Eat to Improve Magnesium Absorption
As we talked about in the last article, food provides less and less magnesium. So, you don’t want to add insult to injury by further decreasing either digestion or absorption because of poor digestive health or less than optimal dietary choices. Let’s explore some parameters that modulate magnesium bioavailability, so you have the tools to decide how to eat to improve magnesium absorption and retention.
Digestive Health and Magnesium Bioavailibility
No matter which route you go, be it the paracellular or transcellular way, you want your magnesium to be:
- Soluble (i.e hydrated form)
- Unbound (i.e free form)
Improve Magnesium Absorption with Optimal HCl Production
The first step in the process is to separate magnesium from whichever compound it is bound to. Magnesium can be bound to inorganic compounds such as phosphate or oxide, or it can be bound to an organic compound such a chlorophyll.
Most of the time, your stomach acid does a great job of dissociating magnesium molecules from their tag-along friends. But there is a caveat, HCl production must be adequate.
Low HCl means incomplete dissociation of magnesium salts or chlorophyll, and – in English – it means that you are left with non absorbable magnesium.
Even if magnesium is not absorbed in the stomach, this is the preparatory phase for absorption, and since acidity is at its max in the stomach this is the only place it can happen to a significant degree. In other words without adequate stomach acidity, your magnesium will only be hitching a ride through your digestive tract and will be eliminated in the feces.
Improve Magnesium Absorption with Optimal Bile Production
Once the magnesium passes the stomach and enters the intestines, absorption per se begins. At this stage the pH is no longer very acidic. The acidic pH of the stomach contents gradually gets more alkaline as the bolus moves in the small intestine. So, if magnesium was not dissociated from its companion molecule this is not going to happen in the intestines.
To further complicate things, other food particles are present in the intestines, notably fatty acids. These guys, if unchecked, due to say, bile insufficiency, can represent a major obstacle for magnesium absorption. When found in excess, unabsorbed fatty acids will be forming insoluble soaps with magnesium and will end up, again, straight down the GI tract, into the feces.
There are some subtleties to this process, and depending on fat properties, solubility will vary. So, medium chain triglycerides have been found to be more soluble than long chain triglycerides, and unsaturated fats are more soluble than saturated fats. 
But there’s more!
The digestive “soup” – usually known as “chyme” – presents other challenges to magnesium absorption. These road-blocks appear in the form of other food components that compete with, or hinder magnesium absorption.
Learn How Phytates and Oxalates Can Lower Magnesium Bioavailability
Phytates and oxalates are the best known “foes” to magnesium bioavailability. These compounds have the vexing tendency to form insoluble complexes with magnesium. This prevents absorption, since only free, small, and soluble molecules can pass the enterocytes’ pores, channels, or tight junctions. 
Let’s focus on phytates first, since they are the worst offenders anyway.
We know phytates as anti-nutrients. But as far as plants are concerned, phytates are a reservoir of phosphate. In fact, plants store phosphorus as phytic acid – also known as inositol hexaphosphate, or IP6. These IP6 molecules are energy rich – due to the phosphate bounds, and are quite similar to ATP. Basically, plants need phytates to fuel their growth. This explains why phytates are mostly found in seeds and nuts (the energy and nutrient supply of growing plants.) Phytates are most concentrated in the outer layer of whole grains and beans. Phytates have recently been demonized, and to be fair, they do pose plenty of issues! Yet, they can also be beneficial, but that’s for another story!
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Phytates are known as anti-nutrients, and it is true, that phytates bind to nutrients and minerals thereby reducing their bioavailability. . But recent studies have shown that phytates also exhibit some potential health benefits. . Phytates can act as anti-oxidants. How so? Binding minerals is not always a bad thing! Doing so can prevent free radicals formation. (As we have seen in a previous post.) . Likewise phytates can bind heavy metals and thereby prevent their absorption in the body. . Phytates also seem to have cardio-protective effects. Their consumption tends to lower triglycerides and increase HDL. . Phytates have an anti-hyperglycemic effect. Plus, they appear to regulate insulin secretion at the level of the beta-cells of the pancreas. . Phytates also tend to increase natural killer cells activity and inhibit tumor growth which give them a protective role in cancer. . So, as everything in nature, phytates are not ALL bad, and may indeed have some beneficial effects under certain circumstances. . The take-away being that, no you should not actively try to consume more phytates! For instance don’t forego whole grains in favor of processed carbs in order to avoid phytates, but don’t seek them out either. . Also, remember that small "irritants" can have a mithridatization effect. The poison is in the dose. . What you should rather become aware of is that focusing on the minutia can be misleading. As a rule, consuming a VARIETY of whole foods will boost your health. . References : Omoruyi FO, Budiaman A, Eng Y, Olumese FE, Hoesel JL, Ejilemele A, et al. The Potential Benefits and Adverse Effects of Phytic Acid Supplement in Streptozotocin-Induced Diabetic Rats. Adv Pharmacol Sci 2013;2013:1–7. doi:10.1155/2013/172494. Greiner, R., Konietzny U. JKD. Phytate – an undesirable constituent of plant- based foods? J Für Ernährungsmedizin 2006;8:18–28. Kumar V, Sinha AK, Makkar HPS, Becker K. Dietary roles of phytate and phytase in human nutrition: A review. Food Chem 2010;120:945–59. doi:10.1016/j.foodchem.2009.11.052. Lee S-H, Park H-J, Chun H-K, Cho S-Y, Cho S-M, Lillehoj HS. Dietary phytic acid lowers the blood glucose level in diabetic KK mice. Nutr R
For today, what matters is how phytates bind minerals in the gut before they get to be absorbed. At a physiological pH of about 6 (as in the intestines) insoluble Mg-phytate or protein-Mg-phytate complexes are formed.  This happens because phytates are negatively charged and therefore can form complex cations at all pH conditions in the gastrointestinal tract. They have a special affinity with divalent cations – hello magnesium! 
Luckily, most phytates (37-66%) are degraded in the stomach and small intestines by enzymatic activity (phytase.) Bacterial activity can further degrade phytates, but in humans, that degradation is minimal. So, once again, in excess, phytates can cause issues. [1,2]
How do you reduce or manage the phytate load of your meals?
A few interventions can go a long way to mitigate the adversarial effects. You can soak, sprout, ferment, and cook the phytate rich plant foods. You can also make sure to add vitamin C-rich foods to meals that are high in phytates. And, of course, make sure that you produce adequate amounts of HCl in the first place. If not, then supplement your HCl.
Now, Let’s turn to Oxalates
Oxalates are universally present in plants, especially the leafy green variety. Such as spinach and brassicas (cabbage, broccoli, and brussels sprouts.)
Oxalates can be classified in 3 groups:
The soluble oxalates are the ones which are of interest to us since physiological pH soluble oxalates become oxalic acids. Oxalic acids are natural chelating agents that have a high affinity with cations. [1,2] So, they can readily form complexes with magnesium. These complexes are poorly absorbable and therefore impede magnesium absorption.
In a cross-over study with healthy humans, magnesium absorption from a meal with an oxalate rich vegetable (spinach), was compared to a test meal with a vegetable low in oxalate (kale.) The authors found that absorption from the OA-rich spinach meal was significantly lower compared to the kale meal [1.] A slight caveat here: some oxalate foods are also very high in magnesium, which can make it a zero-sum game.
At any rate, it is quite easy to reduce the oxalate load from foods. Soaking vegetables and nuts can reduce their soluble oxalates. For instance raw spinach vs cooked spinach will impact magnesium absorption differently. Also younger plants are rich in oxalic acid in an easily absorbable form. You can also think about rotating foods so as not have a lot of them at once. Some example of oxalates rich foods: spinach, beets, nuts, wheat bran, berries, and soy.
Other Food Components
So far we have seen that some food components can interfere or compete with magnesium absorption. But what about the other minerals that are found in food? Can these compete with magnesium?
Supra-physiological Doses of Other Minerals can be Detrimental
You may remember from part 1 that magnesium is a macro mineral. So, it would make no sense for trace minerals to pose any obstacle to magnesium absorption. Yet, you would expect problems to emerge when micro minerals are supplied in supra-physiological doses- and they do!
So, for instance, the intake of 142 mg zinc/d (as zinc sulfate) decreased apparent magnesium absorption and balance in humans significantly. This might hint that both minerals rely on a common transport mechanism. Actually, SLC41A1 and SLC41A2 have been characterized in frog cells and were found to transport a variety of divalent ions through the cell plasma membrane, such as zinc and magnesium. Also TRPM6 is known to regulate uptake of magnesium as well as calcium and probably of zinc, cobalt, and molybdenum. 
But what about the other macro-minerals? Research is still indecisive on the subject but an early experiment by De and Basu found that adding calcium, magnesium, phosphorus, iron, copper, or manganese (as salts) in excess to ones diet was detrimental to the absorption of the other minerals. 
We know that phosphorus can form Mg3(PO4)2 complexes which are not absorbed. And while magnesium helps calcium uptake, excess calcium will decrease magnesium absorption. This is part of a much more complex discussion on the relationship between calcium, magnesium, and vitamin D. There is an intricate relationship between magnesium, calcium and vitamin D.
- Vitamin D in the form of calcitriol may enhance magnesium absorption.
- Supplementing with vitamin D improves serum levels of magnesium, especially in obese individuals.
- Magnesium is a cofactor for the biosynthesis, transport, and activation of vitamin D.
- Supplementing with magnesium improves vitamin D levels. 
Magnesium homeostasis is linked to parathyroid function. Parathyroid hormones improve magnesium absorption. Clinically, magnesium deficiency often coincides with low blood calcium. This situation, if left unchecked, may ultimately result in parathyroid hormone deregulation as well as a suboptimal vitamin D response. 
This could be very accurately described as the calcium/magnesium/vitamin D clusterfuck! Tread carefully and be sure to back up your interventions with reliable tests, it would be easy to mistake magnesium, calcium and vitamin D deficiency for parathyroid gland issues.
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Whether you get your vitamin D from the endogenous or exogenous route it undergoes two hydroxylations in order to be activated. . Step 1 takes place in the liver. The molecule produced is called calcidiol. . Step 2 happens in the kidneys. The end-product molecule is calcitriol, which is the active molecule.
Fiber are in a Grey Zone when it comes to Magnesium Absorption
Hopefully, this is beginning to become very apparent, plant based foods have a bounty of magnesium, but, this begs the question: What about fibers? Soluble, insoluble, fermentable, non fermentable and the in-betweens?
When it comes to fibers, fermentability is the key parameter that will determine whether fibers increase or decrease magnesium absorption. Other considerations are their solubility and phytic acid content. Bear this in mind since it can throw uncertainties on some research papers. [1,2]
Non Fermentable Fibers
Non fermentable fibers generally decrease magnesium absorption. However, there are some uncertainties and confounding factors. Foods rich in dietary fiber are usually also rich in magnesium and phytates. Overall, it seems that insoluble and non fermentable fibers are able to bind free magnesium in the small intestine at a higher pH and hence may reduce magnesium absorption. [1,2]
Fermentable fibers, fructose, and oligosaccharides on the other hand, can increase absorption. It has been found that fructo-oligosaccharides can increase magnesium absorption by 10-25%. [1,2] Science hasn’t elucidated the reason with certainty but one hypothesis is that the bacteria that digest these fibers produce short chain carboxylic acids such as acetate, propionate, butyrate, and lactate. These substances lower the pH, and consequently improve magnesium solubility and absorption in the intestines. The increase remains small between ~3-10% depending on studies. [1,2]
It is highly doubtful that our readers need any other incentive to pay attention to protein intake, but, here is one! Protein enhances magnesium absorption.
One hypothesis being that phosphopeptides “protect” free magnesium from binding to calcium and phosphate in the intestines. [1,2] See, one funny thing about biochemistry is that some seemingly bad things can turn out to play to our advantage. Here, phosphopeptides form “weak” bonds with free magnesium thereby protecting magnesium molecules from forming stronger bonds with calcium and/or phosphate. The weak links can be broken in the intestines whereas the stronger calcium-phosphates-magnesium complexes cannot. This will ultimately increase the solubility and absorbability of magnesium.
It has been found that a dietary intake of 145-200g protein/day as compared to the same diet containing 45-70g protein/day during 14-day periods increased magnesium absorption significantly from 32% to 40%. Even a slight difference in protein intake can swing the pendulum. For instance, a study reported higher magnesium absorption in subjects consuming 30g as compared to 20g of protein/day and 48g as compared to 34g of protein/day during 30-day periods. The difference was 46.1% versus 28.3% and 57.7% versus 42.4%. [1,2]
So, ultimately, your best bet in managing magnesium bioavailability is to maintain a balanced diet that is rich in vegetables and proteins. Also, food rotation remains an extremely valuable daily practice. Of course, a healthy digestive system will help ensure that you enjoy the benefits from these foods!
And, test, never guess! Don’t blindly follow dietary or supplement recommendations without assessing your current status.
In health, the Strength Sensei Legacy Team.
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 Dietary Factors Influencing Magnesium Absorption in Humans, by Torsten Bohn
 Intestinal Absorption and Factors Influencing Bioavailability of Magnesium-An Update, by Jan Philipp Schuchardt and Andreas Hahn
 Invited review: Mineral absorption mechanisms, mineral interactions that affect acid–base and antioxidant status, and diet considerations to improve mineral status, by Jesse P. Goff
 SNPed Lecture on magnesium, https://snppros.com/product-category/library/