Fructose vs. glucose? What is worse when it comes to accumulating body fat and reducing our insulin sensitivity? Today we review a study that attempts to answer this question.
Many of you have probably seen the pro-high fructose corn syrup ads (if not, here is a link to one on YouTube).
They drive me crazy — partially because they are incredibly cheesy, but also because they try to comfort you by telling you that high fructose corn syrup is no worse for you than sugar.
Up until now which is worse was unclear. One study says high fructose corn syrup is worse, while another finds no difference. But are we asking the right question? Should “which is worse” be the question?
While people worry about which is worse the real problem is how much sugar you eat. The average American diet in 2000 was 15.8% sugar (by calories). That’s average — meaning that there are a lot of people who are eating more than that.
That’s what I don’t understand. We know that excessive sugar is bad for you regardless of what kind, but that hasn’t stopped people from eating/drinking a lot of it. The real issue, then, is sugar consumption.
The study I’m reviewing this week compares how bad glucose is compared to fructose, but if you forget about the differences you find out how bad it is to eat a lot (25% of your diet) as sugar.
This week’s study wants to answer a few questions about sugars:
- Does eating fructose cause more weight gain than glucose? Is where the weight is gained different between the two sugars?
- Does eating fructose cause dyslipidemia (negative changes in blood lipids) compared to glucose?
- Does eating fructose decrease glucose tolerance and insulin sensitivity?
Stanhope KL, et al. Consuming fructose-sweetened, not glucose sweetened, beverages increase visceral adiposity and lipids and decreases insulin sensitivity in overweight/obese humans. J Clin Invest 2009 Apr [Epub ahead of print]
Overweight/obese participants were randomly put into either a “glucose” or “fructose” group. For two weeks the participants’ body composition, blood pressure, calories consumed/day, blood measures (lipids, insulin and glucose) and rates of lipogenesis (fat production) were all measured.
|Age (years)||54± 3||56± 2||52± 4||53± 2|
|Weight (kg)||88.4± 2.9||84.0± 4.5||89.3± 2.9||81.9± 4.2|
|BMI (kg/m2)||29.3± 1.1||29.4± 1.3||28.4± 0.7||30.3± 1.0|
|98.9± 2.6||91.0± 4.0||97.3± 3.3||91.8± 4.4|
|Body fat (%)||29.4±1.1||43.2±1.5||28.5±1.3||39.6±2.2|
There was no statistical difference in measures between groups – very important!
Pass the Kool-Aid
After 2 weeks of being poked and prodded the participants got to go home and drink Kool-Aid. Yes, Kool-Aid! Okay, not only Kool-Aid, they ate their normal diet plus Kool-Aid three times a day.
The Kool-Aid had either glucose (in the glucose group) or fructose (in the fructose group) as a sweetener. The Kool-Aid was made up to be 25% of each participant’s baseline calories.
So if a participant was normally eating 2000 calories a day then they would be drinking 500 calories of Kool-Aid on top of the 2000 calories. This went on for 10 weeks — Kool-Aid three times a day. Hopefully they got different flavours.
I think this study is good — fantastic in fact, but I’m a bit surprised that it passed an ethics board (the regulatory people who let you do experiments on people or animals.)
Why? Because these people are already overweight/obese and then they were put on a diet that is 25% higher than what they were eating when they got fat — for 10 weeks.
And the researchers know there will be increased fat, decreased insulin sensitivity and increased blood lipid levels — they just want to know which sugar (glucose or fructose) is worse.
Doesn’t seem like a good idea. My best guess is that it was allowed because for the last two weeks of the Kool-Aid intervention the participants stayed in the hospital for monitoring and testing.
Eating 25% more calories in sugar than you normally eat for 10 weeks leads to weight gain — surprise! What I’m surprised by is how little body weight they gained: 1.55 kg (3.9 lb) in the glucose group and 1.20 kg (2.63 lb) in the fructose group.
Total fat only increased by 1.0 kg and 0.8 kg in the glucose and fructose group, respectively.
Both groups had an increase in abdominal fat, but total abdominal fat and visceral fat went up more in the fructose group (8.6% total and 14% visceral). Eating a lot of either sugar meant packing on the pounds.
The next thing researchers measured was blood lipids: triglycerides and cholesterol. Turns out that fructose increased average triglycerides over 24 hours more than glucose — but both increased triglycerides.
Fasting cholesterol also went up in both groups, but more in the fructose group. Fasting LDL (low density lipids) went up in both groups — again more in the fructose group — but HDL went down in the glucose group while HDL went up in the fructose group.
Insulin sensitivity and glucose tolerance didn’t change in the glucose group but went down in the fructose group; fasting glucose and insulin blood insulin levels went up in the fructose group.
There are two ways of looking at this study:
- I should stay away from fructose it’s bad for me… wait a sec, doesn’t fruit have fructose?
- Or, eating a lot of any sugar isn’t good for me and I should avoid eating all simple sugars in excess.
I would argue the second way of looking at the study should be what you take away from this study. Eating a lot of sugar is going to lead to health problems sooner or later.
The dirty little secret in science is that if you find no difference between groups in your study you’re not getting it published. And if it’s already been published it’s nearly impossible to publish with the same results.
You need something new and exciting. So you have to look for differences, especially significant ones. Are there differences between eating a lot of glucose or a lot of fructose? Yes. Was the study designed to figure out if and what kind of differences there are? Yes.
So you can read this study and think, “I’ll avoid all fructose and eat glucose — that way I won’t have problems with cholesterol, insulin sensitivity, and visceral fat!”
Then you’ll be in deep doo doo fairly quickly, because the reality is there is more of a difference between no sugar than glucose vs fructose.
How much fruit would you have to eat for it to be “bad” for you?
Before you stop eating fruit altogether, or run off to start a religious cult to save people from the hidden evil in fruits, let’s put things in context.
First, in this study 25% of the caloric intake (total calories consumed) was from fructose. So if you eat 2000 calories a day you would need to be eating 500 calories from fructose; if you eat 4000 calories that’s 1000 calories from fructose.
That’s a lot of fructose. I wouldn’t recommend eating that many calories from simple sugars anyway.
Second, if you look at how much actual fruit you need to eat to get to 500 or 1000 calories of fructose you’ll see how little you need to fear if you eat fruit in moderation. Take a look at the table to get an idea of how much fructose is in various foods.
Most fruit has less fructose than glucose, with a few exceptions. According to the USDA database  foods with more fructose than glucose include:
|Food||Fructose g/100g (cals)||Glucose g/100 (cals)|
|Sucrose||50 (200)||50 (200)|
|Apples||5.9 (23.6)||2.4 (9.6)|
|Pears||6.2 (24.8)||2.8 (11.2)|
|Fruit juice||5-7 (20-28)||2-3 (8-12)|
|Raisins||29.8 (119.2)||27.8 (111.2)|
|Honey||40.9 (163.6)||35.7 (142.8)|
|High fructose corn
|55-90 (220-360)||45-10 (180-40)|
Let’s translate what 500 and 1000 calories of fructose looks like in real life:
|Food||How much you need to eat to get to 500 calories of fructose
(25% of 2000 calorie diet)
|How much you need to eat to get to 1000 calories of fructose
(25% of a 4000 calorie diet)
|Sucrose||250 g (42 teaspoons)||500 g (84 teaspoons)|
|Apples||Over 20||Over 40|
|Pears||Over 20||Over 40|
|Fruit juice||Nearly 9 cups of apple juice||17 cups of apple juice|
|Raisins||420 g (0.93 pounds)||840 g (1.86 pounds)|
|Honey||Over 305 g (over 14 teaspoons)||Over 610 g (over 28 teaspoons)|
|High fructose corn
|139-227 g (23-28 teaspoons)||278-454 g (46-76 teaspoons)|
As far as fruit goes you would have to eat a lot — over 20 apples or pears to get to the level of fructose that they have in this study. Why did I pick apples and pears? They have the highest fructose content of fruit.
Berries, citrus fruit and stone fruit (peaches, plums, etc.) have less fructose, which means you would have to eat even more of those!
Even if we look at soda pop that has 39 g (9 teaspoons) of high fructose corn syrup in a 355 mL can — half of which is fructose (19.5g) — you’d have to drink 6.4 cans (2.27 litres) of soda to reach 25% of your caloric intake (assuming 2000 calories is your total intake).
Granted it is possible to drink over 2 litres of soda pop; during exams, I’ve seen people go through 10 cans in a day and vibrate as they studied. Though I’ve yet to see anybody eat 20 apples in a day… gee, I don’t think I’ve ever seen anybody eat 20 in a week (about 3/day).
To sum up, fructose does increase intra-abdominal fat gain, decrease insulin sensitivity and increase cholesterol in overweight and obese people more than glucose — but glucose still increases fat and increases cholesterol.
Should you flee from fruit? No, just don’t eat an excessive amount.
Should you stay away from processed sugars and soda pop? Yes, this shouldn’t exactly be a revelation to anybody.
Is fructose worse for you than glucose? Yes, slightly, but both are bad.
If you follow PN should you count grams of fructose? No, if you follow PN with 90% compliance then you’ll be okay. Though I’m assuming that you’re not hooked up to an IV with soda pop for 10% of your meals.
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