There is no lack of articles regarding the benefits of protein for health. From fat loss to bodybuilding, protein seems to be able to help with it all. So how much protein per day is the right amount?
Current Protein Recommendations
The International Society of Sports Nutrition has set the following recommendations for protein intake:1
Activity Level Grams of protein/kg bodyweight/day
- Sedentary (adult) 0.8
- Recreational Exerciser (adult) 1.0-1.4
- Resistance-Trained (maintenance) 1.2-1.4
- Resistance-Trained (gain muscle)* 1.4-1.8
- Endurance-Trained 1.2-1.4
- Intermittent, High Intensity Training 1.2-1.8
- Weight Restricted Sports 1.4-2.0
Note: Growing teens should add ~10% to all values
*Athletes using anabolic agents (e.g growth hormone, insulin, testosterone), a higher protein intake may be required to maximise gains. For this author personally, I find using 2g/kg of bodyweight/day is a nice even figure to calculate protein intake for the day. So for an average male of 80kg who wants to gain a bit of muscle, the recommended protein intake per day is about 160g. In food terms, this equals to:
- 2 WeetBix with a glass of milk
- 2 protein shakes made on water
- A chicken breast
- A can of tuna
- 2 Eggs
- 15 Almonds
Many weight lifters, bodybuilders and professional athletes take a lot more however. But are higher levels of protein over the recommended levels beneficial or dangerous? Is there an upper limit to amino acid metabolism and absorption?
Protein Metabolism & Excretion
When amino acids are catabolised, it results in build-up of ammonia which needs to be turned into urea to be excreted, otherwise excess accumulation will have dangerous consequences, including death. Bilsborough and Mann (2006)2 used maximum urea excretion rates and essential protein requirements to calculate that maximal protein intake should not exceed 285g/day for an 80 kg man. So, according to this rough figure, the recommended level of intake seems to fall under the safe level of protein intake.
Now, while many food products are great sources of protein, the rate at which that food digests and is absorbed differs between foods. Summarising results from several studies looking at the absorption rate of proteins, Bilsborough and Mann suggests absorption rates as follows:
- Soy Protein Isolate – 3.9g/h
- Casein Protein Isolate – 6.1g/h
- Whey Protein Isolate – 8-10g/h
- Cooked Egg – 2.8g/h
- Milk -3.5g/h
According to these results, an average serving of whey protein providing 30g of protein will be fully absorbed within 3-4 hours. Does a faster absorption rate though lead to greater protein synthesis rate, which is what we want for muscle building. According to Dangin et al (2001)3 and Giordano et al (1996)4, rapidly absorbed proteins such as whey protein and free amino acids are able to moderately inhibit protein breakdown and also stimulate protein synthesis. Dangin et al (2002)5 also showed that a slower digested protein such as casein is able to reduce the breakdown of protein, confirming the common idea that whey protein is an anabolic protein while casein is an anti-catabolic protein. However the 2002 study also found that quickly absorbed amino acids, while promoting greater protein synthesis also leads to greater amino acid oxidation leading to a lower net gain of protein. What this means is that a slower absorbing protein will help to counteract the increased oxidation/breakdown rates of amino acids in the body – giving you a better protein balance for muscle building. The same study compared different proteins and protein balance as measured by leucine balance post consumption. They found that casein protein or whey protein consumed at 2.3g every 20 mins allows for the best protein balance. This study was able to show that faster absorbed protein such as whey protein when consumed at a single amount of 30g may not be able to provide you with the best protein gains. It seems that to ensure the best protein gains with the least amount of losses, an absorption rate of protein of ~6-7g/hr is the best bet, which would put maximum daily absorbed protein at 144-168g/day. So while we are able to tolerate much higher protein intake levels, we might only be absorbing a fraction of it.
Protein Intake for Bodybuilders
So to summarise all the above information and the results from the studies:
- For an 80 kg man – the theoretical maximal intake of protein is ~285g/day
- To promote the best protein retention, an absorption rate of 6-7g/hr appears to be the most beneficial.
- This protein absorption rate equals to total daily absorbed protein of 144-168g/day.
However, this amount is not set in stone and it should be noted that our genetics, how we consume that amount throughout the day and when we consume it has definite effects on our ability to use and retain that protein. Without getting too complicated, small frequent protein meal ingestion6 and timing of protein ingestion7 at before and after workouts has been shown to help decrease protein breakdown and increase muscle protein synthesis respectively.
Protein Intake Recommendations & Tips
With these studies in mind, the following recommendations can be used as a rough guide to promoting the best muscle protein gains while also decreasing protein loss and breakdown for trainers and active people:
- 2g/kg/day of protein consumption is a good figure to follow if you are over 70kg.
- For those who weigh less, aim for approximately 140g/day of protein.
- Small frequent meals containing protein of around 20-30g will help maintain positive protein balance. More may be needed if you weigh more.
- Having protein before and after working out will promote better muscle protein synthesis regardless of total daily protein intake.
- Consuming carbohydrates with protein will help to spare protein loss8.
- Post workout, a protein mix of a fast absorbing protein (free amino acids, hydrolysed protein or whey protein) with a slow absorbing protein (casein) will help achieve the best ratio of protein synthesis and breakdown.
- Similar benefits occur from use of whey protein in small frequent doses of ~7g/hr.
1 Antonio J, Kalman D, Stout JR, Greenwood M, Willougby DS, Haff GG. 'Essentials of Sports Nutrition and Supplements'. International Society of Sports Nutrition. Humana Press 2008
2 Bilsborough S & Mann N. 'A Review of Issues of Dietary Protein Intake in Humans.' International Journal of Sport Nutrition and Exercise Metabolism, 2006, 16:129-152
3 Dangin, M., Y. Boirie, C. Garcia-Rodenas, P. Gachon, J. Fauquant, P. Callier, O. Ballevre,and B. Beaufrere. 'The digestion rate of protein is an independent regulating factor of postprandial protein retention.' Am. J. Physiol. Endcrinol. Metab. 280: E340-E348, 2001.
4 Giordano, M., P. Castellino, and R.A. deFonzo . 'Differential responsiveness of protein synthesis and degradation to amino acid availability in humans.' Diabetes. 1996. 45:393-399,
5 Dangin, M., Y. Boirie, C. Guillet, and B. Beaufrere. 'Influence of protein digestion rate on protein turnover in young and elderly subjects.' J. Nutr. 2002. 132:3228S-3233S.
6 Forslund, A.H., A.E. El-Khoury, R.M. Olsson, A.M. Sjodin, L. Hambraeus, and V.R. Young. 'Effect of protein intake and physical activity on 24-h pattern and rate of macronutrient utilization'. Am. J. Physiol. 1999. 276:E964-E976
7 Tipton, K.D., B.B. Rasmussen, S.L. Miller, S.E. Wolf, S.K. Owens-Stovall, B.E. Petrini, and R.R. Wolfe. 'Timing of amino acid-carbohydrate ingestion alters anabolic response of muscle to resistance exercise'. Am. J. Physiol. Endocrinol. Metab. 2001. 281:E197-E206
8 Lemon, P.W., and J.P. Mullin. 'Effect of initial muscle glycogen levels on protein catabolism during exercise.' J. Appl. Physiol. 1980. 48:624-629