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June 4, 2014

Glycemic load and it’s role in weight loss

by Helene van den Berg

The glycemic index (GI) ranks foods and beverages based on how they affect your blood sugar levels. Foods are scored on a scale of 0-100. Only foods that contain carbohydrates are ranked, since they have the biggest effect on blood sugar.

The GI scores are:

  • Low (below 55) – raw carrots, raw apple, grapefruit, peas, skim milk, kidney beans, lentils etc.
  • Medium (55 – 69) – bananas, raisins, raw pineapple, sweet corn, certain types of ice creams etc.
  • High (70 and up) – white rice, brown rice, white bread, watermelon, white skinless baked potato, boiled red potatoes with skin.

A food ranking high on the GI produces a large spike in glucose after it has been consumed, while a food with a low GI causes a slower, sustained rise in blood glucose. Several factors affect a food’s GI, like it’s physical form (liquid/solid); the amount of fiber and preparation method (raw/cooked) e.g. highly processed food containing refined sugars (crackers, corn syrup) will have a higher GI.

NOTE: The GI for any food vary significantly between individuals, therefore test the food on yourself to determine their effects.

Diets based on the glycemic index are: Zone diet, Sugar busters and Nutrisystem.

There is a difference between a low carbohydrate diet and a low GI diet:

Low carbohydrate diets restrict carbohydrates (low insulin levels), promoting greater use of fat as the source of fuel, while low GI do NOT restrict carbohydrates, but are very selective of the consumed carbohydrates (quality). Glycemic load (GL) combines both the quality and quantity of a carbohydrate in one number. This is an excellent way to predict blood glucose values of different types and amounts of food. The formula is : GL = (GI x the amount of carbohydrate) ÷ 100.

For example: an apple has a GI of 40 and it contains 15gm of carbohydrate. Therefore the GL= 40 x15g/100 = 6. Compared to a baked potato: GL = 80 x 15g/100 = 12. This indicates that a potato will have twice the metabolic effect of an apple.

The ability of a low GI eating plan to facilitate weight loss is heavily debated among scientists and is a complex matter (subject’s demographics, health status, length of investigation etc.). Those who advocate low GI diets, believe low GI foods digest more slowly and keep blood sugar levels in check; it will increase fat utilization and promote feeling of fullness. Guided by a nutritionist, it could be useful if you don’t want to count calories or go low on carbohydrates and want to change your overall eating habits, especially in relation to blood sugar imbalances.

One study found weight loss on a GI diet at six months, but no difference after a year. This could mean that low GI isn’t something that can be maintained for a long period of time. Some evidence suggest that a diet higher in protein and lower on the GI, may lead to a sustained weight loss. Some evidence also suggest that you may lose weight on a low GI diet, simply because you choose more fiber and protein, which helps you reduce portion sizes and eat less. (Fiber intake has been well correlated with body weight reduction and maintenance, as well as lower energy intake). Other studies suggest there is little evidence that having an elevated blood sugar level, leads to weight gain, if you’re healthy. Insulin is vital to good health and becomes a problem only when insulin resistance develops. Insulin resistance doesn’t develop from eating certain carbohydrates or proteins, but from being overweight. The bottom line is that to lose weight, you must reduce the calories you take in and increase the calories you burn. Traditional weight loss advice is to lose 1-2pds/wk (1/2 -1 kg/wk) by reducing calories and fat and emphasize complex carbohydrates. Losing a large amount of weight rapidly could indicate that you’re losing water weight or lean tissue, rather than fat.

The low GI diets have been very effective in improving glucose control for those with impaired glucose metabolism and diabetes and is beneficial for heart disease. Currently, research doesn’t support low GI eating as a magic bullet for weight loss. It comes back to eating less, being more active and consuming a healthy diet containing plenty of whole grains and fiber containing foods, like fruits and vegetables.

GI is an useful tool for exercise performance: eating a low GI pre-exercise snack, results in better maintenance of blood glucose levels during exercise and a slightly higher rate of fat burning; a low GI diet prior to exhaustive exercise improves your endurance; moderate and high GI foods are recommended during and after exercise e.g. sports drinks and energy bars. Eating a high GI snack within 45 minutes after exercise, helps to replenish depleted glycogen stores in the muscles and stimulate insulin secretion. Insulin promotes glycogen storage, protein synthesis and enhances blood flow into the muscle to remove the byproducts from exercise (lactate and carbon dioxide). Due to individual differences, it is important to experiment with meal timing and food choice to find out what works best for you.

Five MYTHS about GI:

  • GI is the best way to determine the amount of sugar (carbohydrates) in a food – GI describes the rate glucose is released in the bloodstream and says nothing about carbohydrate content. The more grams of carbohydrate consumed, the higher the glycemic response, due to an increased glycemic load (GL) – therefore GL is a better indicator!
  • White foods (potatoes, pasta) are high GI foods – Cooking method, food processing and meal combinations affect GI, NOT food COLOUR e.g. the GI of boiled potatoes is lower (56) than microwave potatoes (82). Pasta is a low GI food (40-50). A meal served where protein and fat are served with vegetables, lower the overall GI of some meals.
  • GI can be used to indicate how, healthy versus unhealthy, foods are – Lower GI doesn’t always mean a healthier product e.g. whole milk has a GI of 27 while skim milk has a GI of 32. Both potato chips and ice cream have a lower GI than baked potatoes, even though baked potatoes are more healthy.
  • All simple sugar is high GI – Not all sugar is created equal!. Fructose in fruit has a slower rate of digestion and absorption than glucose. The GI for most raw fruit is 30-50.
  • You can eat as much low GI food as you want and maintain low insulin levels – You can get high insulin responses with low GI eating, due to the quantity of carbohydrates consumed (glycemic response = GI x GL concentration).

Do low GI diets work for fat loss?

  1. Taken out of context: One major concern with the GI is, that it ranks foods in isolation. But in reality, how your body absorbs and handles carbohydrates depends on many factors: how much you eat; how the foods is ripened, processed or prepared; the time of day it is eaten; other foods you eat with it; and health conditions you may have (diabetes). So the GI may not give an accurate picture of how one particular food affects your blood sugar. Although the glycemic load (GL) scores a food product based on both carbohydrate content and portion size, the problem is the larger the portion size, the greater the calories consumed whether the GI is high or low.
  2. Not supported by scientific evidence: A study done in 2008 at the university of Cambridge, has shown that there was no difference in weight between a group who consumed mainly high GI foods and one that consumed mainly low GI foods. Many of the lower GI foods tend to be lower in calories, which helps in creating a caloric deficit, which in turn drives fat loss. Whenever a diet plan focuses on one food group to show you that this is the reason why their plan is superior to all others, it is pure hype!. They’ve simply managed to come up with a way of convincing you to eat less than you need to on a consistent enough basis to see results!. All these roads lead to weight gain in the end!.
  3. It makes things more complicated: It can also be difficult to follow a GI diet on your own. Most foods are not ranked by GI.

If you eat a healthy diet, based on fresh foods that aren’t highly processed, you may get the same benefits as the low GI diet. However, it’s possible that if you choose a lot of low GI foods that are high in calories, sugar and saturated fats, you could develop some of the same health problems the diet hopes to prevent!.


Read more from Glycemic Index

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