How much protein should be eaten

Human body needs quality protein on a daily base in order to repair and rebuild not only muscles but also all other tissues including skin, hair and other organs. Varied diets suggest consuming different amount of protein in order to meet a need for proper body functioning and achieving variety of fitness goals. The main purpose of this article is to provide scientific framework to determine sufficient protein intake.

Protein

Let’s start from basics and describe protein itself.

Protein is a type of macronutrients comprised of amino acids and used by the body to build, rebuild and maintain cells of all tissues and organs. The right consumption of protein is essentially important for proper body functioning.

According to Donna Cataldo, Ph.D. and Matthew Blair, B.S from American College of Sports Medicine, there is three main types of protein: animal, plant and engineered (supplements such as whey, casein, egg albumin, etc. that are artificially synthesized from organic plant and animal ingredients in order to provide easily digested forms of protein with the whole profile of amino acids very often combined with enzymes and precursor-type of vitamins and microelements). Scientifically proved that all plant proteins have incomplete amino acid profile (one or more amino acids are missed). It means that missing one or more amino acids the body simply can’t get enough of building blocks to repair its tissues. In other words, having only plant proteins the body will inevitable suffer from required nutrients deficiency. According to Ripped to Shreds by Sean Petafi the best solution is the right supplementation or mixing of all three types of protein (plant, animal and engineered) in one meal.

Let’s move forward. Mixing protein sources is a great idea but the question is in what proportion they should be mixed and in what proportion to other nutrients they should be consumed. Let’s leave the first question for another article and focus on the second.


Here we have to introduce another term “nitrogen balance”. According to Gastelu D. and Hatfield F.C. (2000) protein contains nitrogen molecules in its structure apart from carbon and hydrogen. Exactly this fact makes protein different from fats and carbohydrates chemically. So, injected protein is broken down by the body into amino acids and they consequently into carbon, hydrogen and nitrogen. The latter is partly used as building blocks for cells and partly excreted with sweat, urine and feces. According to Bender D. from UCL nitrogen balance is simply nitrogen input minus output. In other words nitrogen balance is the key figure to understanding how much protein you have to consume in order to maintain your muscles and other organs. If your nitrogen balance is positive you body has enough protein for proper growth and repair. If balance is negative your protein consumption is too low and should be increased.

So how much protein should be consumed? According to Bender D. (2006) the average amount of protein a day for not training individual is about 80g. However, this figure looks too generic. According to Cataldo D. et.al. the average protein amount consumed should be equal to 0.8g/kg. of body weight. MacDomald M. (2013) suggests that the sufficient consumption of protein for individual participating in endurance sport such as marathons, cross-country skinning and other sport events lasting more then 2 hours is from 1.2-1.4g/kg, for individual participating in strength training such as fitness, sprinting, circle training is 1.7-1.8g/kg and for heavy lifters or bodybuilders is about 2-2.5g/kg of body weigh. Bayesian Bodybuilding in its literature review related to the topic suggests that the ideal sufficient amount of protein to build muscles is 1.8 g/kg. Bodybuilding iconic book Ripped to Shreds suggests that the average required amount of protein for muscle hypertrophy is from 2.5-4g per kg of lean weight. According to Robson D. the golden rule of positive nitrogen retention is about 1g of protein per 1 lb. of lean body weight. About the same amount (1.5-2.5g/kg) is recommended for sport participants by Gastelu D. and Hatfield F.C. (2000). Researches also believe that whole food alone hardly could provide enough protein for maintenance and growth, so, the right supplementation is necessary thing for any sport participant.

As we can see figures are pretty various. And it’s just a little snippet of the literature review. What be the best way to determine the right protein intake for a particular individual?

Here we have to say couple of words about protein-carbohydrate sparing effect. Protein sparing effect is the phenomenon when the injected protein is used by the body for energy needs in the lack of carbohydrates. In other words, if the diet is deficient in carbohydrates the body withdraws consumed protein and convert it into glucose to survive. As a consequence the body doesn’t have enough protein to build and repair as it was used for energy needs. So, we have to emphasise that our further consideration related to protein intake and nitrogen balance is made with an assumption that the carbohydrate content is sufficient in the diet.

There are few frameworks to determine protein requirement for particular individual. Obviously there is no unified ready to use figure. Every particular individual has his/her own metabolism, body type, activity level and other characteristics that should be taken into account.

The first framework to determine protein requirements is based on nitrogen balance measurements.


Here are few steps that could be done to use the framework:

  • determine your body weight and body composition in order to understand how much muscle mass you hold (body weigh – body fat)
  • determine your fitness goal (build muscle, maintain muscle mass, increase strength, decrease body fat, etc.)
  • determine your current protein intake per day by protocoling all protein consumed during few days
  • find a way to measure your nitrogen output in the same days you protocoled protein intakes (nitrogen sticks or laboratory tests)
  • calculate your nitrogen balance using a formula

N retention=(pure protein total in g. consumed/6.25)-(nitrogen output +4)

If you figure is positive you are on a right track to build muscles. However, keep in mind that excess protein could be converted into fat if carbohydrate content is sufficient or used for energy if not. Also too high protein consumption would escalate ammonia level in the urea and put additional burden to the kidney. So make a final check dividing your consumed protein by your lean body weight. If you are an active sport participant, your nitrogen balance is positive and you stay in the range 0.8-1g/lb. of lean body weight your consumption is sufficient. If your figure is higher look carefully at your total diet, your fitness goals, your progress and the body fat percentage in dynamic over 4-6 weeks and adjust your diet accordingly. Ideally, if your progress is little just involve competent nutrition and fitness professionals who will be able to correct your training and diet programs and guide you through the process optimizing output and minimizing risks.

If the figure of your nitrogen retention tests is negative your protein intake is insufficient and should be increased. In order to understand how much it should be increased just multiply the figure by 6.25. For example, if your negative figure is 10×6.25=62.5 g of protein should be added into your diet in order to come to nitrogen equilibrium. If you are willing to increase your muscle mass so increase your protein intake even more. How mush more? We will cover one or the calculation methods below.

The nitrogen retention estimates method, however, has some limitations. Firstly, not every individual has an opportunity to test nitrogen excretion. Secondly, according to Rassel G.R. et.al., even laboratory nitrogen excretion tests in majority of case are underestimated or estimated incorrectly.

Here is could be utilized another more conventional approach to calculate protein requirements. According to Mantovani G. (2006) 0.6g per kg of well-balanced protein a day is sufficient to maintain zero nitrogen balance for an averagely active person. The question is what if the person is not averagely active? What if the person tend to lead sedentary lifestyle or in opposite trains twice a day? How much protein should be consumed in such cases? Another question is how much protein should be consumed in order to not only maintain but also increase muscle mass? Here is a method to calculate the approximate amount provided by Gastely D. and Hatfield F.C. from International Sport and Science Association.

  • First of all, gender and a lean factor of a particular individual should be taken into consideration in order to calculate basal metabolic rate (BMR – calorie requirements to keep the body alive).

So, the formula is:

  • Weigh in kg x gender coefficient (1 for male and 0.9 for female) x 24 hours = Basic metabolic rate
  • BMR x lean factor=adjusted BMR

 


Lean factor is determined by proportion of the body fat towards the body weight. So, lean factor 1 is for less than 14% of body fat for men and less than 18% of body fat for women; lean factor 0.95 is for less than 20% and 28% of body fat for men and women respectively; lean factor 0.9 is for less then 28% and 38% for men and women and lean factor 0.85 is for over 28% and 38% of body fat for male and female.

  • Next, the level of activity should be determined and taken into consideration in order to calculate total daily caloric requirements.

Adjusted BMR x activity multiplier = total daily calories.

Activity multipliers:

1.3 – sedentary life style

1.55 – very light activity (writing, teaching, some walking through the day)

1.65 – moderate activity (walking, jogging, training 1-2 hours a day, active job)

2 – heavy activity (manual job, sport activities between 2-3 hours a day)

2.3 – extremely active (combination of moderate and heavy activities more then 8 hours a day, plus sport training 2-4 hours a day)

  • Finally, type of activity should be determined in order to calculate the percentage of total daily calories that should be taken from protein sources.

Keep in mind that adequate protein intake for people not participation in any sport should be in the range 10-20% of their daily total depending upon goals, current condition, metabolism, body weight and age.

Protein intake for sport participants could be determined more precisely.

All kind of sports could be divided into 4 main groups with its own ideal ratio of protein, carbohydrates and fat:

  1. Anaerobic sports (immediate energy sports such as power lifting, bodybuilding, boxing, football, etc.) – the ideal proportion is 30%P, 55%C, 15%F
  2. Anaerobic glycolytic – (sports where explosive strength and power is required on a sustained and highly repetitive basis such as field hockey, rock climbing, mid-distance skiing, ect.) – the ideal proportion should be about 25%P,55%C,20%F
  3. Anaerobic glycolytic – Oxidative glycolytic (sports such as dancing, fitness, long distance swimming) – the ideal proportion should be 20%P, 60%C, 20%F
  4. Oxidative (aerobic sports such as marathon running, triathlon, all endurances events more than 2 hours long) – the ideal ration is 15%P,60%C,25%F

So, understanding daily total energy needs we could easily calculate protein requirements for a particular person taking into account his/her activity level. However, this method requires certain adjustments over time. Start from the figures you get via calculations and observe how your body reacts on a certain macronutrient modulation. If you notice muscles catabolism increase your protein intake by 10-20% of your previous figure and keep training and observing results. If in 4-6 weeks of intense training you don’t see any changes make a further adjustment or recalculate your daily total.


Reference list

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