Alkaline diets have blown up in popularity. The theory is that over a long time, eating more foods that act acidic in the body (not necessarily having to be acidic in its food form outside the body) will lead to a leaching of calcium from the bones to neutralize blood pH. Some foods claimed to acidify the blood are simple starches, sodas (rich in phosphoric acid) and animal products (higher in cysteine/methionine, sulphuric amino acid).
The blood sits at a pH of 7.34-7.45 - this is very tightly regulated, because too high or too low a pH can alter the rates of enzymatic reactions, protein structures, etc. You wouldn't make it too long if your pH dropped out of this homeostatic range.
This all sounds fine and dandy right? More acid-acting foods, more calcium removed from bone to neutralize this. I've said this before - there isn't always a simplistic logic that allows you to infer anything about health.I've always been very apprehensive to accept this theory, because pH balance is is so tightly regulated by the kidneys (regulates reabsorption/excretion of minerals) and the Lungs (exhaling CO2). pH homeostasis is dependent on the interactions of calcium, phosphorus, magnesium, and potassium and whether they are reabsorbed in the renal tubes - not a whole lot to do with bone really. I never really sat and thought this through to try and have a retort for anyone who makes alkaline diet claims but the simplistic viewpoint of blood pH decreases (more acidic) and then calcium is released from the bone to neutralize this would have never made a whole lot of sense if you've ever taken a micronutrient metabolism course, or if you have kidneys.
I stumbled onto a good review article in the British Journal of Nutrition - I highly recommend reading it for specific details on why this theory is just a theory, not fact. http://www.ncbi.nlm.nih.gov/pubmed/23551968
To sum up the article, your body does a great job at keeping minerals/amino acids/glucose in the blood at a homeostatic levels. Intake of specific nutrients don't affect the extracellular levels of ions such as Calcium/potassium/sodium/phosphate, etc. Your body responds to high and low calcium largely by causing renal excretion/reabsorption. In individuals with normal renal function, there is no evidence to show that other organs (bone) are being utilized to maintain blood pH. Even from administering ammonium chloride into the serum of renal insufficient individuals, bone has been shown to be not responsible for maintaining low levels of serum bicarbonates - if it were, the authors calculate that it would only take 3.6 years for these individuals to lose all of their skeleton. Obviously, they are not, and individuals are living longer than 3.6 years. Lastly, and probably most importantly for anyone considering buying 'alkalinizing' foods, this review cites a 2yr randomized placebo-controlled trial in postmenopausal women where potassium citrate was administered and ended showing no persistent effects on biochemical markers of bone remodeling. There was no reduction in the loss of areal bone mineral density at the end of the 2 years.
People will often use this idea that alkaline diets are better for a number of reasons - usually hating on processed starches, or on animal products. The claim is often made by alkaline dieters that the reason we have the highest dairy content and highest osteoporosis rates is due to the fact that our blood is so acidic. I'd like to take this chance to point out that the idea that dairy causes calcium loss is a bit ludicrous - having interacted with the vegan community for a while, i've heard the 'fact' that dairy takes 2 calcium ions to metabolize for every 1 that it provides. This is positively ludicrous - not only do I have no idea where that is coming from, and no one can seem to point to where those 2 calcium ions are lost at, we would see osteoporosis much earlier in life than ages 60+ - hell, according to that theory, babies who are formula fed with Cow's Milk Formula since birth would never mineralize their bones because they'd constantly have a net loss. If you want to understand osteoporosis a bit more, look at physical activity levels during development(1), strength-bearing exercise throughout the life cycle(2), magnesium(3), vit C(4), K(5), D(6) and antioxidant (7,8) intakes, as well as our still, on average, suboptimal calcium intake. There is more to bone health than just calcium - and the idea that calcium and vitamin D are all you need for bone health might be a part of the problem. This is also confounded by the very little nutrition education MDs (the primary healthcare providers) get in medical school, and the fact that the Dairy Council provides a lot of the information on bone health, but Dairy doesn't have a lot of magnesium + vitamin C/K - why would they promote it? We don't have a Brassica Council (family of dark leafy greens with most bioavailable calcium + vit C, K, magnesium, manganese) that lobbies and shows the benefits that other vitamins/minerals outside of milk have for bone health.
In short, this theory would workout if we didn't have kidneys. but we do. so there's that....
1. http://www.ncbi.nlm.nih.gov/pubmed/19528896
2. http://www.ncbi.nlm.nih.gov/pubmed/10326991
3. http://www.ncbi.nlm.nih.gov/pubmed/16274367
4. http://www.ncbi.nlm.nih.gov/pubmed/11149477
5. http://www.ncbi.nlm.nih.gov/pubmed/12540415
6. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3221132/
7. http://www.ncbi.nlm.nih.gov/pubmed/11860726
8. http://www.ncbi.nlm.nih.gov/pubmed/23588435
The blood sits at a pH of 7.34-7.45 - this is very tightly regulated, because too high or too low a pH can alter the rates of enzymatic reactions, protein structures, etc. You wouldn't make it too long if your pH dropped out of this homeostatic range.
This all sounds fine and dandy right? More acid-acting foods, more calcium removed from bone to neutralize this. I've said this before - there isn't always a simplistic logic that allows you to infer anything about health.I've always been very apprehensive to accept this theory, because pH balance is is so tightly regulated by the kidneys (regulates reabsorption/excretion of minerals) and the Lungs (exhaling CO2). pH homeostasis is dependent on the interactions of calcium, phosphorus, magnesium, and potassium and whether they are reabsorbed in the renal tubes - not a whole lot to do with bone really. I never really sat and thought this through to try and have a retort for anyone who makes alkaline diet claims but the simplistic viewpoint of blood pH decreases (more acidic) and then calcium is released from the bone to neutralize this would have never made a whole lot of sense if you've ever taken a micronutrient metabolism course, or if you have kidneys.
I stumbled onto a good review article in the British Journal of Nutrition - I highly recommend reading it for specific details on why this theory is just a theory, not fact. http://www.ncbi.nlm.nih.gov/pubmed/23551968
To sum up the article, your body does a great job at keeping minerals/amino acids/glucose in the blood at a homeostatic levels. Intake of specific nutrients don't affect the extracellular levels of ions such as Calcium/potassium/sodium/phosphate, etc. Your body responds to high and low calcium largely by causing renal excretion/reabsorption. In individuals with normal renal function, there is no evidence to show that other organs (bone) are being utilized to maintain blood pH. Even from administering ammonium chloride into the serum of renal insufficient individuals, bone has been shown to be not responsible for maintaining low levels of serum bicarbonates - if it were, the authors calculate that it would only take 3.6 years for these individuals to lose all of their skeleton. Obviously, they are not, and individuals are living longer than 3.6 years. Lastly, and probably most importantly for anyone considering buying 'alkalinizing' foods, this review cites a 2yr randomized placebo-controlled trial in postmenopausal women where potassium citrate was administered and ended showing no persistent effects on biochemical markers of bone remodeling. There was no reduction in the loss of areal bone mineral density at the end of the 2 years.
People will often use this idea that alkaline diets are better for a number of reasons - usually hating on processed starches, or on animal products. The claim is often made by alkaline dieters that the reason we have the highest dairy content and highest osteoporosis rates is due to the fact that our blood is so acidic. I'd like to take this chance to point out that the idea that dairy causes calcium loss is a bit ludicrous - having interacted with the vegan community for a while, i've heard the 'fact' that dairy takes 2 calcium ions to metabolize for every 1 that it provides. This is positively ludicrous - not only do I have no idea where that is coming from, and no one can seem to point to where those 2 calcium ions are lost at, we would see osteoporosis much earlier in life than ages 60+ - hell, according to that theory, babies who are formula fed with Cow's Milk Formula since birth would never mineralize their bones because they'd constantly have a net loss. If you want to understand osteoporosis a bit more, look at physical activity levels during development(1), strength-bearing exercise throughout the life cycle(2), magnesium(3), vit C(4), K(5), D(6) and antioxidant (7,8) intakes, as well as our still, on average, suboptimal calcium intake. There is more to bone health than just calcium - and the idea that calcium and vitamin D are all you need for bone health might be a part of the problem. This is also confounded by the very little nutrition education MDs (the primary healthcare providers) get in medical school, and the fact that the Dairy Council provides a lot of the information on bone health, but Dairy doesn't have a lot of magnesium + vitamin C/K - why would they promote it? We don't have a Brassica Council (family of dark leafy greens with most bioavailable calcium + vit C, K, magnesium, manganese) that lobbies and shows the benefits that other vitamins/minerals outside of milk have for bone health.
In short, this theory would workout if we didn't have kidneys. but we do. so there's that....
1. http://www.ncbi.nlm.nih.gov/pubmed/19528896
2. http://www.ncbi.nlm.nih.gov/pubmed/10326991
3. http://www.ncbi.nlm.nih.gov/pubmed/16274367
4. http://www.ncbi.nlm.nih.gov/pubmed/11149477
5. http://www.ncbi.nlm.nih.gov/pubmed/12540415
6. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3221132/
7. http://www.ncbi.nlm.nih.gov/pubmed/11860726
8. http://www.ncbi.nlm.nih.gov/pubmed/23588435
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