A diet with a low glycemic index and low glycemic load is an important element in the prevention of diabetes, insulin resistance, obesity, cardiovascular disease, and cancer. A menu based on products that have a low glycemic index and are rich in dietary fiber is particularly important for people with impaired carbohydrate metabolism or people with a predisposition to this type of disorder. The slower absorption of carbohydrates by the body results in a slower increase in the level of glucose and less insulin delivery by the pancreas in response to food intake. The lower the variations in glucose and insulin in the blood, the easier it is to control your appetite. It is also an effective way to get rid of sleepiness after eating a meal.
Glycemic index – what is it?
Glycemic Index (IG) is a parameter that determines the rate of increase in blood glucose after consuming carbohydrate products in comparison with the increase that occurs after consuming the same amount of carbohydrates as pure glucose. It is a way to measure the rate of conversion of carbohydrates contained in the product into glucose circulating in the blood.
It was assumed that the intake of 50 g of available carbohydrates (glucose) causes an increase in blood sugar level by 100%, this means that glucose has IG = 100. The higher the IG of a given product, the faster it is digested and the faster the blood sugar level is raised, and this, in turn, results in a large discharge of insulin by the pancreas. As a consequence, glucose levels are reduced, often even to values lower than those at baseline, which leads to reactive hypoglycemia.
Reactive hypoglycemia is a condition in which the glucose falls below 55 mg/dl within 4 hours after eating a meal. This usually manifests as weakness, fatigue, confusion, convulsions, dizziness, and fainting. In order not to allow such a phenomenon, one should base in the diet on low and medium GI products. Low GI products are absorbed much slower due to longer digestion and do not cause such rapid fluctuations in glucose and insulin levels.
Due to the postprandial increase in blood glucose concentration, food products were divided into three groups
– products with a low IG ≤ 55,
– products with medium IG 56-69,
– products with a high IG ≥ 70.
It is worth choosing mainly products with the low and medium glycemic index. Products with a high glycemic index may appear in the diet sporadically, in small amounts and it is best to combine them with those with low GI.
Factors influencing the reduction of the glycemic index
Factors lowering IG is
– a high ratio of amylose to amylopectin, e.g. in legumes such as lentils, chickpeas, peas, beans, and also in barley;
– fructose content (present in fruit) and galactose;
– high content of β-glucan (present in grains, mushrooms, and bamboo);
– cooling (boiled potatoes should be cooled in a refrigerator to create a resistant starch, which will reduce the glycemic index of the product, such potato preparation allows inclusion in the diet, although it is not recommended for people with diabetes and insulin resistance);
– low maturity, e.g. green bananas;
– high content of lectins and phytates (included, among others, in legumes, peanuts, tomatoes, aubergines, peppers);
– high content of proteins, fats, organic acids;
– low fineness (rice will have a lower glycemic index than rice flour made from it).
Fats and proteins delay gastric emptying, digestion, and absorption of carbohydrates in the small intestine, and this reduces IG. In practice, it is worth combining a product containing carbohydrates (eg oatmeal) with a protein product (eg cottage cheese) and fat (eg nuts), then the glycemic index of the entire meal will be reduced. Similarly, in the case of buns, which is characterized by a high glycemic index – to lower it, it is advisable to consume buns with cottage cheese paste (source of protein) and fresh vegetables (source of dietary fiber) sprinkled with sunflower seeds (source of fat).
The water-soluble fiber fractions slow down or even inhibit the secretion of the enzyme (amylase) digesting sugar, which also causes a reduction in IG. Insoluble fractions do not affect the digestion and absorption of carbohydrates. Products containing organic acids (lactic acid) have a lower GI, so fermented dairy products such as yogurts, kefirs, buttermilk are characterized by lower GI than milk.
Resistant starch may also reduce IG – the more it is in a given product, the better; also because it is a medium for bacteria of the genus Lactobacillus and Bifidobacterium, which have a positive effect on the microbiota. To increase the amount of resistant starch in the diet, prepare starch products at high temperatures without water or in a small amount (baking or steaming) and consume starchy foods cooled, poured with cold water. The glycemic index of potatoes is high, but if we cool them down, IG will decline. In practice, this means that it is better to cook porridge, rice or pasta a day before and the next day to reheat it than to consume such a product freshly after cooking.
A minimum of one-day bread and immature fruits will also contain higher amounts of resistant starch, which becomes indigestible to the body, and thus – does not undergo conversion into glucose. Also, the dish becomes less caloric and more filling. Starch resistant will also reduce the need for insulin and will not cause fluctuations in the level of sugar.
Factors influencing the increase in the glycemic index
Factors increasing IG
– low amylose to amylopectin ratio, e.g. in rice, potatoes, and wheat flour;
– glucose content (both added to the food product at the stage of its production as well as resulting from the decomposition of starch as a result of long storage of vegetables or fruit);
– low content of β-glucan;
– roasting, extruding and cooking, e.g. corn, popcorn;
– high maturity, e.g. ripe bananas and grapes;
– low content of lectins and phytates;
– low content of proteins, fats, organic acids;
– high fragmentation;
– grain cleaning.
The traditional, long cooking of starch-containing products in the water causes a change in its structure. Under the influence of heat, bonds between molecules of starch start to crack and bind large amounts of water. Starch begins to swell and form gruel. The degree of pasting depends on the amount of amylose in the product. The fewer it is, the faster the product is digested, which means a rapid increase in blood glucose. How to apply this knowledge in practice?
A good example will be porridge prepared in two different ways. The higher glycemic index will have oatmeal prepared from instant oatmeal, which has been boiled for a long time in milk, than porridge prepared based on mountain oat flakes filled with yogurt. Several factors affect the increase in the first porridge of IG – cooking, product fragmentation and the lack of organic acids.
Too long storage of root and tuber vegetables also increases their glycemic index – young potatoes will have a lower GI than those stored a few months earlier. The time of day, the size of the meal and the speed of its consumption are also important. Fast food intake also increases its IG.
If we use the glycemic index, we do not take into account the number of carbohydrates consumed in a given product, but only the quality and rate of glucose absorption. The parameter called glycemic load (LG) takes into account both the quality and the number of carbohydrates consumed.
The glycemic load is calculated by multiplying the number of available carbohydrates in a given portion expressed in grams by the IG of a given product. The value obtained should then be divided by 100.
LG = (carbohydrates digestible in a portion of g × IG) / 100
Due to the glycemic load, food products were also divided into three groups
– products with low LG ≤ 10,
– products with medium LG 11-19,
– products with a high LG ≥ 20.
The following values are used to determine the daily intake of LHS
– low LG diet ≤ 79,
– a diet with an average LG 80-119,
– high LG diet ≥ 120.
It is not worth focusing only on IG, but also consider LAG, the following example may support this. Watermelon has a high IG (75), but due to the low carbohydrate content (about 8 g per 100 g of the product) is characterized by a low ŁG of 6 (ŁG = (75 × 8) / 100), which means that after consuming carbohydrates they will absorb quickly, but the blood glucose will not be high. The condition is, however, eating watermelon in an amount of about 100-150 g.
It is very important to properly compose meals. It is worth combining low IG products with those with medium GI to maintain balance in the meal. A diet with a low glycemic index and low glycemic load will help in weight reduction, glycemic regulation, and lipid profile. It will also reduce the risk of many civilization diseases and, consequently, improve quality and life expectancy.