Making the Switch, Making a Difference
Studies are showing that metabolic syndrome or insulin resistance syndrome is widespread among adults in developed nations, with estimates in Australia alone for example of one in two adults over 25 years having at least two features of what is seen to be a silent disease. People with metabolic syndrome are three times as likely to have a heart attack or stroke compared with people without the syndrome and they have a five-fold greater risk of developing type 2 diabetes (if it’s not already present). David E Laaksonen and his team from Finland report in the American Journal of Clinical Nutrition that a simple dietary modification may lower the risk of developing type 2 diabetes in people with metabolic syndrome by enhancing early insulin secretion. They assigned 72 overweight or obese men and women with the metabolic syndrome to a 12-week diet in which either rye bread and pasta or oat and wheat bread and potato were the main carbohydrate sources (34% and 37% of energy intake, respectively). Body weight did not significantly change in either group during the trial. However, only the pasta-based carbohydrate modification enhanced early insulin secretion (by 33%) and was associated with improved glucose tolerance reducing the risk for the development of type 2 diabetes.
—American Journal of Clinical Nutrition. 82(6):1218-278, 2005 Dec
Reduce blood glucose (sugar) levels and you’ll reduce the risk of coronary heart disease reported Elizabeth Selvin and her colleagues in Archives of Internal Medicine (September 2005; 165, pp1910-1916). ‘For non-diabetics, lifestyle modifications, such as increased physical activity, weight loss and eating a healthful, low-glycemic, index diet rich in fibre, fruit and vegetables, may not only help prevent diabetes, but also reduce the risk of heart disease.’ This study was based on what’s called the Atherosclerosis Risk in Communities Study (ARIC). Analysing the data from this long-term program has helped to give us a clearer understanding of heart disease risks. Set up in 1987 to measure the associations of established and suspected CHD risk factors in men and women, it tracked almost 16,000 people from North Carolina, Mississippi, Maryland and Minnesota. Participants had four medical examinations (1987-90, and 1990-93, 1993-96, and 1996-99), and were contacted every year to update their medical histories.
In Selvin’s study reported in December 2005 Diabetes Care, her team looked at the ARIC data for 2,060 people with diagnosed and undiagnosed diabetes. The researchers identify several associations between HbA1c (a measure of long-term blood glucose) and known CVD risk factors and suggest that HbA1c is independently related to thickening of the carotid artery walls (a sign of heart and blood vessel disease). They conclude that: ‘chronically high blood glucose levels may contribute to the development of atherosclerosis in people with diabetes independent of other risk factors.’
photo: scott dickinson
Sense and Sensitivity
Writing in December 2005 Diabetes Care Liese et al report on the association of digestible carbohydrates, fibre intake, glycemic index and glycemic load with a number of factors including insulin sensitivity in 979 adults from the Insulin Resistance Atherosclerosis Study. The researchers analysed data from the study and estimated nutrient intake using a food frequency questionnaire and concluded that: ‘Carbohydrates as reflected in glycemic index and glycemic load may not be related to measures of insulin sensitivity, insulin secretion, and adiposity. Fibre intake may not only have beneficial effects on insulin sensitivity and adiposity but also on pancreatic function.’
—Diabetes Care 28:2832-2838, 2005
GI Group: The food frequency questionnaire used in the study does not assess an individual’s carbohydrate intake very well. Comparison with another method of assessing an individual’s carbohydrate shows that the food frequency questionnaire has a very poor correlation ( just 0.37) for carbohydrates and thus it would be judicious to question the study’s conclusions.
Assessing a person’s food intake accurately is challenging. People tend to under-report some foods and overestimate others. There isn’t a perfect method. Food records, dietary recalls and list-type methods such as food frequency questionnaires are all subject to some error and bias. That’s why it’s important to assess the relative validity of estimates of nutrient intake statistically by comparison with independent methods to see how well they compare. The GI Group requires a correlation >0.5 for carbohydrate for these types of studies to be accepted and a recent paper published by the Harvard Group (Park et al. JAMA. 2005; 294:2849-57) corroborates this decision.
The average GI for the older Americans in the Liese et al study was 58, with a relatively small variation (standard deviation of 4). The relatively small variation would have meant it would be very difficult to find statistical differences between the groups with high and low insulin sensitivity, insulin secretion and adiposity. This may be because the food frequency questionnaire used does not measure carbohydrates well, or that their study population has a very similar diet from a GI perspective.
Interestingly, research in Australia shows a similar average GI for the older Australian population of around 56, and this appears to be pretty typical for those developed nations that have been studied. Although more research is needed, it appears that the average GI associated with the least risk of developing chronic lifestyle diseases like type 2 diabetes, heart disease and some cancers, is around the low to mid-40s as stated in the Liese et al study . The GI Group has previously suggested that individuals need to decrease the average GI of their diet by around 15 units and this is consistent with Liese et al.