What are they?
Introduction to Diet Low Carb
For the past few years, low-carb diets have been the subject of intense debate between those who propose them and those who continue to defend the Mediterranean food style. The controversy, of course, is about the weight-loss effectiveness of these diets and their impact on the health of those who follow them.
Low-carb diets – which have long been popular in the world of physical culture and in the medical field – are becoming popular in the early 1990s. Taking advantage of the decline in low-fat diets.
The latter, proposed in the United States to address the dramatic spread of obesity, is based on low-fat foods. Although supermarket hulls were full of “low fat” foods, this strategy not only did not yield the expected results.
It also added to the problem due to the alleged abuse of general consumption. For this reason, after reassessing the function of lipids in the food field (see dedicated article), the attention of many nutritionists or presumed such moved to carbohydrates (carbs in English), especially on simple ones added (high glycemic index).
Desserts, sugary drinks, meals, snacks, and various appetizers were soon considered the main culprits of the increasing and worrying rate of obesity.
Today, however, it is known that the main cause of overweight is the combination of excess caloric by fat and energy exuberance from foods rich in refined carbohydrates. Which greatly urges the production of insulin).
As is often the case in this and other fields, someone thought it right to polarize this concept, creating low-carb (literally “low in carbohydrates”) diets.
A bit because of the enthusiasm linked to novelty, a bit because of the skillful advertising campaign.
A bit because of the indisputable weight-loss effect, low-carb diets spread quickly to the USA, the real “idealistic stronghold” of the Mediterranean diet. The discussion, which began some ten years ago, doesn’t seem to have diminished.
Features
When can we talk about a diet low carb?
Low-carb diets can be considered when they provide less than 100 grams of carbohydrates per day, between complex and straightforward.
At the same time, the distribution between energy macronutrients varies according to the current of thinking.
In particular, some argue that a low-carb diet should be rich in fat and retain about the same amount of protein, giving a similar nutritional breakdown to the following:
- 50-60% lipids
- 20-30% protein
Others, however, believe that it is essential to completely eliminate foods containing fluids by freely increasing protein foods and thus leading to a more similar division:
- 50-60% lipids
- 40% protein
It is important to emphasize that the total energy provided by these food systems is almost always lower than that of the norm calorie.
Which makes low-carb diets of the tendentially low-calorie strategies.
Suppose the low-carb diet does not include large amounts of protein and provides a moderate amount of energy.
In that case, it is almost always of a ketogenic type.
It determines the relevant production of ketonic bodies (see below or read Ketogenic Diet).
However, low carb diets “PURE” (i.e., just high fat) are pretty rare, and almost all are also hyper protein (as in the two cases we just mentioned).
Some examples of low-carb diets are Area, Dukan, Atkins, Metabolic, Scarsdale, South Beach cc.
Mechanism
Low Carb Diets Operation
The first question you need to answer is: Why should a low-carbohydrate diet facilitate fat consumption in fatty tissue? Basically, for three reasons:
- Insulin calm: Insulin is an anabolic hormone that, if released in excess, tends to increase adipose storage. Reducing secretion also diminishes the tendency to accumulate lipids in the adipose.
- Increased metabolic fat consumption: when the carbohydrate intake in the diet is drastically reduced in the first 24-48 hours. There is an increase in the oxidation of triglycerides and glycogen (glucose reserve polymer deposited in the liver and muscles).
- Reduction of appetite: due to the anorexizing effect of the ketone bodies (intermediate of “waste” from the oxidation of fatty acids in the absence of glucose), which facilitates the reduction of food intake. We’ll explain more later about what it is.
Metabolic effect of diet low carb
Importance of glucose and glycemia
In the absence of carbohydrates in the diet, the organism uses its glycogen reserves.
The glycogen stocks are, on the whole, small. There are about 100 grams of glycogen in the liver, while in the muscles, there are another 300-500 grams, depending on the global mass.
At this point, there should be another question: Why does the body store carbohydrate stocks?
Because even if food glucose is not considered correctly essential, glucose is still indispensable for survival.
Some tissues work almost exclusively, or mainly, glucose (e.g., nervous and red blood cells). For this reason, the lack of glucides in the long-term diet is not actually sustainable.
Note: In the nutritional field, only the molecules that the organism is NOT capable of synthesizing autonomously are essential and must therefore necessarily introduce with the diet.
Precisely about the importance of glucose, therefore, blood glucose (glucose in the blood), the human body has developed additional resources that increase the chances of survival in the absence of food carbohydrates. The main ones are:
- Neoglucogenesis or gluconeogenesis: it occurs in the liver and consists of the production of glucose from Glucogenic amino acids (from food proteins), glycerol (from food glycerides and adiposis), and lactic and pyruvic acid
- Reuse chemical bodies for energy purposes: it happens in muscles, in the heart, in the brain, and beyond. The tissue that uses most of it is, by force of things, the muscle tissue. Note: at high concentrations, the brain may remain partially intoxicated
- In muscles, direct energy use of branched amino acids
Production of ketonic bodies
It is logical to infer that by taking a few carbohydrates with a diet, the glycogen reserves are gradually worn out, almost empty.
Most tissues, especially muscular tissues, fit the glucose deficiency by increasing the density of enzymes charged to cell consumption of fatty acids (causing slimming). In this way, the remaining glycogen is spared. It is primarily intended for the brain and anaerobic tissues, unable to use fatty acids (such as the aforementioned red blood cells). However, this is not enough.
The brain demands of glucose amount to approximately 4 g/h, while those of anaerobic tissues attest to 1.5 g/h. At this point, complications begin.
Since the liver cannot extract more than 3 grams of glucose per hour from glycogenolysis, and given that reserves run away in scarce conditions.
It is forced to activate the “emergency” metabolic pathway of gluconeogenesis.
This process leads to glucose production from the amino acids in food and muscle proteins and from the glycerol of food and adiposis fats (at rest, lactic acid is not relevant).
The more the diet is low in carbohydrates and the more the use of this metabolic pathway that, when it is particularly active (as in motor activity), is accompanied by a significant drop in muscle mass.
Also, the cell energy production cycle cannot function properly without glucose.
This is because glucose is obtained oxalacetate, necessary to bind the residual A coenzyme molecules from lipolysis, without which the process is “slow” (slowing down of the Krebs cycle) with the release of ketone bodies.
We reiterate that the ketonic bodies are oxidized mainly in the heart and muscle levels. When glucose introduced by feeding and produced by gluconeogenesis is insufficient to meet brain demands, the brain also adapts to use ketone bodies for energy purposes.
Indicatively, suppose a low-carb diet provides more than 75 g of carbohydrates per day.
In that case, the synthesis of ketone bodies is modest, and glucose deficiency is filled mainly through gluconeogenesis.
Side effects
As mentioned above, ketonic bodies (acetone, acetoacetate, and 3-hydroxybutyrate) may also be reused by various tissues for energy purposes; however, they don’t replace glucose.
In part, they are eliminated by renal filtration (with urine, at the expense of body hydration) and with lung exhalation.
Mostly, especially when the intake of total calories and proteins is also scarce, they tend to accumulate massively by determining:
- Tendency to lower the pH of blood (which in healthy subjects is compensated)
- Polyuria and dehydration
- General weakness (from hypoglycemia and hypotension)
- Acid Breath.
These substances, therefore, have the disadvantage of acidifying the blood until, in extreme cases (as in untreated diabetes), the coma and death of the individual.
In the healthy subject, they do not cause problems of this magnitude. Still, they certainly do not benefit the health of the various tissues.
Effectiveness
Diet low carb work: Why?
Low-carb diets promote rapid weight loss, as:
1. The daily energy supply decreases in comparison with:
a limited choice of foods (since all carbohydrate-rich foods such as cereals, baked goods, and a good part of the fruit are excluded);
a massive synthesis of ketonic bodies, in particular Β-hydroxybutyrate, has an anorexizing effect (suppresses appetite).
Also, the high protein intake helps to remove the stimulus of hunger, with an anorexigenic effect higher than lipids and carbohydrates.
2. bodily weight decreases due to water and glycogen depletion:
in the first 7 or 14 days following the beginning of low carb diets, glycogen’s liver and muscle reserves are progressively depleted.
These deposits amount to about 350-500 grams. Since each gram of glycogen binds about three grams of water, depleting these stocks reduces the body weight by one or two kg.
It is, therefore, a fictitious slimming because it is not accompanied by a real fat loss.
3. body weight can also decrease due to muscle catabolism:
More sensitively than low-fat, low-calorie diets, low-carb diets are also inevitably accompanied by a reduction in muscle mass.
Which is affected to obtain energy and glucose from some of its amino acids. However, the high protein intake characterizes low-carb. High protein diets save a lot more muscular tissue than low-fat, low-calorie diets and low-carb, high-fat diets.
For this reason, some authors speculate that thanks to the satiating power and higher thermogenic effect. Low-carb diets are preferable to those more protein-rich, even if one has to increase nitrogen waste.
4. body weight decreases as fat deposits decrease:
metabolic changes induced by low-fat diets, associated with the lower caloric intake, encourage the oxidation of lipid reserves, and decrease body weight. There is still not enough data in the literature to give a higher slimming effect to low carb compared to traditional low-calorie diets.