GI News Briefs

Putting your genes on a diet
It’s a commonplace to say you are what you eat, but Petteri Kallio and colleagues writing in the American Journal of Clinical Nutrition in May suggest that’s pretty much what’s happening at a molecular level in a study that highlights changes in gene expression in people consuming diets with different effects on post-meal insulin concentrations. The researchers from the University of Kuopio in Finland randomly assigned 47 men and women with metabolic syndrome either to a rye-pasta diet producing a low insulin response or an oat-wheat-potato diet producing a high insulin response for 12 weeks and assessed the effect by looking at the effect on subcutaneous fat (that’s the fat under the skin). They found the genes regulating insulin signalling were down-regulated on the rye-pasta diet, and genes related mainly to stress were up-regulated on the oat-wheat-potato diet.

In an accompanying editorial entitled ‘Putting your genes on a diet’, Dr Sandra Salsberg and Dr David Ludwig say: ‘The present study has direct implications concerning our understanding of the dietary glycemic index (GI). High-GI meals produce greater postprandial insulin concentrations and C-peptide excretion than do nutrient-controlled low-GI meals. Observational and interventional studies have linked GI to the risk of obesity, diabetes, heart disease, and cancer, although the topic remains much debated …. The results of the present study emphasize the age-old wisdom to “use food as medicine” – in this case, for the targeted prevention and treatment of obesity, diabetes, and heart disease.’
– American Journal of Clinical Nutrition 2007;85:1417–27
– http://www.ajcn.org for the accompanying editorial

Dr David Ludwig

GI Group: Gene expression is the process by which a gene’s DNA sequence is converted into the functional proteins of the cell. For more detail check out Wikipedia.

Is the jury in or out on the long-term effects of low carb-high protein diets?
In the past 20 or so years, people struggling to get rid of extra pounds frequently opted for a high protein-low carb diet on the basis of promises that these diets led to faster weight loss and better weight control. Recent evidence has in fact suggested that these diets do deliver faster weight loss. But, a more serious question is whether sticking to these diets long term is compatible with long-term health? Fans of these diets gave a collective sigh of relief last year when a US observational cohort study based on the Nurses Health Study revealed no link between a low carb diet and mortality, particularly from heart disease. Two new studies from Sweden (Dr Lagiou’s) and from Greece (Prof Trichopoulou’s) appear to flatly contradict this, both concluding on the basis of similar long-term studies with large numbers of women that prolonged consumption of a diet that’s low in carbohydrate and high in protein was associated with increased total and particularly cardiovascular mortality among women. So where does that leave us? Harvard’s Prof Walter Willett to the rescue. In an editorial comment in the Journal of Internal Medicine, he makes the point that the complexities of human diets make comparisons of patterns between one population and another difficult, suggesting that the most likely interpretation of the inconsistency between the US and Swedish studies is that both are correct in the context of their respective populations and diets. He says:
‘Within the relatively lean and younger Swedish women, replacement of largely whole grains with the protein packages consumed in that population probably have an adverse effect on cardiovascular disease. In contrast, within a heavier and older population of US women, replacement of mainly refined starch and sugar with almost any source of calories is not likely to increase the risk of cardiovascular disease. This conclusion emphasizes the most fundamental conclusion of research into diet and cancer during the last decade: it is the type of fat and type of carbohydrate rather than the total amounts of either that influence risk of cardiovascular disease. Thus, in the Nurses’ Health Study, a low-carbohydrate pattern that emphasized vegetable sources of protein and fat was associated with a significantly lower risk of coronary heart disease … There is every reason to believe that a moderately low carbohydrate intake (approximately 30–40% of energy) can result in low risk of cardiovascular disease if the proteins and fats are mainly from plant sources (but do not include hydrogenated oils) and the remaining carbohydrates are from whole grains, fruit and vegetables.’
– Journal of Internal Medicine 261; 366–374 (Swedish study) and 363–365 (Walter Willett)
– European Journal of Clinical Nutrition (2007) 61, 575–581 (Greek study)

Exercise benefits women with PCOS
A structured exercise training program is a simple way to help reduce cardiovascular risk in women with PCOS say researchers from the University of Naples writing in The Journal of Clinical Endocrinology & Metabolism. There are other benefits as well as this small study shows. Ninety overweight young women with PCOS but otherwise healthy took part in the randomised trial. Half undertook a supervised and structured exercise program that included aerobic activity 3 times a week with 30 minutes on a bicycle. The other half did no structured exercise. Both groups were encouraged to follow a healthy balanced meal plan with 50% of calories from carbohydrates, 25% from protein and 25% from fat. All the women completed the trial. After 3 months (84 days to be precise), the exercisers had achieved a significant reduction in BMI, waist circumference, hip to waist ratio and insulin resistance. Sixty per cent also had normal menstrual cycles. No changes were observed in the non-exercisers.
– JCEM Vol. 92, No. 4 1379–1384
– http://www.medscape.com (login required)

Want to take part in a PCOS diet study?
The University of Sydney is conducting a dietary study for women with PCOS. If you have PCOS, live in Sydney (Australia), are aged 18-40, and are not taking the pill or trying to get pregnant, contact pcosdietstudy@nnd.com.au for more information.

Australians get help in managing type 2 diabetes
Medicare rebates are now payable for group services provided by eligible diabetes educators, exercise physiologists and dietitians for people with type 2 diabetes, on referral from a GP. The new rebates are in addition to the current Medicare items for individual services provided by health professionals. For more information and a referral ask your doctor.