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I recently heard the claim that eating bananas on an empty stomach is bad for you, because of something related to magnesium or potassium levels in your body. A quick search found articles like the following:

Eating bananas on an empty stomach is not good for your health, because when the stomach is empty, there is nearly no food in the stomach that can be digested.

If in this moment one eats bananas, it will speed up the stomach's movement and the promotion of blood circulation, to increase the heart load. It is very easy to induce the myocardial infarction.

Banana is rich in magnesium. Eating banana with an empty stomach will suddenly increase the magnesium in the body and damage the balance between magnesium and calcium in the blood, which may has an inhibiting effect on the cardiovascular and is not conducive to human health.

Are there negative health effects associated with eating bananas on an empty stomach?

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    Neither of those articles have any references. They are not written to the standard that is expected of an answer on Skeptics. The burden of proof rests on those making the extraordinary claim. The second article's claim turns out to be really about eating "too much bananas" (which isn't even grammatical English) not about eating any quantity whatsoever. Of course, you can define "too much" as being exactly that quantity which causes some kind of problem.
    – Kaz
    Commented May 8, 2012 at 23:36
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    Always check the domain registration info behind a website. Just who is lookchem.com? This domain is registered to one xiaobin ying of angzhou WeiKu Information Technology Co., Ltd. somewhere in China. That explains all the bad grammar. peacefmonline.com is evidently Interlink Network Services somewhere in Holland, yet the site is for some radio station in Ghana. The credibility is just oozing out of these two.
    – Kaz
    Commented May 9, 2012 at 0:03
  • Perhaps you could focus on the claim that you to maintain a "balance between magnesium and calcium in the blood" and that eating a banana disrupts that. This question is not answerable because it is very hard to prove a negative about all possible problems that could arise. But that claim is specific enough to be addressed here.
    – Chad
    Commented Jun 20, 2012 at 13:00
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    @Kaz: You are right that the articles are ill-referenced. You are right that they are not to the standard expected of an answer on Skeptics. However, this is a question, and so they don't need to be credible, merely notable. I think finding two sources with the same claim demonstrates that. You are right that the Burden of Proof should lay on the claimant, but the nature of Skeptics.SE means we, by unfortunate necessity, lay that burden in the wrong place - i.e. on the answerer.
    – Oddthinking ♦
    Commented Jun 20, 2012 at 14:44
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    ...does that first quote amount to saying that eating anything when your stomach is empty is bad?
    – Yamikuronue
    Commented Jun 5, 2014 at 13:39

2 Answers 2

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After you start eating, blood is redistributed to the gastro-intestinal tract to increase nutrients absorption. After a meal the blood pressure decreases a little and the heart rate increases. This is more common to the elders [1]. Food volume and caloric load are important determinants of gastric emptying and postprandial splanchnic hyperaemia, which appears to be a major contributor to hypotension [2]. It seems that postprandial changes in blood pressure are due to the nutrient composition of the meal rather than the actual energy load [3].

So, in a patient with ischemic cardiopathy or angina a square meal can trigger an infarction due to the increased oxygen needs of the miocardial muscle (increased heart rate) and hypotension. But this has nothing to do with bananas.

Magnesium absorption is not dependent on the stomach. Most studies suggest that Mg is absorbed predominantly in the distal intestine. At usual Mg intakes, Mg absorption occurs primarily by intercellular diffusional and solvent drag mechanisms. There is evidence for a saturable component of Mg absorption in the small intestine and the descending colon that is important at low dietary Mg intakes [4].

A study made on rats suggest that bananas have protective properties on the gastric mucosa not only because of their phosphatidylcholine and pectin content [5]. But bananas contain dopamine at high levels in both the peel and pulp. Dopamine levels ranged from 80-560 mg per 100 g in peel and 2.5-10 mg in pulp, even in ripened bananas ready to eat. Banana is thus one of the antioxidative foods [6]. Dopamine induces acid secretion via activation of the dopamine D1 receptor, located on the cholinergic neurons and on some nonneuronal cells (study was made on rats) [7]. In this way, a banana on an empty stomach may trigger acute episodes of peptic ulcer over chronic lesions.

References:

  1. Westenend M, Lenders JW, Thien T. The course of blood pressure after a meal: a difference between young and elderly subjects.
  2. Puvi-Rajasingham S, Mathias CJ. Effect of meal size on post-prandial blood pressure and on postural hypotension in primary autonomic failure.
  3. Potter JF, Heseltine D, Hartley G, Matthews J, MacDonald IA, James OF. Effects of meal composition on the postprandial blood pressure, catecholamine and insulin changes in elderly subjects.
  4. Hardwick LL, Jones MR, Brautbar N, Lee DB. Magnesium absorption: mechanisms and the influence of vitamin D, calcium and phosphate.
  5. Dunjić BS, Svensson I, Axelson J, Adlercreutz P, Ar'Rajab A, Larsson K, Bengmark S. Green banana protection of gastric mucosa against experimentally induced injuries in rats. A multicomponent mechanism?
  6. Kanazawa K, Sakakibara H. High content of dopamine, a strong antioxidant, in Cavendish banana.
  7. Tsai LH, Cheng JT. Stimulatory effect of dopamine on acid secretion from the isolated rat stomach.
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    "In this way, a banana on an empty stomach may trigger acute episodes of peptic ulcer over chronic lesions." - I assume nobody has run a clinical study on that... is this a serious concern for healthy people, or is it a "yes, maybe, if all of the stars align just right, it might possibly happen once" kind of thing?
    – Kevin
    Commented Dec 10, 2018 at 2:17
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The Mayo Clinic lists the mEq of potassium in a number of common foods.

Yogurt, low-fat, plain (1 cup) 14

Banana (medium) 12

Potato with skin, baked 22

As you can see, a cup of low fat yoghurt has more potassium than the banana. In comparison, a baked potato looks lethal!

In comparison, potassium used for lethal injection is given as an IV push of 100 mEq. Medscape says that the maximum safe rate normally in use is 20 mEq per hour, though 40 mEq per hour can be given in an emergency.

Anyway, since many foods have more potassium than the banana, and are clearly safe to eat on an empty stomach, the claim is patently false.

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  • Someone sent me a comment to say I didn't have references. Perhaps they might care to look again to see the embedded links.
    – HappySpoon
    Commented Jun 5, 2014 at 0:27
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    I think the potassium limits suggested in Medscape are for IV push only. Oral intake is sort of self-limiting in that it causes diarrhea (medscape.com/viewarticle/771121).
    – Josh Anderson
    Commented Jun 5, 2014 at 20:31
  • Yes, for IV infusion rates. That's why it's in a new paragraph.
    – HappySpoon
    Commented Jun 5, 2014 at 20:57
  • I did see that it was in a new paragraph, but thanks for highlighting that. My point was that it's not an especially useful comparison for oral-intake K. It wasn't a personal attack on your answer, just a clarification, hence it being a comment instead of an answer. Carry on.
    – Josh Anderson
    Commented Jun 7, 2014 at 11:55
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    "and are clearly safe to eat on an empty stomach" - "are clearly" is a pretty anti-skeptical phrase. I'm not disagreeing with the conclusion, but that logic jump is not well-supported by the text. Maybe yoghurt is dangerous in an empty stomach. Do we have evidence that it is not?
    – Ben Barden
    Commented Dec 7, 2018 at 21:47

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