Carbohydrates have been under scrutiny for a while, in particular since the Atkins diet became popular. Are carbohydrates bad? If the answer is simple in popular media, the reality is, as usual, a bit more complex.
First of all, it is important to realize that carbohydrates are not a homogeneous group of nutrients. They can be divided in three categories: fast carbs, slow carbs and fibre.
Fast carbs are called that way because they pass into the blood stream quickly after being ingested, and provide 4 calories per gram. They are small molecules. They are commonly known as sugars and the most common ones are glucose, fructose (a typical carb from fruit as the name indicates) and sucrose (the powder sugar you find in stores). Sucrose is a combination of one molecule of glucose with one molecule of fructose. The purpose of fast carbs in the body is to provide energy quickly, in particular to provide the brain with glucose, as it is the only fuel the brain can use to function. For as much as they are very useful for a quick energy boost, they will be metabolised and stored as body fat if the body cannot burn the quantity sent in the blood stream. This latter characteristic is important to understand from a nutritional point of view. Do not eat more sugar than you can burn in the short term because it will go to your hips. They are useful during intense exercise. Professional cyclists often use glucose from their bottle. Here is a little calculation to show how it works:
Since fast carbs should be 40% of total carbs maximum and carbs should be 60% max of total calories, the maximum amount of calories you can have from fast carbs is 40% x 60% = 24% of total calories. For a person who needs 2,000 calories per day, the maximum of fast carbs would be 24% x 2,000 = 480 calories. Apples and oranges are about 50 calories per 100g, carrots about 40 and bananas above 80. Let’s say you have 500 g of fruits and veggies per day. This would roughly amount to 5 x 50 = 250 calories. As you can see, with a few fruits and vegetables you get all the fast carbs that you need. Remember, 40% of 60% is the maximum. It is better to get fewer calories than this from fast carbs. But if you want a juice or a soft drink, how much could you have? If the total calories from fast carbs is 480 and you got already 250 from fruits and vegetables, there is room for only 480 – 250 = 230 calories. Since 1 gram of carb provides 4 calories, that would a maximum of 230/4 = 57.5 grams of fast carb per day. If you take a drink at 10% sugar, the maximum quantity of liquid is then 57.5/10% = 0.575 litre. If the drink contains 15% sugar, the number becomes 57.5/15% = 0.383 litre.
Slow carbs are quite different. The typical slow carb is starch, which can be found in grains (wheat, corn, barley, rice, etc…), pasta, potatoes and many legumes (beans, peas, lentils, etc…). They do not pass into the blood stream right away. Starch is a long chain that consists of glucose molecules. During digestion, and with intervention with insulin, starch is metabolized into a shorter chain, called glycogen, which is stored in the liver. As its name indicates glycogen is a word that means glucose-forming substance. Depending on the sugar level in the blood (aka glycaemia), the glycogen in released “on demand” with help of insulin to provide the organism with the needed glucose but just in the right quantity at the right time. This has two advantages. One is that glucose is not provided in one shot, as it would be metabolised and stored as body fat. Glucose is released just to be burnt. It is almost comparable with a high-efficiency furnace. The other one is that through this system, the carbs eaten during the meal will provide energy for a couple of hours at least, depending on the level of physical activity. Then, it is not a surprise that hunger happens around 11:00 am so about 3-4 hours after a breakfast with an appropriate amount of slow carbs. There is no need for snacking between meals if the meals are proper. Slow carbs also provide 4 calories per gram.
A small word is useful about gluten. The word starts with “glu” and is a normal component of grains, but on the contrary to what many people seem to think, gluten is not a carbohydrate. It is a protein. Gluten gives bread its network structure.
Fibres have a rather different function. The main form of fibre is cellulose, which is also a long chain of glucose molecules, but arranged differently than in starch. Cellulose is not providing energy as such, as it cannot be metabolised in the body. Fibres play the role of ballast. They help dilute the calorie density of foods (think of fruit and vegetables) and they probably also play a role in the clearing of the intestine during transit. Fibres may also play a role in reducing the risk of colon cancer.
As you can see, carbohydrates are useful, but they must be part of a balanced diet. Because of their characteristics, one should not splurge on fast carbs, because the excess quantity will be metabolised into body fat. A good guideline is to have no more than 60% of the total calories of the diet from carbs, fast and slow combined. The percentage of calories coming from fast carbs should be less than 40% of the total carbs calories, and less is even better. If you eat fruit regularly, you probably will have enough fast carb. It is better not to add sugar in tea, coffee or yoghurt to name a few, even though sweet tastes nicer for many people. Also pay attention of how much fast carb you have in the foods and beverages you buy. Soft drinks, juices and drink yoghurt can contain between 10 and 20% fast carbs. The best drink really is water (zero calorie).
Slow carbs are a bit less of a problem, because of the gradual release of glucose from glycogen. That said, a proper diet is a diet that just covers the needs of the body, and excessive consumption will inevitably lead to more body fat.
To sum up, carbohydrates are OK as long as consumed in a balanced diet. Too much carbs is bad, and so are too much fast carbs and too much slow carbs. The same is true with all groups of nutrients. Fat is fine but too much fat is not, and the same applies for protein as well.
© 2019 – Christophe Pelletier – The Happy Future Group Consulting Ltd.