Low-Carbohydrates Diets

salmon-2997240_640We live in a world where low-carb diets are extremely popular. This type of diet in most cases is classified as a diet with less than 30% of calories coming from carbohydrates. Foods like starchy vegetables, fruit or grains are restricted and higher intake of protein-rich and fat rich food is recommended.  You may find many fitness professionals who advise us to cut back on carbs in order to lose some weight. And while low-carb diets may be beneficial in some health conditions, like epilepsy or type 1 diabetes, not anyone will benefit from this type of diet. Low-carb diets did show great potential when people want to lose weight, but can you really imagine eating like that your whole life? And if you exercise regularly, you should know your exercise performance will most probably be affected. So let’s talk about carbohydrates.

Carbohydrate reserves in our body

In our body, carbohydrates are stored in the muscles and in the liver as long chains of glucose units also known as glycogen. The amount of glycogen in the body depends on the amount of glucose supplied after a meal and the amount of glycogen that is broken down during periods of fasting when the glycogen is used to supply our blood with glucose. So after a meal our glycogen reserves in the liver increase, and between the meals and especially after a sleep, the glycogen reserves are depleted. A very important thing to mention here is our nervous system uses blood glucose as the primary energy source.

And during physical activity, our glycogen reserves in the body can only be enough for around 2 hours of exercise. After this time, fatigue and decreased endurance performance may occur. The expression among runners for this state is „hitting the wall“.

What happens in our body when we don’t eat enough carbs?

When our carbohydrates intake does not match our body’s carbohydrate needs i.e. carbohydrate demands exceed carbohydrate intake, our body shifts to a backup system to meet its energy demands. Because there is a lack in an important substance to run the Krebs cycle (a major metabolic pathway in our cells in which the energy stored in food is released and carbon dioxide and adenosine triphosphate (ATP) are created) for a short period of time the energy demands are not met. The Krebs cycle system does not discriminate when it comes to nutrients: carbohydrates, fats and proteins can all enter the Krebs cycle to be broken down and regenerate energy. It is just that without adequate carbohydrate metabolism and without one necessary organic compound (oxaloacetate: the by-product of carbohydrate metabolism), this important metabolic pathway will slow down. With the adequate fat intake and from the body’s fat supplies, with time and depending on the individual, the liver initiates a process and takes another molecule (acetyl-CoA) and converts it into ketone bodies. This ketone bodies then pass from the liver to the general circulation and are absorbed by body’s tissues where they can be used as fuel. Most cells in the body can use both glucose and ketone bodies for fuel. Ketone bodies also can serve as a source of energy for the brain and the central nervous system. In our tissues then (for example in the muscle) ketone bodies are converted back into acetyl-CoA which is then used in the cell to provide energy and to initiate various metabolic activities. When this happens the body is in a metabolic state called ketosis.

During this adaptation process, many people will feel like they are sick or like they have flu. The usual symptoms are headaches, nausea, tiredness, and fatigue.

This adaption is sometimes called “fat adaptation” as body relies more on fat than carbohydrate intake. For some people, this metabolic adaptation will cause them to feel better and look better, even perform better. A study from 2017 shows “the elevated fat oxidation rate and glycogen sparing effect may improve performance in ultra-endurance events”. But according to the study, it takes at least several months of adaptation to a low-carb-high-fat diet for the metabolic changes to occur. This means several months of feeling tired, sore, and unable to focus… Other individuals never get used to this metabolic “challenge” and they are doing much better when ingesting more carbohydrates.

What would be the benefits of low-carbohydrate diet?

  • Previously, some studies (https://www.ncbi.nlm.nih.gov/pubmed/12761364) have shown that a low-carbohydrate diet may help people lose weight more quickly than a low-fat diet. This is probably why so many people have decided to try this type of diet. But the most recent study from February 2018, found no important differences in weight loss comparing a low-carbohydrate diet with a low-fat diet.
  • Diet low in carbohydrates can lead to a decreased levels of blood triglycerides
  • A low-carb diet can boost insulin sensitivity, therefore this diet may be beneficial for type 1 or type 2 diabetes
  • Other health benefits of low-carb diet might be lower blood pressure and higher levels of “good” HDL cholesterol in the blood
  • Research has shown that the low-carb-high-fat diet can cause massive reductions in seizures in epileptic children


What would be a downside of restricted carbohydrate intake?

Keeping carbs intake too low for too long can have health consequences. For example, if you like to exercise regularly, restricting your carb intake too drastically can lead to:

  1. Increased cortisol levels: A very low-carbohydrate diet for a prolonged period of time can increase cortisol levels, a hormone often called the “stress hormone”.  Its main function in the body is to increase blood sugar in the body from substances other than carbohydrates, such as fats and proteins, to aid in the metabolism of macronutrients (fat, protein, and carbohydrates) and to suppress the immune system. It is released in response to stress and low blood-glucose concentration (that would be a very low-carb diet). Too much cortisol over a prolonged period of time can lead to weight gain, mood swings, muscle weakness, high blood pressure, osteoporosis, skin changes, etc. This increased levels of cortisol also interfere with the production of thyroid hormones, leading to a state of hormonal imbalance.
  2. Decreased thyroid output: A low-carbohydrate diet can lead to impaired thyroid function. Thyroid hormones are essential to maintain and regulate energy metabolism, including carbohydrate metabolism. When carbohydrate intake is drastically reduced, the levels of very important thyroid hormone called T3 (the hormone responsible for blood glucose management and proper metabolic function) drop. Lower levels of T3 hormone results in lower metabolism and you may experience symptoms like fatigue, constipation, cold hands, depression, etc. Do not forget thyroid hormones do not only have the effect on weight, they also have profound effects on our overall health and energy levels.
  3. Decreased testosterone levels: when energy availability is very low due to dieting, the levels of testosterone and other androgens are substantially reduced. A very low-carb diet can lead to a reduction in testosterone levels, and rise in cortisol levels. So the body is under stress and in starvation mode. When this happens, the body begins to slowly shut down systems that are not critical for survival, including the reproductive system. Especially if you train regularly. Research showed that people who exercise regularly need to get enough carbohydrates in their diet or their testosterone levels will drop and their cortisol levels will rise.
  4. Problems with women’s hormones: Not eating enough carbohydrates can interfere with a woman’s delicate hormone balance. A diet too low in calories or carbohydrates can act as a stressor, causing HPA (hypothalamic-pituitary-adrenal) dysfunction. These three major glands (hypothalamic, pituitary, adrenal) interact in complex ways to keep our hormones in balance. It is said before that a low carb diet for the prolonged period of time can cause increased production of cortisol hormone, which makes the problem worse. HPA dysfunction can lead to low levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), estrogen, progesterone, testosterone and other hormones. This hormonal imbalance with time may cause irregular menstrual cycles or amenorrhea.
  5. Problems with the immune system: About 80% of our immune tissue is located the gastrointestinal tract. Additionally, our microbiota (gut flora) helps in development and function of the immune system. So maintaining a healthy balance of good bacteria in the gut is very important. But low-carb diet, with restricted intake of fruits, grains, starchy vegetables and dietary fibre in general, can compromise the microbiota balance in the intestine. Many studies have shown that maintaining a healthy gut microbiome is critical to human health. So improperly designed low-carbohydrate diet for the longer period of time can compromise the function of the immune system and if you search the Internet (some blogs and websites) you can find people who can confirm this from their own experience.

Finally, there is a good chance you will feel tired, lightheaded and generally not very well, especially during the period when your body will have to adapt to new metabolic pathway i.e ketosis.


There is a wide variety of evidence showing that low-carb diets can help with weight loss and metabolic problems. An intelligently designed low-carb diet for a defined period of time (max. 3-4 months) may have beneficial effects on body composition.

Also, a wide variety of evidence suggests that the ketogenic diet could have beneficial disease-modifying effects in epilepsy and also in a broad range of neurological disorders like Parkinson’s disease or Alzheimer’s disease. The research and clinical experience suggest that low-carb diets can be effective therapeutic tools for other conditions like diabetes (both type 1 & type 2), metabolic syndrome and PCOS (Polycystic ovary syndrome). The underlying mechanism of action is not entirely known.

And if we talk about sports performance, some athletes on a low-carb diet can achieve better results than others who will experience the opposite. A low-carb or ketogenic diet could help preserve glycogen stores and keep the athlete from “hitting the wall” during endurance exercises. But this is very individual and differs from one man to another.

But for most of us, a low-carb diet on a long run would probably not work. For most of people, a balance of a reasonable amount of high-quality carbs (brown rice, whole wheat bread, yam, beans and lentils, pumpkin, etc) lean protein and healthy fats work best. You should decide for yourself if this diet fits you and your lifestyle. Each person is unique when it comes to carbohydrate requirements. After all, most of the people are not elite athletes so there is no need take the nutrition to extreme levels.



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