The second of a series of Newsletters intended to explain the basic science underlying the nutrition of weight loss in simple user-friendly language.

Protein

Our first newsletter was about thermogenesis, and pinpointed protein as a major contributor to thermogenesis under physiological conditions. Increasing thermogenesis is, however, only one of the reasons why we need protein in weight loss diets. Before dealing with this and the other reasons why we need protein, we should define what a good diet actually is.

The good diet gives an energy deficit; less calories must be consumed than are required to meet both the basal metabolic requirements (the energy cost of running the body) and the energy cost of daily activity.  In other words, it provides less calories than you are burning each day, so you draw on your fat reserves to make up the difference.

The good diet preserves full functionality of physiological and biochemical systems and compensates for adaptations to the low energy intake which otherwise would reduce or prevent loss of weight.  Normally, when you consume less calories than you need, your metabolic rate falls, and you burn fewer calories.  This is a normal response built into humans to help them get through times of famine (not a problem now-a-days), but is not helpful for weight loss.  The good diet prevents your metabolic rate from falling.

The good diet favors loss of weight predominantly from fat tissue and permits no greater loss of lean body mass than is physiologically acceptable.  Fat is what you need to lose, but some bad diets actually cause you to lose muscle and organ tissues, which you may never get back!  This weakens you, and if you are a yo-yo dieter on bad diets, you will get weaker with every cycle, because you are losing muscle!

The good diet must prevent occurrence of deficiencies.  Many bad diets do not allow for enough essential fatty acids, potassium or other essential nutrients, and may cause serious side effects.

Unless diet programs meet all these requirements, they are potentially hazardous and may not only cause adverse effects, but may result in irreparable harm in either short or long term.  High protein weight loss diets, appropriately supplemented with vitamins, minerals and essential fatty acids, have proven the safest and most effective types of diet in weight loss.

Why do you need that protein? Firstly, because it is thermogenic!

It is difficult to prioritize the numerous reasons why adequate amounts of protein are essential in a weight loss diet. but we can start with thermogenesis.  Protein is thermogenic, for example, a meal containing 30 grams of good quality protein given to obese volunteers in a study performed at McGill University a few years ago was shown to increase RMR by an average of 13.8%.  In the same study, giving the protein meal together with a Bitter Orange supplement gave a further (and significant) increase to 18.3%, an additive effect.

The body has to expend energy (and thus increase the metabolic rate) to digest protein and absorb the resultant amino acids, and even more energy will be required to distribute these amino acids and metabolize them. One of the main reasons for the thermogenic action of protein is that it contains the essential amino acids, phenylalanine and tyrosine.  When assessing the quality of a protein, these are usually considered together, because either can be utilized in the body as a precursor of catecholamines, namely dopamine, noradrenaline (norepinephrine) and finally adrenaline (epinephrine).  Noradrenaline is the main mediator of physiological thermogenesis in peripheral tissues (muscle, liver, adipose tissue).  Ensuring availability of the essential amino acids the body requires to make this hormone facilitates thermogenesis.

Secondly, because some essential amino acids play other roles in assisting weight loss!

Noradrenaline also plays a role in the central nervous system since it is the neurotransmitter mainly responsible for controlling the hunger center in the hypothalamus.  In this role, increased availability of noradrenaline (and possibly also dopamine) in the hunger center suppresses hunger.

Since we are talking about an additional role for noradrenaline as a neurotransmitter in the central nervous system, one that does not involve thermogenesis but does affect sensations of hunger and eating behavior, we also need to mention another essential amino acid that gives rise to the neurotransmitter serotonin.  Serotonin complements noradrenaline by acting on the satiety center, which is also in the hypothalamus, and in fact high levels of serotonin in the area of the satiety center induces satiety (the sense of feeling full, or that one has eaten enough).  The essential amino acid concerned is tryptophan, which is converted into serotonin.

Thus two centers, both in the hypothalamus, control whether we feel hunger and satiety, and both are sensitive to neurotransmitters derived from dietary protein.  Suppressing hunger reduces the desire to eat, while increasing satiety makes us stop eating more quickly. 

As with all physiological systems, control of hunger and satiety is much more complex in reality than the above would suggest.  Not only do the hunger and satiety center interact with each other, but they are responsive to levels of nutrient substrates and hormones in the blood, ranging from insulin and glucagon through the various neuropeptides produced in the gut, to glucose and free fatty acids.  In addition, they are also controlled by the vagus nerve; increased vagal activity from a distended stomach, for example, results in diminished hunger and increased satiety.  The response of the satiety center to increased levels of free fatty acids in blood is of some interest since it links peripheral (classical) thermogenesis to the central nervous system.  Thus a thermogenic response that results in increased lipolysis also results in increased satiety!

Other parts of the brain also affect eating behavior and increased availability of dopamine in the so-called dopaminergic systems can assist weight loss by reducing emotional attachment to food and food cravings.

Just a little footnote.  While our main interest in serotonin and the catecholamines relates to weight loss, we should not forget that they also affect mood.  Serotonin in particular can improve mood, and a study performed about 20 years ago related the occurrence of depression in women given a rather low protein weight loss diet to low levels of tryptophan in the blood (and thus in the brain).  So good high-protein diets can also prevent depression occurring in those who use them.

Thirdly, because an adequate protein intake prevents loss of lean body tissues!

It was first shown in the 1950’s that reducing caloric intake below that required to maintain stable body weight could result in loss of protein from the body.  Several studies performed at that time, mainly in patients receiving parenteral nutrition either intravenously or through nasogastric  indicated that for every 40 kilocalories that energy intake was reduced, 1 extra gram of protein was required, otherwise the patient went into negative nitrogen balance (indicating loss of protein; protein is 16% nitrogen)

Further research performed and published over the last 25 years also indicates that high protein weight loss diets consumed conventionally offer substantial advantages over isocaloric diets with lower amounts of protein and are completely safe, whereas low calorie diets with insufficient protein may cause considerable damage through loss of protein from important body tissues. The term nitrogen balance is, in effect, synonymous with protein balance, and ensuring that the body is in nitrogen balance (or equilibrium) is an important consideration when low calorie diets are given for more than a few days.   A normal guideline is a minimum of 1.5 g protein per kg of ideal body weight per day, with a maximum of about 2.5 g protein per kg ideal body weight per day, with a portion of your protein intake being of high biological value.

How much of your protein intake should be of high biological value when on a high protein diet?

This amount was validated by the World Health Organization (WHO) more than 25 years ago.  Their studies indicated that 50 grams per day of protein of a high biological value provides adequate amounts of all essential amino acids (EAAs), which are: Histidine, Isoleucine,Leucine, Lysine, Methionine + cystine, Phenylalanine + tyrosine, Threonine, Tryptophan, and Valine.

Once the absolute amounts of EAAs have been consumed, the quality of the remaining protein consumed within the context of a high protein weight loss diet is not too important, since after the physiological demands for EAAs have been met (and EAAs are treated preferentially in the body), the remaining amino acids, be they essential or not, simply go into the amino acid nitrogen pool where they are used for synthesis of non-essential amino acids or broken down for energy.  So simply put, once the dieter has consumed three or four protein supplements as high quality protein, they can consume the rest of their protein in the form of lower quality proteins.  It is the plentiful availability of amino acid nitrogen in the pool that ensures the preservation of lean body mass on low-calorie diets!

In practice, it is nice to get a little more than 50 g of high quality protein a day into the diet, because of the importance of phenylalanine/tyrosine and tryptophan.  When the diet calls for 100 – 120 grams of protein a day, giving at least 2/3rds as high quality prtoein makes sense.

Last, but not least!

Protein has an anabolic effect that is at least in part related to its amino acid content.  For example, arginine stimulates release of growth hormone, which in turn stimulates the uptake of amino acids by cells and their conversion into tissue proteins.  The combination of good circulating levels of amino-acids, improved synthesis of protein and facilitation of amino-acid transport across membranes which thus results from a high dietary intake of protein also contributes to the prevention of a possible loss of lean body mass (protein) from the body during weight reduction, particularly from vital organs and muscle tissue, and furthermore can materially assist with increasing existing lean body mass, for example muscle.  So protein diets can also lay the groundwork for reshaping the body after successful weight loss!

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