There are many ways to compare various foods in terms of protein, carbohydrate, fats, fibers, vitamins, minerals, antioxidants etc content.
One of the important ways to compare foods are their Glycemic Index (GI) and Glycemic Load (GL).
Glycemic Index is numerical value between 0 and 100 and it basically describes how eating one food will raise blood sugar levels. GI 100 is for pure glucose. Foods with GI below 55 are considered to have low glycemic index, those with GI between 55 and 70 are considered to have medium GI and those with GI above 70, are considered to have high and very high glycemic index.
GI levels of food is important for many reasons, however, it doesn't take into account amounts of food, since it is not the same if you have consumed 50g of glucose or 50g of carbohydrates from, for example, blueberries - it is required to eat around 350g of blueberries in order to consume 50g of carbs!
Glycemic Load rectifies this problem by taking into account portion sizes - to calculate GL (Glycemic Load) divide food's Glycemic Index by 100 and multiply it by the grams of digestible carbohydrates (that means excluding fibers) in a served portion. Generally, a GL of below 10 is considered low GL, 11 - 19 GL is considered average and GL above 20 is considered high GL.
For example, blueberries contain ~14.5g of total carbohydrates including 2.4g of fibers per 100g of fruits - meaning 12.1g of digestible carbohydrates. Blueberries have GI between 40 and 53 (various studies show various results since not all varieties have the same amounts of nutrients and water). Worst case scenario is to assume GI of 53. One cup of blueberries on average has 150g (little more than 5 ounces) of blueberries.
So, glycemic load (GL) of this nice portion of blueberries would be:
GL = (53 / 100) * (12.1 * 1.5) = 9.6
(Actually, parentheses are not required since there are only multiplications and a single division, but formula is more understandable this way.)
If you take just 100g of blueberries, GL of those blueberries is only 6.4.
Glycemic Index and Glycemic Load Chart - Food Comparison
Next table presents basic nutritional data of certain foods, berries included, with their Glycemic Index and Glycemic Load values for various serving portions.
|Food||Glycemic Index||Serving size||Available Carbohydrates||Glycemic Load|
|Apple Juice (no added sugar)||40||0.25l||30g||12|
|Beans, black-eyed, boiled||42||150g||30g||12.6|
|Beans, kidney, soaked, boiled||28||150g||25g||7|
|Cranberries, dried, sweetened||62||40g||31g||19|
|Milk, full fat||27||0.25l||12g||3.2|
|Rice, brown, boiled||55||150g||33g||18.1|
|Rice, white, boiled||65||150g||35g||22.7|
|Yogurt, low fat||15||200g||9g||1.3|
It really must be emphasized that portion control plays very important role in balanced nutrition. For example, watermelons have high GI (72) and if you eat half a kilo (500g) of watermelon (35g of digestible carbs), GL of such meal is around 25 - rather high. But if you eat only 150g of watermelon (rather small portion), GL of that snack is around 7.6. And that is a big difference. That is one of the reasons why it is better to eat smaller meals, more often.
Low Gylcemic Index Foods
Berries generally have low GI - 40 or less. Since their digestible carbohydrate content (total carbohydrates - fibers = digestible carbohydrate) is rather low, their GL is almost always low, since it depends on the portions, too.
Unfortunately, GI of many berries is not yet verified and many studies have to be done in order to obtain accurate values. Even then, values can have certain offset - this is normal, since the values depend on varieties, growing conditions, ripeness of the fruit etc.
Green and leafy vegetables have GI below 15 and their GL is also very low - that is why fresh salads are so important for balanced nutrition. And when you combine such salads with berries, it is nutrition heaven :)
Long story short - even if you are on some kind of calorie restricted diet, be sure to include fresh fruits in your daily nutrition and stay away from sweetened and processed foods as much as possible.