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Discover what the glycemic index and glycemic load are, two concepts connected to the impact food has on glucose levels in the blood. Learn how to calculate the glycemic index and how foods are classified according to the speed with which they increase blood sugar.

A proper diet, in accordance with health regulations, includes the intake of all nutrients in the right portions and in enough amounts to preserve good health with the energy and satiety required.

Said plan should include a varied intake of foods from different groups on a daily basis–vegetables, fruits, cereals, root vegetables, legumes, and animal-origin products. At the same time, a diet needs to be in harmony with a person’s social and cultural circumstances, as well as not to represent any health risks. 

Every day we choose the foods that make up our diet. To a large extent, our physical health, as well as our emotional and social wellbeing, depends on said choices. However, our decisions are based on multiple aspects which could impact our eating habits, for example:

  • Unconscious or Misinformed Decisions
  • Biological, e.g. Appetite or Sense of Taste
  • Financial, e.g. Product Price and Availability
  • Social, e.g. Culture, Beliefs, Knowledge on Diets and Patterns, Family and Work Environment
  • Psychological, e.g. Mood and Stress Levels

Appetite and satiety are physiological needs with a direct influence on the choices regarding our diet and the foods in it. Energy and nutrient supply are essential to survive and respond to said sensations. Macronutrients, proteins, carbohydrates, and lipids present in all foods trigger different satiety signals.

Scientific evidence shows proteins have the highest satiating capacity, followed by carbohydrates–with a middle satiating capacity, and leaving lipids in a third place.

Carbohydrates, proteins, and lipids are the macronutrients that supply the energy the body requires. Out of these three, carbs are absorbed at the fastest rate in the body and those which are commonly blamed for our excess.

Carbohydrates are found in a wide array of foods and are categorized, from a chemical structure point of view, in simple and complex. Sugars–table sugar or saccharose, glucose, lactose, among others–are simple carbs and are present in sweet deserts, as well as in cereals, fruits, and vegetables.

At a chemical level, carbohydrates are simple sugars which are easily absorb into the bloodstream. Complex carbohydrates, on the other hand, include starches present in plant-origin foods like whole grain cereals and their byproducts, tubers, legumes, and fiber (found in the plant cells’ walls of these foods). Energy produced by complex carbohydrates is absorbed more slowly.

Glycemic index and fiber determine carbohydrates’ satiating capacity. Fiber is made up of elements our bodies are not able to digest which source volume and a low amount of energy. This prolongs the digestive process and produces a sense of satiety, delaying the absorption of energy provided by the food we eat.

Food supplies energy, yet some offers more than other. Carbohydrates and proteins provide 4 kcal/g, while lipids produce more than twice as much–9 kcal/g.

The American Association of Clinical Endocrinology (AACE) advises eating plans to be tailor-made taking into account the person’s age, physical activity, sex, food availability, and even their financial situation and comorbidity.

According to the AACE and the Official Mexican Standard (NOM, by its acronym in Spanish) NOM-015-SSA2-2010–on the prevention, treatment, and control of diabetes mellitus–, dietary energy supply, that is the kcal people need to ingest during the day to keep a healthy weight, should be defined in such a way that there is a macronutrient distribution of fifty to sixty per cent of total calories. Likewise, it is recommended for them to derive from complex carbohydrate intake, limiting to less than ten per cent the simple sugars consumption.

Carbohydrates are the main source of energy for the body and the digestive system is responsible for their transformation into glucose–needed for a proper brain and muscle function and the preservation of body functions.

However, not all carbohydrates are synthetized in the same way. Simple ones are digested and absorbed quicker than complex carbs; for that reason, the former are capable of rising glucose levels in the blood faster and to a greater extent. Complex carbohydrates work more slowly which prevents acute and fast peaks of blood sugar levels. Glycemic index refers to said differences and allocates a number to each food.

In order to match insulin dosage with carbohydrate intake, the AACE recommends limiting the intake of foods with a high glycemic index preferring raw fruits and vegetables.

But What Are the Glycemic Index and Glycemic Load?

Glycemic Index

Glycemic Index (GI) is a numerical value assigned to foods according to the speed with which each of them increases glucose blood levels in comparison with the effect had by pure glucose intake. 

The first research conducted on the matter took place in 1981 by David J. Jenkins and his team. They succeeded in determining the degree to which foods containing carbohydrates increase sugar levels in the blood.

As a result of these research studies, a scale was set–from 0 to 100–in which the reference value corresponds to pure glucose that was given 100. Based on the values set forth in this scale, foods are divided into three categories:

  • Low GI, below 55
  • Intermediate or moderate GI, from 56 to 69
  • High GI, above 70

Recent studies show carbohydrate amount is not the only element that has an influence in blood sugar levels, also known as glycemia. There is evidence that physical characteristics, ripeness, processing, cooking methods using high temperatures or long time could make food have a high glycemic index. That is why the GI should not be taken as a sole reference when choosing food, just because it might seem healthier.

Regarding raw fruits and vegetables intake, certain points that could modify their GI should be taken into consideration. They are advised to be eaten full since fiber slows down glucose absorption and, consequently, lowers the GI compared to their intake without skin or as juice. The riper the fruit, the higher the IG. However, frequency of consumption and portion size are also important. 

Processing conditions are also extremely relevant. Food processing takes place regardless the place food is prepared, whether at home, a restaurant or a factory. For instance, LTLT cooking allows for carbohydrates to be absorbed faster and, therefore, have a higher GI. 

Industrial processes follow strict variable controls–cooking temperature and time, for example–, which not always happens at home or restaurants. Different varieties of some foods might also have different GI values. Short-grain white rice has a higher GI than short-grain brown rice; however, long-grain white rice has a lower GI than long-grain brown rice.

Glycemic index can bring some benefits, yet it can also represent some issues:

  • It makes it impossible to identify how one food, compared to a combination of many, might affect glucose levels in different ways.
  • It does not take into account all the variables affecting glucose levels in the blood, such as cooking method and amount eaten.
  • It only includes foods with carbohydrates; it does not classify those with a low or no content of said nutrient.
  • It does not classify foods according to their nutrient content. Foods with a high GI might be low in calories, sugar, or saturated fats.

Glycemic Load

Foods are not just made up of one nutrient and so their GI is influenced by other factors. Glycemic Load (GL) quantifies the impact a portion has in relation to carbohydrate content on glucose levels in the blood. Foods have been classified as follows according to their GL:

  • High GL, above 20
  • Medium GL, between 11 and 19
  • Low GL, below 10

In general terms, most foods with low GL also have low GI. All the same, a key element for GL values is portion size. For instance, white bread has a high GI (100), yet one serving has a GL value of 15. Consequently, the more servings, the higher the glycemic response.

According to studies published in Appetite Magazine in 2016, eating foods with a high GI does not derive in glucose and insulin peaks in the blood nor it increases appetite or shortens satiety periods. 

It must be observed that both proteins and fats are involved in decreasing GI, since digestion becomes slower and counters glucose peaks by slowing down bowel emptying. A the same time, fiber intake regulates glucose ingress to the blood–meaning that the way in which foods are eaten will determine glycemic response. 

Learning how to combine foods, in variety and portion size, is a way to control glycemic response. For example, whole wheat bread can be combined with peanut butter or hazelnut spread, with salmon and avocado, or butter and berries. Likewise, wine can be paired with cheese and olives.

In general terms, it is recommended to eat different varieties of whole wheat or whole grain foods, combine fiber from fruits and vegetables with plant protein in legumes and dried fruits with carbohydrates commonly present in a diet. Taking the time to taste and enjoy food will help identify the satiety feeling and, in doing so, prevent eating more calories than needed.

Since foods are digested and absorbed differently, and when combined nutrient absorption changes, a health specialist should guide the selection process of what foods are right for each person.

Reference List

 

 

Healthy Diets

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