Low-Carb Diet – Key Questions and Answers

What is the difference between the ketogenic diet and the low-carb one?

The ketogenic (keto) diet is one type of low-carbohydrate (low-carb) diet. Low-carbohydrate diets include various dietary models that limit the supply of carbohydrates.

The main difference between the low-carbohydrate (low-carb) diet and the keto diet thus lies in the amount of net carbohydrates consumed daily. The low-carb diet, depending on how restrictive it is, can provide up to about 40% of calories from carbohydrates. The keto diet restricts carbohydrates much more severely (up to 50 grams per day), and its overriding goal is to enter a state of ketosis, in which the body uses fat, rather than glucose, as its main source of energy. By contrast, the objective of the low-carb diet is not ketosis at all, but better well-being and improved health, which is supposed to result from carbohydrate restriction.

The keto diet is therefore much more restrictive than the low-carb diet. It requires the exclusion of certain food groups (e.g., starchy vegetables such as potatoes), which the low-carb diet only restricts.

Read also: Five Recipes for Ketogenic Barbecue Dishes in Meat and Vegetarian Versions

How many carbohydrates can I eat on the low-carb diet?

According to the recommendations of the Institute of Food and Nutrition, in a healthy diet, carbohydrates account for about 45-65% of the daily energy supply, with the proviso that the menu should provide no less than 130 g of them. The low-carbohydrate diet defies these recommendations.

There is no clear framework defining a proper low-carbohydrate diet, but one can already speak of the low-carb diet when the carbohydrate supply provides less than 45% of daily energy. In practice, people on the low-carb diet typically derive between 10 and 44% of their energy from carbohydrates.

As an alternative to the percentage-based breakdown, the daily net carbohydrate supply can also be considered. Here are some examples of percentage-based distribution of the energy derived from carbohydrates in the low-carb diet, along with calculations for carbohydrate intake (assuming a total daily energy supply of 2,000 kcal):

• >10% of energy – less than 50 g of carbohydrates – ketogenic diet,
• 10% of energy – 50 g of carbohydrates,
• 15% of energy – 75 g of carbohydrates,
• 20% of energy – 100 g of carbohydrates,
• 25% of energy – 125 g of carbohydrates,
• 30% of energy – 150 g of carbohydrates,
• 35% of energy – 175 g of carbohydrates,
• 40% of energy – 200 g of carbohydrates,
• 45% of energy – 225 g of carbohydrates.

Thus, the term low-carbohydrate diet can include extremely different dietary models:

• An extremely low-carbohydrate diet, in which less than 10% of energy comes from carbohydrates or about 20-50 grams of carbohydrates per day are consumed. Then it is a ketogenic diet.
• A low-carbohydrate diet, in which less than 26% of energy comes from carbohydrates or less than 130 grams of carbohydrates per day are consumed.
• A moderately low-carbohydrate diet, in which about 26-44% of energy comes from carbohydrates.
• A high-carbohydrate diet, in which more than 45% of energy comes from carbohydrates.

Most commonly, however, “low-carb” is understood as a diet in which about 25% of energy is obtained from carbohydrates.

Is the low-carb diet high in protein?

Since carbohydrate intake is limited in the low-carb diet, the percentage of other macronutrients – fat and protein – naturally increases. However, this does not mean that every low-carbohydrate diet is high in protein. It is possible to follow the low-carb diet without a significant increase in protein supply – in which case the “lost” energy from carbohydrates comes mainly from fats.

Although there are dietary models that are simultaneously low-carbohydrate and high-protein, such as the Dukan diet popular in the 1990s, all high-protein diets should not be considered the same. The Dukan or Atkins diets are examples of restrictive approaches that can theoretically be classified as low-carb, but most people who follow this style of eating do not identify with these particular diet plans.

Optimal protein intake should be about 1-2 g per kg of body weight (depending on desired effects, health status, physical activity, age). Protein supply should therefore not be influenced by how rich in carbohydrates the diet is. Protein is not a macronutrient whose main function is to provide energy, so it should not compensate in the diet for restricted carbohydrates (whose main function is to be a carrier of glucose and energy).

In practice, the use of low-carb menus – especially in the intuitive eating model – allows you to seamlessly balance protein supply. Switching to the low-carb diet often involves a natural increase in protein intake, since low-carbohydrate foods usually simply contain more protein.

Does the low-carbohydrate diet have proven benefits?

While low-carbohydrate diets have their supporters and opponents, research points to some potential benefits of them. These include:

• Facilitating weight loss. For some people, low-carbohydrate diets facilitate appetite control and increase feelings of satiety, which supports weight loss. In addition, with the low-carbohydrate diet, glycogen is burned faster. Scientific papers comparing low-carb diets to diets with classic macronutrient distribution indicate that the effects in terms of weight loss for low-carb diets usually appear faster, but after about a year are comparable to the effects of classic weight loss diets.
• Support for the treatment of type 2 diabetes. Some studies indicate that low-carbohydrate diets can improve glycemic control and, in the long term, reduce glycated hemoglobin (HbA1c) levels in people with type 2 diabetes. While these are promising reports, it is important to remember that the low-carb diet is not the only option for diabetics. The researchers stipulate that a similar effect can be achieved with strict control of the glycemic load of the diet.
• Reducing triglyceride levels. In several studies, the low-carbohydrate diet led to lower triglyceride levels and an increase in the desired HDL fraction cholesterol. On the other hand, some studies indicate an unfavourable increase in LDL fraction cholesterol. The effect of the low-carb diet on blood lipid parameters thus remains inconclusive. For people struggling only with high triglyceride levels, lowering the share of carbohydrates on the menu can yield really good results.

However, researchers emphasise that benefits of the low-carb diet depend on individual patient characteristics, such as age, physical activity and current medical conditions. It is also worth remembering that some of the long-term effects of low-carb diets are still under-researched.

The overall assessment of health properties of the low-carb diet largely depends on its composition. Low-carb in the Mediterranean model, with a menu based on oily fish, nuts and healthy unsaturated fats, can be very healthy. A Western diet model with a low-carbohydrate macronutrient distribution, but based on fatty meats, full-fat dairy and shying away from vegetables will not produce positive health effects.

Can the low-carbohydrate diet negatively affect thyroid function?

Low-carbohydrate diets have the potential to negatively affect thyroid function, especially in people who already have problems with this gland, as there is a risk of reducing the conversion of thyroxine T4 to the active hormone T3. Lower levels of T3 can lead to a so-called sensation of slowed metabolism, which can manifest as fatigue, difficulty losing weight or greater sensitivity to cold temperatures.

According to official recommendations, the amount of carbohydrates in the diet should not be less than 100 g per day, precisely because of the potentially adverse effects on the thyroid gland. However, it is worth noting that not every low-carbohydrate diet has a negative impact on this gland. Nevertheless, extreme carbohydrate restriction is not considered fully safe and caution is advised in its use. Moderately low-carbohydrate diets, containing 30-44% of energy from carbohydrates, thus appear to be a safe alternative.

Will the low-carbohydrate diet work for diabetes?

Low-carbohydrate diets are often recommended for diabetes, as a way to improve sugar regulation. However, this diet is explicitly discouraged for type 1 diabetes and those taking insulin.

For type 2 diabetes, the low-carb diet is considered an alternative diet – not a dietary model recommended on a large scale by the National Centre for Nutrition Education, which sets the official guidelines. On the other hand, some studies show improved results after introducing diets that limit carbohydrate intake in diabetics. Short-term, low-carb diets may facilitate weight loss and glycemic control. However, there are studies that suggest that, in the long term, low-carbohydrate diets may increase the risk of cardiovascular diseases, to which people with diabetes are at higher risk anyway.

In my opinion, the use of a moderately low-carbohydrate diet in a Mediterranean model in type 2 diabetics may be reasonable and support health. However, it is very important to take care of the quality of this diet, and not just limit carbohydrates. It is worth maintaining the right balance of fats consumed and ensuring an optimal supply of antioxidants and fibre. If you have diabetes, it is a good idea to consult a dietitian and a doctor before starting the diet.

Is low-carb a weight loss diet?

The low-carb diet is not (or rather: does not have to be) a weight loss diet. However, many people opt for low-carb for losing weight. Remember that, ultimately, the calorie balance– that is, the difference between calories expended and calories consumed – is responsible for whether or not a diet is a weight-loss one. If the calorie balance is negative, the diet can be considered a weight loss diet. Carbohydrates are a high-energy component of the diet (1 g of carbohydrates is 4 kcal). Limiting them, therefore, can automatically cause you to enter a calorie deficit, unless you compensate by increasing your intake of other macronutrients, such as fats. Thus, the low-carbohydrate diet may facilitate generating an energy deficit, but it does not guarantee it.

In studies comparing low-carb diets to diets with classic carbohydrate content, low-carb sometimes performs better in the first stages of weight loss – people following this diet lose weight faster. However, after a year or so of following the diet, the effects level off, and it is then difficult to determine a “better” dietary model.

People who praise low-carb as a weight-loss method indicate that it makes it easier for them to control satiety – but this is not clearly confirmed by research. Low-carb requires limiting carbohydrates, so it automatically excludes certain food groups, such as sweets, snacks and sugary drinks. If these products were a big part of your diet before switching to a low-carbohydrate eating pattern, you will definitely feel the difference after excluding them. However, this will not necessarily be a “low-carb effect”, but the result of limiting calorific food.

Is it okay to eat bread and fruit on the low carb diet?

Whether you can eat bread and fruit on the low-carb diet depends on how restrictive it is. In less stringent versions, providing less than 30% of energy from carbohydrates, you can include classic bread or any fruit on the menu. On the other hand, in the more restrictive versions that limit the consumption of grain flour, bread and rolls are replaced with low-carbohydrate alternatives, such as bread made from grains alone or baked goods based on coconut and almond flours.

When it comes to fruits, those with low sugar content are preferred: strawberries, citrus, avocados and various berries. Fruits with higher sugar content, such as mangoes, pineapples, grapes and bananas, are consumed in smaller, controlled portions. Dried fruits are generally avoided due to their high sugar content.

However, in low-carb diets there are no explicitly forbidden products in the bread or fruit group. It all boils down to taking into account the right portion to suit the diet version. If you plan to eat about 100 grams of carbohydrates every day, you can freely “distribute” them among various products, including fruit and bread in moderation.

Read also: 10 Myths About Fruits

Is it possible to follow the low-carb diet and train intensely?

In the classical approach to the diet of active people, carbohydrates are the main source of energy needed for physical activity. However, with the growing popularity of low-carb diets, it is claimed that they can improve sports performance. However, this is not true, especially in the case of intense exertion. According to scientific studies, the greater the share of carbohydrates in the diet, the more energy is available. From a biochemical point of view, burning carbohydrates enables the release of more energy (kcal) with less oxygen. This directly translates into greater fitness, the ability to perform more intense workouts and better sports performance.

Although one can find isolated studies suggesting improved performance in some athletes following the low-carb diet, the vast majority of evidence refutes this claim. One study, conducted with walkers, evaluated the effects of the low-carbohydrate diet on training performance and efficiency. The results showed a deterioration in “the economy of effort”, meaning that the body had to use more energy to do the same work. Reduced training efficiency and lower ability to train at high intensities were also observed.

The low-carb diet is definitely not a recommended dietary strategy for most sports and those exercising intensively – with a few exceptions.

In what sports does low-carb work?

The low-carb diet does not provide much benefit for those who do strength or endurance training. However, low-carbohydrate strategies can be considered in exceptional sports cases. There is some indication that a well-chosen low-carb diet may work well, for example, for runners participating in ultra-marathons (although not necessarily better than a well-chosen diet high in carbohydrates).

Low-carb can also be useful in the short term in sports that require rapid and fairly drastic weight loss, such as combat sports or strength disciplines, in order to qualify for the given weight category. Low-carbohydrate strategies burn liver and muscle glycogen faster, which can contribute to relatively fast and more effective weight loss. However, this is only a short-term effect, because once carbohydrates are introduced, glycogen stores will be replenished.

Other advantages of low-carb can also be demonstrated in sports that require mental effort, such as chess players.

Who should not follow the low-carb diet?

Despite some (more or less officially proven) advantages, the low-carb diet should definitely not be used for people with type 1 diabetes, pregnant women and those with kidney or liver diseases. Using low-carb is also not recommended if you are taking certain medications. Low-carbohydrate diets are unlikely to benefit athletes or physically active people focused on improving their endurance or performance. Before starting the low-carb diet, it is best to consult individually with an experienced dietitian and/or doctor.

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