D-mannoheptulose in avocado inhibits insulin secretion

[dime]

Avocados contain a specific sugar, D-mannoheptulose [1], which has been shown to inhibit glucose phosphorylation [2], which in turn inhibits insulin secretion and messes up the glucose metabolism.

Basically, they raise blood sugar making you less efficient at using glucose as energy source. They might be good if you're hypoglycemic (there are actually avocado extracts for this purpose, e.g. [3]), but obviously not so good for normal people, and are especially bad if you're hyperglycemic. I'd at least try to reduce sugar intake for some time after eating avocados; probably it would be safest to eat them before sleep. But even this might not be enough, people have reported that the effect lasts for as long as 4 days [4].

1. http://en.wikipedia.org/wiki/Mannoheptulose
2. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1202814/
3. http://www.glycoteam.com/mannoheptulose.htm
4. http://www.medpedia.com/news_analysis/1 ... lood-Sugar

[RRM]

All foods contain substances affecting the metabolism of other substances.
Glucose, for example, inhibits fructose phosphorylation.
(and D-mannoheptulose only inhibits fructose phosphorylation by glucokinase; not the fructose phosphorylation by fructokinase)
Only if you have an increased sensitivity to one of these substances, you may experience an issue / problem.
You seem to be such a person.
This however, does not validate your suggestion that avocado might 'not be so good for normal people'.
'Normal people' usually dont experience what you experience when eating an avocado.
Obviously, your body is not so good in 'working around' D-mannoheptulose.

Everybody is different, because our sensitivities are different.
Its fantastic that you now know about your sensitivity regarding avocadoes.
But your sensitivity is not the general rule; nobody i know experiences what you experience when eating avocadoes.

...D-mannoheptulose [1], which has been shown to inhibit glucose phosphorylation [2]

Yes, it inhibits the conversion of glucose into glucose-6-phosphate, to yield glycogen or pyruvate and energy (ATP).

, which in turn inhibits insulin secretion and messes up the glucose metabolism.

No, D-mannoheptulose directly inhibits insulin secretion.
If D-mannoheptulose only inhibited using the glucose for energy or glycogen, then the blood sugar level would rise,
which in turn would stimulate the secretion of insulin (instead of inhibiting insulin secretion).

[dime]

True, many people eat avocados and obviously not everyone is so affected by this. I guess normally you should be able to handle that rise in blood sugar better. Long-term I feel it will still have some consequences though.
Anyway, it's good to be aware of it, and at least limit consumption of avocados; I know people eating as many as five per day.

[RRM]

Long-term I feel it will still have some consequences though.

You mean for people in general?
The amount of D-mannoheptulose in avocado is very small... and eventually used for energy.
Particularly when compared to all the fatty acids, glucose and fructose that we consume.
Also, the inhibitory effect of D-mannoheptulose on glucose utilisation is not always a sure thing.
When the glucose gets phosphorylated, it may be alpha-D-glucose or beta-D-glucose,
and at low concentrations D-mannoheptulose may actually increase the phosphorylation of alpha-D-glucose. Zang Y et al
or have no effect on glucose metabolism in general at all when the glucose concentration is low. Picton S et al
The observed inhibitory effects of D-mannoheptulose is particularly great at high glucose concentrations.
(due D-glucose and D-mannoheptulose countertransport in pancreatic islet cells) Ramirez R et al
(the uptake of D-mannoheptulose in those cells is enhanced by glucose Malaisse WJ et al, partially because they use the same carrier / transporter (GLUT2) Ramirez R et al,
but also because glucose inhibits the conversion of D-mannoheptulose into energy (catalyzed by glucokinase). Courtois P et al)
So that when not so much glucose is present when one eats avocado, the inhibitory effects of D-mannoheptulose are much smaller, absent or even reversed.
The effects of D-mannoheptulose on glucose metabolism are limited to the pancreatic islets, btw. Scruel O et al

...and at least limit consumption of avocados; I know people eating as many as five per day.

Actually, i think it might normally be a good thing when avocado somewhat inhibits a decrease in blood glucose levels (normally occurring through conversion into glycogen or energy),
because avocado is very satisfying, though containing only 0.4% sugars (in total) and one tends not eat other sugary fruits with it.
So, normally one would need additional sugar to compensate for the lack of sugar in avocado (to keep the blood sugar level up),
but as D-mannoheptulose may somewhat prevent a decrease in the blood glucose level,
more glucose would remain available to be absorbed into the brain, while all the fatty acids in avocado (24%) can be used for energy.

One might conclude that avocado is not a good energy booster (for physical activity or glycogen build up),
but is better suited for consumption while remaining physical inactive (a 'lazy food'), as is egg yolk.
Its no problem to eat 5 avocadoes a day, but dont eat them prior to physical activity or as you want to bulk up on glycogen.