Carb quality, weight loss and heart health
With the obesity epidemic a front-page story, ‘diet wars’ is a hot topic. And at the centre of the debate is the quantity and quality of carbohydrate. What should it be: low carb or slow carbs? The findings of a study by researchers from the University of Sydney’s Human Nutrition Unit and published in July Archives of Internal Medicine clearly show that carb quality really counts for weight loss and heart health. Led by Joanna McMillan-Price, the research team carried out the world’s first 12-week, parallel, randomised, controlled trial to compare systematically the relative effect on weight loss and cardiovascular risk of four low GI and high protein diets. Both high protein and low GI diets will help you shed fat they found, but a diet rich in low GI carbs will also significantly reduce your risk of heart disease.
Speaking to GI News, Joanna McMillan-Price said that: ‘While high protein and low GI diets may seem to be diametrically opposed, they in fact will both reduce glycemic load. That is they both reduce your blood glucose and insulin levels. This fits with what we know about our hunter/gatherer ancestors. Although they ate large amounts of meat when it was available, they also ate large amounts of plant foods (leaves, berries, nuts, seeds) which would have been gathered every day ensuring that their diet was naturally low GI and low GL. And of course whether hunting or gathering, they would have been much more active than we are today.’
– Archives of Internal Medicine 2006; 166:1466–1475
GI Group: So what’s the take home message? First of all, one diet doesn’t have to fit all: What’s important is that you set yourself attainable goals and your diet is one you enjoy and can live with over the longer term. If it involves a lot of sacrifice and discipline on your part (eg no sugar or carbs of any sort), it’s bound to fail sooner or later. Our tips:
Step 1: Focus on reducing saturated fat and eating the good fats instead.
Step 2: Choose low GI smart carbs to maximise body fat loss as well as cardio benefits.
Step 3: Aim to eat at least five serves of vegetables and two serves of fruit every day (preferably of three or more colours) including leafy greens, beans and peas, salad vegetables, pears, apples, oranges etc.
And be active. Get those legs, not the fingers, to do the walking.
Editorial comment from Dr Simin Liu, Department of Epidemiology, UCLA:
‘What should physicians do differently based on the findings of this new study? My best recommendation is to move forward incrementally. For example, as a first step, we should encourage the use of GI and GL concepts in conjunction with caloric density and nutrient composition, especially for ranking high-carbohydrate starchy foods, since the classification of carbohydrates incorporating GI does work better than the “simple vs complex” classification for predicting glucose and insulin responses …. In more practical terms, we need to teach our patients to identify low-GI foods within different food groups … Without any drastic change in regular dietary habits, for example, one can simply replace high-GI grains with low-GI grains and starchy vegetables with less starchy ones and cut down on soft drinks that are often poor in nutrients yet high in GL’
– Archives of Internal Medicine 2006; 166:1438–39
Dr Simin Liu
Keeping the kilos off
People on diets high in slowly digested carbohydrate and low in saturated fat can successfully lose weight and keep it off finds a study presented at the Australian Institute of Food Science and Technology Incorporated Convention in July. University of Melbourne research dietitian Liz Delbridge and her team put 173 overweight or obese people on a 12-week low-energy weight loss diet before switching them randomly to either a high carbohydrate or high protein diet (low–moderate GI carbohydrate choices were recommended for both diets) to maintain their weight. Results showed that a high protein diet had no advantages over a high carbohydrate diet in maintaining weight loss over a 12-month period. ‘Some people lose weight and keep it off, whereas others lose weight and put it all back on again,’ said Ms Delbridge. ‘We wanted to see if the type of diet people adopted after weight loss had an influence on people’s ability to keep the weight off.’
– Australian Institute of Food Science and Technology Incorporated Convention
High GI carbs linked to oxidative stress
We have all received the message that it’s important to eat plenty of anti-oxidant rich fruit and vegetables to fight the bad guys, those free radicals (see below) that have been implicated in the cause of numerous diseases. Free radicals are formed in the environment by things like pollution, cigarette smoke, solvents and pesticides; and in the body as a byproduct of metabolism, wherever oxygen is involved. Recent research has suggested that high blood glucose may also increase free radical production. In a report published in American Journal of Clinical Nutrition, lead author Gladys Block says that ‘increasing intakes of low GI foods such as most fruit, vegetables, dairy products and whole grains may be beneficial in terms of reduced oxidative stress.’ The researchers measured plasma MDA and IsoP concentrations (two widely used markers of oxidative stress – see below) in 292 healthy individuals and found a direct relationship between dietary GI and oxidative stress. In their conclusion they say that: ‘Chronic consumption of high GI foods may lead to chronically high oxidative stress. A low GI diet, not a low carbohydrate diet, appears to be beneficial in reducing oxidative stress.
– American Journal of Clinical Nutrition 2006;84:70–6
A free radical is an atom or molecule with at least one unpaired electron, making it especially reactive to other atoms or groups of atoms. If free radicals react with certain chemicals in the body, they may interfere with the ability of cells to function normally.
Oxidative stress is related to the body's ability to eliminate free radicals and can result in cell damage within the body.
Herbs and spices bring more than fragrance and flavour to our food. Research in recent years suggests that some spices such as turmeric, garlic, ginger and cinnamon and chilli may have healthy benefits for our digestion, blood glucose control, fat metabolism and for fighting free radicals.
Cinnamon: Two promising studies report that as little as the equivalent of ¼ teaspoon of cinnamon daily may improve blood glucose control. In the earlier Diabetes Care (Vol 26, pp3215–18) study, Dr Alam Khan from the NWFP Agricultural University in Peshawar, Pakistan gave 60 diabetic men and women between 1 and 6 grams of cinnamon or a wheat flour placebo each day for 20 days. Those who took cinnamon showed significant improvements in blood glucose, LDL cholesterol and triglyceride levels. More recently, researchers from the University of Hannover led by B. Man randomly 79 diabetic volunteers a cinnamon solution (in a capsule) equal to 1 gram of cinnamon or a placebo each day. After four months fasting blood glucose levels improved in the cinnamon group by an average of 1.1 mmol/L (European Journal of Clinical Investigation Vol 36, pp340–44). The GI Group looks forward to seeing some spicy follow up research on cinnamon with controls for overall diet and physical activity levels.
Chilli: Research in recent years has provided some evidence that capsaicin, the chemical that gives chilli peppers their bite, can raise your metabolic rate. But the studies have tended to be small, or used supplements rather than the real thing and certainly not definitive. Hot off the press from the American Journal of Clinical Nutrition (2006;84:63–9) comes news that will be popular with spice lovers; a meal containing freshly chopped chilli may help reduce insulin levels. Kiran Ahuja and researchers from the University of Tasmania’s School of Life Sciences compared the effects of a chilli meal after four weeks of eating bland (spice-free) meals and a chilli meal after four weeks of spicy meals, with eating a bland meal after four weeks of bland meals. In their randomised, crossover intervention study with 36 participants, they found that eating a chilli meal reduced the amount of insulin required to bring down postprandial blood glucose levels. Their results also suggested that the effect is likely to be more pronounced in individuals with a greater BMI (equal to or greater than 26) and when chilli was regularly eaten. Medscape members can read further information on this study at www.medscape.com.
photo: Scott Dickinson
High GI diets and fatty liver disease
As the incidence of obesity in adults and children increases, so does non-alcoholic fatty liver disease (NAFL) – excess fat in the liver. It is strongly associated with insulin resistance and relatively common in people with type 2 diabetes. Currently there are no effective treatments other than weight loss, which makes the findings of a new Italian study published in the American Journal of Clinical Nutrition timely. Valtueña and colleagues suggest that a low GI diet may help people with NAFL more than low carb or high fibre diets and be a complementary tool for preventing or treating it. In their cross sectional study of 247 healthy individuals, the researchers looked at dietary correlations with NAFL assessing the effects of both the quality and quantity of carbohydrate. They found that the GI of the diet is a good marker for fatty liver. The higher the GI, the greater the prevalence of fatty liver, especially in insulin resistant people. In an editorial in the same issue, Prof David Jenkins calls for further studies to ‘assess whether a low-GI diet, given as an intervention, makes a difference in the natural history of NAFL.’
– American Journal of Clinical Nutrition 2006;84:136-42
– American Journal of Clinical Nutrition 2006;84:3-4 (Editorial)