In this article we deepen our knowledge of protein, its benefits in nutrition, body weight and as always, we bust myths!
Most studies show that diets that are relatively high in protein are more conducive to weight loss and subsequent weight maintenance, when it comes to free energy intake conditions, rather than diet conditions that provide the same calories.
These diets contain a sufficient absolute amount of protein (usually around 20-30% of total energy) and involve the required intake of normal protein in grams, while energy intake is reduced.
Most of the studies on protein intake in relation to weight management show improved body composition (i.e. increased lean/body fat mass ratio) that can lead to an improved metabolic profile with a relatively high protein diet.
The impact of macronutrient composition on energy homeostasis, and therefore on weight control, depends on the sum of their effects energy intake, energy expenditure and their balance.
Several mechanisms have been proposed for the effect of high-protein diets on weight loss.
The increase of thermogenesis induced by diet (TEF / Thermic Effect of Food or DIT / Diet-Induced Thermogenesis) is one of the mechanisms that are very often mentioned in the literature.
Studies with meals providing equal calories have clearly shown the thermogenic advantage of dietary protein, with caloric effects for individual nutrients being 0-3% for fat, 5-10% for carbohydrate and 20-30% for protein.
The increase in energy expenditure caused by food (i.e. dietary thermogenesis) consists of two parts: a mandatory part required for the digestion, transport and (mainly) storage of nutrients and an optional part for heat production.
As a result, all this implies that for every 1000 kcal consumed as protein, about 200-300 kcal are consumed during the process of digestion, transport and storage, compared to 50-100 kcal for carbohydrates and 0-30 kcal for dietary fat.
One of the main reasons for this is that theoretically, the biochemical efficiency of the protein is about 84%, which is low. In practice, studies in animals, infants and children have shown that the requirements for its deposition are usually even higher. A value often used is 2.38kJ per kJ of energy deposited (1.38kJ extra energy is required to deposit 1kJ of protein value), which translates to 55.3 MJ/kg, assuming the energy value of protein is 23.5 kJ/g.
This means that to create lean mass, theoretically, an additional energy feeding of 32.43 MJ per kg of protein deposited is required (55.3 MJ/kg, which is the total cost of protein deposition minus 23.5 MJ, which is the energy value of the protein).
But here things take a bad turn. You see, the efficiency of converting ingested protein into lean body mass is reduced when protein is ingested in sufficient quantities or more (about 1.3g/kg of weight per day). That said, this reduction can be significantly suppressed by weight training, suggesting that this may help maintain or improve the efficiency of protein anabolism.
Similarly, the rate at which the protein is broken down, Grow in response to familiarity with high-protein dietswhich means higher losses between meals caused by increased rates of proteolysis. Having said that, there are data suggesting that this effect can be mitigated by supplementation with essential amino acids, as well as offer greater suppression of protein degradation.
Of the protein consumed, only ~55% is released into the circulation and only ~55% ~10% is used for protein synthesis for skeletal muscles. This 10% is about the 27% of total protein synthesis that of the 55%.
In addition to diet-related factors, physiological factors have also been shown to influence the incorporation of amino acids into muscle tissue.
Η exercise before a meal has been shown to lead to greater de novo muscle protein synthesis. Η aerobic exercise at high intensity and the weight training increase de novo muscle protein synthesis for 24-48 hours.
On the other hand, short-term muscle inactivity results in the reduction of de novo muscle protein synthesis.
So I guess we're beginning to understand that building muscle is not easy and the effects of protein on body composition are not a simple matter of making predictions.
And it gets worse, as theoretically, the biochemical efficiency of fat is 98%, with studies typically estimating that the requirements for its deposition are more than half those for protein, with a commonly used value being 1.17kJ per kJ of energy deposited (0.17kJ extra energy is required to deposit 1kJ of fat), meaning that it will always be easier to convert dietary fat into body fat than protein deposition. This translates to 45.513 MJ/kg, assuming a fat value of 38.9 kJ/g.
This means that fat production, in theory, requires an additional energy consumption of 6.613 MJ per kg of fat (45.513 MJ/kg, which is the total cost of fat deposition minus 38.9MJ, which is the energy value of the fat).
In other words, this additional energy consumption of 32.43 MJ is mostly for fat storage and will not result in as much muscle mass gain, as 1 kg of weight gain requires about as much extra energy for the average person.
In summary, it would make sense that a very low absolute protein intake would contribute to the risk of weight regain, an "absolutely required" amount of protein would be sufficient for weight loss, body fat loss and weight maintenance, but increased protein in the diet would be necessary to improve lean body mass and resting energy expenditure.
It therefore appears that there are observations on protein intake and energy efficiency under certain conditions that can support the "Case of Stock".
This states that under overconsumption conditions, a diet that is either high or low in protein is less "metabolically efficient" than a diet that provides an average protein intake.
However, subsequent studies have failed to replicate this theoretical "metabolic inefficiency" of high-protein diets.
This has also led many researchers to formulate the hypothesis of "protein leverage" for obesity, or "protein leverage hypothesis".
This theory suggests that the body seeks to consume a certain level of dietary protein and that a reduction in dietary protein will lead to compensatory increases in total energy intake resulting in obesity.
However, protein consumption did not decrease significantly during the increase in obesity in the US.
In addition, not only a number of studies, both short and long-term, such as this, this and this in humans, or this and this in animals failed to replicate this effect, but diets higher in protein content should also demonstrate higher levels of adherence to them, as well as outperforming other diets in terms of weight regain, while not achieving neither one, nor the other.
So how do all these things come together?
As we saw in "FUNDAMENTALS OF DIET PART III - a successful diet needs realism", losses of muscle mass can predict weight gain. Let's add more data:
So here, the group that lost the most muscle also had the most adherence to this diet? Isn't that contrary to what we've seen so far?
Not if we look at what happened in protein intake between the groups:
So, the groups that increased or maintained their protein intake also had the highest adherence to the diet and we can actually say that this is reflected in the studies showing that lean mass maintenance is crucial for maintaining weight loss. It's the relatively higher protein intake compared to the other groups.
In addition, the increase in lean mass can lead to increased hunger and weight gain, since the lean body mass is a determining factor as regards on appetite and energy intake, which is true from our infancy.
This is underlined by the phenomenon that under iso-energy conditions no statistically significant difference has been shown between weight loss in high energy diets and weight loss in low energy diets. proteins or carbohydrates.
The explanation for all this is that satiety, the feeling of fullness that comes with a meal, is a key factor in the implementation of a high-protein diet.
This can be demonstrated by the fact that although the greater thermogenic effect of high-protein diets appears to be insufficient to cause greater weight loss than low-protein diets when comparisons are made with constant energy intake, under free feeding conditions participants eat less when given high-protein diets.
Or else, just because the Stock and Protein Leverage hypotheses are not true, this does not invalidate the fact that protein contributes to satiety with a meal. In fact, it should probably be the basis of your diet.
In summary, as far as fat loss is concerned, protein's unique role in satiety is what sets it apart from other macronutrients, while the benefits to lean mass come in second and sweatiest place, with dietary thermogenesis being last on the list.
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