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I'm not an expert, but as far as I understood a sugar solution is completely neutral since sugar can't take hydrogen ions out of the water or donate them in. Sugar is a non ionic compound, so it does not release H and OH ions in the water so it will not make the solution acidic or alkaline.

I keep on reading and seeing charts of how sugars make your body acidic, like this one:

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What process makes a neutral pH solution into an acidic one? I'm not into chemistry at all and therefore the simpler the answer the better.

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    $\begingroup$ Charts like these are unscientific nonsense, ignore them. $\endgroup$
    – Waylander
    Commented Dec 10, 2018 at 8:19
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    $\begingroup$ @Mr.Web the opposite is proven - these foods (and any other foods) do not acidify the body. Science formed the hypothesis in the 19th century and disprove it in the early 20th century. People keep making these charts, but they are simply wrong. $\endgroup$
    – rumtscho
    Commented Dec 10, 2018 at 12:08
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    $\begingroup$ You've got to love the sheer gumption of putting citrus fruits in a column headed 'Alkaline'... $\endgroup$
    – AakashM
    Commented Dec 10, 2018 at 12:26
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    $\begingroup$ @Mr.Web In general, if you see a chart alleging anything about food without citing at least one scientific study in a journal which, when Googled, doesn't turn up on any predatory journal lists, it's a steaming pile of bullshit. Especially about which foods are "healthy". (That's not always the case, of course -- for example, the charts found in those studies -- but if people are stealing those charts without citation they're plagiarizing and probably leaving out important context.) $\endgroup$
    – anon
    Commented Dec 10, 2018 at 17:48
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    $\begingroup$ Okay everyone, why in the name of the chemistry gods has this been closed and of all reasons why was unclear chosen? The question is crystal clear. As the comments point out, it is based on an outdated, inherently flawed concept but one that was originally considered scientific and it can be answered easily by this site. It should remain open. $\endgroup$
    – Jan
    Commented Dec 12, 2018 at 1:14

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It is not proven that "sugar makes your body acidic"!

Your body's pH is very tightly regulated by the body's internal systems; it is also different in different parts of the body - the stomach is acidic (1.0-2.5), the intestine are mildly basic (jejunem 7-9) terminal ileum 7.5 reference here. Blood pH is 7.35, and any deviation from this is indicative of serious illness.

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    $\begingroup$ It is almost impossible to "make the body" acidic while keeping it alive and functioning. Diets that advertise "acidic" or "alkaline" do little (nothing) to change the body PH. Instead they focus on other properties. ref $\endgroup$
    – Mindwin Remember Monica
    Commented Dec 10, 2018 at 14:54
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    $\begingroup$ It is perfectly true that the "alkaline" foods recommended above will do you little harm, and some good if you replace the "acid forming foods" with them - just not for the reasons advanced. $\endgroup$
    – Waylander
    Commented Dec 10, 2018 at 15:06
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    $\begingroup$ in the end they are just (wrongly used) marketing buzzwords (lies). $\endgroup$
    – Mindwin Remember Monica
    Commented Dec 10, 2018 at 16:06
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    $\begingroup$ @Mindwin While it is correct that there is a lot of quackery around using diet to alter "the body's pH", you will find that your counter is completely false. The existence of a physiological buffer does not mean the pH doesn't change in disease states. It often does. There is an entire chapter in Cecil Medicine on the topic (Ch 120). Yes, alkaline diets are quackery. But no, it's not because your physiologic buffer is inviolable. Various pathophysiologic processes of varying severity can cause disturbances in the buffer system. $\endgroup$
    – De Novo
    Commented Dec 10, 2018 at 19:30
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    $\begingroup$ @Mindwin don't counter quackery with false simplifications. Counter it with facts. Absent some pre-existing disease process, alkaline diets don't substantially change the pH of any body compartment (other than urine), and they aren't shown to be any more effective than any other kind of diet. (vs. "it is almost impossible to make the body acidic while keeping it alive and functioning") $\endgroup$
    – De Novo
    Commented Dec 10, 2018 at 19:34
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One place where sugar does cause acidity is your mouth. The bacteria living in your mouth feed on sugar and excrete lactic acid. It's part of their metabolism. Wikipedia has more details about dietary sugars and acidity in mouth.

It's not clear from the chart what part of the body it refers to, or what it claims the acidity to cause. But it does sound similar to the alkaline diet advice. It was originally related to acid ash hypothesis, which claimed acidic diets to cause osteoporosis. However, scientific research has not found evidence for the hypothesis. There is also a significant difference: the original acid ash hypothesis classified foods based on the pH of the ash left when burned - not the sugar content (all sugar will burn away).

In conclusion, there is no general link between sugar and acidity in body, but in some very specific cases such as caries bacteria in mouth, there is a connection.

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On the point of ‘makes your body acidic’ you already have an answer to which I have nothing to add.

However, you also claim that sugar be completely neutral—at which point I must intervene.

A lot more compounds can act as acids and bases than the shortlist of common acids you probably had in chemistry class. Most things with a lone pair can be a base and practically any $\ce{X-H}$ bond where $\ce{X}$ has a higher electronegativity than hydrogen can be an acid. In $95~\%$ of cases, these compounds are probably still not acidic or basic though.

And then there is the (much smaller, but still vast) class of compounds that can act as acids or bases in standard aquaeous solutions but usually do not. In sugar’s case, it has a lot of $\ce{O-H}$ bonds and a lot of oxygen atoms. All oxygen atoms can be protonated if a strong acid is introduced to the mixture so sugar is a base about as strong as water. On the other hand, the hydrogen of the $\ce{O-H}$ bonds can also depart as a proton if a strong enough base is in solution. This means sugar’s hydroxy groups are also weak acids—again, about as strong as water.

Then there is a final convoluting factor. One of these hydroxy groups in glucose is attached to a carbon that is bound to a second oxygen ($\ce{R-O-CHR'-O-H}$). Here, the electronegative oxygen exercises a negative inductive effect, i.e. draws electron density away from the hydroxy group. Therefore, this one proton is slightly more acidic than all others. It is also ever so slightly more acidic than water so it acidifies the solution ever so slightly.

For all practical intents and purposes, this effect can be fully neglected, however, as it is so minor.

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  • $\begingroup$ Ok so, to keep it easy, pouring pure sugar into a stomach, doesn't it make it more alkaline? Or does it change the ph in any way? $\endgroup$
    – Mr.Web
    Commented Dec 10, 2018 at 18:23
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    $\begingroup$ @Mr.Web: The initial effect will be to dilute your natural stomach acids, making it less acid. But the acidity of the stomach is regulated by the body, producing more acid to digest consumed food. $\endgroup$
    – MSalters
    Commented Dec 10, 2018 at 20:08
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    $\begingroup$ @MSalters and, as the stomach produces more acid, the blood becomes more alkaline for a period of time (an effect known as the alkaline tide). There is no "keeping it easy" when it comes to acid base physiology. $\endgroup$
    – De Novo
    Commented Dec 10, 2018 at 21:27
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    $\begingroup$ @Mr.Web All of my answer should be titled ‘what happens in water’. As for the body itself, I refer to Waylander’s answer (as in my first paragraph): the pH range of all parts of the body is tightly regulated. While adding anything will briefly disrupt the stable state, counter-processes immediately kick in and re-regulate the pH to where it should be. $\endgroup$
    – Jan
    Commented Dec 12, 2018 at 1:09

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