Variously on this site I’ve discussed the notion that ‘a calorie is a calorie’. Simply put, this concept, widely populated by doctors, dieticians and other health professionals, is that when it comes to their effects of weight, all forms of calorie are the same. In terms of its impact on body weight, a kilogram of fat will have the same as a kilogram of carbohydrate. Same for protein.
There is a certain logic to this, I suppose, but on the other hand, one could argue that it assumes that all forms of calorie are metabolised with equal efficiency. Imagine for a moment within your body you have a lit barbeque (this represents your metabolism). If you put petrol (gasoline) and charcoal briquettes on the barbeque, would they burn at the same rate and as completely? Of course not. Could this be at all true for fuel (food) in the body?
One way to test this theory is to feed individuals diets of the same calorific value but different composition (e.g. high-fat/low-carb, and low-fat/high-carb) to see if the effects on weight over time are the same. Some studies have yielded results which suggest that the composition of the diet does indeed have a bearing on their impact on body weight, while other studies have not. One of the problems with these studies is that it can be difficult to ensure individuals are eating what they’ve been instructed to eat, even when cooped up in a hospital ward. And even if the diet can be completely controlled, it can be difficult to conduct such studies for long enough for any real difference between the diets to emerge.
One way round such problems is to do relevant experiments in animals, as I describe here. In this post I describe and experiment in mice which shows very clearly that it is possible for a diet to offer weight loss advantages (a so-called ‘metabolic advantage) in a way that has to do with not just the number of calories it contains, but the form they come in . Specifically, this study found that mice eating a high-fat, low-carb diet lost weight, while those eating a high-fat, high-sugar diet of the same number of calories gained weight.
One fundamental difference between these diets was the amount of carbohydrate (in the form of sucrose, maltodextrin and starch).
I was interested to read about a study published this week which assessed the effects of different dietary composition on weight in rats . This study came in two parts. In the first part, rats were fed:
1. sucrose (table sugar) solution for 12 hours a day and rat chow in unlimited quantities
2. high fructose corn syrup (HFCS) for 12 hours a day and rat chow in unlimited quantities
3. high fructose corn syrup for 24 hours a day and rat chow in unlimited quantities
4. rat chow alone and in unlimited quantities
Rats eating the HFCS for 12 hours a day gained more weight than those consuming the sucrose solution, despite the fact that overall both groups of rats ate the same number of calories. The HFCS group did, however, consume fewer calories from HFCS than the sucrose-group consumed in the form of sucrose.
In the second part of this experiment, male rats were fed either diet 2, 3, or 4 (above) for a period of 6 months.
Also, female rats were fed one of diets 3 or 4 for a period of 7 months.
Over the same period, female rats were also fed either HFCS and chow for 12 hours or sucrose and chow for 12 hours.
In summary, compared to controls (chow only), male rats:
gained significantly more weight on both HFCS diets (diets 2 and 3).
gained significantly more fat on both HFCS diets.
this excess weight tended to accumulate around the abdomen (it is abdominal fat in humans that is most strongly linked with chronic diseases such as heart disease and type 2 diabetes).
saw significant rise in levels of unhealthy blood fats known as triglycerides on both HFCS diets.
In female rats, all the above was true for rats eating diet 3 (HFCS for 24 hours a day plus regular chow).
Overall, what these results suggest is that high-fructose corn syrup had special capacity to induce fat accumulation, particularly around the abdomen, as well as high levels of triglycerides in the bloodstream. Importantly, these effects (including those on weight) are to do with something other than mere calories.
How much relevance these results have to humans is not clear. However, my suggestion is that these results have at least some relevance, particularly as there is clinical research in humans which has linked fructose with adverse effects on health, and quickly too. See here for more about this.
What this study reminds us of is the potential hazards of consuming high fructose corn syrup, a sweetening agent that, increasingly, is pervading our diet. It should also remind us that, when it comes to the impact foods have on weight and fatness, a calorie is not necessarily a calorie, after all.
1. Kennedy AR, et al. A high-fat, ketogenic induces a unique metabolic state in mice. Am J Physiol Endocrinol Metab 2007;292:E1724-E1739
2. Bocarsly M, et al. High fructose corn syrup causes characteristis of obesity in rats: In creased body weight, body fat and triglyceride levels
“.. rat chow in unlimited quantities”
So this study cannot be used to conclude anything about a calorie is not a calorie.
From the above post:
It looks like too much dietary fructose reduces kcals burned, in a similar fashion to trans-fats.
We see this in young adult patients who typically drink large quantities of sweet sodas. They often suffer from non alcoholic fatty liver disease. This is a good metabolic predictor for diabetes, obesity and general metabolic syndrome. This is strongle linked to high fructose intake.
Remember the guy who eat McDonalds exclusively for a month, “Super size me”. His liver enzymes went throught the roof in a short space of time and he gained 25 lb in weight in less than a month. This diet involved very large intake of fructose from the drinks and the burger buns (4grams of fructose in a Mc burger bun).
Your comment reminded me of a study which looked at the relationship between fast food consumption and liver function derangement. It turned out that the only element of the diet that appeared to account for this was carbohydrate (not protein, fat or calories). See here: http://www.drbriffa.com/blog/2008/02/15/why-carbs-can-turn-your-liver-into-foie-gras/
I strongly suspect it is one of the main culprits in the development of insulin resistance.
One interesting question to pose is this actually why low carb diets are so effective at aiding weight loss because they are naturally lower in fructose?
It appears that fructose also interferes with appetite regulation aswell and can effect the action of leptin. Causing major disadvantage to dieters.
Is HFCS the same as glucose syrup? I seem to have recently become intolerant of anything with glucose syrup in it and it makes me really tired, miserable and weak. I’ve also noticed that I have felt less fat and flabby since I made the effort to eliminate it from my diet.
“Is HFCS the same as glucose syrup?”
HFCS is made up of mainly fructose and glucose (about half and half).
You’ve certainly made me even more convinced that HFCS is a baddie to be avoided.
But with regard to Gary’s reminder about “Super size me”, I would point out that the guy concerned was forcing himself to eat far, far more than he felt comfortable with: he was force-feeding himself.
I think that force-feeding far beyond the demands of appetite – whatever the food, be it McDonalds or even healthy food – would be likely to do damage to the body, and it was a pity that the “Super size me” guy loaded the dice against McDonalds in this way. The harm he did himself in his experiment was a conjunction of McDonalds and force-feeding, and we cannot know how much harm came from the McDonalds element and how much from the force-feeding.
Based on what corn *oil* does to me, I’m starting to think that corn *itself* is uniquely fattening. It doesn’t seem to matter how I eat it.
My question then, is why are the HFCS vs sucrose results so different, if HFCS only contains slightly more fructose than table sugar? Is it that the fructose is “free” and not bound to a glucose molecule as it is in sucrose? Or is there something else in HFCS that is the issue? I’ve never been able to find a clear answer to this.