1 May 2010

News Briefs

High GI carbs increase women’s heart risk
‘A high consumption of carbohydrates from high GI foods, rather than the overall quantity of carbohydrates consumed, appears to influence the risk of developing coronary heart disease in women’ according to a large prospective study (the EPICOR study) published in Archives of Internal Medicine.

Dr Sabina Sieri Fondazione
Dr Sabina Sieri Fondazione

Dr Sabina Sieri Fondazione IRCCS Istituto Nazionale dei Tumori, Milan, Italy, and colleagues analysed data on 44,132 adult volunteers (30,495 women and 13,637 men, aged 35 to 74 years old) who did not have cardiovascular disease at the start the study. They looked at the diet of the volunteers and followed them up for an average of nearly 8 years to see who developed coronary heart disease. They then compared the risk of developing heart disease among those with low GI and low GL diets with those with high GI and high GL diets.

In women (but not men), high carbohydrate intake and higher GL were associated with more than double the risk of developing heart disease during the 8 years. GI alone was not directly linked to heart disease but the researchers discovered something unique: increasing amounts of carbohydrate from high GI foods were associated with higher risk, while increasing amounts of low GI carbohydrate were not. (So you can eat your healthy low GI carbs with a guilt-free conscience). In men, there was no link between overall carbohydrate intake, GI or GL and heart disease risk. This could be because the adverse changes associated with carbohydrate intake, including triglyceride levels, are stronger risk factors for heart disease in women than in men, the authors note.

‘We tentatively suggest that the adverse effects of a high glycemic diet in women are mediated by sex-related differences in lipoprotein and glucose metabolism, but further prospective studies are required to verify a lack of association of a high dietary glycemic load with cardiovascular disease in men,’ they conclude.

Fruit and veg and the other big C
The study that really hit the headlines in April was published in the Journal of the National Cancer Institute and reported only a borderline reduction in risk of cancer with increased consumption of total fruit and vegetables. The European Prospective Investigation into Cancer and Nutrition showed that for every 200 grams (about two servings) of total fruits and vegetables eaten per day, the incidence of cancer was reduced by 4 per cent.

Apart from the usual problem of accurate (or inaccurate!) self reporting in studies like this, NHS Choices Behind the Headlines points out that ‘… this study did not assess the number of pieces or portions of fruit and vegetables eaten, only the total mass. On the basis of the study report, this could arguably have been made up of only a single fruit or vegetable.’

Woman with bowl of vegetables

Harvard’s Prof. Walter Willett in an accompanying editorial reminds us that there’s still a pretty strong reason to get your five a day. It’s called cardiovascular disease (the biggest killer of men and women on most Western countries). He writes: ‘… in the same population of men and women that showed no association between fruits and vegetables and total cancer, incidence of coronary heart disease or stroke was 30% lower. Data from a large randomized trial showing that increasing intake of fruits and vegetables reduces blood pressure, a major determinant of cardiovascular disease, make the case for causality compelling, although benefits through additional pathways are also possible. Thus, recommendations and actions to increase intake of fruits and vegetables have a sound basis.’

The GI of your diet is a predictor of type 2 diabetes and cardiovascular disease risk
A systematic review and meta-analysis of 37 prospective cohort studies on the association of dietary GI and the risk of developing common lifestyle-related diseases published in the American Journal of Clinical Nutrition showed that diets with a high GI or a high GL increase your risk of type 2 diabetes and cardiovascular disease. It also showed some evidence for links between the GI and gallstones and some types of cancer. ‘The key message,’ says lead author Dr Alan Barclay, ‘is that the GI of your diet is a predictor of your disease risk.’

Can you put a number on a low GI diet?
‘A GI of 45 or less is a reasonable definition of a low GI diet or meal,’ says dietitian and researcher Dr Alan Barclay. ‘This is because what we now know from numerous observational cohort studies around the world is that the daily average GI of the diet of people in the lowest quintile (20% of the population) is about 40–50. Similarly, in a meta-analysis published in Diabetes Care of 15 experimental studies investigating the role of low GI diets in managing diabetes, the daily average GI was 45. Since this average GI has been proven to have significant health benefits in people with existing diabetes and in reducing the risk of chronic diseases like heart disease and diabetes, and importantly, people can and do achieve it in real life, we believe a GI of 45 or less is what we all need to be aiming for.’

GI 45

Why it pays to be prudent and go low GI
Although further research into the role of GI in the prevention and management of obesity and chronic disease is needed, a large body of evidence provides robust support for the current popularity of low GI carbohydrate diets in the prevention of obesity, diabetes, and cardiovascular disease. Prof Jennie Brand-Miller and colleagues argue the case for low GI diets as a dietary strategy that is superior to that of lowering carbohydrate intake or increasing dietary protein in a review of the evidence published in the Journal of the American College of Nutrition.

‘Similar to other dietary factors (such as calories or kilojoules), the GI should not be the sole focus upon which food choices are made,’ they conclude. ‘Rather, the GI should be applied judiciously to select foods within the context of a prudent diet. However, it is not correct to assume that wholemeal (wholewheat), wholegrain, and high fiber foods are low GI. Indeed, a vast majority of ‘‘wholegrain’’ breads, breakfast cereals, and processed cereal products have a GI over 70. Moreover, the GI cannot be guessed by examination of the nutritional composition or physical attributes of a food. The need for GI testing of local foods is critical to the practical application of low GI diets.’

‘A low GI diet is a popular choice,’ says Jennie Brand-Miller speaking to GI News, ‘because it’s actually a very simple swap this for that message. You simply swap this high GI source of carbohydrate foods for that low GI one within the context of an overall healthy or what we like to call “prudent” diet. People find that they can stick to this way of eating because they aren’t being asked to restrict whole food groups. Our advice has always been to continue to eat what you like eating, but to fine-tune your choices by, say, replacing jasmine rice with basmati or one of the lower GI rices that have been tested.’

GI Group: Want to see how easy it is to switch to a prudent low GI diet? Download a copy of the GI Symbol Program's free booklet, Making Healthy Choices Easier.


Steve Parker, M.D. said...

French epidemiologists recently reviewed the scientific literature on heart disease and its association with fruit and vegetbable intake.

They found NO protective effect from fruits and vegetables.


Reference: Dauchet L., Amouyel, P., and Dallongeville, J. (via MedScape). Fruits, vegetables and coronary heart disease. Nature Reviews Cardiology, 6 (2009): 599-608. doi: 1011038/nrcardio.2009.131

Anonymous said...

I wonder if the serves of fruit and vegetables had been organically grown if the cancer rates would have been less. amistefi