Paleo Diet and Paleolithic Diet Questions & Answers

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http://paleohacks.com/questions/19548/top-limit-of-protein-intake

The above topic discusses Protein limits. A few questions on this: (1) What ARE the limits to usable protein? a)per meal b)per day (2)what are the signs/symptoms that one has exceeded these bounds(fatigue; temporary brain death/fog)? (3)The notion of an "amino acid pool"(ie. storage of aminos) seems questionable at best..

I have checked out a few studies re: assimilation rate of protein and, assuming one wishes to maintain a certain amount of muscle mass(through positive nitrogen balance), they would indicate that meals should be consumed no greater than the limit of assimilation so that amino acids are constantly present in the body. The post-prandial assimilation rates of various proteins would also indicate that fasting would lead to muscle catabolism(given no aminos present). A question remains to be answered: how much can be assimilated(ie. digested, converted into aminos and utilized for repair/growth of muscle tissue and not converted into glucose)? Many would contend that greater than 50 grams under normal conditions can be assimilated by the 'normal'(average weight/metabolic rate/physiology) male at a given time, Personal experience disagrees. Having attempted to consume greater amounts per sitting a great feeling of fatigue('symptoms' of excess?) arose, lasting for up to 2 hours after eating. This was on a VLC diet. Proportional to the amount of protein consumed. It would be interesting to 'know one's limits' on a scientific basis. P.S: I have investigated Leangains and the site makes claims it tends to confute: fast(yet take BCAAs). How is it fasting except in a loosey-goosey way when substances(aminos) are claimed to be avoided for 16 hour intervals, yet others(BCAAs....aminos) are not? I'm sure Cavemen didn't have bottles of BCAAs like Dorian Yates in their 'gym lockers'. Feedback please!

flag	asked May 15 2011 at 18:06 PersonMan

	Good question. Gym talk was always that only 30-50 grams can be assimilated at a time. Looking forward to someone producing a real study on this. – Mark V May 15 2011 at 20:21
	Why has noone yet answered this post? Is it because they have no answer...? – PersonMan May 16 2011 at 23:13

Alex · Answer 1 · 2011-06-01 20:09:26Z UTC

Maximal Rates of Excretion and Synthesis of Urea in Normal and Cirrhotic Subjects

This is the study that Paul Jaminet uses to justify a maximum safe protein limit per day - about 230g for an 80kg individual and also suggests that toxicity begins to occur above 150g -> Here

Alan Aragon talks about protein absorption rates in this Article

The fastest absorbed protein was 10g/hour - this would put the daily limit at ~240g. It's not clear if this includes digestion (I don't have access to the full review cited) but this could potentially slow the process.

Hopefully these can go some way to answering your question.

As for per meal I guess physical stomach size is the limiting factor? - I've personally eaten 200g (1kg of pork loin) with veggies over about an hour and been full but not ridiculously uncomfortable.

In the past I've eaten around 300g from turkey over the course of a day - this definitely felt like too much protein - not good.

Symptoms of protein toxicity? Not too sure really. If you haven't got enough carbohydrate or fat then you might feel pretty tired due to the energy needed for digestion and the inefficiency of direct metabolism.

For reference, at the moment I eat two meals a day with ~75g of protein each and feel fine.

If I can just briefly stick up for Martin's Leangains method - I think you are referring to his morning fasted training setup?

The BCAA's are something of a compromise as he says - "Will we still derive the benefits from regular fasting if we consume small amounts of protein throughout the fast post-workout? Yes. If carbs are omitted, the increased insulin sensitivity will quickly bring back basal insulin to fasted state levels despite consuming 120 calories worth of fairly insulinogenic amino acids. The fasted state is almost fully maintained post-workout."

This makes sense to me if you believe that the benefits of fasting are due to prolonged low insulin levels and hepatic glycogen depletion.

peter · Answer 2 · 2011-06-13 10:32:54Z UTC

Found it.

A diet with 35 % of energy from protein leads to kidney damage in female Sprague-Dawley rats.

Abstract High-protein (HP) diets for weight loss remain popular despite questions surrounding overall safety. In a recent study using the pig model, we showed that long-term intakes from whole proteins at 35 % energy (en %) cause moderate renal histological damage. To examine whether this observation may be species specific or more generalisable, the effect of this diet in rats was examined. Using plant and animal whole proteins, 70-d-old female Sprague-Dawley rats were randomised to either a normal-protein (NP; 15 en %) or a HP (35 en %) diet for 4, 8, 12 and 17 months. Renal function was assessed by creatinine clearance and urinary protein levels, and pathology was assessed by examination of glomerular hypertrophy, glomerulosclerosis and tubulointerstitial fibrosis. Rats consuming the HP diet had 17 % higher kidney weights (P < 0·0001), three times higher proteinuria (P < 0·0001) and 27 % higher creatinine clearance (P = 0·0012) compared with those consuming the NP diet. Consistent with this, HP-fed rats had larger glomeruli (P < 0·0001) and more glomerulosclerosis (P = 0·0003) compared with NP-fed rats. The HP diet also resulted in altered levels of free monocyte chemoattractant protein-1 (P < 0·0001). The histological changes are consistent with those observed in the pig model. In contrast to the pig model, the elevated proteinuria and creatinine clearance observed in the rat model are also usually observed with HP consumption in human subjects. These results indicate that the rat is a useful model for HP effects on the kidney and, along with previous results using the pig model, suggest that long-term intake of high levels of protein may be detrimental to renal health.

Its on PubMed if you want to read

http://www.ncbi.nlm.nih.gov/pubmed/21535903

And yes i know, we're not pigs or rats.

Protein limits unresolved

2 Answers