Low-carb Nutrition – Greater Benefits or Losses

In a low-carbohydrate diet, the total consumption of carbohydrates is key, but how low is low and how high is still high to qualify a diet as low-carbohydrate? According to the nutritional standards of the Polish population, the lower limit of daily carbohydrate intake is 45% of the energy value (M. Jarosz et al. 2020). Therefore, the term 'low' can be used to describe the amount of carbohydrates below this value, however, specific ranges will have a significant impact on metabolism. In response to reduced access to carbohydrates and lower intake of insulin in the blood, the body should enter a state of increased fat-burning, which leads to ketosis. The production of ketone bodies is a response of the body to hunger. Ketones serve as an alternative source of energy for almost all cells, but not for all. Erythrocytes require glucose as the only source of energy, therefore, even if it is not provided through food, the body begins to produce it on its own (e.g., from certain amino acids, glycerol or lactic acid). In prolonged fasting, amino acids used in gluconeogenesis are derived from the breakdown of structural proteins, leading to a decrease in muscle mass, not only of skeletal muscles, but also of heart and smooth muscle mass, which form the structures of all organs. Below a certain threshold of carbohydrate intake, this metabolic change is particularly pronounced. The benefits of the ketogenic diet are interpreted with the assumption of 20-50 g of carbohydrates per day (F. Brouns 2018). If a larger amount is consumed in the liver, fewer ketone bodies are produced, therefore, it is assumed that the term 'low-carbohydrate' refers to a diet that includes up to 150 g of carbohydrates per day, which does not induce ketosis in the body, as in the case of the ketogenic diet (up to 50 g).

A meal comprises three fundamental components: protein, carbohydrates, and fats. Although many scientific works only refer to the effects of a low-carbohydrate diet, in reality, these kinds of dietary regimens have increased fat and/or protein content concurrently. When one macronutrient is reduced, the quantity of another should be correspondingly raised to maintain the same energy value in the menu. Observed benefits of a specific diet are then based on two factors – e.g. reduced amount of carbohydrates and increased amount of fat or protein. All conclusions should therefore be considered in these two contexts (F. Brouns 2018). However, many studies openly argue that the benefits of a low-carbohydrate diet are not due to the low amount of carbohydrates, but rather to the increased amount of protein or generally – to the reduction of body weight.

Limiting carbohydrate intake to minimal levels is closely associated with reducing the consumption of processed products containing sugar, which can lead to weight loss and improved glycemia. However, it also entails drastic restrictions on the consumption of grain products such as bread, pasta, rice, and certain fruits and vegetables, as well as legumes. The absence of legume plant products in a diet that requires a high protein intake necessitates the consideration of a high level of animal protein metabolism. In this way, we eliminate a valuable group of products that exhibit anti-inflammatory effects. Incorrectly restricting such a large number of food products can lead to a risk of nutrient deficiencies - whole grains, vegetables, and fruits are treasure troves of nutrients. Reduced consumption of thiamine (vitamin B1), folic acid, vitamin C, magnesium, calcium, iron, and iodine has been observed in individuals following a low-carbohydrate diet (Ch. Churuangsuk et al. 2019). Furthermore, the elimination of a wide range of products that are a source of dietary fiber can lead to a reduction in their consumption. Animal studies have shown that a high-fat diet with reduced intake of fermentable dietary fiber can lead to changes in the gut microbiota (P. D. Cani et al. 2008). This, in turn, can lead to increased inflammation and metabolic disorders.

The initial weight loss that occurs in a low-carbohydrate diet is mainly due to the loss of water and energy stores in the form of glycogen. While on a low-carb diet, it is possible to lose weight not only from water and glycogen, but it will not be due to a reduction in carbohydrates and calories. However, should you give up your favorite spaghetti if the only goal is to lose a few pounds? There is no significant difference in weight loss between a healthy low-fat diet (<20% of energy) and a low-carbohydrate diet (<45% of energy) (Ch. D. Gardner et al. 2018). In one study, it was noted that it was the amount of protein, not carbohydrates, that was responsible for weight loss (S. Soenen et al. 2012). High-protein diets led to greater weight loss than those with standard protein amounts – regardless of the amount of carbohydrates. This is due to the fact that protein is the most thermogenic (and most satiating) macronutrient. It requires 20-30% of energy for digestion and metabolism, which in turn lowers the energy value of the consumed meal (K. R. Westerterp 2004). However, in some weight loss interventions, the reduction of carbohydrates led to a greater loss of lean body mass (LBM) compared to more balanced, low-calorie diets, which is unfavorable for health (C. F. Kirkpatrick et al. 2019).

Many individuals who adhere to a low-carbohydrate diet notice a decrease in their hunger and a reduced appetite. The possible mechanisms involved in this process are changes in gut hormones, but also a justification in such a dietary model. A higher protein content may be responsible for prolonged feelings of fullness after eating and slower gastric emptying (C. Giezenaar et al., 2018). However, this is not directly linked to low carbohydrate intake. Interestingly, it has also been observed that a low-fat diet reduces peptide YY (which regulates feelings of fullness) more than a low-carbohydrate diet. Consequently, fullness may be better maintained in a low-carbohydrate model (T. Hu et al., 2016).

Scientific research has found that individuals with a predisposition to diabetes or already suffering from the condition experience a range of positive changes during a low-carbohydrate diet, such as weight loss, improved insulin sensitivity, reduced blood glucose level fluctuations, and lower fasting blood glucose levels. These changes indirectly lead to a reduced risk of cardiovascular diseases. Some researchers attribute these effects primarily to weight loss, rather than reduced carbohydrate intake (F. Brouns 2018). Any diet that results in reduced energy intake leads to weight loss and associated beneficial metabolic and functional changes. In several studies, low-carbohydrate diets have been shown to have a greater impact on blood glucose control in type 2 diabetes compared to high-carbohydrate diets (F. Brouns 2018). However, in the long term, reducing carbohydrate intake alone does not lower HbA1c (glycated hemoglobin, a long-term blood glucose indicator) in the prevention or treatment of type 2 diabetes, as multiple mechanisms are involved (Ch. Churuangsuk, M. Lean, E. Combet 2020). Recent studies suggest that low-carbohydrate diets appear safe and effective in the short term, but do not show statistically significant differences compared to higher-carbohydrate models and cannot be recommended as the default treatment for individuals with type 2 diabetes (P. Dyson 2015).

Low-carb diets may be preferred for a variety of reasons. Such a diet plan completely excludes processed foods with added sugar, a high protein content provides satiety, and due to lower fluid retention, effects in the form of lost kilograms can be quickly observed. But can we assert that carbohydrates lead to weight gain? In one study, overconsuming carbohydrates resulted in a progressive increase in their oxidation and led to the accumulation of 75–85% excess energy (T. J. Horton et al. 1995). On the other hand, overconsuming fat had a minimal impact on its oxidation and led to the deposition of 90–95% excess energy. This suggests that it is easier to gain weight due to overconsumption of fat than carbohydrates. However, it is important to remember that weight gain is due to an excess of calories, not a surplus of a specific macronutrient.

In controlled studies, low-carbohydrate diets have not been shown to be physiologically or clinically superior to high-carbohydrate diets in terms of weight reduction, fat loss, energy expenditure, or long-term glycemic control (Ch. Churuangsuk, M. Lean, E. Combet 2020). However, this model may have benefits in terms of appetite control and reduction in medication use in the treatment of type 2 diabetes. The choice of alternative foods in a low-carbohydrate diet, which is also high in fats and proteins, should take into account potential effects on the increase of LDL-cholesterol and total cholesterol in the body (Sh. Chawla et al. 2020). In the long term, these changes can lead to cardiovascular diseases. Other disadvantages of the low-carbohydrate diet include: – an initial decrease in energy and deterioration of sports performance due to a decrease in muscle glycogen and the need to switch metabolism to alternative energy sources; – possible nutritional deficiencies due to the restriction or exclusion of certain foods, including grains, legumes, fruits, and vegetables; – slowing down of bowel movements and unfavorable changes in the intestinal microbiome due to a reduction in dietary fiber; – restrictive character of the diet, which can lead to an unhealthy relationship with food. The latest recommendations from experts – including the WHO – state that diets rich in fruits, vegetables, grains, legumes, and moderately high in fat and calories, combined with sufficient physical activity, are the best method for maintaining a healthy body weight and preventing chronic diseases (Sh. Mendis et al. 2014). The unanimously recommended daily dose of fat in the diet is less than 40% of daily energy intake, and the recommended amount of carbohydrates is more than 40% of energy (A. E. Buyken et al. 2018).

Diets with low carbohydrate content do not result in better fat reduction outcomes. Their primary advantage appears to be abstaining from the consumption of simple sugars (particularly sweets), which contributes to improved glycemic parameters and a leaner physique. Although it is challenging to adhere to the principles of a low-carbohydrate diet over the long term, the rapid results of weight loss are often motivating enough to persist. In reality, however, all observed clinical effects are more related to weight normalization than to a reduced carbohydrate content in the diet. Therefore, if we derive pleasure from fresh bread, we do not necessarily have to abstain from it in order to lose weight. It is important to emphasize that any caloric deficit will lead to weight loss, regardless of which macronutrient causes it.