Can Fructose Make You Fat?
The Fructose dilemma
There are two conflicting ideas out there about fructose. One says that fructose is dangerous and can make you fat and the other is that fruit, which has plenty of fructose in it is good for you. So where is the truth in all of this?
As is the case with a lot of the shock foodie headlines you hear about you really have to know the details behind the headlines if you are going to make any sense of the arguments and to know those you have to dig into the science a bit.
In this article i am going to explain how fructose can make you fat and how fruit can be good for you and i promise i’m going to make it easy to understand how both can be true. It’s simpler than you might think, once you line things up a bit.
As far as foods go fruit has a lot going for it. It has some simple digestible sugars. It has fructose, which is also a sugar but one that does not spike your insulin levels. Fruit normally comes with some water and there a few vitamins and antioxidants in there too. All well and good you might say. So what might be the issue? Well, there are a few.
The sweet, sweet days of summer.
The first issue you need to understand is when fruit would normally be eaten, and no, i don’t mean at what time of the day or at which meal. I mean, when in the year would fruit typically be eaten. You might be forgiven if you answer, “Any time of the year.” And that is our first problem. You did not evolve eating fruit at “Any time of the year.”
Until very recently you could not eat fruit out of the season in which it grew because ripe fruit rotted on long voyages and fast travel and refrigeration had not yet been invented. In fact these technologies are so new that compared to the course of human evolution and our relation to food they almost have not even happened yet, that’s how new they are. Even a hundred years ago ripe fruit was almost unheard of for most of the year outside of the tropics, never mind for the millennia before that when your body was evolving to eat and survive on what the seasons had to offer. (And, yes i know some people have done some of their evolving in the tropics and so have a better genetic ability to handle sugars but there is more to this fructose story as you will see as you read on).
Making hay while the sun shines
Okay, so fructose used to be hard to get. So what. It’s a bit sugary but it isn’t like drinking a can of cola. This is true, but your can of cola wasn’t around until very recently either. Which begs the question, why do we like sweet foods like fruit and cola so much in the first place? Well the reason is we are designed to like sugary and carby foods. If fact our desire for these foods have been aggressively selected for in order for us to be able to survive long cold winters.
For a couple of hundred thousand years as humans, and for millennia before that our species evolved to eat every bit of sugary, carby food we could get our hands on. These foods only grow in the late summer and early autumn and our bodies evolved to get as fat as possible on these sweet tasting foods because after autumn comes winter, and in winter food is scarce and it gets cold. And if you are going to survive the winter with nothing more than a few furs and a cave to keep you warm then you want to store as many calories as you can; firstly to help keep you warm and secondly to feed you. For most of our evolution food has been scarce in the winter months and what there was came in the form of animal protein and fat, which it is surprising difficult to get fat on, (despite what we have been told for the last 50 to 60 years).
So, when you are living only on what the seasons can offer up and summer comes and you find your self coming across a pear tree you are going to eat yourself sick if you can. And after you pass out in a sugar coma you will wake and start eating again. This is because the eating of sugars triggers evolved mechanisms in our body that cause us to want to go back for more and more and more.
How Fructose can make you fat.
Oddly one of the sugars that is predominant in fruit and which is particularly fattening is Fructose. This might seem a bit bizarre when you consider that i mentioned earlier that fructose does not even spike your insulin; the usual suspect when we relate sugar to body fat. So if fructose doe not trigger insulin how does it make you fat? Well, it works like this.
Because fructose does not trigger insulin and cannot be stored away in muscle tissue like other sugars, there is only one place it can be stored and that is in your liver. But your liver only has a limited capacity for storing sugars; about 70 to 90 grams on average. So what happens when that space fills up? Fat starts to build in the liver and fat building up in the liver is not good. In fact it leads to fatty liver disease and if your liver goes… so do you. And because all your sugar capacity in the liver is quickly filled up this means that other sugars that could normally be processed and used in the liver cannot get in there. Therefore, they must be sent out to the muscles and other organs which are also also filling up. Once there is nowhere for the sugars to go they must be stored and that means more body fat.
This system of gaining body fat in the presence of fructose is so effective that as soon as the liver begins to get fat it triggers the rest of the body to store more fat also. This is done by signaling an increase in insulin release every time sugar enters the system. The liver can’t handle even small amount of sugar once it starts to get fat and a sugar build up in the body is very dangerous so all excess sugar must be shoved out of the system into storage as quickly as possible. So as the liver gets fatter it triggers the whole body to do like wise.
This ability to gain fat is a perfect situation, evolved by our bodies over millennia to help the body store as much fat as possible in the sugary months of late summer and autumn. But of course we don’t only eat sugar and fructose in the summer months anymore, we eat it all year round. When we have access to sugar all year round then the system crashes because it is put into a permanent state of summer storage.
We have basically swapped 3 months of fat gains and 9 months of fat burning each year, for a 12 month a year battle with fat storage. And we wonder why we have so much obesity and ill health!
The sweet life
The next issue with fructose has to do the fact that most of the fructose we eat is not coming from fruit at all. In fact if the only fructose we got was from fruit then most of us would not be eating enough of it to cause a big problem. Most of the fructose we eat is hidden to us. Most of it comes from man made processed foods, which were never part of our seasonally evolved eating patterns in the first place and so greatly boost our fructose intake without us ever realizing it.
Our can of cola, as mentioned earlier, has about 39 grams of sugar in it. And most brands use High Fructose Corn Syrup as one of the main sugar ingredients. So right there, from just one can of cola, you are getting a lot of fructose you had not counted on and a large percent of the total sugars your liver can hold. Other brands might not add HFCS at all (some even advertise this to show how much healthier they are) but use regular sugar instead, or cane sugar, which is just less refined sugar. The problem is, sugar (the regular white stuff), is made from 50% fructose and 50% glucose so at least half of the sugar in the product (it’s not food, so let’s not even call it that), comes in the form of fructose. Without ever knowing it you are pilling more and more fructose into your system all the time. And what about all those sweet tasting low fat foods that are pushed at people with the promise of low calories…. more and more sugar. 
Sugar is everywhere in our society. In order to hide it, food manufacturers use at least 56 different names for sugar.  Fructose is just one of them, although it is one of the ones most used because it is the sweetest tasting of them all and chemists have become very good at attaching it to other sugars to hide its name.
So, is fructose bad for you?
Well that depends what the rest of your diet looks like. If you are already getting a lot of fructose from other sources then yes, the sugars in your fruit will only add to the problem and make you even fatter and sicker. But if you keep your daily sugars low, real low, then no, the sugars you get from some fruit will not be bad for you.
If nothing else i hope this article nudges you in the direction of eating more whole, real foods and where possible eating a little bit more seasonally and more than anything i hope it encourages you to to cut your sugar levels as much as possible and to look a little closer at just what is in the foods you are eating.
Obesity and many of the modern diseases that go with it, such as type 2 diabetes, heart disease, cancer and dementia are all at least partly products of us moving away from how we evolved to eat. Instead of seeking and finding food that has grown and lived locally we are instead sold food manufactured, shipped and advertised to us solely on it’s ability to generate profit by taking advantage of our biological propensity to seek out more and more sugar once the stimulus has been triggered. To fix these modern diseases perhaps you might be better looking to the foods you evolved to eat and to eat them in the seasons you are evolved to eat them in. It certainly won’t harm you in any way by eating more naturally, so why not give it a go for a while. You have nothing to lose, and perhaps a lot to gain.