Fructose is not a friend of many nutrition minded people these days. With videos by Robert Lustig and dozens of studies on rats, fructose is being cast in a much worse light than its monosaccharide cousin glucose. There are even human studies supporting the idea that eating fructose instead of glucose will give you belly fat, diabetes, high triglycerides, and other health maladies:
However, someone recently pointed something out to me: almost every fructose bashing study used fructose alone, or free fructose. Yet hardly anyone consumes very much free fructose unless they’re using agave syrup. Most fructose we consume comes with glucose, often in the form of sucrose. Well, what if the negative effects of fructose were largely removed when looking at sucrose, or fructose + glucose?
I went asking around for evidence that sucrose was worse for health than glucose or starch or whatever. Nothing. So I went looking for evidence of the health differences myself. Here’s what I turned up:
I found a few studies that suggest sucrose raises triglycerides compared to starch, including these two:
Since sucrose doesn’t increase HDL, this might be bad because it would mean an increased ratio of triglycerides to HDL, which appears to be a marker of heart disease risk:
However, I also found some studies which had slightly different findings than the first two:
In the first study, when starch replaced sucrose in the diet of 5 subjects, triglycerides increased in 3 subjects and decreased in the other 2. Interestingly, the patients with the highest trigs were the ones who saw decreases on the starch diet. In the other three studies, no significant differences in triglcyeride concentrations were seen between sucrose and starch or maltose (which is form of glucose).
So sucrose may increase triglycerides compared to starch, or it may do nothing or even decrease them.
I also found some studies on the effects of glucose and sucrose during exercise:
The first study gave twelve subjects water with sucrose, glucose, or fructose during 115 minutes of exercise on stationary bikes. Sucrose and glucose produced equal effects on things like cortisol levels, cycling speed, perceived exertion, and gastronomical distress. Fructose, meanwhile, performed poorly by comparison.
The second study gave 10-14 year old boys either water, glucose, or a 50-50 mixture of glucose and fructose during exercise (also on stationary bikes). The glucose and glucose-fructose both outperformed the water on things like VO2 and time to exhaustion, with no significant different difference between the two (actually, only the fructose-glucose group had a time to exhaustion that was significantly greater than water).
Finally, the third study is a review article that concluded “No apparent differences exist between glucose, sucrose, or maltodextrins in their ability to improve (exercise) performance. Ingesting fructose during exercise, however, does not improve performance and may cause gastrointestinal distress”.
I also found some studies on sucrose and glucose on glycogen levels:
The first study fed subjects various sugar containing drinks during exercise and found that sucrose and glucose refill muscle glycogen to an equal degree (sucrose filled glycogen more, but it wasn’t statistically significant).
The second study gave soccer players drinks containing glucose, a mixture of 66% glucose and 33% fructose, or a placebo during exercise. No differences were observed between the glucose and glucose-fructose groups, although the glucose-fructose group had greater exercise capacity and higher post workout glycogen levels, the difference wasn’t statistically significant.
Finally, the third study is a review article which concluded “Ingestion of glucose or sucrose results in similar muscle glycogen resynthesis rates”.
So it looks like, at least for exercise, sucrose and glucose appear to be equal.
I found two studies which suggest sugar does not differ from starch for weight loss and weight maintenance when calories are equal:
In the first study, subjects were placed on isocaloric low calorie diets for weight loss. One diet contained 43% of calories as sucrose while the other diet replaced that sugar with starches such as bread and rice. At the end of the diet trial, both groups lost an equal amount of weight (including an equal amount of belly fat loss) and no difference in energy expenditure were found.
In study number two, subjects were given equal calorie diets containing either 10% or 25% sucrose, with the difference being made up largely by starch. An insignificant amount of weight was lost, with no difference between the two groups. Once again, when calories and nutrients are controlled, the effects of sugar and starch on body weight appears to be the same.
Also, energy expenditure has been shown to increase more after consuming sugar than consuming starch:
So sucrose does not appear to have any worse effects on weight than starch during weight loss and weight maintenance when calories are equal.
I found some studies which saw mixed effects of the exchange of sugar and starch:
In the first study, sucrose appeared to cause worse effects on insulin resistance than starch, although I think the effect looks rather small. In the second study sucrose again appeared to worsen insulin resistance as it also apparently increased blood glucose levels (I cant find the full text for this study, so I don’t have the details). Still, the third study found no such effect on blood glucose levels or apparent insulin resistance between sucrose and starch.
So it does appear that sugar may be worse for insulin resistance than starch, but its hard to say how strong of an effect it is.
These were but a few variables I looked, but I was honestly pretty surprised that starch didn’t outperform sucrose more significantly. It does look like starch came out ahead, though not to the degree I would have expected. I’ve come to the conclusion that fructose gets excessively over demonized when an equal or greater amount of glucose comes along with it.
Still, these results should be interpreted cautiously. I’m not saying we should welcome sugar back into our lives with open arms. I still think sugar, being sweet, well generally be more fattening than say a bowl of rice, especially when looking at sugar sweetened beverages (not that this matters if you are weight stable). But real foods like fruit? If I read another person knocking all fruit for being a “bags of fructose” while giving a green light to eating potatoes, I’ll humbly disagree.
In a future post I’ll reflect on why fructose has especially unhealthy effects alone, but not when consumed with glucose.
Addendum: some foods do contain a lot of fructose relative to glucose, including agave syrup, apples, melons, and pears. Given this, I think agave syrup should be eliminated and it may be worth not eating large quantities of the fruits.