More effective weight loss and heart health benefits with
low GI carbs plus or minus protein
The first study to compare low GI and high protein diets head-to-head, systematically varying the glycemic load (GL) from high to low was published in Archives of Internal Medicine July 24. It is also the first study to prove that low GL diets reduce blood glucose and insulin levels over the entire day.
Conducted by Prof Jennie Brand-Miller, Joanna McMillan-Price and colleagues from the University of Sydney, the study was a randomised, controlled comparison of four diets of varying GL on weight loss and reducing cardiovascular disease risk in young overweight or obese adults. All four diets were healthy diets based on high fibre foods with less than 30% of energy as fat (less than 10% as saturated fat). Two of the diets were high protein diets and two were low GI diets.
There are four key messages:
Moderate reductions in GL make losing weight easier, particularly for women.
A high carb diet based around low GI foods was overall the most effective for heart health - good news for those who love their carbs.
If you have high triglyceride levels, the optimal diet for you will combine both high protein and low GI foods. (This was the diet with the lowest GL).
Low GI wholegrain foods (such as traditional porridge oats) provided heart health benefits over and above those of high GI wholegrains (such as wholewheat flakes).
How the Study was Carried Out
The trial led by Joanna McMillan-Price of the University of Sydney's Human Nutrition Unit enrolled 129 overweight/obese, free-living, young adults (98 women and 31 men with a BMI greater than 25) who were willing to eat red meat. The participants were randomly assigned to one of four weight-loss diets.
DIETS 1 and 2 were high carb (55% energy) with high GI or low GI carbs respectively and average protein intake (15%).
DIETS 3 and 4 were high protein (25% energy) and carb reduced (45% energy), again with high and low GI carbs respectively.
Day-long profiles confirmed that mixed meals in the four diets produced differential blood glucose and insulin responses as predicted by their calculated GL, carb content and GI.
One day a week, the young adults collected their key carb foods, portions of red meat and specially prepared frozen meals. They were given eating plans to help them to lose weight (6000 kJ/1400 cal for women and 8000 kJ/1900 cal for men) and encouraged to 'eat to appetite'. At the same time they met with a dietitian who provided encouragement and answered any questions.
During weeks 1, 4 and 8 they kept a 3-day food diary so that the researchers could estimate food intake and assess compliance with the eating plans. Their weight was recorded each week and changes in body composition (fat mass and lean mass) at the beginning and on completion of the program. Fasting blood samples were measured for glucose, insulin and other measures before beginning the diet and during weeks 6 and 12.
The Findings
All four diets resulted in weight reduction but there were significant differences in the proportion of young adults who lost at least 5% of initial body weight (that is a clinically significant amount) over the 12 weeks.
The low GI, high carb diet (DIET 2) produced the best outcome overall, reducing both fat mass and LDL (bad) cholesterol.
The volunteers who followed the low GI, high carb diet (DIET 2) or the high protein, high GI diet (DIET 3), were twice as likely to achieve the goal of at least 5% weight loss. Unfortunately, DIET 3 also produced an elevation of total cholesterol and in LDL (bad) cholesterol.
DIET 4 with the lowest GL of all gave the best outcomes only in those who had high triglyceride levels which is a feature of the metabolic syndrome. They lost more body fat and showed the best improvement in the good HDL cholesterol ratio.
The conventional diet (DIET 1) was associated with the highest level of postprandial (post-meal) glycemia as well as the slowest rate of weight loss.
The Conclusions
In concluding, the researchers say: 'This study suggests that dietary glycemic load and not just overall energy intake, influences weight loss and postprandial glycemia. Moderate reductions in GL appear to increase the rate of body fat loss, particularly in women. Diets based on low GI wholegrain products (in lieu of wholegrains with a high GI) maximise cardiovascular risk reduction, particular if protein intake is high. Reassuringly, this advice can optimise clinical outcomes within current nutrition guidelines without the concerns that apply to low carbohydrate diets.'
'GL may be more relevant to women than men,' they say. 'Women generally lose weight more slowly and display differences in postprandial glucose and fat oxidation which might influence rate of fat loss.'
Speaking to GI News, Joanna McMillan-Price makes the point that: 'While high protein and low GI diets may seem to be diametrically opposed, they in fact will both reduce GL. That is they both reduce your blood glucose and insulin levels.'
'This fits with what we know about the paleolithic diet and our hunter/gatherer ancestors,' she says. 'Although they ate large amounts of meat when it was available, they also ate large amounts of plant foods (leaves, berries, nuts) which would have been gathered every day by the women ensuring that their diet was naturally low GI and low GL.'
The Take-Home Message
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 cardiovascular 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.
- Archives of Internal Medicine 2006;166:1466-1475 'Comparison of 4 diets of varying glycemic load on weight loss and cardiovascular risk reduction in overweight and obese young adults: a randomised controlled trial.'
- Online
http://archinte.ama-assn.org/cgi/content/short/166/14/1466
Funding
The National Heart Foundation of Australia and Meat and Livestock Australia contributed funding but did not participate in the study design or the collection, analysis, interpretation, writing of the manuscript or the decision to submit the paper for publication.
