What is the glycemic index? Why is Glycemic index important?
The glycemic index is a value assigned to foods based on how slowly or how quickly those foods cause increases in blood glucose levels (also known as blood sugar). The glycemic index of glucose is arbitrarily set at 100. The ratings of other foods are calculated by ranking them in comparison to glucose. Regulation of blood sugar is important as heightened blood sugar levels have been linked to blindness, kidney failure, and increased cardiovascular risk.
Foods low on the glycemic index (GI) scale tend to release glucose slowly and steadily. Foods high on the GI scale release glucose rapidly. Both types of food have value, however low GI foods are more likely to increase weight loss, while foods high on the GI scale are more useful for energy replenishment following exercise. In a nutshell, low GI foods slowly release the glucose/sugar you need for consistent basal function, while high GI foods provide a burst of glucose/sugar during strenuous activities. Therefore, if you are not consistently participating in strenuous exercise such as long distance running, low GI foods should be your primary selections (see the chart below for a list of foods and their glycemic indexes). Low GI is considered anything below 55, moderate GI is 56-69, and high GI is anything above 70.
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Admittedly, there is a lot of information out there about what the best “diet” is for weight loss. The American Heart Association and the American Dietetic Association endorse the idea that the majority of calories in the daily diet should come from carbohydrates (55% to 60%); fat should provide no more than 30% of total calories; and protein should be kept to 10% to 15%. However, many popular low carb diets including the Atkins diet, the Zone diet, Protein Power, and other “alternative” dietary approaches turn thumbs down on carbohydrates to promote inclusion of more fat and/or protein in the daily diet. Theoretically, low carb diets lead to weight loss by reducing the body’s production of insulin via reduction of sugars being introduced to the body – but the extreme of removing carbohydrates from your diet long term is something few patients are willing or able to commit to. This is why the low glycemic index (low-GI) diet is such a valuable tool. The low-GI diet splits the difference between the low-carb and low-fat approaches. It maintains the low-carb diet’s focus on insulin, but it suggests choosing certain carbohydrates over others rather than restricting carbohydrate intake. In conjunction with weight loss, evidence suggests that a low-GI diet could help prevent heart disease, and serve as a potential treatment/prevention strategy for diabetes.
How do you follow a low GI diet?
Using the guidelines set forth by entities such as the American Dietetic Association, you can make modifications such as choosing carbohydrates that fall toward the lower end of the glycemic index scale. Books such as The Glucose Revolution give a great deal of information on how to make these choices.
What evidence do we have to support low GI diets and weight loss?
Research utilizing 107 overweight adolescents tested the effectiveness of a low GI diet on weight loss. Participants were divided into two groups: a low-GI group and a low-fat group. The low-GI group was followed a diet consisting of 45% to 50% carbohydrates (preferably low-GI carbohydrates), 20% to 25% protein, and 30% to 35% fat, without restricting the overall number of calories. The low-fat group received instructions for a standard low-fat, low-calorie diet divided up into 55% to 60% carbohydrates, 15% to 20% protein, and 25% to 30% fat. Over a period of about 4 months, participants on the low-GI diet lost approximately 4.5 pounds, while those on the standard diet lost fewer than 3 pounds. While there were complicating factors in the design of the study, several additional studies have mirrored these results indicating that low GI diets contribute to increased weight loss over time.
Why should you consider a low GI diet?
Evidence suggests that a low GI diet could improve your health and help you lose more weight over time. Low GI foods provide you with a steady and stable release of energy, avoiding extreme spikes in glucose that can be damaging to your body. Research indicates that a low GI diet could protect you from heart disease, diabetes, and complications associated with those pathologies. Please utilize the food table above next time you are shopping for groceries!
Spieth LE, Harnish JD, Lenders CM, et al. A low-glycemic index diet in the treatment of pediatric obesity. Arch Pediatr Adolesc Med. 2000;154:947-951.
Fiona S. Atkinson, Kaye Foster-Powell, and Jennie C. Brand-Miller International tables of glycemic index and glycemic load values: 2008. Diabetes Care, Vol. 31, number 12, pages 2281-2283
Low Glycemic Index Diets. HCA Healthcare. September, 2014. https://hcahealthcare.com/hl/?/38396/Low-Glycemic-Index-Diets
Glycemic index for 60+ foods. Harvard Health Publishing. February, 2015.