In the past decade a lot of rumors have assigned carbohydrates to be the main cause of obesity, cardiovascular diseases, diabetes, and many other diseases related. Luckily, many of these rumors were left behind as simple 'myths', and now carbohydrates don't seem to be as bad as they thought to be. However, there are still some disinformation regarding this matter.
In this review we'll go through the main myths about carbohydrates, and why those are not to be trusted. But before getting into the myths, it is important that you understand what carbohydrates are and the reason why they are important for our organism.
Carbs are one of the three macromolecules found in our diets. With proteins and fats, they make up 99% of the foods we eat on our daily basis.
Biochemically speaking, carbohydrates are biomolecules consisting of carbon (C), oxygen (O) and hydrogen (H), mainly. Their simplest form are called monosaccharides. These are the building blocks to build more complex chain, in where we can find oligosaccharides or polysaccharides.
Oligo-/polysaccharides are chains of monosaccharides joint together by glycosidic bonds.
These bonds allow to build the biomolecules and confers them stability and biological properties.
Although the structure of carbohydrates and their biochemical properties are not the scoop of this article, I encourage you to click HERE and read more about it!
GLUCOSE, THE KING OF MONOSACCHARIDES
Monosaccharides differ in their numbers of carbon atoms, the distribution of the groups attached to them, and the ring structure. Based on these facts, we can find a wide variety of monosaccharides but for sure, glucose is the very king of all of them.
Glucose is a six membered ring monosaccharide. It is shown both on their open and close structure. Talking about metabolism, glucose is the main source used to produce energy.
This is done by the glycolytic pathway, in where the molecule is broken down to produce ATP and release reduced coenzymes, which will be further used for production of ATP as well.
When energy requirements are fulfilled, glucose is stored in the muscle and liver in the form of glycogen.
The structure of glycogen allows to store bigger amounts of glucose without disturbing the equilibrium state of the metabolism, thus being more efficient.
METABOLISM OF CARBOHYDRATES
Carbohydrates are not strictly essential for our survival. This is because our organism has resources to convert other biomolecules into carbohydrates to simulate their presence. However, that takes energy, and energy is quite valuable and cannot be wasted. Thus, carbohydrates play important roles in our metabolism. Their main functions are (1):
- Source of energy
- Synthesis of other biomolecules
SOURCE OF ENERGY AND ENERGY STORAGE
As we mentioned above, glucose is the preferred molecule by our metabolism to produce energy. When carbohydrates are taken through the diet, these are absorbed throughout the digestive tract and broken down into glucose, which is further used to produce ATP (energy currency). This process involves three steps: glycolisis, citric acid cycle and oxidative phosporylation (2).
When there's excess of glucose, the molecule is converted into glycogen and stored until more glucose is needed to produce energy. Glycogen stores are found in the liver and the skeletal muscle. Glycogen in the muscle is mainly used to produce energy. On the other hand, glycogen in the liver is used to convert it back to glucose and provide more glucose to the blood. (Source: Nelson DL, Lehninger AL, Cox MM. Lehninger principles of biochemistry. Macmillan; 2008.)
Some carbohydrates, commonly named Structural carbohydrates (SC), are used to provide structure and protection to biological structures such as cell walls in plants, stalks, or stems, among others.
An example of these SC are those that form what we know as cell wall, protecting the plant cell from the external environment.
In relation with human metabolism, polysaccharides are found in the plasma membrane, conferring structure and stability. They are mostly found covalently bound to other molecules such as lipids and proteins.
Carbs also attach to proteins are/or fats to form complex conjugates such as glycoproteins or glycolipids. They function as receptors for exogenous molecules trying to enter the cell, thus working as lighthouses for our cellular buddies.
Additionally, carbohydrates form what is called glycocalix. Glycocalix is also found in the outer layer of the plasma membrane. It acts providing protection to the cell and acting as an intercellular signal. Also, there has been lately research on the relation between glycocalix and human medicine, possibly being a main cause of pathology (study)
Monosaccharides serve as precursors for the synthesis of other biomolecules, in where we can find nucleic acids (RNA and DNA). Nucleic acids are composed of a phosphate group, a pentose (carbohydrate), and a nitrogenous base. Looking at the structure of nucleic acids, it is evident that the presence of carbohydrates in the metabolism plays a crucial role for the synthesis of these molecules.
Additionally, they can be converted to proteins and/or fats through different metabolic reactions. When glucose breaks down into pyruvate, it can take different fates. The main fate is through the citric acid cycle (CAC), but it also converts into amino acids such as aspartate or glutamate. Also, metabolic intermediates of CAC serve as precursors for different pathways.
- Carbs are formed by monosaccharides joined together by glycosidic bonds
- Glucose is the main source of energy of our metabolism
- The main functions of carbohydrates are energy production and storage, structure, building blocks and signalling.
CARBOHYDRATES AND SPORTS
Sports can be classified in two main classes (based on O2 requirements); aerobic and anaerobic.
We know that energy demands when practising sports are high. During anaerobic sports, the main sources of energy are glycolisis, ATP and phosphagens system. On the other hand, the main sources of energy on the aerobic disciplines are oxidative pathways and glycolisis. Both glycolisis and oxidative system are highly dependent on glucose as substrate initiating the pathwaty.
The ability of producing ATP during sports practice is essential for an optimal performance. Carbohydrates, in this case, will play an important role providing enough glucose and substrates for energy production. As you know already, glucose is the preferred substrate for energy production. In other words, if we have presence of both glucose (carbohydrates) and free fatty acids (fats) our organism will use all glucose available first.
Carbohydrates to enhance sports performance has been a main subject for a long time. Studies have shown that carbohydrates intake before, after, and during sports practice can be used as an ergogenic aid. Let's go through the reasons why each carbs intake at each moment could help us:
BEFORE: ensure enough glucose to fill glycogen storages in skeletal muscle and liver to produce energy (study)
DURING: avoid any possible depletion of glycogen storages during the session and delay fatigue (study).
AFTER: resynthesis of glycogen and refill the glycogen storages after being depleted (study).
Concluding, we can say that there is a lot of evidence saying that carbohydrates intake is an important fact when trying to optimize sports performance.
However, our organism is able to produce carbohydrates from other molecules or even form other molecules to simulate carbohydrates' roles (ketone bodies).
These don't seem to be as efficient as carbohydrates are, and more research should be done to reach an optimal protocol using these other substrates to enhance sports performance.
MYTHS AROUND CARBS
Since carbs are the only macronutrient "non-strictly essential" for our organism, there have been a lot of myths questioning the presence of carbs in our diets. However, most of them are not based in any scientific study, thus not having the backup of science.
Some of these myths will be discussed in this post:
CARBS MAKE YOU GAIN WEIGHT
To start with, there's no a single food able to make you gain weight by itself. In fact, the overall amount of calories ingested during the day is what it will determine wether you gain weight or lose it.
Only with this simple argument and without looking at any scientific article, this myth is refuted. However, it's true that choosing the right sources of carbohydrates can make you gain weight more easily.
Why's that? There's something called satiety index. (study) It's a measurement that tells us how full -and for how long- we'll get after eating isocaloric amounts of different foods.
If we look at simple sugars (croissants, donuts, chips, french fries,...) their satiety index is way lower than other sources such as potatoes, vegetables, fruits, rice,... This means that if we are following a diet based on the first mentioned, we'll be most likely to get hungry more often, and the overall amount of calories will be higher. On the other hand, if our diet is based on potatoes, vegetables, fruits,... we'll get more full, doing less meals, and controlling the caloric intake will be much easier.
Carbohydrates don't make you gain weigt. What it does is making wrong choices when it comes to decide what to eat. Having a pack of cookies for a mid-day snak is probably not the best option, and you'll be starving before you notice. Instead, if you take a piece of fruit and a pack of rice cakes, the caloric intake will be the same or less, and you'll get more full.
CARBS LATE AT NIGHT ARE BAD FOR YOU
We are going to be clear here; our body doesn't know whether you are doing a carbohydrate-rich meal at 8:00am or 8:00pm. What's important is to fulfill the carbohydrates requirements of the diet and the caloric intake.
Not only that, but carbohydrates intake late at night can help you achieving a better sleep. In this study made with night workers (study), they found that the group ingesting higher amounts of carbs before bed had longer and better sleeps. This is because carbs are precursors of tryptophan, aminoacid used for synthesis of hormones such as serotonin and melatonin. These two hormones play a crucial role on sleep and circadian rythms (study) (study)
In the figure shown above (source), we can see the pathway by which melatonin and serotonin are synthesized from tryptophan. Therefore, if we are defficient in tryptophan or any other precursor, the synthesis of these two hormones will be lower, and sleep quality will be compromised.
To conclude with this myth, we can say that not only aren't bad for you, but high-carb meal before bed can help you sleeping better and for longer. However, having a rich meal right before bed can compromise sleep quality, so keep it in mind and take your last meal at least 1 hour before going to bed.
KETO DIETS ARE HEALTHIER THAN REGULAR DIETS
This myth, from a start point, is not properly formulated. There are many ways to perform a ketogenic diet.
Both plates shown can be classified as "keto-friendly". However, it's evident that in terms of health they are not the same. With this I want to explain that the myth is inconsistent itself. There's no healthier diets. It all reduces to how you perform that diet and the adherence to it.
If you are doing a keto diet but you give up after two weeks, bad habits will come back... On the other hand, if you follow a regular diet, flexible, with a bit of everything and you are adhered to it, it will stay on the long term, and the results will be better.
SUGARS IN FRUITS ARE BAD FOR YOU
This is, in my opinion, the most stupid myth I've ever seen about carbs. To start refuting this myth, fruits are not only carbohydrates. The nutritional matrix of fruits are high in micronutrientes such as vitamins and minerals. These molecules play an important role in metabolism and tissue function (study). Sufficient intake of micronutrients is important for overall health and well-functioning metabolism. Additionally, sugars in fruits are natural sugars with no harm to our metabolism. Harmful sugars are synthetic or added in big amounts.
The main sugar in fruits is called fructose. As glucose, fructose is a monosacharide, with the main difference on the number of carbons, having five carbons instead of six. Once in our intestine, it is converted into glucose to function as energy source.
To this point, we see no huge difference between sugars in fruits and other carbohydrates sources. Also, fruits intake previous to physical activity can help filling glycogen storages. Fructose and glucose are transported into blood plasma by different transporters (GLUT5 (source) and SGLT1 (source) , respectively). Because of this, a good strategy to optimize sports performance would be to add both fructose and glucose before exercise, achieving a faster and increased level of glucose available for oxidative processes (study)
- Caloric intake will determine your energy status
- High-carb meal before bed improves sleep and rest overnight
- There are no healthier diets. It all depends on how you plan them.
- Fruits are defininetly good for you, beig foods containing natural sugars and high content of micronutrients.
- Fruits accompanied by a rich-glucose source is a good strategy to optimize sports performance
In this post we have seen the importance of carbohydrates in our metabolism and the main function that they perform. Additionally, because they are the main source of energy, deleting them from our diet is not the optimal strategy to enhance sports performance. When it comes to practising any sports, carbohydrates play an important role assuring enough energy to perform the task.
There are many myths around about carbohydrates. However, we have seen here that most of them are fake, concluding that carbohydrates are not the enemy. The enemies are major factors such as sedentarisms, excess of ultra-processed foods, and lack of good choices such as vegetables, whole-grain sources, potatoes, fruits,... We usually blame things that are insignificant before admitting where the real problem is. Carbohydrates are not the enemy. They have been with us for millions of years. What has appeared lately is the food industry, and with it all that we all know of.
As my last take-home message, please find a right balance on your diet and make the right choices.