GI News Briefs
What women athletes need
Whether you are a serious endurance athlete or exercising seriously to lose body fat, the results of a study from researchers at Nottingham and Loughborough Universities show that being choosy about your carbs before training or events can help maximise fat oxidation (burning). In a study involving 8 healthy, active, young women Dr Emma Stevenson reports that ‘altering the GI of a mixed meal eaten 3 hours before exercising significantly changed the post prandial hyperglycemic and hyperinsulinemic (see below) responses in the women’. In 2 separate trials the women were given a high GI breakfast (GI 78) or a low GI breakfast (GI 44) 3 hours before a 60-minute run at 65% VO2max on a motorised treadmill. Both breakfasts provided 2 grams of carbohydrate per kilogram of body weight.
The women had a higher rate of fat oxidation during exercise after the low GI breakfast than after the high GI one reports Stevenson. This is because large glycemic and insulinemic responses to a high GI meal lead to increased carbohydrate oxidation and a reduction in the mobilisation and oxidation of free fatty acids. Increasing fat oxidation during exercise is what you need to do to lose body fat. Stevenson and her co-authors make the point that further research needs to look at exercise at different intensities and of shorter duration and also in older women and oral contraceptive users.
– American Journal of Clinical Nutrition 2006;84:354–60
More low fat dairy food, less type 2 diabetes
Older women who eat plenty of low fat dairy foods could reduce their risk of type 2 diabetes reports a new study from Harvard in July Diabetes Care. The researchers looked at the associations between dairy food and calcium intake and incidence of type 2 diabetes in 37,183 women without a history of diabetes, cardiovascular disease or cancer at the start of the study. ‘Each serving-per-day increase in dairy intake was associated with a 4% lower risk of type 2 diabetes, says Liu. While acknowledging that dairy food’s lower GI may contribute to the reduced risk, the researchers conclude: ‘our results show independent associations after adjusting for glycemic load. These data are consistent with the possibility that milk seems to influence glucose tolerance more through its insulinotropic effect (stimulating the release of insulin) than its relatively lower glycemic load.’
– Diabetes Care, 29(7), July 2006
High blood glucose increases coronary artery disease risk
Diabetes is well recognised as a major risk factor for heart disease. Impaired fasting glucose is increasingly common (affecting some 35 million Americans), so the next big question is at what point does elevated blood glucose (often associated with impaired glucose tolerance) in the absence of diabetes become a risk factor? In a retrospective study published in Diabetes Care using the records of 24,160 non-diabetic patients (mostly men) from US Veterans Affairs medical centers, Dr Christopher Nielson and his co-researchers looked for associations between morning glucose and subsequent incidents of heart attack and angina etc. They found that elevated fasting glucose greater than 100 mg/dl (5.5 mmol/L) was associated with a greater incidence of coronary artery disease (CAD) independent of typical risk factors such as age, weight, blood pressure etc. This retrospective study both extends the previous descriptions of the association between glucose and CAD and suggests that the commonly used morning glucose test can provide a useful indication of CAD risk.
– Diabetes Care, 29(5), May 2006
Giving children a healthy life
‘Best estimates are that a white child born in the United States in the year 2000 has a 1 in 3 chance of developing diabetes in his/her lifetime, and a 1 in 2 chance if he she is black or Hispanic’ writes Dr Patrick Hughes and co-authors in the Wisconsin Medical Journal in the introduction to their Wasau SCHOOL Project study. Designed to measure the prevalence and magnitude of known risk factors for heart disease and diabetes in school-age children in Wausau, Wisconsin, the SCHOOL Project was small cross-sectional study of a representative sample of students in grades 2, 5, 8 and 11. Here’s what they found: ‘Of the children studied, 39% had at least 1 lipid (blood cholesterol) abnormality and 22% had 2 or more. Abnormal blood pressure, overweight and cigarette smoking were present in 29%, 16% and 11% respectively. While elevated fasting glucose levels were uncommon, insulin resistance was noted in 25% of the sampled population and nearly 50% of sampled children with a BMI greater than the 85th percentile in the survey … Multiple risk factors rose dramatically with age. By 11th grade, 38% of those surveyed had 2 or more risk factors and 23% had 3 or more.
The authors conclude: ‘Primary prevention of atherosclerotic cardiovascular disease must begin in childhood. At an early age, children will find it easier to learn and adopt healthier lifestyles if the encouragement they receive from parents, teachers and society is reinforced by example and actions.’ Here are some of the healthier lifestyle changes that they suggest. ‘Daily physical education classes at all grade levels, an emphasis on life sports, promotion of nutritious foods in schools and restaurants, freedom from environmental tobacco exposure in public places throughout the community, and widespread, actively promoted, year-round opportunities for physical activity regardless of socioeconomic status.’
– Wisconsin Medical Journal 2006, 105(3)
Why a low GI diet can help women with PCOS
In September, accredited practising dietitian and diabetes educator Kate Marsh addressed the annual polycystic ovarian syndrome conference in Sydney on how diet can help women manage the symptoms of PCOS. The conference was organised by the Polycystic Ovarian Syndrome Association of Australia Inc – www.posaa.asn.au
Polycystic Ovary Syndrome (PCOS) is a hormonal (endocrine) disorder that affects 5–10% of women. Symptoms include irregular or absent periods, infertility or reduced fertility, hirsutism (excess hair growth on the face, chest and abdomen), alopecia (scalp hair loss), acne, obesity and difficulty losing weight and increased risk of miscarriage. Many women also complain of excessive tiredness and fatigue, hypoglycaemia (low blood sugar), and poor memory and concentration. We don’t know why PCOS develops, but we do know that there are a number of different causes and that for many women it’s high levels of insulin in the blood resulting from insulin resistance. Having insulin resistance means the body is insensitive to insulin and because the insulin isn’t working effectively, the pancreas pumps out more and more to keep blood glucose levels under control. It’s these high levels of insulin circulating in the bloodstream that cause many health problems including PCOS.
Here’s why. High levels of insulin act on the ovaries to cause increased production of male hormones, which disrupt the normal ovulation cycle and cause many of the symptoms of PCOS. The link between these two conditions also means that women with PCOS are at an increased risk of developing health problems including impaired glucose tolerance (the stage before diabetes), gestational diabetes (diabetes during pregnancy), type 2 diabetes and cardiovascular disease. The good news is that treating insulin resistance significantly improves all or most of the symptoms because it reduces androgen (male hormone) levels and restores ovulation.
Here’s how. You can improve insulin resistance with lifestyle changes such as a healthy eating plan, exercise and weight loss. You may also need medication, but is only effective if used in combination with lifestyle changes. Making these lifestyle changes has restored ovulation in women with PCOS, even with weight losses of as little as 5% of body weight. There are other benefits too. Eating well helps regulate your blood glucose levels, improve your energy levels and reduce your risk of type 2 diabetes and heart disease.
The best type of healthy eating plan is low in saturated fat and high in fibre and includes low GI carbs. Low GI foods are more filling and satisfying, which helps to control hunger and assists with weight loss. They result in lower levels of insulin circulating in the bloodstream, which means fat is less easily stored by the body and is more easily burnt. Lower insulin levels also mean that less male hormones are produced, which can improve many of the symptoms of PCOS, help to reduce the risk of diabetes and heart disease and improve blood fat levels. Spreading your food intake evenly across the day is important too, as this helps prevent spikes in your blood glucose and insulin levels.
But, the most important thing with any eating plan you choose, is that you can actually stick to it long term – short term quick fix weight-loss diets are doomed for failure. If you have PCOS and need help with your diet, make an appointment to see an accredited practising (registered) dietitian who specialises in this area to develop an eating plan to suit your needs.
Diet alone is not enough. You need to combine your healthy eating plan with some regular exercise – at least 30 minutes of activity on most days. It is best to include a combination of both aerobic exercise (walking, running, dancing) and resistance training (weights) – a number of studies have now shown the benefits of lifting weights for improving blood glucose and insulin levels.
– Kate Marsh BSc, M Nutrition Dietetics, Graduate Certificate in Diabetes Eduction & Management
GI Group: To find out more about the PCOS and low GI diets, check out The Low GI Guide to Managing PCOS by Prof. Nadir Farid, Prof. Jennie Brand-Miller and Kate Marsh. This should be available in all good bookshops in Australia, NZ, the US and the UK or from Amazon.