*This is a guest post from Jonathan Carp, MD, drcarp.com.
Across the internet, there are lots of posts about how we need to be careful about fruit “because of the fructose.” I wanted to discuss why fruit is an essential part of your diet and understand the fructose hysteria.
We have a capability of tasting sweet from birth, where we taste the lactose in milk. That -ose at the end of lactose means that it is a sugar. Sceintists measure sweetness based on sucrose (table sugar) as the standard. So on a scale from 1-100 with 100 representing sucrose, lactose measures 15-40 and fructose from fruit measures 130-180(1). Naturally then, we perceive fructose as sweeter.
In processed food, the addition of sugars obviously makes food more palatable, but it also enhances the stability and shelf life of the product due to increased osmotic pressure. (Incidentally - this is reason honey has been used to treat wounds, the high osmotic pressure will not allow bacteria to grow).
Industrial food makes another kind of sweetener called HFCS (high fructose corn syrup) because it is cheaper. Corn syrup which is a combination of maltose and other sugars is converted into HFCS by changing some of the glucose into fructose. There is HFCS-55 and HFCS-42, the number representing how much fructose is in the formula.
Interestingly, this makes it not too different chemically from table sugar which is 50% fructose. I stress that only CHEMICALLY it is not that different.
Does our body see HFCS different than table sugar (sucrose)?
A study shows that in rats HFCS leads to decreased survival and reproduction (4). This is not a human study, but it should point us in the direction of caution. It should be noted that some people think that the worldwide collapse of honey bees could also be related to feeding bees HFCS (6). Generation after generation of scientists have made the error in making assumptions on how the body will react to something because they think they know how it “should" react.
It seems logical to assume that since they are chemically-related, the body should react the same, except that we are still learning how the body truly functions. The body still holds many mysteries from us. This, of course, does not make table sugar much healthier. It is as deadly as ever, I am just making the distinction that the body does see them as different. They are both terrible for you.
Fructose in the body
When a large amount of fructose is eaten, it goes to the liver and the excess carbon found in the fructose gets converted into triglycerides, which is a main source of fats in the body. Lets repeat that so you are clear, sugar (in this case fructose) gets converted into fat in the liver This feature of fructose metabolism is responsible for fructose having a low glycemic value meaning that it does not elevate blood sugar that much when eaten. The glycemic index of fructose is 19 whereas the glycemic index of table sugar is 65.
When these facts are taken by itself, it may it seem beneficial but that would be ignoring what we know about triglycerides. Elevated levels of trigyclerides are associated with metabolic syndrome and heart disease (3) and could be the subject of a whole blog. So what does this mean for your diet and whether you can eat fruit or not?
What about fruits?
Fruits contain various percentages of sugars like fructose, sucrose, and glucose. In fruit, the percentage of fructose among these sugars is 45-70%(2) We know from studies showing liver toxicity of fructose(5) and high blood pressure associated with fructose in diabetes (6) that fructose from fruit is not implicated, only added industrial fructose.
It gets even more interesting when you look at studies comparing what happens to blood sugar when you compare fruit juice with sugar water. It appears that even without the fiber of the fruit - there are polyphenols in fruits that regulate the uptake of sugar so that the blood sugar spike in fruit juice is quite different from water with a similar amount of sugar(8).
In fact, there are other studies that show that added fruit to white bread BLUNTS the sugar response even though you just added all that extra fruit sugar (10). I'm not recommending white bread and fruit here. I'm just demonstrating that the whole fruit is amazing.
Now this is not to say we should go out and start drinking fruit juice without a second thought because for most people it is just too many calories without the feedback of feeling full. Also, the study mentioned above was with black current and lingonberries, which have a lot more antioxidants than say apple juice, which has been studied and is a really no better than sugar water (10).
If you choose to drink a cup of fruit juice, make sure it is one made of a fruit with a huge amount of polyphenols. Pomegranate and Grape have high levels. So, it appears that fructose in fruit has little if any negative effect on the human body as the fiber and the antioxidants and polyphenols provide protection.
The caveat here is if we are eating processed food with added sugars instead of eating fruit, we have to worry about weight gain and other metabolic problems. The answer as always comes down to eating real food. Don’t eat fake food. Fruit is most certainly a real food.
What can we use to sweeten if we want to?
Well, in the last 10 years we have some alternative sweeteners that have come out.
Agave Syrup - Can have up to 85% Fructose without that many polyphenols. Now you know why that can’t be good.
Stevia - Has no fructose and is from a leaf and appears to be fine, but is also sweeter than sugar, which can impair your ability to appreciate natural sweetness.(12)
Lakanto - A combination of monk fruit extract and erythritol, which are both natural, matches the sweetness of sugar, which will likely prevent it from damaging your palate to appreciate natural sweetness. It also does not affect blood sugar. You can find it here. It's what I use if I want to sweeten my tea.
I didn’t discuss artificial sweeteners because quite frankly they are all bad in my opinion.
Do you have questions and insights to share? Please let me know in the comments section below.
(1)Modern Nutrition in Health and Disease — 11th Edition / editors A. Catherine Ross et al. p40
(2)Modern Nutrition in Health and Disease — 11th Edition / editors A. Catherine Ross et al. p49
(3) Lancet : 2010 May 8;375(9726):1634-9. doi: 10.1016/S0140-6736(10)60545-4
(4) Journal of Nutrition : 2015 Mar;145(3):434-41. doi: 10.3945/jn.114.202531. Epub 2014 Dec 10
(5) Proc Natl Acad Sci U S A. 2016 Jan 26;113(4):E488. doi: 10.1073/pnas.1525259113. Epub 2016 Jan 19
(6) Diabetes 2013 Oct;62(10):3307-15. doi: 10.2337/db12-1814.
(7) Journal of Hepatology 2014 Mar;60(3):677-8. doi: 10.1016/j.jhep.2013.10.018. Epub 2013 Oct 26.
(8) Mol Nutr Food Res. 2010 Dec;54(12):1773-80. doi: 10.1002/mnfr.201000019.
(9) Journal of Nutrition 2013 Apr;143(4):430-6. doi: 10.3945/jn.112.169771. Epub 2013 Jan 30.
(10) Godycki-Cwirko M, Krol M, Krol B, Zwolinska A, Kolodziejczyk K, Kasielski M, Padula G, Grebowski J, Kazmierska P, Miatkowski M, Markowski J, Nowak D. Uric acid but not apple polyphenols is responsible for the rise of plasma antioxidant activity after apple juice consumption in healthy subjects. J Am Coll Nutr. 2010 Aug;29(4):397-406.
(11)Am J Clin Nutr 2016 103: 50-60;