Honey, Apples and Advanced Glycation Endproducts
Jacob Schor ND, FABNO
January 18, 2013
The current issue of Cooks Illustrated suggests that dipping raw apples or potatoes in a dilute solution of honey will prevent them from browning for a good 8 hours. They suggest 2 Tablespoons of honey diluted in 1 cup of water and soaking the apple slices in it for about half a minute. They tell us that the honey deactivates polyphenol oxidase, an enzyme that promotes browning.
For those of you who know little about polyphenol oxidase and are curious about it, Helga George provides a decent detailed summary online at: http://suite101.com/article/polyphenol-oxidase-causes-browning-of-fruits-and-vegetable-a243450.
Let me give you the simple summary. Polyphenol oxidases (PPO) are a family of enzymes found in plants, molds, bacteria and animals. They catalyze the chemical reactions that cause the browning of foods, what we commonly call Maillard reactions. The chemicals created in these reactions go on to react with other proteins creating a black pigment called melanin. PPO activity is responsible for the development of dark coloring in coffee, chocolate and tea.
Jan Oszmianski from Cornell University was probably the first to report that honey could prevent these Maillard reactions in a paper published in 1990. This was a nifty discovery as until then sulfur dioxide was the standard treatment to prevent foods from browning, not quite ideal as it often triggered undesirable reactions in consumers. The ability of honey to inhibit browning varies depending on the floral source. According to a 2000 report by Chen et al, soybean honey is the most effective form. 
This whole business is interesting and also peculiar in a larger context. Enzymatic browning is an example of glycosylation. A very similar chemical process in which similar reactions occur, but without the aid of an enzyme, is called glycation. The browning of bread during baking is a good example of glycation or what is also called non-enzymatic glycosylation. In this example, high oven temperatures drive the reaction rather than an enzyme. These glycation products are responsible for the color and taste we appreciate in many sugar and starch containing cooked foods. The differences in flavor between a French fries and boiled potatoes are due to the glycation products formed by the high cooking temperatures in the fryer.
When these reactions occur in food they are called exogenous glycation reactions because occur outside the body. Glycation also occurs in vivo, within the body. These internal reactions are more likely to occur when blood sugar levels or oxidative stress levels are high. Over the course of several weeks the early glycation products undergo a series of chemical reaction to become irreversibly crosslinked protein derivatives referred to as advanced glycation endproducts (AGEs).
These AGEs are incredibly stable and our bodies cannot readily break them down or excrete them. AGEs that form or collect in the body are now implicated with causing many of the complications of diabetes and with the deleterious changes associated with aging. In particular, accumulation of AGEs contributes to plaque formation, basement membrane thickening, and loss of vascular elasticity leading to cardiovascular disease.
These AGEs trigger oxidative stress, inflammatory reactions and thrombosis, and vascular damage. Reduction of AGEs is now considered a goal to maintain good health.
Dr Alan Gaby explained this elegantly years ago to me when he pointed out that what we commonly call ‘age spots’ were simply accumulations of AGEs. AGEs is quite the appropriate acronym.
One sugar in particular triggers glycation more than others both in foods and internally, and that sugar is fructose. Dr Gaby and others have pointed this out and expressed concern that the high fructose levels in the modern diet may lead to greater rates of glycation and greater production of AGEs, that is faster aging. Some researchers go so far as to express concern that higher fruit consumption in vegetarians and their higher intake of fructose will lead to increased AGEs in their bodies.
With this ‘fear of fructose’ in mind, it is interesting to consider the Cooks Illustrated and earlier Cornell University information that honey prevents browning reactions in foods. One would think honey, since it is high in fructose, would increase AGEs when eaten. It doesn’t appear to. A 2010 trial reported in the British Journal of Nutrition described a clinical trial in which participants ate 20 grams of honey a day. No change in AGEs were found as a result.
In fact rather than aging the skin and causing brown spots, honey may do the opposite. On a recent one of my ‘hunting and gathering’ trips to Costco, I spotted a product called “Egyptian Magic” an all-purpose skin cream. The ingredients got my attention as they seem to be nearly the same recipe of honey, beeswax, olive oil and propolis that we have mentioned over the years when we quote the research of Noori Al-Waili PhD. The Egyptian Magic skin cream, according to their company website is made by “ Lord-Pharaoh ImHotep-AmonRa,” This does not sound like the same fellow. Their website descriptions sound like the Lord-Pharaoh may be related to the late Dr. Bronner, the soap maker.
Honey often seems to do things inside humans that are unexpected and defy our predictions.
For example, a study published earlier this month tells us that giving honey to type 1 diabetics leads to significant improvements in their health. Type 1 diabetics were fed honey for about three months, a dose of 0.5 mL/kg body weight of honey each day. How much is that? That would be about 5 teaspoons per day for someone weighing 100 pounds, more obviously for heavier people. Doing this resulted in significant decreases in fasting blood sugar, total cholesterol, triglycerides and low-density lipoprotein along with all sorts of other positive improvements that are somewhat esoteric and which I won’t bore you with here. Though this seems almost bizarre, it should not come as a total surprise. Earlier animal studies suggested that we should have expected this reaction in humans.
While accumulation of those advanced glycation endproducts has been linked to increasing risk of CVD etc, feeding honey to rats normalizes their high blood pressure.
My readers may expect me to now explain why honey can have such effects as these but I’m not going to. That’s because I’m not sure that anyone really knows. Let’s just leave it at this, honey stops apples and potatoes from turning brown, and perhaps may do something similar inside people, though we don’t really know how.
Cooks Illustrated, January 2013, page
Oszmianski J, Lee CY. Inhibition of polyphenol oxidase activity and browning by honey
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