New light on dietary recommendations for good heart health
A new study (known as the RISCK trial) published in the American Journal of Clinical Nutrition has shed light on practical and achievable dietary recommendations for reducing the risk of heart disease.
Prof Susan Jebb
‘The RISCK trial is important’ says lead author Prof Susan Jebb, Head of Nutrition and Health Research at the MRC Human Nutrition Research Unit ‘because in one study, it has tested the impact of changing the amount and type of fat and carbohydrate in the diet of individual participants to test the effects on their health, using very detailed measurements. It suggests that you can achieve favourable blood lipid (fats) profiles, associated with reductions in cardiovascular disease risk, by reducing saturated fat and substituting this with monounsaturated fat and by substituting high GI carbohydrates with low GI carbohydrates.’
The trial included 548 overweight people at risk of cardiovascular disease. All followed the same ‘reference’ (weight maintenance) diet for a month and were then randomised to one of five diets for 6 months (24 weeks):
The study indeed confirmed the well established finding that reducing saturated fat intakes results in decreases in total and LDL (bad) cholesterol. However, interestingly, the researchers also found that simply following a lower GI diet led to significant further reductions in total and LDL cholesterol with the greatest improvement in blood lipids – including an increase in HDL (good) cholesterol – seen in the high monounsaturated fat/low GI group.
- One group continued with the reference diet.
- Two groups were provided with foods that, although relatively high in fat, had around a third of the saturated fat component replaced predominately with monounsaturated fat (carbohydrate was 45% of total energy intake for these groups).
- The remaining two groups reduced the saturated fat in their diet by replacing the energy with carbohydrate (55% total energy).
In the study, the researchers provided the participants with key foods and the target differences between the high GI and low GI groups was 11 and 13 GI points respectively. ‘In the event,’ says Prof Jebb ‘the dietary records suggest we achieved a smaller difference than the target – about 8. We based the low GI dietary intervention entirely on swaps – one type of bread or breakfast cereal for another as we were very keen to keep the rest of the diet unchanged as far as possible. Where we did struggle was to find low GI snacks, which fitted with our broader dietary goals for fat type as well as GI. If more suitable products were available that would have helped to achieve a bigger reduction in GI. For example, we didn't want people to go from biscuits to fruit as this would have upset the calorie intake and fat/carbohydrate intake as well as GI.’
We asked Prof Jebb to comment on the suggestion made previously in GI News (Dr Alan Barclay) that a GI of 45 or less is what we all need to be aiming for ‘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.’
‘We were no where near 45 for the diet as a whole,’ said Dr Jebb. ‘However, it is important to remember in the RISCK study what we were looking at is what could be realistically achieved at a broad community level in the UK – not for individual clinical cases. Our focus is more on supporting people in the UK community at large to make healthy changes with very practical advice.’
You can read more about the RISCK study HERE.
GI and heart disease
A study from Mexico in the Journal of Nutrition and Metabolism reports that both the quality and the quantity of carbohydrate consumption significantly influence blood cholesterol and triglyceride (a type of blood fat) concentrations and heart disease risk in Mexican adults who don’t have diabetes. The researchers analysed data from 5830 participants from the Health Worker Cohort Study and assessed dietary GI and GL using a validated food frequency questionnaire.
‘Our data strongly support the hypothesis that diets with a low GI and GL – which include foods like whole grains (e.g., whole grain breads, barley and wheat germ), vegetables, legumes, fruits, and nuts – are associated with a more favorable lipid profile that may be cardioprotective,’ they conclude.
New international yardstick for GI claims
Consumers around the world will benefit from the release of the new International Standard designed to measure the glycemic index (GI) of foods (ISO 26642:2010), which sets out the now internationally recognised scientific method to determine the GI of foods. It will play an important role in ensuring nutrition and health claims made on food labels can be trusted and will assist food producers formulate healthier low GI products.
Put simply, the GI ranks the glycemic potency of different carbohydrate-containing foods as they are eaten. Foods with a high GI cause a dramatic rise in blood glucose levels while foods with a low GI value have much less of an impact. Studies from major medical research institutions and research universities have found that the GI is a clinically proven tool in its application to the dietary management of diabetes, coronary health and weight control.
Dr Alan Barclay, Chief Scientific Officer at the Glycemic Index Foundation commented that: ‘Consumers looking for healthy foods need to be confident the claims made by food manufacturers on their labelling and in advertisements are accurate and reliable,’ he said. ‘Historically, not all GI claims have been reliable with some based on extrapolation or inappropriate methodology. A food’s GI value cannot be predicted from its appearance, composition, carbohydrate content, or even the GI values of related foods. The only way to know a food’s GI value is to test it, following the now international standardized methodology.’
French and English language versions of the ISO standard are available HERE.