Above all in the field of aesthetic culture but also of health, for several years, carbohydrates have been considered potentially harmful or counterproductive nutrients and to be avoided as much as possible, especially in the evening; needless to say, like most absolutisms, this statement can also be considered inaccurate.
The intake of carbohydrates at dinner, or worse in the spit that precedes sleep, is in fact still not recommended by many coaches, personal trainers and nutritionists. The "presumed" reason would be of a metabolic nature, with particular reference to the hormonal axes, their rhythms and behavior. In short, taking carbohydrates in the evening would increase the aptitude to gain weight and the predisposition to hyperglycemia - a risk factor for type 2 diabetes and directly related to hypertriglyceridemia.
Although it has a logical basis, it is nevertheless a conceptual distortion; below we will understand better why.
Carbohydrates in short
For humans, carbohydrates are ternary energy macronutrients (carbon, hydrogen, oxygen). There are many types, which can be classified in different ways, for example: on the basis of complexity (monosaccharides, disaccharides, oligosaccharides, polysaccharides), solubility in water, monomeric structure, polymeric organization, type of any chemical bonds interposed between monomers (position and nature of the bond) and relative availability for humans, etc.
Carbohydrates of vegetable, animal and fungal origin are known. The digestible and absorbable ones provide 3,75 kcal / 1 g, while those not available - especially of vegetable origin - perform the nutritional role of prebiotics (energetic substrate for the intestinal physiological bacterial flora).
The most abundant glycide in the human body, albeit technically not essential - because to a certain extent, under certain conditions and for a certain period of time it can be produced endogenously - is the glucose. The fact that it is not an essential nutrient may be a concept misleading. Many think that, precisely for this reason, it is not such an important nutrient; on the contrary, to guarantee survival, the organism had to develop a system of neo-glucogenesis (production of glucose from other substrates such as amino acids, glycerol and lactic acid) and create two differentiated stocks (in the form of glycogen, a polymer of glucose): one in the liver, to keep blood sugar constant - essential for the functioning of the brain - and one intrinsic to skeletal muscles. The kidneys also contain small stores of carbon hydrates.
The exogenous sources, therefore food, of glycides are of vegetable origin. Primitive sources of soluble carbohydrates, simple or disaccharides, are considered fruit (citrus fruits, apples, pears, etc.), vegetables (zucchini, asparagus, chard, etc.), milk and honey. Starchy seeds such as cereals (wheat, rice, corn, etc.), legumes (beans, chickpeas, lentils, etc.), pseudocereals (quinoa, amaranth, buckwheat, etc.), tubers provide non-soluble, therefore complex, carbon hydrates starchy (potato, sweet potato, cassava, etc.) and some starchy fruits (such as chestnuts and the fruit of the breadfruit); for proper digestibility, these require cooking. Obviously, all derived or processed foods containing these ingredients and synthetic sugars provide carbohydrates.
The importance of glucose stems from the fact that there are glucose-dependent tissues, whose functioning and survival depend on the immediate (or almost) availability of this energy substrate. This is the case of central nervous tissue, red and white blood cells, bone marrow, adrenal medulla, retina, testes and lens. Others, on the other hand, such as muscle tissue (especially rich in fibers I and intermediates) can function "more or less" correctly even using fatty acids and branched chain amino acids.
This is a crucial point for understanding the article. Given its importance for glucose-dependent tissues, its entry into these cells occurs directly, without the need for any hormone, thanks to the presence of membrane transporters of the GLUT family, especially GLUT-1 and GLUT-3. . On the contrary, in fabrics DON'T glucose dependent, particularly in skeletal muscle, GLUT-4 is widespread, requiring the presence of a hormone called insulin. In insulin-dependent tissues, this hormone therefore functions as the key to the GLUT-4 transporter.
Let us now turn to a brief description of insulin and its effects on metabolism.
What is insulin?
To fully understand what we are going to develop, it is essential to clarify the relationship between carbohydrates and insulin.
Insulin is a hormone anabolic of a protein nature - stimulates the production of IGF-1 - secreted by the endocrine portion of the pancreas. Its production is stimulated by food intake and intestinal absorption of the three caloric macronutrients (monosaccharides, amino acids and fatty acids) and by ethyl alcohol. The extent of insulinemia depends first of all on the importance of the meal, that is, on the quantity of energetic macronutrients introduced, and secondly on its composition.
It should be noted that carbohydrates, proteins and fats have a different impact on the secretion of the hormone; for example, for the same serving size, refined carbohydrates and alcohol appear to be the most effective. This is important but does not take into account an essential factor, namely that foods and meals have a mixed composition and as such have a variable digestion and absorption time; the longer the time for nutrients to enter the blood, the less the stimulus to produce insulin. For example, fibers, fats and proteins slow down the absorption of carbohydrates.
The functions of insulin, reserved for insulin tissues employees,it, are to: allow or improve the entrance glucose and its cellular use, amino acids, fatty acids and potassium from the blood to the cells; promote construction and inhibit the breakdown of protein tissues, glycogen stores and stores of adipose tissue; reduction area of lipolysis (splitting of adipose fats for energy purposes) and best before date energetic cellular of fatty acids; optimize cell differentiation; promote the production of cholesterol; contribute to the feeling of satiety after meals. As mentioned above, insulin must bind to a transporter called GLUT-4 to be picked up by cells.
The amount of nutrients consumed, their composition, insulin production and its impact on tissues are factors closely related to body composition - lean mass / fat mass ratio and their extent.
Why is the evening meal considered more critical than the others?
Returning to the focus of the article, let us now clarify why the evening meal "should" be more critical than the others. The reasons are mainly two; let's proceed with order.
Evening hours and insulin sensitivity
For several years now, the study of biorhythms has highlighted the diversity of production, release and metabolism of hormones and neurotransmitters over a 24-hour period. These chemical mediators can be influenced by external stimuli such as: meals, fasting, physical training, light etc; internal, such as psychological stress, gestation etc; or be "almost" totally independent. For all, however, there is a sort of attitude, a real predisposition, which determines a more or less significant fluctuation of the respective blood levels. Sometimes it is a very important variation, as in the case of somatotropin (GH or growth hormone) which increases during sleep, while for others it is almost marginal, for example in the case of the increase in testosterone in the morning hours.
But what does insulin have to do with it, which as we have said is mainly influenced by meals? Simple. Insights into the action of insulin revealed that its metabolism, closely linked to that of glucose, therefore of dietary carbohydrates, is more effective in the morning rather than in the evening. The sensitivity of the target tissues would mainly benefit, therefore not the chemical structure of the mediator or pancreatic production.
Better insulin sensitivity results in: minor permanence of post-prandial insulinemia and glycaemia, therefore a carbohydrate metabolism "leaner"And result reduction area of lipogenesi (production of fats to be deposited in adipose tissue), reduction of capacity inhibitory on lipolysis and on the cellular use of fatty acids. Conversely, as can be easily understood, a negative effect would be obtained.
Night time and calorie consumption
Speaking of a sedentary person, without particular needs or habits, it is undeniable that the night time is the one characterized by the lowest caloric expenditure compared to the day.
Dinner is the last main meal of the day, which - in the absence of a pre-sleep snack - anticipates the night's rest. We know that every meal has a "function", that is to support the activities that will take place in the following hours. Among these, however, we must not forget the functioning and the replacement of tissues and organs other than simple muscles; ergo, even when standing still, the body needs water, proteins, fats, carbohydrates, vitamins, minerals, etc. On the other hand, logically, the overall energy consumption is lower than that of the day, since the motor activity is lower. In fact, the muscles consume most of the calories introduced with food and this "gap" increases and decreases with the level of movement that characterizes daily life.
Since the organism works mainly on glucose, a large part of the dietary composition (about half of the total energy) is characterized by the presence of carbohydrates. In compliance with the above, however, these should not be placed in the evening meal, since the caloric expenditure that will follow is reduced. Therefore, logically, the glycides should be distributed in the hours preceding a greater energy expenditure, ie in the morning and until lunch.
Both of these arguments are flawless; however they are "incomplete", misleading, because what is lacking is precisely the considerations that oppose the circumstances analyzed. Let's go into detail.
Importance of carbohydrates in the evening
Those who eliminate carbohydrates in the evening generally plan to lose weight or normalize the tendency to hyperglycemia.
Let's start by specifying that the dietary composition varies mainly according to motor activity. Therefore, what is true for a sedentary person may be incorrect for an athlete and vice versa.
Secondly, to those who read this article looking for a solution to lose weight more easily, I clarify that: the increase or reduction of adipose tissue is given above all by the energy balance; in terms of calories, if I eat more than I eat, I gain weight, and if I eat less, I lose weight. This, if the energy difference is significant, occurs independently of the nutritional distribution. However, it is undeniable that the hormonal action of insulin can become problematic in which case its blood concentrations are excessive and for too long, and especially in the presence of too many energy nutrients.
When we talked about glucose dependent tissues, we mentioned first of all the central nervous system; this is because about half of the daily blood sugar - of a sedentary - is consumed by these tissues, for a total of about 120 g / day. Everyone knows that sleep is an essential moment, but few know why. During sleep, the brain does not rest, it rests recharges. This complex process therefore needs the full support of blood glucose, nourished by the last evening meal and liver regulation - through glycogenolysis, a process mediated by other hormones such as glucagon, the insulin "antagonist". This means that, under eunnutrition conditions, excluding carbohydrates from dinner may not have any negative effects; this can change if you are on a low-calorie weight loss diet and especially if it is a low-carb type (low carbohydrate content). In this case, side effects such as sleep loss and lack of recovery are not uncommon.
For sports enthusiasts, the situation is further different. Especially in aerobic activities, the consumption of glucose is very high, and with it that of muscle glycogen. A debt is therefore created, which after a meal greedily recalls dietary carbohydrates, compensating for the loss imposed by exercise. If the carbohydrates of the following meal are insufficient, the glycogen recharge of the liver (necessary for glycemic maintenance) is also compromised, increasing the neoglucogenesis process. Furthermore, if the meal in question consists of a carbohydrate-free dinner, muscle recovery itself is also compromised, with a relative decrease in performance. Post-workout carbohydrates are therefore very important and, if you want to lighten dinner, you can take them during and immediately after training - especially if placed in the late afternoon or in the evening.
To conclude, carbohydrates can be taken in the evening, but in a manner related to daily energy consumption, to the overall composition of other meals and to the type of motor activity (if practiced).
Avoiding them completely, especially for a sportsman, is completely counterproductive and even potentially harmful. If, on the other hand, it is a sedentary person, perhaps overweight and with compromised carbohydrate metabolism, dinner can also be structured without carbohydrates, provided that in the rest of the day a sufficient quantity of carbohydrates is distributed to maintain the body's total homeostats.