By snack we mean a secondary meal, therefore different from the three main meals, which are breakfast, lunch and dinner. In a balanced diet, snacks should be at least two per day (preferably three) and each provide 5-10% of the total daily kilocalories (kcal); to give a concrete example: in a 2000kcal diet the energy of a snack could fluctuate between 100 and 200kcal.
Having clarified this, let's try to understand what the function of the snack (or secondary meal) is and how it should be structured.
Let's say that, in general, the nutritional recommendations for a balanced snack derive mainly from the need to comply with the sense of appetite (and not hunger!) That arises between main meals. Snacks therefore serve to postpone the need to eat, but also to support the body during regular daily activities; the basic requirements are: practicality of use, ease of consumption and digestive lightness.
As with other meals, even snacks subordinate to subjective nutritional needs, therefore their management / organization can change significantly in an intra and interpersonal way. For example, a sportsman's snack will hardly be the same as a sedentary one, just as the secondary meal of a single athlete cannot be standardized between training and rest days.
The chemical composition of a snack is to be established respecting the criterion of nutritional balance; for example, if in some cases it must ONLY comply with energy needs, in others it has the function of compensating for plastic (protein) needs. Obviously, it is a good idea to always avoid junk foods and food supplements, preferring non-processed and natural foods; for example, rather than crackers (containing refined flours and hydrogenated fats) it is better to prefer fruit and oil seeds (which include fructose, polyunsaturated fats, water, more mineral salts, various vitamins and dietary fiber). Similarly, instead of a drink based on isolated proteins (which provides nothing but peptides), it is better to opt for protein foods (also rich in minerals, vitamins, probiotics, etc.).
In the next paragraph we will try to better understand WHEN the snack must be mainly protein (plastic).
As anticipated, the snack varies according to need. It is often used to support the main meals in the intake of fiber, potassium, magnesium, water and energy (through the consumption of fruit and cereal derivatives); at other times it helps to prevent muscle catabolism (in adult athletes, in subjects with intestinal absorption defects, etc.) and to promote anabolism (in bodybuilders and in growing subjects who practice sports).
Protein foods to be used comfortably in the context of a snack are: low-fat yogurt (traditional, thickened, Greek, etc.), cottage cheese, cooked egg whites, roast beef, canned tuna (less advisable compared to the previous ones) etc .; these foods, in addition to containing high amounts of proteins, also boast an excellent biological value.
The protein snack therefore plays a fairly important role in achieving plastic needs ... but this does not mean that it is ALWAYS the correct choice! It can benefit essentially people who do not tolerate main meals very rich in protein (for digestive issues), those who fail in intestinal absorption (elderly, subjected to partial resection of the intestine, etc.), diabetics (to guarantee an index and a load low glycemic levels), overweight people (who benefit from a higher specific dynamic action), etc.
Outside of these contexts, in various circumstances the intake of protein in the diet is even excessive; obvious examples are the diets of bodybuilders and those who practice high-protein diets for aesthetic purposes (diets aimed at reducing fat mass beyond the individual predisposition or regardless of the state of health). In these cases, the plastic requirement is largely covered by the main meals and, through the use of protein snacks, it can become EXCESSIVE, subjecting the liver and kidneys to an unnecessary workload.
Based on the above, the secondary protein meals can be of different kinds; then: "How to choose them?"
Breakfast is one of 5-6 ordinary meals of the day. It is customary to call it "the most important", even if most people are unable to justify the real reason. From the "quantitative" point of view, breakfast provides (or rather, should provide) about 15% of the total daily calories. On the contrary, the other two main meals (ie lunch and dinner) should provide approximately 40 and 35% of the energy; at the same time, secondary meals (2-3 snacks) are limited to contributing overall for the remaining 10% (up to 25%) of the calories. So, if the math is not an opinion, by respecting the criterion of "caloric quantity", breakfast seems much more like a secondary meal than a main one. However, its importance lies in a metabolic rather than a mathematical mechanism.
Breakfast is intended to refresh the body after a fast that lasts from the end of the previous dinner. In principle, assuming that the last meal of the day is eaten between 19:30 and 20:30, and that the next breakfast takes place between 7:30 and 8:30, this time frame should correspond to about 11-13 hours. It goes without saying that, logically, breakfast should provide much more than 15% of the daily calories (remember the saying: "eat a king's breakfast, a prince's lunch and a poor man's dinner"?); also because, observing the circadian cycles, insulin secretion and its peripheral uptake are greater in these hours of the day rather than in the afternoon or at night. Nevertheless, in the morning (perhaps due to nervousness or time), the average people do not easily tolerate large portions of food and prefer to consume them for lunch or dinner. Furthermore, it should be remembered that night fasting occurs in conditions of deliberately limited energy expenditure (in essence, it corresponds to the basal metabolism); the nocturnal one, therefore, is certainly not comparable to a morning, afternoon or evening abstinence, periods in which the organism is more active and expensive. It should then be specified that, being the first meal, reducing its entity or completely eliminating it runs the risk of accumulating appetite (which turns into HUNGER) and exceeding portions in subsequent meals; in practice, not taking this energy at breakfast, this is then added to lunch or dinner, increasing the fat deposits due to calorie excess.
These are the reasons which justify the importance of the morning meal and which, at the same time, limit its size to a modest 15% of the total.
The choice of the type of protein snack is rather trivial; it is a question of taking into consideration: nutritional needs (especially mineral salts and vitamins), any particular physiological conditions (such as allergies and food intolerances), respecting the principle of food variety and not forgetting specific personal tastes.
To give some examples, the ideal protein snack for a person who does not brilliantly reach the quota of omega3 and / or vit. D in the diet could consist of canned tuna or mackerel, as long as the subject does not suffer from hypertension (as the preserved fish is always high in sodium).
At the same time, the growth phase requires high concentrations of calcium (Ca) and the supply of this mineral can be guaranteed through the intake of dairy products (for example: yogurt, cottage cheese, spreadable cheeses, ricotta, etc.); the same category, if characterized by excess weight, will certainly prefer skimmed foods.
The alternation of fish and dairy products could help moderate the progression of osteoporosis (thanks to vitamin D and calcium), therefore it is more suitable for the diet of postmenopausal women (more prone to this disease than men).
Those who practice low-calorie diets and need a good plastic intake can now find on the market low-fat (skimmed) and thickened-concentrated (richer in protein) yoghurts. The peptide intake is much higher (sometimes almost double) compared to the traditional one and, like other dairy foods, it boasts a COMPLETE pool of essential amino acids. The only problem with the use of these foods is the presence of lactose which, in subjects with food intolerance, can give rise to a rather annoying gastro-intestinal symptomatology; on the other hand, when intolerance is minor or transient, yoghurt is one of the few foods used for the gradual reintegration of dairy products in the diet.