Thirty grams of protein per meal seems to have become one of those "nutrition rules of thumb" that has been passed around so long that it has become accepted as an "unbreakable nutrition law." Some people claim that the human body can only digest 30 grams of protein per sitting (others claim the limit is 40 grams).
There has been a lot of research done on protein needs, although not much of it has focused specifically on the maximum amount digestible per meal. There have been studies where a large bolus of protein was eaten at one time rather than in small, frequent meals, and yet positive nitrogen balance was achieved. This would suggest that the 30 grams per meal limit does not exist and that 60 grams over three meals would allow your body to utilize the majority of that 180 grams.
30-40 grams per meal may be a pretty good rule of thumb for bodybuilding diets with an eating frequency of 5-6 small meals per day (slightly less for females). However, I have never found any research which says that the body has a "30 grams at a time" absolute limit and it doesn't seem likely that one fixed amount could apply to every person in every situation, with no accounting for body weight and activity level.
Nutritional needs - including protein - are highly variable depending on the individual. For example, are the protein needs for a 250-pound bodybuilder the same as a 105-pound ballerina? Are they the same for a 17-year-old football player and a sedentary 70-year-old? The obvious answer is no, and this is why you should look at dietary recommendations made as "absolutes" with caution. Instead, it's optimal to think in terms of customization for each individual.
The best way to figure out how much protein you need in one sitting is to first calculate your total daily protein needs. One gram per pound of bodyweight is a common recommendation (for active, strength-trained individuals), although total protein needs should be customized according to age, gender, body size, lean body mass, activity levels, energy status (deficit or surplus) and personal goals. Then take your daily needs and divide that amount by the number of meals you eat each day; usually five or six in a bodybuilding-style nutrition program.
As a bodybuilder or someone participating in regular strength training, the one gram per pound of bodyweight guideline is a pretty good estimate for daily protein needs (although some competitive bodybuilders go as high as 1.25 to 1.5 grams per pound on reduced carb pre-contest diets). If you weigh 180 pounds and youíre eating six times per day, then bingo Ė thereís your 30 grams. (180 grams divided by 6 meals). If youíre a 240-pound male bodybuilder, and you eat six times per day, now youíre up to 40 grams per meal.
If youíre a 125 pound female athlete, then 125 grams a day would suffice; spread over 5 meals a day, thatís 25 grams per meal. On a pre contest fitness or figure competition diet, many women eat up to 150-175 grams of protein per day, which, over five meals, is 30-35 grams per meal.
Some people think that the 30 grams of protein "rule" was started by protein supplement company marketing because thats the amount of protein they put into each serving of their product. However, looking at these examples, you can see that 30-35 grams of protein per meal is pretty close to the average amount that's consumed on a typical bodybuilding diet. My belief is that this is where the 30-gram "rule" came from - it's simply an average figure. But just because the "average" comes out to around 30 grams per meal, doesnít mean that 30 grams is the most that you can digest.
The digestibility rate of high quality protein sources is 94 to 97% and even the protein in grains and beans is 78-85% digestible. Generally what happens with a large meal, including a large protein intake, is that the meal will simply take longer to digest, but the body will increase the rate of gastric emptying and nutrient absorption in response to the larger food intake. So while the 5 or 6 small meals a day is an accepted practice among bodybuilders, there doesn't seem to be any proof that you couldn't utilize the protein if you took it across only 3 meals instead.
On the other hand, if the total amount of protein exceeds what your body requires and if you are in a caloric surplus, you can convert the excess into body fat. Although protein is the least likely of the macronutrients to be converted to fat (due to an energy inefficient conversion process), a caloric surplus will always lead to fat deposition, even if the surplus comes from protein. In a caloric deficit, protein consumed beyond the body's needs for skeletal muscle and body tissue protein synthesis can be converted to glucose through a process called gluconeogensis.
Bottom line: Even large protein servings can be digested and absorbed, and it appears there is no 30 gram absolute limit. On the other hand, huge servings of protein at one time are not necessary for muscle growth. Beyond what is needed for growth, repair and energy, an excess of protein can get "wasted" if you are referring to being stored as fat or burned for energy.
2. Protein pulse feeding improves protein retention in elderly women. Arnal, M, et al. American Journal of clinical Nutrition. 69. 1202-1208. 1999
1. Plant proteins in relation to human protein and amino acid nutrition. Young V. and Pellet P., American Journal of clinical Nutrition. 59. pp 1203S-1202S. 1994
Tom Venuto is a lifetime natural bodybuilder, an NSCA-certified personal trainer, certified strength & conditioning specialist (CSCS), and author of the #1 best selling diet e-book, Burn The Fat, Feed The Muscle. Tom has written hundreds of articles and has been featured in IRONMAN, Australian IRONMAN, Natural Bodybuilding, Muscular Development, Exercise for Men and Menís Exercise as well as on hundreds of websites worldwide. Tom is also the founder and CEO of the Internet's premier fat loss support community, the: Burn The Fat Inner Circle. To get notified of updates to TomVenuto.Com, subscribe to the free newsletter at: www.TomVenuto.com/free_newsletter.
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