Test is Best
The GI was introduced to rank the glycemic nature of the carbohydrate in individual foods. The purpose was to exchange one carbohydrate source with another in mixed meals or snacks. People often ask about the effect of extra protein and fat in the food on GI and blood glucose response. Eaten alone, protein and fat have little effect on blood glucose levels, but that’s not to say they won’t affect your blood glucose response when combined with a carb-rich food. This is because protein and fat both tend to delay stomach emptying, thereby slowing the rate at which carbohydrate can be digested and absorbed. So a high fat meal will have a lower glycemic effect than a low fat meal even if they both contain the same amount and type of carbohydrate. As most GI testing to date has been with carb-rich single foods, there’s been some uncertainty and controversy about the best way to apply it to mixed meals and whether it can be predicted using GI tables.
Prof Jeya Henry and colleagues from Oxford Brookes University set out to investigate the impact of protein and fat toppings on the glycemic response to three popular carb foods (potato, pasta and white toast). Writing in the European Journal of Clinical Nutrition the researchers report that toppings of cheddar cheese, chilli con carne, baked beans or tuna on baked potato, pasta and toast had a consistent lowering effect on the GI. The high fat cheese topping (42 g fat, most of it saturated) produced the greatest reduction in the glycemic response, especially when combined with the potato which, when eaten alone, had the highest GI value of the three staples (from GI 93 down to GI 39). In concluding the authors say that the ‘findings highlight the importance of investigating the GI of composite meals’. (The study was sponsored by the British Potato Council.)
– European Journal of Clinical Nutrition 2006 Jan 25
GI Group: As we said in January GI News, the common cut-offs for high (GI 70) and low GI (55 or lower) were based on the scatter of GI values among single foods. If the future holds more testing of the glycemic impact of mixed meals, then the cut-offs may need to be redefined, taking into account the observed range. More importantly, a meal’s GI value doesn’t make it good or bad for you. You need to base your food choices on the overall nutritional content along with the amount of saturated fat, salt, fibre and of course, GI value. We have found that people who simply substitute a low GI food for a high one in their everyday meals and snacks (especially with their choice of breads, breakfast cereals, starchy vegetables) reduce the overall GI of their diet, gain better blood glucose control and lose weight.
See ‘Feedback’ for more on fats, spikes and glycemic response.
A Public Health Time Bomb
‘The obstacles are enormous in contemporary society where daily physical activity opportunities are limited for some youngsters, entertainment is sedentary, and high-fat, high-energy foods are cheap, ubiquitous, convenient and heavily promoted’ writes Dr Arlan L. Rosenbloom in the May issue of Archives of Pediatrics and Adolescent Medicine. He was responding to Glen Duncan’s data published in the same issue suggesting that the US faces a public health time bomb – around 39,000 teenagers aged between 12 and 19 may have type 2 diabetes and 2.8 million impaired fasting glucose levels. Duncan put some realistic figures on the potential size of the problem in the US using data from the National Health and Nutrition Examination Survey (1999–2002).
The estimates have important implications for public health because of the high rate of conversion from impaired glucose fasting level to type 2 diabetes in adults and the increased risk of cardiovascular disease in individuals with type 2 diabetes. It’s unknown, says Rosenbloom ‘whether weight loss will prevent or slow the progression to diabetes in this age group.’
– Archives of Pediatrics and Adolescent Medicine Vol 160 May 2006
Teenagers Make Healthy Changes Given the Chance
Simply replacing sugar-sweetened beverages with non-caloric drinks in the home (where young people get most of their food and beverages) helped a group of teens cut consumption of high calorie drinks by more than 80%. They also shed pounds according to a randomised pilot study reported in the March issue of Pediatrics.
Consumption of sugar-sweetened drinks – sodas, sports drinks, juice drinks, iced teas, lemonades and punches – has surged in recent decades, in step with the surge in childhood obesity. So is there a connection? Researchers from Children's Hospital Boston carried out a controlled trial led by Cara Ebbeling, PhD, and David Ludwig, MD, PhD, to test the effect of decreasing sugar-sweetened beverages on body weight. ‘We opted to study one simple, potentially high-impact behaviour, and made it easy for adolescents to replace sugary drinks with non-caloric beverages in the home’ says Ebbeling.
They enrolled 103 children aged 13 to 18 through a Boston area high school. The teens were offered a $100 mall gift certificate if they stuck with the six-month study, and they all did. Half the group, received weekly deliveries of non-caloric beverages of their own choosing – bottled waters and artificially sweetened drinks. They were instructed on how to avoid sugar-sweetened beverages and given tips on choosing non-caloric drinks outside the home. Prompts included monthly phone calls and refrigerator magnets (‘Think Before You Drink’). The rest of the teens, serving as a control group, continued with their usual eating and drinking patterns. At the end of six months, the beverage delivery group had an 82% reduction in consumption of sugary drinks, while sugary drink intake in the control group remained unchanged.
The heavier the teen was initially, the stronger the effect on body weight. Among the heaviest one-third of teens, there was a marked decrease in body mass index (BMI) in the beverage-delivery group, and a slight increase in the control group – a group-to-group difference of almost 1 pound per month. Other factors affecting obesity – physical activity levels and television viewing – did not change in either group.
– Pediatrics, March 2006
Corollary: Stopping School Soda Sales – Taking a Step in the Right Direction
Cadbury Schweppes PLC, Coca-Cola Co. and PepsiCo Inc have agreed to halt nearly all sales of sodas to US public schools (vending machines and cafeterias) agreeing to sell only water, unsweetened juice and low-fat milks to elementary and middle schools. Diet sodas would be sold only to high schools. The agreement should cover around 87% of the public and private school drink market. The Alliance for a Healthier Generation, a collaboration between the William Clinton Foundation and the American Heart Association, helped broker the deal.
Sugary soft drinks will also be banned from school canteens and vending machines in Australia from 2007. Ian Caterson, the Boden Professor of Nutrition at Sydney University said banning the soft drinks would help get the message across to parents that they were bad for children.
– GI Symposium –
Carbohydrates, Glycemic Index and Health: The State of the Art
When: 2 September 2006
Where: Powerhouse Museum, Ultimo, Sydney, Australia
Convenor Professor Jennie Brand-Miller, University of Sydney
Sponsor The University of Sydney Nutrition Research Foundation
For more information or to register, contact:
GI Symposium Secretariat
PO Box 949, Kent Town SA 5071, Australia
Phone +618 8363 1307
Fax +618 8363 1604
- Professor Jennie Brand-Miller, University of Sydney, Australia
‘Overview of carbohydrates, GI and health, strengths and weaknesses of the GI concept’
- Associate Professor Frank Hu, Harvard University, USA
‘Saturated fat or refined carbohydrates: which is the worse villain for heart disease?’
- Dr Anette Buyken, Forschungsinstitut für Kinderernährung, Germany
‘The European experience of using GI – potential pitfalls’
- Dr Emma Stevenson (or Clyde Williams), Nottingham University, UK
‘GI, exercise and fuel partitioning’
- Ian Barclay, NSW, Australia
Title to be confirmed
- Kate Marsh, NSW, Australia
‘Putting the GI into good practice’
The University of Sydney is conducting a dietary study for women with PCOS. If you live in Sydney, Australia, are aged 18–40 with PCOS and are not taking the pill or trying to conceive, contact email@example.com for more details.