News Briefs

Cochrane Review finds low GI diets more effective
Not only is it hard to lose weight, there’s not a lot of consensus about the best way to do it other than ‘eat less and exercise more’. But that piece of advice on its own doesn’t seem to be able to deliver the necessary results for most of us – if we can stick to it. A Cochrane Review published in 2007 looked at six carefully conducted randomised controlled trials running from 5 weeks to 6 months and involving 202 participants. They found that overweight and obese people lost more weight (on average 1 kilogram or 2.2 pounds more) on low GI diets than on similar energy high GI or other conventional energy-restricted weight loss diets. Not only that, the low GI diet had heart health benefits, too. ‘Low GI diets appear to be particularly effective for people who are obese,’ says lead author Dr Diana Thomas, who is the Scientific Director of the Centre for Evidence Based Pediatrics, Gastroenterology and Nutrition. She went on to comment that this may be because it’s easier for people to stick to low GI diets as there’s less need to restrict food so long as the carbs have a low GI.

Finding out about fat metabolism
A study published in the European Journal of Clinical Nutrition suggests that differences in dietary GI can influence fat metabolism. The researchers looked at the effect of dietary GI on GLUT4 and FAT/CD36 gene expressions in human skeletal muscle (these are the muscles that move and support the skeleton) after a single bout of exercise. Skeletal muscle plays important role in the regulation of whole-body metabolism. In skeletal muscle, uptakes of glucose and fatty acid from circulation are facilitated by transmembrane substrate transporters (sorry we can’t make it simpler) GLUT4 and FAT/CD36, respectively.

In two separate trials in this crossover study, 8 healthy men were given a high GI meal (GI 76) or a low GI meal (GI 36) immediately after a 60-minute cycling exercise at 75% maximal oxygen consumption. Both meals had similar proportions of carbs, fat and protein. Muscle samples from deep vastus lateralis were taken by needle biopsy immediately after exercise and 3 hours after exercise.

After exercise, the high GI diet produced significantly greater glucose and insulin responses compared with the low GI diet. Both diets resulted in rapid reductions in plasma fatty acid and glycerol below fasting level. GLUT4 mRNA was downregulated by both high GI and low GI diets to a comparable extent, whereas GLUT4 protein levels were not changed during this short period. FAT/CD36 mRNA and protein levels were substantially decreased with the high GI diet below baseline, but not with the low GI diet.

Regular cola drinking linked to diabetes in pregnancy says study
Writing in December 2009 Diabetes Care, researchers report that after adjusting for known risk factors, intake of sugar-sweetened cola was positively associated with the risk of developing diabetes during pregnancy. ‘Compared with women who consumed less than 1 serving per month, those who consumed more than 5 servings per week of sugar-sweetened cola had a 22% greater GDM (gestational diabetes mellitus) risk,’ notes Dr Chen. While the data indicated a link between GDM and sugary cola, no relationship was found for other sugar-sweetened drinks. The reason for this is not clear, but Chen said one of the explanations could be the tremendous popularity of cola in the US.

Writing in an editorial of the same issue, Dr Robert Moses and Prof Jennie Brand-Miller state: ‘Epidemiological studies have limitations and often pose more questions than they provide answers. Apart from a greater focus on the prevention of maternal obesity, and a logical presumption that a high-fiber and low-GI diet could be beneficial (and are unlikely to do harm), there is currently insufficient evidence to base any firm dietary advice about how to reduce the rate of GDM. Until that evidence becomes available, we can cautiously advise that the overall quality of carbohydrates, fats, and proteins are probably more relevant than the intake of any one single food. In this context one serving of a sweetened soda beverage even on a daily basis is unlikely to do harm.’