Meat!

Usually in an exploration of functional foods, one hears a lot about vegetables, fruits, herbs, phytochemicals and such. That's all cool to learn, but most humans are after all omnivorous. That is, man does not generally live by plants alone.

Even a review of the anthropological literature suggests that we've been butchering animals for a very long time. I'm not sorry if that disturbs some people. I like my big brain and I like my smallish gut. But beyond evolutionary arguments, there are good things to know about meat... good things for bodybuilders who might be living exclusively on milk proteins.

With what I'm about to share in mind, it's almost disturbing that meat often gets slammed in public education efforts. Sure a clever, opinionated person can indeed manage to live without meat, but it takes far more planning than most people think. Let's take a look at why meat is so bloody helpful (pun intended!)...

The Obvious

Think about the food chain for a moment. Herbivores graze all day long on relatively nutrient-poor plants. They have huge guts (intestinal tracts) to extract as much of the nutrition as possible for their bodies. Day after day they spend nearly all of their time grazing. Then along comes a predator and aggressively pins down and eats one of the herbivores. Bam!

All of the nutrients that were so gradually and constantly accumulated in the tissues of the plant-eater become instant nutrition for the carnivore. It may be hard to witness, but the bloody feast is so rich in nutrients that the carnivore doesn't have to eat for a comparatively long time.

Now, the price of this lifestyle is that carnivores have to be cognizant and clever. They have evolved in more ways than just forward facing eyes toward this end. Bigger, often highly intelligent brains may be energetically costly to maintain, but they help plan attacks and score meaty meals. Such feasts allow for days or even weeks "off" to do other things... mate, take care of young, form complex social groups, learn, go bowling, etc.

What does this have to do with a modern bodybuilder? Well, meats remain very nutrient-rich. Sadly, with so much hoopla these days over nutrient density (you know, key nutrients divided by total kcal), this gets overlooked. A guy or gal looking for quality mass should not be swayed by talks of nutrient density that so often get promulgated to the over-fat public.

Broccoli, for example, is extremely nutrient dense, but despite its many merits, will not pack muscle tissue on an athlete when over-consumed. There are just too few calories (kcal) for it to be eaten a dozen times per day. I'm sure you see my mathematical point by now: Dividing a food's nutrient content by nearly zero kcal equals very high nutrient density (again, a ratio of vitamins, minerals, etc. to its kcal), but that's not total nutrient content.

Gross nutrient content is where meats shine. Look in almost any college textbook for sources of key vitamins and minerals. With a few exceptions, meat is near the top of the list! Makes you glad you're an apex predator, doesn't it?

The Not-So Obvious

I have absolutely nothing against fruits and vegetables. Beyond vitamins and minerals, they boast thousands of cool phytochemicals (phyto = plant) in complex combinations that help our health and physique. But researchers are increasingly coming back to meat – which I'll define loosely as animal muscle – because it's rich in "zoochemicals".

That's right. So, in addition to a rational intake of several servings of veggies per day, meat is getting recognized for special, almost pharmaceutical properties. Do the various sources of animal flesh differ metabolically or behaviorally come dinner time? Yes.(36) But we're talking about eating the muscles of critters in general. Here are some compounds and potential benefits:

• Quality protein (duh)

• Vitamin B₁₂ (essential nutrient, red cell formation, energy)

• Heme Iron (readily absorbed form, fights fatigue in some persons)

• Zinc (readily absorbed, sub-par in most diets)

• n-3 fatty acids (potent EPA and DHA compared to the plant-based linolenic acid)

• Creatine (muscular power and cell volume)

• Carnosine (cellular buffering, antioxidant effects, longevity)

With all the recent attention given to beta-alanine as a necessary carnosine precursor, you may already be fretting about human carnosinase as a fault in my list but bear with me. To be sure, meat in realistic quantities cannot match a supplement (for creatine or carnosine dosage), but you may be surprised what researchers are saying. First, however, let's look at B₁₂ and iron – stuff that meat provides like no other food.

Quality Protein

I won't dwell on the simplicities of complete versus incomplete proteins. Clearly, meat is a good, solid complete protein source. It contains all the essential amino acids. The biological value of beef is 75 (egg and milk are 100 and 93, respectively) and its PDCAAS is 0.92 (egg white and casein being 1.00). Although these numbers look a bit inferior to some of the other "bodybuilder proteins", there's more to it than that.

First of all, the comparatively solid nature of meat as it enters the stomach slows gastric emptying, providing a nice controlled anti-catabolic stream of amino acids over time (handy at bedtime).

And if we get a bit more speculative, it's interesting to note that cod protein may have special bodybuilding-friendly qualities.(40) Even fishmeal compares very favorably to plant proteins, particularly when livestock are put on anabolic agents.(4, 30) In humans, some researchers have reported superior muscle growth using meat versus lacto-ovo-vegetarian sources.(7)

That would echo the anecdotes from many competitive bodybuilders who swear that tons of meat are the key to massive growth. Of course, the latter findings should be read in light of somewhat contradictory follow-up data and a consideration of which non-animal sources were available.(17) Nonetheless, the quality proteins do add nicely to the very rich combination of other nutrients in beef, chicken, and fish.

B₁₂

Vitamin B₁₂, cyanocobalamin, has long enjoyed interest among athletes beyond its essential role in the body. Thousands of persons swear by its fatigue-fighting effects and its coenzyme has even been sold as an anabolic agent. (Anyone get huge on dibencozide yet?) Now, whether or not you buy into such things, B₁₂ is clearly an essential nutrient as evidenced by those with untreated pernicious anemia.

Sadly, such individuals may have their condition masked to some extent by the folate fortification that's now law, but the nerve degeneration that still develops clearly shows how the body needs B₁₂. And where does a healthy person get this vitamin? You guessed it: meat!

Heme Iron

Yep, I am the one who wrote about the dangers of excess iron in men. They are real. But there are also risks for some of us regarding low iron status as well. So I'll relate a cautionary tail. As someone with a family history of "thick blood" (polycythemia), my own bimonthly blood donations – plus an over-reliance on skim milk, whey and casein and a very high fiber diet – actually left me low in this important nutrient.

Did you know there's an old school term called "milk anemia"? It has to do with factors in dairy that interfere with iron absorption, including calcium. Did you know that hard frequent training and even (otherwise) healthful eating can cause iron problems too? Here are a few quotes:

"In a study of men aged 19 to 29 years, resistance (strength) training was associated with a significant reduction in serum ferritin and other iron indices."(National Cattlemen's Beef Assoc.).

"...whole body iron loss was significantly greater during exercise... than rest... and the average iron loss was significantly greater in males (0.09 mg.m-2.h-1) than females (0.04 mg.m-2.h-1)." (Waller & Haymes, 1996)

"High doses of fish oil concentrates (5 mL/kg/d) reduced serum iron [in rats]". (Rabbani, 2001)

"Coffee and tea are widely consumed as beverages with meals or directly after meals. These beverages have a high content of phenolic compounds and have been shown to strongly inhibit the absorption of nonheme iron. A cup of tea (200 mL) reduces iron absorption by ~75 – 80%. Variations in the results of different studies are probably related to the different amounts of phenolic compounds in the tea resulting from differences in the amounts, brands, and steeping time of teas used. A cup of coffee (150 mL) reduces iron absorption by ~60%." (Hallberg & Hulthen, 2000)

I won't go on. There are certainly other types of interference from whole wheat (e.g. phytates) to high total fiber intake to egg consumption. Many bodybuilders fit – or at least approximate - one or more of these scenarios. Should they be supplementing iron? Almost certainly not.

Most guys don't donate blood (or otherwise profusely bleed) very often and the majority of men have excess rather than inadequate iron status. There are, however, a fair number of athletic men who could sure use the robust boost from meats! Not only do meats provide heme iron that is robust to other dietary influences, but flesh foods also bolster the non-heme iron that constitutes most of one's daily intake. Getting in 8-30 mg of iron per day from meats is not a bad thing. But back to my little story...

Crushing fatigue hit me to the point that I asked an endocrinologist to check my thyroid function. Negative. I thought that I may have chronic fatigue syndrome. Not likely. Then my lab results came back. My transferrin saturation levels were down near 10% (30-40% is normal).

Surely, the blood donations (each draining about 250 mg of iron) were the primary cause, but that's when I noticed I was also living nearly exclusively on whey-casein powders and bars. The clear benefits of these proteins (anabolism, anti-catabolism, immune bolstering, even sleep quality) are beyond the scope of this article, but my own lack of time left me relying on their convenience - at the expense of iron-rich lean meats.

Fortunately now six months and many pounds of chicken, beef and fish later, my transferrin saturation is normal and my fatigue is vastly reduced. I've learned my lesson that one does not have to be anemic to have performance drops from low-iron status!(12)

Zinc

Not only has zinc obviously been sold with magnesium as anabolic/ hormonal support but this essential mineral is also complexed with carnosine (below) as an increasingly recognized anti-ulcer medication.(25, 24) It also plays a role in wound healing. Whether or not zinc is under-consumed by Americans, as some data suggest, it is essential for health, growth and repair – and we can add it to the nutrient richness of meat.

n-3 Fatty Acids

I've explored the powerful pharmaceutical-like effects of long chain highly-unsaturated fatty acids in many articles, such as Something's Fishy, Practical Fats and others. Suffice it to say that the modern world creates a state of actual deficiency regarding EPA and DHA (fish oil's "active ingredients").

Any nutritionist knows how much more likely benefits are when deficiencies are corrected than when super-physiological doses are attempted. I should point out that linolenic acid may indeed have benefits of its own but it's worth understanding that it can be looked at as weaker than EPA and DHA biologically. Can one seek a vegetarian source of DHA? Yes, from algal residues.(18, 35) But for the most part, score another one for animal flesh.

A quick note on something called astaxanthin: Crustaceans accumulate it and salmon is pink because of it. (Yes, some gets added to salmon artificially, too.) It's not an exclusively zoological nutrient by any means – quite the opposite – but its presence in marine critters gives me a chance to bring it up. It's worth a Google or Wikipedia search for you at any rate.

Chock full of astaxanthin!

This carotenoid has some powerful quenching abilities against singlet molecular oxygen and it even has anti-carcinogenic and anti-inflammatory qualities. It's been reported to have anti-hypertensive and neuro-protective activity as well. No references for now – just take a look for yourself. Can you say future "Biotest Antioxidant Formula"?

Creatine

Okay, this non-essential nutrient has been beaten to death in the bodybuilding world but suffice it to say that meat is where we get it in the diet. It's true that it would take roughly 10 pounds of uncooked steak to approach a typical "loading" dose, but I have another little story for you.

Back in grad school, when creatine was red hot, we undertook an investigation at a nearby hospital using magnetic resonance spectroscopy (think MRI but not for imaging). We loaded creatine and spent what seemed like hours in a claustrophobic MR chamber, flexing our calf muscles repeatedly against a rigged pedal apparatus.

The data were solid and suggested reduced fatigue. But perhaps the real lesson came upon our return to the medical center a month later. Three of the eight or so subjects' gastrocnemius muscles remained almost fully creatine loaded – after no maintenance dosing. I was one of these creatine retainer-types as it turned out in post-analysis discussions. These discussions suggested something interesting: all three "retainers" were big time meat eaters. Since that time I've rolled my eyes a bit every time I read supplement company propaganda surrounding repeat creatine loads every couple of weeks. And the take home story relative to this article? Yep – meat is (again) good.

Carnosine

I'm guessing this is the "functional food" aspect of meat you've been waiting for. And I have a little story behind this one, too. You see, for a time I had phone conversations with Tim Patterson and TC about potential vitamin and antioxidant products. They may not even recall it now but during those informal chats, I felt I had to bring up carnosine.

I felt this way because of the almost unbelievable research commentary I'd seen on the substance. Most Testosterone readers realize how non-sensationalistic and reticent I tend to be regarding dietary supplements, but carnosine was not going away. The literature had been growing steadily since I first heard about this compound in early 90s lab chats with my old mentor, Peter Lemon. I'll just offer about a dozen quotes from the horses' mouths so you see that I'm not embellishing:

"It is suggested that carnivorous diets contain a potential anti-glycating agent, carnosine (beta-alanyl-histidine), whilst vegetarians may lack intake of the dipeptide." (Hipkiss, 2005)

"In this study, we report on the antioxidant activity of carnosine on muscle lipid and protein stability from both in vitro and in vivo experiments." [rats] (Nagasawa, 2001)

"Its effect is apparent on physical and behavioral parameters and on average life span." [mice] (Boldyrev, 1999)

"The data presented suggest that carnosine is a perspective immunomodulating tool which has many applications in medicine." (Boldyrev, 1992)

"These results indicate that dietary carnosine is absorbed into human plasma after the consumption of beef. Since carnosine has several potential health benefits, evidence of its bioavailability suggests that it could be a bioactive food component." (Park, 2005)

"Should we eat carnosine-containing food (i.e. meat) when drinking alcoholic beverages, given carnosine's ability to inhibit acet-aldehyde-mediated damage? (Hipkiss, 1998)

"Carnosine (beta-alanyl-L-histidine) is found exclusively in animal tissues. Carnosine has the potential to suppress many of the biochemical changes (e.g., protein oxidation, glycation, AGE formation, and cross-linking) that accompany aging and associated pathologies." (Hipkiss, 2006)

"Carnosine is a potential dietary antioxidant because it is absorbed into plasma intact." (Decker, 2001)

"We were greatly inspired by the pioneering work... The naturally occurring dipeptide carnosine (beta-alanyl-L-histidine) has been found to exert an anti-senescence effect when used as a dietary supplement. The polypotent effects of carnosine which are described throughout this journal and the wider literature make it an ideal candidate as a so-called "geroprotector" – an agent which may delay or prevent some conditions intrinsic with old age." (Gallant, 2000)

"In 1975 the author regarded L-carnosine as a natural chemical mediator in the promotion of spontaneous healing." (Nagai, 1980)

"Zinc complex of L-carnosine... L-CAZ was approved as an anti-ulcer drug of membrane protection type. L-CAZ can remain in stomach juice without rapid dissociation and adhere to ulcerous lesion specifically, after which L-carnosine and zinc are released to heal the ulcer. L-CAZ exhibited high efficacy in clinical use without any serious side effect." (Matsukura & Tanaka, 2000)

Interesting stuff, don't you think – particularly considering the ongoing investigation over just how much carnosinase – the enzyme that breaks down carnosine – actually prevents its dietary usefulness. Perhaps other substances in meat, like proteins, protect carnosine and/or improve its uptake and/or enhance its metabolism.

Evidence in mice does suggest it (11) and similar issues surround meat-derived iron, as we've discussed, even in humans. But now I'm speculating. In any case when I read almost excited statements like those above, from usually cool objective researchers, I have to wonder.

Plus, there's that study by Chez, et al. using 800mg oral carnosine dosages over eight weeks to improve autistic children's' behavior and communication abilities.(9) For a clinical improvement, something must have reached their blood and tissues. Perhaps there's a population-specific phenomena among autistic kids or perhaps the effectiveness was related to the co-administered vitamin E and zinc.

But there's more meaty information to be had: new data confirming rising serum concentrations of carnosine, peaking at about 2.5 hours after beef ingestion in healthy persons.(31, 32) Those data really pique my interest in meat as a usable carnosine source. If indeed the investigations on oral availability continue to be promising, we're really onto something as carnivores.

Suggestions for future therapeutic benefits extend to diabetes and atherosclerosis, both diseases that exhibit carbonyl-mediated degenerative overload.(2) It's even being suggested now that meat (and carnosine) intake may be positively, not negatively, related to longevity!(5, 19, 20, 37)

It's worth pointing out that beef contains only about half the concentration of carnosine as it does creatine (3). But according to references I have, beef has about double the carnosine of chicken, depending on whether it's white or dark meat (white vs. red fibers).(3, 8) Further, chicken breast extracts can raise blood levels of anserine but apparently not of carnosine.(38) Since this latter study suggested better buffering capacity in exercisers nonetheless, we're back to looking at meat as a beneficial whole, rather than looking at just one compound therein.

Okay, let's remain grounded. Doing some simple math suggests that if it takes 10 pounds of uncooked beef to get a creatine loading dose (~20g daily), it would take a ridiculous 20 pounds of beef to consume an equivalent amount of carnosine.

Of course, these numbers are just for comparison. Unfortunately, the long term carnosine (histidine dipeptides) dose from meat that "makes a difference" is by no means fully understood. Even if we were to somehow hope that beef-derived carnosine is as effective as beta-alanine on a milligram-for-milligram basis (not likely), a little more math suggests it would still take 4-6 pounds of beef to approximate a 4-6 gram daily dose of beta-alanine.

And that's before catalytic enzymes get a hold of it. What I'm saying is that we're not going to be obtaining a large supplemental dose of carnosine through regular dietary means. Rather, this "functional food" aspect of meat is more supportive of existing supplementation or perhaps just helpful in an antioxidant, anti-glycation, anti-carbonyl or longevity sense.

In The End

The intent of this article isn't to suggest that whole foods always rival the power of supplements like creatine monohydrate or beta-alanine. But I do know many persons who are fascinated with the pharmaceutical aspects of well-chosen foods and how they might aid physique progress or health. Meats have a rightful place among the more often touted plant foods.

Perhaps, as has been suggested with creatine, a reasonable intake of meat might prolong or enhance the supplemental effects of beta-alanine. Or the animal flesh might provide a key missing nutrient in your diet; there certainly are many to be found therein. Or maybe it'll help with satiety when you really need it some evening. For those who might have experienced similar biological/ dietary/ behavioral issues as I have - regarding times of plentiful versus scarce meat intake - hopefully this article will shed some light.

Now where's that bottle of fajita marinade...

References and Further Reading:

1. Abe, H. Human urinary excretion of L-histidine-related compounds after ingestion of several meats and fish muscle. Int J Biochem. 1993 Sep;25(9):1245-9.

2. Aldini, G., et al. Carnosine and related dipeptides as quenchers of reactive carbonyl species: from structural studies to therapeutic perspectives. Biofactors. 2005;24(1-4):77-87.

3. Belitz, H. and Grosch, W. Food Chemistry. 2^nd Ed. 1999. pp 38-39, 527-580. Springer-Verlag: Berlin, Germany.

4. Beermann, D. H., D. E. Hogue, V. K. Fishell, R. H. Dalrymple, and C. A. Ricks. 1986a. Effects of crimaterol and fishmeal on performance carcass characteristics and skeletal muscle growth in lambs. J. Anim. Sci.62:370.

5. Boldyrev, A., et al. Carnosine, the Protective, Anti-aging Peptide. Bioscience Reports, Vol. 19, No. 6, 1999.

6. Boldyrev, A. Carnosine: biological role and prospects for use in medicine. Biokhimiia 1992 Sep;57(9):1302-10.

7. Campbell, W., et al. Effects of an omnivorous diet compared with a lactoovovegetarian diet on resistance-training induced changes in body composition and skeletal muscle in older men. Am. J. Clin. Nutr. 70: 1032 -1039; 1999.

8. Chan, K. and Decker, E. Endogenous skeletal muscle antioxidants. Crit Rev Food Sci Nutr. 1994;34(4):403-26.

9. Chez, M., et al. Double-blind, placebo-controlled study of L-carnosine supplementation in children with autistic spectrum disorders. J Child Neurol. 2002 Nov;17(11):833-7.

10. Decker, E., et al. Inhibition of low-density lipoprotein oxidation by carnosine histidine. J Agric Food Chem. 2001 Jan;49(1):511-6.

11. Ferraris, R., et al. Dietary regulation of intestinal transport of the dipeptide carnosine. Am J Physiol. 1988 Aug;255(2 Pt 1):G143-50.

12. Friedmann, B., et al. Effects of iron repletion on blood volume and performance capacity in young athletes. Med Sci Sports Exerc. 2001 May;33(5):741-6.

13. Gallant, S., et al. Carnosine as a Potential Anti-senescence Drug. Biochemistry (Mosc). 2000 Jul;65(7):866-8.

14. Gardner, M., et al. Intestinal absorption of the intact peptide carnosine in man, and comparison with intestinal permeability to lactulose. J Physiol 1991 Aug;439:411-22.

15. Hallberg, L., and Hulthen, L. Prediction of dietary iron absorption: an algorithm for calculating absorption and bioavailability of dietary iron. Am J Clin Nutr. 2000 May;71(5):1147-60.

16. Harris, R., et al. The absorption of orally supplied beta-alanine and its effect on muscle carnosine synthesis in human vastus lateralis. Amino Acids. 2006 May;30(3):279-89. Epub 2006 Mar 24.

17. Haub, et al. Effect of protein source on resistive-training-induced changes in body composition and muscle size in older men. Am J Clin Nutr76(3): 511; 2002.

18. Herber, S. and VanElswyk, M. Dietary marine algae promotes efficient deposition of n-3 fatty acids for the production of enriched shell eggs. Poult Sci. 1996 Dec;75(12):1501-7.

19. Hipkiss, A. Would carnosine or a carnivorous diet help suppress aging and associated pathologies? Ann N Y Acad Sci. 2006 May;1067:369-74.

20. Hipkiss, A. Glycation, ageing and carnosine: are carnivorous diets beneficial? Mech Ageing Dev. 2005 Oct;126(10):1034-9.

21. Hipkiss, A. Carnosine, a protective, anti-ageing peptide? The International Journal of Biochemistry & Cell Biology 30 (1998) 863±868.

22. Jackson, M., et al. Purification and properties of human serum carnosinase. Clin Chim Acta. 1991 Feb 15;196(2-3):193-205.

23. MacFarlane, N., et al. Synergism of histidyl dipeptides as antioxidants. J Mol Cell Cardiol 1991 Nov;23(11):1205-7.

24. Mahmood, A., et al. Zinc carnosine, a health food supplement that stabilises small bowel integrity and stimulates gut repair processes. Gut. 2006 Jun 15; [Epub ahead of print]

25. Matsukura, T. and Tanaka, H. Applicability of Zinc Complex of L-Carnosine for Medical Use. Biochemistry (Mosc). 2000 Jul;65(7):817-23.

26. Mori, H., et al. Chemoprevention by naturally occurring and synthetic agents in oral, liver, and large bowel carcinogenesis. J Cell Biochem Suppl. 1997;27:35-41.

27. Nagai, K. The inhibition of inflammation by the promotion of spontaneous healing with L-carnosine (author's transl). Langenbecks Arch Chir. 1980;351(1):39-49.

28. Nagasawa, T., et al. In vitro and in vivo inhibition of muscle lipid and protein oxidation by carnosine. Molecular and Cellular Biochemistry 225: 29 – 34, 2001.

29. National Cattlemen's Beef Association. Dietary beef and exercise. Beef Facts. 1-4.

30. National Research Council. Metabolic Modifiers. National Academy Press. Washington, D.C., 1994. http://newton.nap.edu/openbook/ 0309049970/ html/R1.html.

31. Park, Y., et al. Quantitation of carnosine in humans plasma after dietary consumption of beef. J Agric Food Chem. 2005 Jun 15;53(12):4736-9.

32. Park, Y., et al. Bioavailability of carnosine from beef. Session 30C: Food Chemistry: Proteins. 2002 Annual Meeting and Food Expo; Anaheim, California. http://ift.confex.com/ift/2002/techprogram/paper_11590.htm

33. Rabbani, P., et al. Subchronic toxicity of fish oil concentrates in male and female rats. J Nutr Sci Vitaminol (Tokyo) 2001 Jun;47(3):201-12.

34. Sadikali, F., et al. Carnosinase activity of human gastrointestinal mucosa. Gut. 1975 Aug;16(8):585-9.

35. Sanders, t., et al. Influence of an algal triacylglycerol containing docosahexaenoic acid (22 : 6n-3) and docosapentaenoic acid (22 : 5n-6) on cardiovascular risk factors in healthy men and women. Br J Nutr. 2006 Mar;95(3):525-31.

36. Soucy, J. and LeBlanc, J. Protein meals and postprandial thermogenesis. Physiol Behav. 1999 Jan 1-15;65(4-5):705-9.

37. Stuerenburg, H. and Kunze, K. Concentrations of free carnosine (a putative membrane-protective antioxidant) in human muscle biopsies and rat muscles. Arch Gerontol Geriatr. 1999 Sep;29(2):107-13.

38. Suzuki, Y., et al. Carnosine and anserine ingestion enhances contribution of nonbicarbonate buffering. Med Sci Sports Exerc. 2006 Feb;38(2):334-8.

39. Tallon, M., et al. The carnosine content of vastus lateralis is elevated in resistance-trained bodybuilders. J Strength Cond Res. 2005 Nov;19(4):725-9.

40. Tremblay, F., et al. Dietary Cod Protein Restores Insulin-Induced Activation of Phosphatidylinositol 3-Kinase/Akt and GLUT4 Translocation to the T-Tubules in Skeletal Muscle of High-Fat-Fed Obese Rats. Diabetes 52:29-37, 2003

41. Waller, M. and Haymes, E. The effects of heat and exercise on sweat iron loss. Med Sci Sports Exerc 1996 Feb;28(2):197-203.