Last night, we ran out of sugar so I suggested to add honey in tea but my cousin said it would have very harmful effect on health and then he showed me these link1, link2 claiming:
While warm water is fine, according to Maharishi Ayurveda, above 42 degrees centigrade, the all-important ‘medicinal’ molecular structure of honey is changed irrevocably, making it indigestible (in a sense…toxic!!!).
Is it true?
Let me start off with my conclusion as a chemist...
I absolutely don't believe that heating honey in hot water would make the liquid indigestible or toxic.
The claim
The webpages cited by the OP, and many others, claim that heating honey in water makes it "unsafe" (I'm lumping indigestible and toxic into one category).
Without any reference to some other more authoritative source it is impossible to track the assertions back to a reputable source. So the story becomes based on reference to a vague and unknown authority.
The OP states: While warm water is fine, according to Maharishi Ayurveda, above 42 degrees centigrade, the all-important ‘medicinal’ molecular structure of honey is changed irrevocably, making it indigestible (in a sense…toxic!!!).
User IMSoP points out that Maharishi Ayurveda is a controversial system of alternative medicine, and the definitions of "medicinal" and "toxic" here are likely to be very different from those used by mainstream science.
General Scientific background
"Detecting" harmful substances
Analytical chemistry has progressed to the point where trace and ulta-trace levels of substances can be detected. For instance it may come as a shock but all the food that you have eaten has been radioactive, and scientists can easily detect that radioactivity. For example in the upper atmosphere nitrogen is converted to a radioactive isotope of hydrogen known as tritium and a radioactive isotope of carbon known as carbon-14. Cyanide can also be detected in some foods and naturally in the human body. So just because some "toxic chemical" can be detected doesn't make the food itself toxic. So ALL foods have some sort of toxic component and we obviously can't stop eating any food.
5% Detection level for a problem in a study.
Let's say that a rat study has found a 5% chance of a problem of some sort -- total body weight, liver weight, lung weight, tail length, rickets, whatever. That is basically like flipping a coin and get 4 heads in a row. Not very likely if you only do one trial of four tosses, but if you do 50 trials (i.e. test for 50 different things) then you are bound to detect some "abnormalities."
Null result in an animal study
The worse result for an animal study is to find no problems at all. Thus all the money (time and effort) spend to do the animal study yielded nothing. Rather think of an animal study as a stress test. The animal testing hopefully uses doses of the chemical which hopefully will cause some problems but not just instantly kill the animal. So out of the thousand ways that the chemical might harm the animal the study will hopefully find the first half-dozen that are the most sensitive to the chemical (i.e. the canary in the coal mine warning). Additional testing can then focus on those metabolic systems or organs. For instance is it the chemical itself that causes the problem or is it some metabolic product of the chemical that causes the problem?
Impossible to prove a chemical is safe
It is impossible to prove that a chemical is safe. The chemical could always be harmful at a level too low for the particular study to detect. So does 1 person in a 100 get cancer or 1 in a 1,000 or 1 in 10,000 and so on. Obviously you don't to use any chemical that causes cancers, but no rat study has ever been done with a million rats. So rather than using a million rats, a few rats are given doses of the chemical high enough to stress the rats used. So it is possible only to test to show that a chemical is unsafe at a particular level.
Number of chemicals tested
The appalling truth is that only a tiny fraction of the chemicals that chemists have identified have been adequately safety tested.
Chemical X
If 100 trace chemicals in honey were tested and not shown to be problematic critics can always point to the mysterious Chemical X which hasn't yet been detected as the culprit. With millions of chemicals identified there is always another one.
Scientific Background of Problem
Honey is about 73% of various sugars and about 17% water according to Wikipedia.
5-(Hydroxymethyl)furfural (HMF) is a chemical that is derived from dehydration of certain sugars. Basically it is formed as one of the chemicals formed early in the caramelization process.
HMF forms due to Time or temperature
HMF isn't found in "new" honey just deposited by bees, but it is formed in honey that has been heated. HMF will also form as a function of time. The general rule of thumb in chemistry that every 10 C (18 F) increase in temperature doubles the reaction rate.
When honey is diluted with water then the reaction rate to form HMF would slow down. So HMF forms fastest in concentrated sugar solutions.
It is recommended, Mayo Clinic for example, that babies less than one year old not be given any honey because of the risk of C. botulinum spores. After a year the human stomach contains enough acid to kill the spores.
Honey is not process at pressuring canning temperatures 115 C (240 F) which would kill the spores because that would significantly caramelize the honey. Think of the "off-taste" of canned milk as compared to fresh milk.
Scientific Evidence for the claim
Annapoorani A, Anilakumar KR, Khanum F, Murthy NA, Bawa AS. Studies on the physicochemical characteristics of heated honey, honey mixed with ghee and their food consumption pattern by rats. Ayu. 2010;31(2):141-146. doi:10.4103/0974-8520.72363.
The Journal is The International Quarterly Journal of Research in Ayurveda.
I have no idea how prestigious this journal is, but I have my doubts.
They did find 5-(Hydroxymethyl)furfural (HMF) but that chemical is found in numerous other food products including baked goods (really high in toasted bread) and roasted coffee beans (Wikipedia).
Their data did not find any harmful effects. (i.e. statistically significant differences)
Only the last sentence of the article throws in the statement "The study revealed that heated honey (>140°C) mixed with ghee produces HMF which may produce deleterious effects and act as a poison in due course." [emphasis mine]
Thus it seems that the assertion of being "harmful" is suddenly made to support the teachings of Ayurveda rather than based on scientific evidence.
The conclusion of the study also notes that "The study has shown that heating of honey reduces the specific gravity with a subsequent raise in ash value..." The rise in ash value makes no sense chemically. To ash a sample you heat it to a red hot heat to burn off any organic material. Ash is mineral reside. The key point here is not really to challenge the study but to point out that if you test for 50 things at a 5% confidence level then you're bound to get some false positive results.
There is evidence that bees are killed by HMF. For instance a study by Zirbes et al. and Krainer et al. Also a study of high-fructose corn syrup (HFCS) as a sucrose replacement for honey bees by LeBlanc et al.
I didn't go to far down this rabbit hole. Note though that 500 mg/kg and 500 ppm (parts per million) are 0.05% of the food weight. Also note the bee larva were only fed with HMF containing food.
There was at least one rat study that found HMF harmful.
Scientific Evidence against the claim
Magic temperature of 42 Celsius claimed by Ayurveda.
There is absolutely nothing magic about the temperature of 42 C. Yes water freezes at 0 C and boils at 100 C. But there is a valid chemical reason why those numbers are special. Any reaction in honey that takes place at 42 C will take place at 41 C only the reaction will be about 7% slower. So a magic temperature of 42 C is nonsense chemically.
There is no scientific study which shows that HMF is harmful to humans as supported by a 2011 study by Abraham et al.
A Section of the Wikipedia named "As an Unwanted Component" (with scientific references) notes that HMF is found in numerous foods. The point is that detection in honey isn't that unusual chemically.
HMF has been considered as a drug to treat sickle cells in humans.
Honey has been analyzed for HMF to indicate "quality" of honey, but not that HMF makes honey toxic.
Chemical reactions happen slowly at low temperatures and more quickly at high temperatures. So high HMF levels could indicate that the honey has been stored too long (3 years say), or that it has been stored at too high a temperature (140 F warehouse).
HMF was also used to check for adulterated honey. Thus honey extended with sugar syrup could be detected.
Anecdotal Evidence against the claim
There is no scientific study that I could find which claims that heating honey in water makes the liquid toxic to humans. The temperature and time profile won't create "significant" levels of HMF.
People have been adding honey to tea for centuries. If tea drinkers had noticed a problem it would seem that some scientist would have studied the tea/honey problem. Why are there no such tea/honey studies?
The recipe for making baklava includes a step where you add sugar and honey to water and boil it. You then soak the baked pastry in the liquid. Baklava eaters aren't complaining either.
Beemaid honey is pasteurized to 160 F (71 C) to kill yeast which might ferment the honey.
What company would want its honey to ferment on the shelf? So I strongly suspect this is more common than most grocery store bands want to admit. For instance Barkman (Buzy Bee Brand) only admits that their honey is "gently warmed."
There are numerous recipes in which honey is baked.
For examples: A Honey Bun, Honey Wheat Rolls, Honey Candied Bacon, Honey Puff Pancakes and Mexican Honey Flan.
In winter my store bought honey will sometimes crystallize. I microwave it to warm it up. I am still alive writing this ...
Conclusion
I certainly would not advocate changing your diet to include 10% HMF. But at low levels (really trace levels...) it has not been shown to be harmful.
Please note that if you do believe that trace amounts of HMF are harmful then adjust your WHOLE diet accordingly. This means that any food product with natural or added sugars which has been heated should be excluded. So no coffee (the beans have sugar and are roasted), no baked goods, no jellies, no maple syrup, no commercial applesauce, etc etc etc.
As a chemist I'm amazed how the general public thinks all "chemicals," or any "chemical treatment" is toxic. All the food we eat is chemical in nature. Don't let the mention of the word chemical give you the hives [bee pun intended ;-) ]. To a chemist a strawberry is not "a" chemical but a bag full of thousands of chemicals.
