However, when it comes to what manufacturers can put on the label, there’s no international definition of ‘wholegrain’. It can mean slightly different things in different countries. Food Standards Australia and New Zealand (FSANZ) have expanded the current legal definition for packaging labels to allow more foods including refined wholemeal foods to include ‘wholegrain’ on the label. A manufacturer can now label a food ‘wholegrain’ if ‘the intact grain or the dehulled, ground, milled, cracked or flaked grain, where the constituents—endosperm, germ and bran—are present in such proportions that represent the typical ratio of those fractions occurring in the whole cereal,’ says Lydia Buchtmann, FSANZ Communication Manager.
If you have diabetes or metabolic syndrome and low GI foods are an important part of your diet, what should you do? If there’s no GI rating on the label, follow our rule of thumb, if you can’t see the grains, then don’t assume it’s low GI. Why not follow up and encourage the manufacturers to have their products glycemic index tested?