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Glycemic Index and weight management

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Intro
High GI foods are believed to alter appetite and energy partitioning in a way that is conducive to body fat gain. So what is it about low GI foods that make them so beneficial for weight management?

 

Authors: Kaye Foster Powell, Alan Barclay and Kathy Usic

 

Making healthy choices easy    

High GI foods are believed to alter appetite and energy partitioning in a way that is conducive to body fat gain1. Numerous intervention studies reveal the favourable impact of low GI diets on weight management2 and epidemiological studies suggest that those people naturally eating low GI diets are at lower risk of being overweight and gaining weight in the future3,4,5,6.

 

So what is it about low GI foods that make them so beneficial for weight management?

How do low GI carbs work?

Several features of low GI foods help facilitate weight loss.

  • Low GI diets reduce insulin levels  

The effect of low GI foods on blood insulin levels is likely to be an important reason for their effectiveness in weight management. While insulin is the primary regulator of glucose metabolism it also plays a key role in fat metabolism. High insulin levels following high GI foods promote carbohydrate oxidation and fat storage. Persistently high insulin levels, as occur in people with insulin resistance, result in decreased expression of the rate limiting enzymes involved in fat oxidation and thereby alter the potential for fat burning.7 This is why people with insulin resistance often struggle to lose weight and accumulate fat - around the waist, in the liver (fatty liver), in the blood (high triglycerides) and inside muscle cells.

 

  • Low GI foods and meals promote higher rates of fat oxidation

In contrast, low GI foods tip the balance in favour of fat oxidation. Stevenson et al.8, demonstrated significantly greater fat oxidation following low, versus high-GI meals. This is the case at rest and during exercise9. Compared with a high GI/low-protein standard breakfast, a low GI/high soy protein meal replacement produced greater fat oxidation in the postprandial period, coinciding with favourable changes to appetite regulating hormones10.

 

  • Low GI diets facilitate greater fat loss

Several intervention studies indicate that low GI diets yield greater reductions in body weight, total fat mass and body mass index than high GI or conventional energy-restricted diets2. In one Harvard study of overweight adults following either a conventional high fibre, low fat diet or an isoenergetic low GI diet lost similar amounts of weight over 18 months, but those subjects who had high insulin levels lost nearly 6kg on the low GI diet compared to only 1kg lost by those on the conventional low fat diet11. Moreover they lost 3 times more body fat and had greater improvements in cardiovascular disease (CVD) risk factors. 

McMillan-Price12 found that weight and body fat loss were over 50% greater in obese adults following a low GI, high protein diet compared to a conventional low fat approach. In animal studies where the diet can be tightly controlled, rats fed a high GI diet were found to have approx 40% more body fat and almost 10% less lean mass than those fed a low GI diet, after only 9 weeks of an 18 week intervention13. More recently Rizkalla et al14, found greater shrinkage of adipocytes in weight loss brought about by a high protein, low GI diet compared to a conventional low fat diet, as well as improvements in CVD 
risk factors. 

 

  • Low GI foods and meals promote satiety and delay hunger 

The satiating effect of low GI foods is partly related to their slower rate of digestion and absorption. They stay in the gut longer and reach lower parts of the small intestine, triggering receptors that increase the secretion of satiety hormones such as GLP-1 and CCK15.  Both of these hormones produce feelings of satiation and GLP-1 has the added bonus of increasing insulin sensitivity.

 

Low GI meals, compared to their high GI equivalents, can also result in less energy intake at subsequent meals15. This is thought to occur through the influence of GI on the availability of fuel sources in the postprandial period. High GI foods with their associated high levels of insulin and low levels of glucagon, stimulate the uptake of glucose and fatty acids and suppress lipolysis. The consequent drop in circulating metabolic fuels can lead to a rise in counter-regulatory hormones that stimulate appetite and promote eating16.

 

  • A low GI diet helps maintain weight loss 

A great advantage of low GI diets is the value-added benefits they offer for long-term weight management and life-long health. Low GI diets bring about less of a fall in resting energy expenditure (REE) during weight loss17 and along with the macronutrient composition of the diet are a key factor in weight loss maintenance18. The Diabetes, Obesity and Genes study (DiOgenes)19 was designed to examine the effect of diets varying in protein and glycemic index on a number of health parameters during a period of weight maintenance. After an initial weight loss of ≥8%, participants were randomised to one of five ad libitum diets with either high or low glycemic index and protein content or a regular healthy diet as a control. During the 26 week weight maintenance period the low GI, higher protein diet was the most effective in maintaining weight loss. It also brought about favourable reductions in CVD risk factors20. What’s more, it’s turning out to be the arm with the lowest drop out rate, suggesting that this type of diet might be the one that you can stick to in the long run as well.

 


Summary

A healthy Low GI diet facilitates weight management* by:

  • Reducing insulin levels
  • Promoting higher rates of fat oxidation
  • Facilitating greater fat loss
  • Promoting satiety and delaying hunger
  • Helping to maintain weight loss


How do you achieve a low GI diet?

Lowering the GI of the diet is simply a matter of swapping low GI carbs for those that are high GI.  The greatest impact is achieved by focusing on the starchy carbohydrate staples.

  

 

Minimise high GI options

Maximise low GI alternatives

Breads

Soft white breads

Genuine sourdough

 

Light & airy wholemeal & white breads

Dense, wholegrain and seeded breads e.g.Bürgen®
pumpernickel

Cereals

Most refined, commercial, processed cereals

Traditional grains like minimally rolled oats, pearl barley, 
quinoa and cereals made from them like natural muesli e.g. Morning Sun® or Kellogg’s® Sustain® & Guardian®

Main meal carbs

Potatoes: mashed, chips and french fries

Carisma, Nicola and baby new potatoes, parsnip, corn, 
lentils, chickpeas, kidney, cannellini, baked beans & more

 

Jasmine, Calrose, Pelde, Arborio, glutinous, 
short grain, brown or white rice

Basmati rice, Doongara CleverRice®, prepared sushi

 

Polenta, millet, rice and corn pasta,

Pasta ‘al dente’, soba noodles, beanthread, Blu Gourmet Pearl couscous, buckwheat

Snacks

Water crackers, crispbread, doughnuts, 
confectionary, processed fruit bars, pretzels, 
rice crackers

Dried fruit and nuts, reduced and low fat yoghurt, some muesli bars e.g. Uncle Toby’s® muesli bars, nut, seed and grain bars, fresh fruit such as apples, pears, grapes, banana; dried fruit bread, wholegrain crackers

Sweeteners

Sugar, golden syrup, treacle

Agave nectar, pure maple syrup, LoGICane, pure floral honey, Fruisana

Beverages

Cordials, soft drinks

Wild About Fruit juices and water, reduced or low fat milk 
or soy drink


 


Useful Links and references

 

 

 


 

 

For recipes, meal plans & a daily Low GI food guide for weight loss go to www.gisymbol.com

Glycemic Index and weight management