In comparison to the other sciences, it’s only relatively recently that nutrition has gained some of the prominence it holds today. It’s a field of study that finds itself maturing and I believe the future will see many more people recognizing just how important a healthy diet is. We are, however, far from having one consensus on what exactly constitutes a “healthy diet”. Things can seem divisive among people to say the least, with plenty of disagreement, misinformation, and the occasional ridiculous bullshit being spewed onto anyone who’ll believe it. Because of this it can be hard to differentiate a scientifically sound argument from a fallacious concept. There are numerous theories on nutrition out there and it can be tough figuring out which ones are accurate.
One theory that has been around for awhile is the basis for an eating plan known as the alkaline diet. Though variations of this diet exist, they’re all fairly similar and are based on the following concept: our body is naturally alkaline. Because the food we eat has an affect on our body’s pH we should therefore eat a diet that supports an alkaline (rather than acidic) PH. This means eating a majority of alkaline foods (usually fruits, vegetables and some nuts) and generally avoiding acidic foods (usually meats, grains, and sugars). The purpose of all this is due to the idea that an acidic body is prone to certain diseases (everything from osteoporosis to cancer) and an alkaline body is ideal.
That’s the idea anyway.
The alkaline diet isn’t very well known to most people, but it has a fair amount of followers. I’ve encountered it many times and have been curious about its validity, especially since many of the popular sources supporting the alkaline diet have the tendency to make it seem like pseudo-science. This includes, but is certainly not limited to:
- The author makes broad, hyperbolic claims (saying something along the lines of ”If you don’t follow my dietary suggestions and/or buy my book you’re going to die slowly and painfully!”)
- There are very few (if any) accessible scientific studies backing said claims
- The promise of a quick fix to numerous health maladies is made or suggested
Possessing these traits is by no means an indicator of whether or not the suggested diet is based on faulty principles, but it tends to make me suspicious, so I decided to look into the alkaline diet and how scientifically supported it was. Specifically, I wanted to look at 2 important claims central to the diet as well as my take on the scientific literature supporting or opposing such claims.
Claim #1. Acidosis causes notable health problems
It can often be difficult to differentiate health problems caused by acidosis (such as cardiac arrhythmia) from health problems that cause acidosis (such as renal failure). This can easily lead to post hoc arguments regarding the many health problems supposedly caused by acidosis. There do, however, appear to be a few negative health ramifications to acidosis.
One oft cited claim is that acidosis results in calcium being leeched from the bone as the body attempts to neutralize the acid and maintain an alkaline pH. There are some studies which seem to support this claim, though it’s important to note that researchers in the many of these studies gave subjects ammonium chloride, a chemical which is a significant acidifying agent. Honestly, I’m willing to bet most people aren’t sitting down to a dinner sprinkled with ammonium chloride every night (I hear it doesn’t even taste that good), so take these results with a grain of salt (or a grain of ammonium chloride, if you like). Still, this illustrates an important idea: when acidosis occurs, one of the body’s important homeostatic mechanisms for keeping pH within ideal limits involves drawing alkalizing minerals from the bone (calcium included).
Another side effect of acidosis seems to be loss of skeletal muscle. This appears to happen because the body breaks down a constituent of muscle, the amino acid glutamine, to produce bicarbonate (an alkalizing compound) in a process known as ammoniagenesis. This has been demonstrated in NH4Cl and renal failure induced acidosis.
Finally, studies on rats (examples here and here) suggest that acidosis (again induced by ammonium chloride) depresses growth function by altering the way growth promoting hormones GH and IGF-1 function.
There is undeniably a number of serious of serious ailments caused by being dealing with a state of acidosis. Evidence seems to support the idea that acidosis leads to bone loss, muscle loss, and a disruption of growth hormones. There isn’t a lot of evidence to support some of the myriad claims about other (sometimes hard to believe) acidosis related illnesses (e.g. cancer, obesity, etc.), still I would bet a number of unfortunate things happen when the body is dealing with acidosis, as this has been shown to be the case in numerous studies on acidemic cows (which results when feeding cattle grain rather than grass–just a few of these studies can be found here, here, and here).
Still, this only represents one pillar of the alkaline diet and doesn’t tell us everything we need to know. Sure, acidosis appears to be detrimental to health. However, we have to acknowledge that we’re looking at studies on rats, cows, and humans either fed unnatural diets or with kidney damage. This isn’t a very applicable to most people, so we need to figure out what dietary elements cause metabolic acidosis and what elements can reverse or prevent it.
Claim #2. Eating an excess of the (specifically detailed) acid forming foods can cause metabolic acidosis.
Typical proponents of the alkaline diet usually recommend that people partially avoid animal products and/or animal protein, sugar, alcohol, most grains, coffee, and soda. Let’s look at whether these recommendations are valid.
Animal foods: Meat and milk are typically shunned due their proposed acid forming nature. This is supposedly a result of their protein and, more specifically, their higher concentrations of sulfur containing amino acids (cysteine and methionine). Because bone health frequently suffers when metabolic acidosis is experienced, one could look at whether a higher protein diet (specifically from animal products) leads to calcium loss from the bones; this does not appear to happen and, frequently, higher (but not excessively high) animal protein intake actually improves bone health (in part by increasing calcium absorption). Dietary animal protein may have a theoretical, or even slightly plausible role in causing acidosis-induced calcium loss under certain conditions, but it appears that the body is well equipped to handle it and, additionally, such an intake is beneficial in most of the ways it has been presented as dangerous.
Sugar: Refined sugar, table sugar, high-fructose corn syrup, high sugar fruits, etc. These are all frequently cited as acid forming foods by the “experts” on the alkaline diet. Fructose, one of the three main “simple sugars” is found in large number of foods (notably sucrose, but also in fruit and honey) and it does appear to increase uric acid in the body, so there may be a shred of truth to that claim. Still, when looking at glucose, the other half of of sucrose, there seems to very little evidence to suggest it directly causes acidosis. Indirectly, it could be a result of glucose’s effect on insulin, but I find this unlikely. Another theory is that sugar (especially when consumed chronically or in excess) stimulates the sympathetic nervous system into an overactive state, which may lower pH through alterations in Na(+)K(+)-ATPase activity. This seems most plausible, but I’m really just speculating.
Alcohol: Excessive alcohol does appear to increase acidosis through multiple methods. Alcohol increases uric acid and lactic acid in the blood, both of which contribute to acid build up. It also acts as a diuretic, potentially leading to dehydration and inhibiting acid excretion.
Grains: As with sugar, the idea that grains are acidic due to carbohydrate content or their effect on insulin is unlikely. There isn’t a lot of evidence showing how acidifying grains are, except when compared to other foods. One study demonstrated that cereal grains are more acidifying than fruits and vegetables, another study showed rice produced acidity more than potato. The effect of grains on producing sympathetic nervous system overactivity, though less convincing than when applied to refined sugar, is plausible (especially with refined grains). Still, the case for grains being acid forming is theoretical but not heavily studied. Once again the alkaline diet becomes hard to evaluate due to a lack of scientific studies evaluating its theories.
Soda: I think the idea that soda is acidifying claim is valid. Many sodas, such as Coke and Pepsi, contain phosphoric acid. Phosphoric acid is a strong acid that may have a potential correlation with bone loss (one of the possible results of acidosis). Caffeine, a frequent component of soda and coffee, seems to influence acidosis through an increase of lactic acid, mostly during exercise. Caffeine, in addition to being a diuretic, may also cause metabolic acidosis through that mechanism as well. Whatever the action, caffeine appears to be mildly acidifying (which could explain why coffee is frequently cited as acid forming food). Carbonation of beverages alone does not appear to be acid forming.
A Simpler Explanation.
We can go down the row carefully examining whether foods are acidic in the body, but I think we’re missing the point; the evidence seems to support a simple explanation for which foods are acid forming or alkaline forming, a big picture which is ultimately the main factor explaining how food affects our body’s PH. This definitely involves food (as well as how we respond to food), but I think the typical alkaline diet gurus oversimplify this (at best).
One of the foremost investigators into the acid/base forming nature of dietary compounds is Anthony Sebastian, a professor of medicine at the University of California, San Francisco. Dr. Sebastian has published dozens of academic papers on the subject and his explanation for the acid forming nature of foods is along these lines: diets in which precursors of alkalizing bicarbonate (HCO3-) is proportionally scarcer than acidifying hydrogen ions (H+) produces metabolic acidosis. The emphasis is placed on bicarbonate deficiency being more commonly the cause (over hydrogen ions being in excess). Finally, potassium and sodium chloride (table salt) play a part, with potassium helping prevent acidosis and sodium chloride potentially causing it.
One of these academic papers is a fascinating article (alright, I find it fascinating; our tastes may differ) entitled “Adverse Effects of Sodium Chloride on Bone in the Aging Human Population Resulting from Habitual Consumption of Typical American Diet”–quite the doozy of a title, but it gets the point across. The paper cites 43 pieces of scientific literature on the subject and explains that the typical American diet is adept at producing net metabolic acidosis. The reasons they include as causes of this include a deficient fruit and vegetable intake, an excessive salt intake, and an increase in cereal grain intake. An interesting aspect of this paper was the underlying contrast between the typical acid forming American diet and the human ancestral diet, low in grains and salt and high in fruits and vegetables. For visualization purposes, they included this helpful flow chart:
They gathered a lot of evidence to come to their conclusions and the anti-salt and pro-fruit/vegetable view seems best supported. What I’ll sum up about the alkaline diet is that some of the science behind it stands up to scrutiny, some does not. Basically, evidence suggests that bone loss, muscle loss, and growth problems can occur during or in compensating for acidosis. As for the dietary recommendations, what seems most supported is expressed in the above chart: don’t eat too much salt, eat your damn fruits and vegetables, eat less cereal grains, and finally I’ll add that the “meat=acid=bone loss” link is inconclusive and overblown. Finally, I’ll add that dairy seems to falls into a sort of gray area as it appears to be acid forming yet may contain vital nutrients which could negate the negative effects.