PROTEIN INTAKE - EVIDENCE BASED RECOMMENDATIONS
A brief guide to eating the correct quantity of protein
Protein is used to build and repair the body. As fitness professionals we are particularly concerned with the building and repair of muscle tissue after exercise – especially resistance training. There are many ideas around how much protein is the right amount for muscle gain, weight loss etc. But which ideas are backed by science and what are the real evidence-based recommendations?
Measuring protein ingestion
Firstly, we need to look at how we can determine the amount of protein that is being ingested into the body from what we eat. An indicator of the protein requirements of the body is that of ‘nitrogen balance’. Nitrogen is a structural component in a protein molecule. Therefore if we eat more protein, we acquire more nitrogen within our body. Nitrogen balance is a measure of whether the body is gaining or losing protein from its’ mass. The body is in nitrogen balance when the amount of protein taken in the food eaten is equal to that lost in faeces, urine, and sweat. This can be measured in a laboratory. A positive nitrogen balance infers that more protein is ingested than is lost, whereas a negative nitrogen balance occurs when more is lost than taken in the diet.
Amounts of protein required
Of course, we can’t measure our client’s actual nitrogen balance, so instead we have to use average values based on the defining variables. The various government agencies and the World Health Organisation make their recommendations for protein intake based on average nitrogen balance requirements for; gender, age and activity.
Gender – Whether you are male or female makes a difference to the amount of protein you can ingest and how much you may need. Women do not have the same levels of anabolic hormones within them. Therefore the ability to ingest and use protein to grow muscle tissue is reduced. Lower muscle mass also means that there is less tissue to repair, meaning that protein levels ingested may be less than for males.
Age – As we age, we tend to lead more sedentary lives. Therefore less protein is required to maintain our reduced muscle mass. Even highly active older adults who in theory require increased protein intake may actually only be able to use a reduced amount in any case, due to the aging effect lowering the levels of anabolic primary sex hormones (specifically testosterone) circulating within the body.
Activity – Studies have shown that increases in physical activity – particularly resistance training can lead to a negative nitrogen balance, therefore additional protein should be taken in, in order to restore the balance.
The WHO general guidelines given are that sedentary individuals should consume 0.8 grams of protein per kilogram bodyweight, with very active individuals at 1.8 grams of protein per kilogram bodyweight. Furthermore, studies with athletes have shown that for those undertaking rigorous activity, a protein intake of 2.5 grams per kg bodyweight could be beneficial. Please note: unless your clients are professional athletes, they will not require this level of protein intake!
Dietary protein increases are particularly useful for sedentary individuals, or individuals who have had a change in training routine. Increased protein ingestion prevents a negative nitrogen balance in the first 14 days of training as the client adapts to the new training stimulus – We all know how bad your DOMS can be at these times, right?! However, once clients are adapted to new training regimens, dietary protein amounts can be reduced accordingly.
Protein gluconeogenesis and bodyfat
Although protein helps with recovery from activity, eating in excess of what you actually need for protein synthesis has been shown to be disadvantageous. Protein contains calories that if not used for growth or repair, will ultimately be converted to stored body fat.
During protein ingestion, protein is first metabolised into amino acids (used for growth) and ammonia (excreted in urine). Any left over carbon compounds not required for growth are then converted into glucose (gluconeogenesis), which your body can use for energy. However, if your cells already have enough glucose, and there is no space left to store it as glycogen in your muscles or liver, the excess glucose is converted into fat. Generally speaking, our client’s are well stocked with glycogen, therefore this is a viable mechanism to be aware of!
Not only does excessive protein intake potentially result in body fat acquisition, gluconeogenesis can result in higher levels of ketones and nitrogenous waste which is toxic to the body – in the short term causing headaches, and over long periods of time, potentially becoming a risk factor for Coronary Heart Disease. This process is particularly relevant to those on a low carbohydrate diet/high protein diet. The body requires approximately 160-190 grams of carbohydrate each day in order to feed the brain and other organs. If this is not taken in via the diet, then gluconeogenesis will certainly occur. Prescribing fasted exercise for clients – particularly at higher exercise intensities (not recommended or particularly beneficial anyway!) would also cause gluconeogenesis.
The role of carbohydrate in relation to protein ingestion
Eating carbohydrate during exercise has been shown to a have a protein sparing effect – especially during long endurance activities. This can help to reduce the amount of post-workout protein intake required. During recovery, eating carbohydrate alongside protein can also help you ingest more of the protein, as your insulin levels (an anabolic hormone) will be raised to control blood sugar levels. Higher Glycaemic Index carbohydrates are recommended for this benefit to be maximised.
Protein meal times
Protein ingestion is more prevalent immediately post workout due to raised anabolic agents circulating within the body. Numerous studies have shown that a 2-3 hour delay in ingesting protein will have a negative impact on your nitrogen balance – effectively meaning that you are not using the protein to grow or repair.
I’m a Personal Trainer, what advice can I give?
Your personal trainer qualification with TrainerMaker gives you the knowledge to advise your clients based ONLY on WHO/government agency guidelines. It does not give you the knowledge to understand and therefore prescribe anything other than that. Within the WHO guidelines however, there is ample ‘wiggle room’ for you to tailor your advice. Remember, that you are NOT a dietician or nutritionist/nutritional therapist! Your client may have a medical condition, food intolerance etc that may be affected by your advice, therefore ensure that you complete an informed consent for the advice you give explaining the benefits and risks associated with dietary changes.
The following are some recommendations taken from the UKSCA article ‘Protein, carbohydrates and muscle recovery’ written by Don MacLaren Cert.Ed., BSc(Hons), MSc, PhD
1) Ensure adequate amounts of carbohydrate are eaten i.e. 6-8 g/kg body mass per day when training intensely. The only time carbohydrates may be avoided or reduced is when there is a need to reduce body fat since excess carbohydrates are stored as fat.
2) Ensure carbohydrate and essential amino acids are ingested 60 minutes before intense training.
3) Ingest carbohydrates (1-2g/kg body mass) and protein in a 3:1 ratio in the hour after training.
4) Consider increasing protein intake (say to 2.5g/kg/day) a few days before a change in training intensity and continue for 10-14 days if the level of training remains high. Thereafter, reduce the intake to levels not lower than 1.5-1.8g/kg body mass a day.