The Effect of Two Energy-Restricted Diets, a Low-Fructose Diet vs. a Moderate Natural Fructose Diet – Research Review

Madero M et. al. The effect of two energy-restricted diets, a low-fructose diet versus a moderate natural fructose diet, on weight loss and metabolic syndrome parameters: a randomized controlled trial. Metabolism. 2011 May 27. [Epub ahead of print]

One of the proposed causes of obesity and metabolic syndrome is the excessive intake of products containing added sugars, in particular, fructose. Although the ability of excessive intake of fructose to induce metabolic syndrome is mounting, to date, no study has addressed whether a diet specifically lowering fructose but not total carbohydrates can reduce features of metabolic syndrome. A total of 131 patients were randomized to compare the short-term effects of 2 energy-restricted diets-a low-fructose diet vs a moderate natural fructose diet-on weight loss and metabolic syndrome parameters. Patients were randomized to receive 1500, 1800, or 2000 cal diets according to sex, age, and height. Because natural fructose might be differently absorbed compared with fructose from added sugars, we randomized obese subjects to either a low-fructose diet (<20 g/d) or a moderate-fructose diet with natural fruit supplements (50-70 g/d) and compared the effects of both diets on the primary outcome of weight loss in a 6-week follow-up period. Blood pressure, lipid profile, serum glucose, insulin resistance, uric acid, soluble intercellular adhesion molecule-1, and quality of life scores were included as secondary outcomes. One hundred two (78%) of the 131 participants were women, mean age was 38.8 ± 8.8 years, and the mean body mass index was 32.4 ± 4.5 kg/m(2). Each intervention diet was associated with significant weight loss compared with baseline. Weight loss was higher in the moderate natural fructose group (4.19 ± 0.30 kg) than the low-fructose group (2.83 ± 0.29 kg) (P = .0016). Compared with baseline, each intervention diet was associated with significant improvement in secondary outcomes. Reduction of energy and added fructose intake may represent an important therapeutic target to reduce the frequency of obesity and diabetes. For weight loss achievement, an energy-restricted moderate natural fructose diet was superior to a low-fructose diet.


Every since John Parillo said that fruit makes you fat over 30 years ago, fruit has held an odd place in the world of dieting.  It’s quite common to see contest dieters talking about ‘dropping out fruit’ and removing fruit from the diet is not an uncommon recommendation when someone stalls on their diet.

More recently, the rabid furor and hype over refined fructose (and especially High-fructose corn syrup or HFCS) has only added to this.  If reports I’m seeing are right, the consumption of fructose and/or HFCS will make you fat, drive up blood pressure and make your muscles fall off.  HFCS is responsible for the problems with the economy (when Obama isn’t being blamed), the war in Iraq and just general human meanness and unhappiness.  Ok, I may be exaggerating slightly but it’s only slightly.

I addressed the issue of HFCS in Straight Talk About High-Fructose Corn Syrup: What it is and What it Ain’t. – Research Review, an article that drew quite the share of comments (inane and otherwise) and I’d point readers towards that article for a more detailed look at what I’m going tot talk about next.

Make no mistake, studies have clearly shown that excessive fructose intake (and this is usually due to an excessive HFCS intake and that is typically due to the consumption of non-diet soda) cause problems. But often the studies are, well, let’s just call them silly.  They almost always revolve around the chronic intake of simply non-physiological intakes of whatever is being studied (sometimes pure fructose, sometimes HFCS).

In one that people like to cite at me, rats (rarely a good model for humans) were fed a 60% fructose diet for 6 straight months and this induced leptin resistance.   I was actually going to do a research review on it (mainly to point out everything wrong with it) but couldn’t be bothered.  The short version is that a 60% fructose diet isn’t even possible in humans.  Humans don’t do well with large amounts of pure fructose intake as it causes stomach upset.

And if you’re going to argue that most fructose in the diet comes from HFCS (which is about half fructose), that means that the equivalent 60% fructose diet in a human would consist of 120% of the diet being from HFCS.   Except that that is impossible.

I’d mention, humorously, that the rats didn’t actually gain weight during the 6 months of fructose overfeeding; rather,  it was during the high-fat part of the study that the weight gain occurred.  But the anti-HFCS crusaders (who are often pro-fat) missed that point since they seem to only read abstracts on this stuff.  Not that it applies in either case because it’s freaking rats and the diet was completely impossible for a human to achieve in the first place.

In another study, humans were given 200 grams of pure fructose to see what happened.  I don’t recall the details but the results were negative.  First and foremost, that’s 800 calories of pure fructose which is just a ton.  Second, again going by the fact that HFCS is only about 1/2 fructose (the other half is glucose) that would be the equivalent of someone eating 400 grams of HFCS. 1600 calories per day just from HFCS.

That’s about 16 standard sized non-diet sodas per day (or one super duper mega insane Big Gulp).  Now, I’m not saying that’s healthy, I’m not disagreeing that that is a problem.  But have you ever seen someone drinking that much soda who didn’t have the rest of their diet look like absolute shit?   Usually the ones refilling the 128oz cup with coke are eating a ton of other junk food.   My point being that the HFCS may not be the only thing causing issues here.  Yet folks are fixated on HFCS as the source of all evil.

Which isn’t to say that smaller amounts of fructose don’t or can’t cause issues.  I wrote an article over 10 years ago looking at this issue and it was clear that beyond a certain level (about 50 grams of pure fructose per day) there was the potential for issues.  At the time, the big endpoint had to do with blood triglycerides.  Fructose is metabolized almost exclusively in the liver (quite in fact almost zero incoming fructose will ever reach the bloodstream in humans) and this is a rate limited process.  Above a certain point, fructose starts being converted to fat in the liver.

It’s worth mentioning that some studies have also found that, because it doesn’t raise insulin, fructose consumption doesn’t blunt fat oxidation after you eat it.  So while eating a ton of fructose at once (which is abnormal) can cause fat production in the liver, the body burns more fat.  Almost as if it all sort of cancels out.

But the above invariably was looking at either absurd levels of pure fructose or HFCS.  What about fruit?  To a degree, fruit has become sort of guilty by association.  One of the sugars in fruit is fructose and the hysteria over HFCS (again coming primarily from non-diet soda and refined foods) and the fructose content has caused people to lose their minds.

Basically, people have written off anything containing HFCS or fructose IN ANY AMOUNT.  If either are on the label, that food is ‘evil’. Evil I tell you.  Even consider eating it and your muscles will fall off and you’ll explode with fat.  You’ll start beating your pets and probably become a serial killer and end up with your story on Law and Order: SVU.  Fructose is serious stuff if Internet message boards are to be believed.

But it’s key to realize that fruit doesn’t even contain that much fructose in the first place, about 7% by weight.  So a 100 gram piece of fruit (a medium sized apple or banana for reference) might contain about 7 grams of fructose in addition to the other calories.  Even if you use a 50 grams per day cutoff, that’s 7 medium pieces of fruit.  Not impossible but that’s a lot of fruit.

A second issue is that fruit, as opposed to pure fructose or HFCS, contains other stuff, micronutrients, anti-oxidants, flavonols and everything else that might, just might, impact on how it’s metabolized in the body.  You can’t automatically throw out the fruit with the dishwater (yes, I’m mixing my metaphors) because studies of purified fructose/HFCS using insane amounts have found problems.

Finally is an issue that the dynamics of how nutrients are handled while dieting (that is, in a hypocaloric state) are often vastly different than when someone is weight stable or gaining weight.      So yeah, it’s pretty clear that large amounts of fructose/HFCS are a big issue for the average person who is inactive, gaining weight and for whom the entirety of their diet is pretty much crap.  But that doesn’t mean that fruit as part of an overall hypocaloric weight/fat loss diet is automatically the same problem.  And that, finally brings us to today’s paper.


The Paper

The researchers set out to address two questions.  The first was whether a calorie restricted diet that specifically restricts fructose would improve markers of the metabolic syndrome.  They also hypothesized that a diet high in natural fructose (From fruit) would be superior to one where fruits were limited.

Towards this end, 131 patients were recruited of which 107 finished the study, all were obese (average body fat 40%) and nearly 80% of the subjects were women.  After determining basal caloric requirements, subjects were placed on meal plans of 1500, 1800 or 2000 calories.  The diet itself consisted of 55% carbs, 15% protein and 30% fat and the main difference between the two groups was the fructose content.  One group was limited to less than 10 grams of fructose per day, the other was allowed 50-70 grams of fructose per day coming almost exclusively from fruits.

Food was not provided for the subjects (arguably the biggest limitation of the study); rather they were given meal plans and had to record their food intake at least once weekly (food reports can be notoriously inaccurate and I’ll come back to this).  Adherence to the diet was defined as at least 80% attendance for scheduled clinic visits.

A variety of things were measured including weight and waist measurement along with body fat percentage.  A Tanita BIA scale was used and I’d note (as I discuss in Measuring Body Composition: Part 1 and Measuring Body Composition: Part 2) BIA is not a perfect method as it can be drastically impacted by changes in hydration state.  A vast number of metabolic variables including blood glucose, blood pressure, insulin, creatinine, uric acid cholesterol, triglycerides and others were also measured.  A measure of quality of life was also made in both groups.

The study lasted 6 weeks and these were the results.

In terms of changes in the measured health parameters there were no significant differences between groups in terms of anything.  The fructose group showed a slightly better drop in blood glucose (no surprise there) and the low-fructose group showed a slightly better drop in blood pressure; neither of these reached statistical significance.

I’d comment here that this isn’t uncommon: in a dieting situation, most things change/improve as a function of the weight/fat loss and diet composition tends not to matter.  This is a point lost on many who look at dieting situations (such as a recent study where a high fat intake caused no problems when weight was being lost) and extrapolate it to situations where someone is weight stable or gaining weight.    Basically, weight/fat loss tends to trump just about everything else but that doesn’t meant that the same results will be seen if the person is gaining weight.

But what about the weight/fat loss?  The two groups’ weight losses were 4.19+-0.30 kg and 2.83 +-0.29kg after six weeks.  And perhaps to the surprise of many, the high-fructose group was the one that lost the greater amount of weight.  Body Fat percentage also dropped 2.09+-6.32% in the low-fructose group compared to 2.89+-6.33% in the high-fructose group but this wasn’t statistically significant. The BMI drop was also higher in the high-fructose group but the change in waist to hip ratio was not.

I’d note that there was massive overlap in total weight loss and I’ve reproduced the actual results below.


Weight Loss for High vs. Low Fructose Diets
Weight Loss for High vs. Low Fructose Diets



Like I said, a huge amount of overlap even if the weight drop was larger in the high-fructose group.  There was an improvement in quality of life in both groups with no difference between them.


My Comments

Ok, so what does this paper say?  I think the first point I’d make is that this current idea that carbs make you fat or prevent weight/fat loss is clearly incorrect.  I wish someone would send this paper to Gary Taubes to help him try to remove his head from his ass.  Both groups lost a significant amount of weight and fat and did it eating 55% carbohydrate.

And clearly, at least in the population tested (obese subjects, mostly women), fructose in the form of fruit caused no problems.  At worst, the high-fructose diet was no worse than the low-fructose diet (in terms of all health parameters measured).

And, at least looking at weight loss, it may have been slightly superior.   The researchers had no real explanation for the differential given that the caloric intakes were supposed to be identical.    They suggest that perhaps the higher intake of anti-oxidants, etc. from the fruit might have played a role.  They also point out that the low-fructose diet had a higher glycemic load (since natural fruits had to be replaced by higher glycemic index carbs, I doubt this given the Glycaemic Index Effects on Fuel Partitioning in Humans – Research Review.

Rather, I suspect that the difference in weight loss is just a weird artifact of the study especially given that there was no significant difference in changes in body fat percentage or waist/hip ratio.  While higher insulin doesn’t really impact on fuel utilization, it does impact on water retention, causing the kidney to resorb water.  Lowering insulin (as would occur in the fructose group) might have caused greater water loss.

There is also the issue of the diet not being perfectly controlled since only meal plans were given.  Fructose tends to blunt hunger in many people (this occurs through a vagally mediated mechanism in the liver which sends a fullness signal); perhaps the high-fructose group ate a bit less.  Again, this isn’t really supported by the lack of body fat or waist/hip ratio changes.

Regardless, clearly the idea that the data on massive intakes of either fructose or HFCS doesn’t seem to apply to fructose coming from fruit.  At least not in the population tested.  As I mentioned above, the fruit group did at least as well on all measured markers and was slightly superior in terms of weight loss.  The idea that fruit needs to be eliminated because it contains fructose would seem to be flawed, at least in this group.

Of course, readers of this site are wondering if this applies to leaner individuals and this study can’t answer that question. I’d note that for every anecdotal report of someone removing fruit and getting lean, there are just as many (and many coaches) who keep fruit in the diet and their guys get plenty lean.  One is Borge Fagerli (aka Blade) who has found, in many clients, that the re-addition of fruit to the diet helps people get lean.  But that’s not research, just his observation.