Among the number of fad diets, emerges a scientifically sound diet called low glycemic index diet. This diet again focuses on carbohydrates, blood sugar levels and insulin levels.
But it is way different from low carb diets, since it allows you to eat good carbohydrates. (Read carbohydrates and weight loss).
This plan is not just about eating pasta while losing weight, but a manner of eating healthy carbs and balancing other food groups and still lose weight.
What is Glycemix Index?
Glycemic index is a scale from 0 to 100 that rates food items on the basis of how their consumption raises blood sugar levels. Consumption of different foods with different nutrient levels raises blood sugar levels to different levels.
Dr. Jenkins developed this scale based on an experiment he had conducted in 1981. Interestingly starchy foods raised the blood sugar levels more than sugary foods. Hence he developed the Glycemic Index in which different foods are ranked based on their effect on blood sugar levels.
GI will tell us whether a particular food will elevate the blood sugar levels sharply or moderately or only slightly. Low GI foods are those that elevate blood sugar only slightly or moderately while high GI foods bring a high rise in blood sugar.
High GI foods have a ranking of 70 or more while low GI foods have a rank of 55 or less. You can find details of GI of different foods on www.glycemicindex.com This is an international database maintained by Sydney University Glycemic Index Research Services in Sydney,Australia.
Glycemic index does not report the quantity you would require to eat that would raise your blood sugar to that level. Watermelon has glycemic index of 80 but it is low in digestible carbohydrates which raise your blood sugar levels.
That would require you to eat a lot of watermelon before it starts affecting your blood sugar.
Therefore another parameter has been developed called glycemic load. GL describes the effect a particular food has on your blood sugar based the quantity and quality of carbohydrate present in it.
Glycemic load is GI x number of carbohydrates divided by 100. Apple has a GI of 40 and has 15g of carbohydrates so its GL would be 6. Low GL lies between 1 to 10, medium GL 11 to 19 and above 20 is under high GL.
How does the GI diet work?
Low glycemic index diets focus on eating food items that are ranked low in GI levels and cutting out on foods with high GI. This reduces spikes in blood sugar levels.
High blood sugar levels lead to increased secretion of hormone insulin which breaks down blood sugar rapidly.
Reduced blood sugar levels leave you feeling hungry and unsatisfied. Also this rapid drop in blood sugar level causes excess blood sugar to be stored as fat.
Eating low GI foods leads to slowly release of glucose in blood which is metabolized efficiently. Also their fibre and water content promotes satiety thereby reducing your calorie intake. Low GI diet reduces cravings.
How is GI diet different from low carb diets?
Both low carb and low GI diets work towards maintaining low insulin levels which in turn supports burning of fats.
Low carb diets almost cut down carbohydrates to negligible levels. Low GI diets on the other hand promote you to have good deal of carbohydrates like fruits and vegetables.
These carbohydrates are rich in fibres and are beneficial to digestive system. Therefore unlike low carb diets you will not face the ‘carb flu’ symptoms like headache and fatigue.
What does research have to say about the role of GI diet in weight loss?
Quite a bit of research has been done on the effects of GI diet on body weight and metabolic health.
1. Low glycemic index diet brings about modest weight loss
Their results showed that low glycemic index diet brought about a significant decrease in body weight, total fat, cholesterol levels in comparison to the control diet.
Low calorie low glycemic index diet for 12 weeks is found to bring about significant reductions in body fat and abdominal obesity and improvement in fertility in overweight or obese women. Sloth et. al reported an average 1.9kg weight loss in 10 weeks with low glycemic index diet.
Visceral fat is fat surrounding the organs and this fat can lead to metabolic issues. Low glycemic index diet is found to be beneficial in reducing visceral obesity. Studies show that low GI diets can reduce abdominal obesity.
A 6 month study was conducted to compare the effect of low GI, high GI and low fat diets on weight. At the end of 5 months it was observed that low GI diet brought about a significant reduction in body weight compared to low fat diet and it also brought about improvement in insulin function.
With high GI diet no significant change in weight was observed. Another study showed that low glycemic index diet brought about a significant decrease in body weight and waist circumference whereas high GI diet did the exact opposite.
When compared to other dietary approaches such as calorie reduction and portion control, low glycemic index diet is not found to cause any different weight loss outcomes than these diets.
Though short term studies and clinical trials suggest that low glycemic index diets cause weight loss, a review of 23 studies shows that this data when pooled together is inconsistent. Some show significant weight loss while some show insignificant trends.
It would be safe to say that low glycemic index diets bring about modest reductions in weight.
What does this mean?
Low glycemic index diet brings about modest weight loss outcomes. Low glycemic index diets are beneficial for reducing abdominal obesity and maintaining weight loss.
2. It can promote fat oxidation
Pohlmeier et. al conducted a study wherein 8 weeks of low glycemic index diet provision led to a significant reduction of body weight (average 8.1kg). Also it was observed that there was efficient carbohydrate metabolism and increased fat oxidation or breakdown of fats.
Research shows that high GI diet can impair fat oxidation rate in comparison to low GI diet which can cause subsequent weight regain after weight loss. These findings suggest that low GI diet can be favourable in weight maintenance.
Exercise as we all know helps in burning fat and carbohydrates. A low GI meal prior to exercise aids in maintaining blood sugar levels and supports burning of fats during exercise.
High or moderate GI are recommended after exercise since they are easily digested and absorbed and provide immediate energy.
The high GI foods after exercise increase insulin secretion and this insulin supports glycogen storage, increases protein synthesis by muscle and increases blood flow to muscle.
What does this mean?
Low glycemic index diet reduces insulin response which in turn favors burning of fat. Low glycemic index diet potentiates the fat burning effect of exercise.
3. It promotes satiety and reduces cravings
Silva et. al report that that a breakfast low in GI and high in fibre reduces blood glucose spikes and also reduces hunger hormone.
A review of 32 studies shows that diets low in glycemic index can reduce appetite in short term. In comparison to low GI diets, high GI diets are found to increase food cravings and stimulate the brain’s reward pathway.
What does this mean?
The slow release of sugar in the blood by low glycemic index diets and the protein content aids in reducing appetite in short term.
4.It improves metabolic health
A diet rich in protein and low glycemic index foods improves blood sugar control and also reduces abdominal obesity in individuals with type 2 diabetes. Research shows that this diet also aids in reducing symptoms of metabolic syndrome.
Low glycemic index is found to help in metabolic conditions like non alcoholic fatty liver disease , glucose tolerance in gestational diabetes , reduction in cholesterol levels , reduction in obesity induced inflammation , improvement in diabetes related parameters , prediabetes , obesity induced diabetes .
What does this mean?
Low glycemic index diet have a favourable effect on blood sugar control, cholesterol and blood lipid reduction, treatment of fatty liver disease and obesity induced inflammation.
5. Low glycemic index diet is beneficial for childhood obesity
Kong et. al conducted a 6 month clinical trial where obese adolescents were assigned to either low glycemic index diet or control diet. After 6 months it was observed that there was significant reduction in weight and waist circumference in group following low glycemic index diet.
Researchers concluded that low GI diet can be an alternative to conventional diet in obesity management in adolescents.
A similar 6 week study demonstrated that low glycemic diet reduced body fat and cardiovascular risk factors in obese children.
What does this mean?
Research suggests that low glycemic index diet brings about significant benefits in childhood obesity.
What to eat on a low GI diet?
On the low GI diet, the basic idea is to eat more of low GI foods (55 or less), limited amounts of moderate GI foods (55 to 69) and avoid high GI foods (70 and above).
The diet should contain 40% of calories from unrefined carbs, 30% from lean protein and 30% from healthy fats.
www.glycemicindex.com can provide details about glycemic index of various foods and aid in selection of low GI foods. Some practical tips would include:
- Opting for whole grain bread instead of white bread.
- Replace highly processed breakfast cereals with traditional porridge of oats or other cereals.
- Include legumes in your diet.
- Opt for fruits and non starchy vegetables.
- Eat less of sugary foods.
Considerations when on the GI diet
GI rank just indicates the effect the food item will have on blood sugar but does not tell much about its nutritional value. This can make it difficult to choose what to eat and what not.
Proteins and fat lead to slow absorption of carbohydrates. Therefore chocolate that is high in fat is ranked low on GI scale. Cooking and processing also affects the GI of the food.
Another limitation is that you cannot identify glycemic index of a meal. As mentioned earlier certain foods are low on GI, packed with proteins and fats but do not contain required nutrients.
Also some really healthy food items have high GI ranking like brown rice. But then again this diet allows you to eat low GI bread and pasta.
There is not much guidance or structure as to what should be eaten and how many calories to consume. For example watermelon has GI of 80 but one serving has only a GL of 5.
Low glycemic index diets are scientifically proven to cause weight loss in comparison to other low calorie diets. They also have a beneficial effect on metabolic health which is quite pronounced in comparison to effects brought about by other diets.
The only catch about this diet is that you are on your own when it comes to choosing low GI foods, deciding calories and planning meals. Jennie Brand-Miller has written quite some practical books that can aid in selection of low GI foods and practising this diet.
If you have tried the low GI diet for weight loss, we would love to hear about your experience and approach towards it.