No, ketchup does not cause cancer

ketchup and coke

Do these things really cause breast cancer? (Spoiler: no)

Less than two days into the new year, and I’d already found what might well be one of the silliest health headlines of the year. What is it I hear you ask? Well, it was in a national newspaper on New Years Day, and it was this:

Sugar found in ketchup and Coke linked to breast cancer

This, to borrow a favourite line from an online greetings card company, had me rolling my eyes so hard I could practically see my brain. Why? Because even without reading any further, I knew immediately that it was the equivalent of saying, “too much of thing found in most stuff might cause cancer!”

But let’s not be one of the 70% of users that only read the headline, let’s dig a little further. The newspaper article, which in fairness isn’t too bad – it’s just a bit of a silly headline, alludes to work carried out the University of Texas’ MD Anderson Cancer Centre. If you click on the link I’ve added back there, you’ll see that MD Anderson’s headline was:

“Sugar in Western diets increases risk for breast cancer tumors and metastasis”

Note, they just say ‘sugar’, not sugar in two apparently randomly-selected foodstuffs. The researchers divided mice into four groups, fed some a diet high in sucrose (more commonly called table sugar – in other words, the stuff in the sugar bowl) and compared them to others fed a low-sugar, ‘starch-controlled’ diet. They found that the high-sugar diet lead to increased tumour growth, particularly in mammary glands.

I’ve covered forms of sugar before but still, here’s a quick reminder before we go any further: this is a molecule of sucrose:



Sucrose is made of two ‘bits’ joined together: one unit of fructose and one unit of glucose.



These two molecules are what chemists call isomers. They contain the same number and type of atoms, just joined up differently. They’re both sugars in and of themselves. Glucose is used directly by cells in your body for energy. Fructose, on the other hand, is trickier. It has a lower glycemic index than glucose, in other words, it doesn’t raise your blood sugar as rapidly as glucose, but this doesn’t mean it’s healthier. It’s metabolised almost exclusively in the liver and, long story short, invariably ends up being converted into, and stored as, fat.



Fruit is high in fructose, and fructose tastes very sweet to us (sweeter than either glucose or sucrose). This is nature’s way of telling us, and other animals that might eat the fruit, that it’s high in nutrients. From the plant’s point of view, it’s an incentive to eat the fruit and, ahem, spread the seeds around.

Humans have, of course messed around with this perfectly sensible survival mechanism by stuffing all kinds of easily-available and not particularly nutrient-rich foods with fructose, and herein lies the problem. Co-author of the paper that started all this, Lorenzo Cohen, Ph.D., professor of Palliative, Rehabilitation, and Integrative Medicine, said “we determined that it was specifically fructose, in table sugar and high-fructose corn syrup […] which was responsible for facilitating lung metastasis and 12-HETE production in breast tumors.” Notice that he mentions fructose in table sugar; this is because, once you eat sucrose, it breaks down into units of glucose and fructose.

The article goes on to suggest that sugar-sweetened beverages are a significant problem, so was the newspaper wrong to pick on Coke? It’s a popular drink after all, and a standard can of Coca-Cola contains approximately 35 grams of sugar (which might come from either sucrose or high fructose corn syrup mainly depending on where you buy it). The guidance for adults is no more than 30 grams of sugar per day, so a single can of regular Coca-Cola would take you over that limit, and it’s very easy to drink two or even three cans without giving it a second thought.


Soft drinks and fruit juice both contain a lot of sugar

However, the same goes for pretty much any non-diet soft drink.  Pepsi, for example, has a similar amount. Lemonade can be even more sugary, with some drinks hitting 40 grams per 330 ml can. Ginger beer might well be the worst; there are 53 grams per 330 ml in Old Jamaica Ginger beer for example. Fruit juice is no better, with many juices containing 35 g of sugar per 330 ml, although at least fruit juice might contain some other nutrients such as vitamin C.

So really, I’d say it’s a bit unfair to single out Coke in a headline like this.

What about the ketchup (note they didn’t pick a specific brand here, just generic ‘ketchup’)?

Well, ketchup IS high in sugar. It contains about 24 grams of sugar per 100 grams. But hang on, 100 grams of ketchup is quite a lot. A more realistic serving size of a tablespoon is only about 15 grams, which works out at about 3.5 grams of sugar. Still quite a lot, but probably a drop in the ocean compared to all the sugar in cake, bread, drinks, fruit juice, breakfast cereals and the tubs of Roses and Quality Street you scoffed over Christmas. Unless you make a habit of drinking ketchup by the bottle (apparently some people do) this is frankly a ridiculous foodstuff to pick on.

I imagine that someone did a quick search for ‘foods that contain fructose’ and picked Coke because, well, everyone knows that Coke’s bad, right? So that sounds credible. And ketchup because we all sort of suspect it’s probably not that healthy, but it hasn’t been the subject of a health scare recently so that makes it stand out. Great clickbait, bad science.


Mice are not people

Plus, let’s be absolutely clear, the study was in mice. Mice are not people. While a study that shows an effect in mice is an interesting start, and may well be good reason to conduct more studies, quite possibly in humans, it’s not proof that this mechanism exists in humans. Humans have, after all, evolved to eat a very different diet to mice. There might well be a link, but this doesn’t prove it, and even if a link does exist we certainly can’t say anything about the significance or size of it from this research.

I’m not a dietician, but I’m going to go out on a (fairly sturdy) limb here and say that cutting back on sugar will not do you any harm and is likely to be a jolly good thing. Let’s also be clear that sugar in fruit juice, agave, honey etc is still sugar and is no healthier than table sugar. Eating too much of the sweet stuff is almost definitely bad for your waistline and, as we all learned as children, bad for your teeth too – something which is often overlooked but really shouldn’t be, poor dental health having been linked to other serious health problems including diabetes and heart disease.

ketchup on bread

Maybe cut back on the fried ketchup sandwiches

But, and here’s my big problem with the newspaper’s headline, none of this means that Coke and ketchup directly cause breast cancer which is how, I fear, some people will interpret it. Cut out sugary fizzy drinks by all means, and perhaps ditch the ketchup sandwiches (especially fried ones), but please don’t worry that the occasional dollop of red sauce is going to kill you. I’m pretty certain it won’t.

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A small edit was made on 6th January to clarify that pure fructose isn’t used as an ingredient in Coke, but rather high fructose corn syrup.



12 thoughts on “No, ketchup does not cause cancer

  1. It’s a pity that certain chefs don’t read this. On the radio yesterday, I heard one talking about ‘natural’ sugar if fruit etc as if it were any different from the stuff in our bowl…


  2. A few quibbles.

    First, I am not aware of a locale where Coke is made with straight fructose. You must mean high-fructose corn syrup.

    HFCS comes in a bunch of blends, As far as i know, the blend most commonly used in beverages is HFCS55, which is 55% fructose, 45% dextrose/glucose. (see footnote).

    As you said, sucrose is one unit of fructose and one unit of glucose.

    Sucrose is not particularly stable. It will break into fructose and glucose in the presence of heat, light, or acid.

    As you know, Coke is acidic. And as you’ve said, fructose is sweeter than sucrose. This means that on the shelf, over time, particularly when exposed to light, the flavor profile of Coke made with sucrose will change. HFCS isn’t just cheaper than sucrose (in north america, due to corn subsidies) – it provides a more stable product.

    Your stomach is also acidic. It is seriously unlikely that any significant quantity of sucrose enters the bloodstream of a normal healthy human being intact.

    So, consuming sucrose rather than HFCS55 means that at best you have reduced your fructose intake by 10%.

    Incidentally, honey has almost exactly the same glycemic makeup as HFCS55, just with more other stuff in it. Agave nectar is also as much as 56% fructose.

    (Footnote for non-chemists: Dextrose and Glucose are stereoisomers. That means that they are mirror images of each other. Dextrose, with it’s prefix dex, from the latin dexter meaning ‘on the right’, is merely right-handed glucose. Since corn syrup is made by breaking down corn starch with caustic soda, the resulting sugar is a roughly 50/50 blend of glucose and dextrose. In aqueous solution – like a syrup – at any given moment some of the glucose is turning into dextrose and some of the dextrose is turning into glucose, and it doesn’t matter one bit because they are identical as far as your cells are concerned. I’d crack a joke about glucose being sinister, but i wouldn’t be able to live with myself).


    • Well, less quibbles, more clarification 🙂 You are, of course, correct in everything you say! I’ll make a small edit to specify HFCS rather than just ‘fructose’.


    • Actually, starch is composed entirely of dextrose. During hydrolysis it is broken down to α and β dextrose (and I suppose you meant those isomers) ‘Glucose’ is a name of sugar (both D and L isomers).

      By the way, L-glucose is unavailable to human organism – cant be used as an energy source.

      I admit though , it is pretty disappointing- seeing on various Internet forums how some people are searching for foods ‘with sugar, not that syrup with evil, evil fructose’.


  3. Pingback: The Chronicles of the Chronicle Flask: 2016 | the chronicle flask

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