How Soft Drink Might Make You Fatter

How Soft Drink Might Make You Fatter

Diet drinks are no help in the fight against obesity and may actually encourage over-eating, according to a US academic who recently argued this point in the journal Trends in Endocrinology and Metabolism.

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Susan Swithers reviewed studies that suggest normal or mildly overweight people who consumed artificially-sweetened drinks were more likely to gain weight when compared to those who did not.

The studies showed that, in two separate groups of adolescents, drinking artificially-sweetened drinks was associated with increased body mass index and body fat.

This suggests these drinks don’t even help people maintain normal body weight and may, in fact, be detrimental. But Swithers recognises that this association may be a case of “reverse causality” — people who are genetically prone to obesity are more likely to drink low-calorie drinks to limit calorie intake.

So, it’s the obesity tendency that leads people to drink artificially-sweetened drinks, not that artificially-sweetened drinks lead to obesity.

A better way

To exclude the possibility of reverse causality, it’s necessary to undertake a randomised prospective study. The ideal would be to recruit about 200 volunteers and randomly assign each volunteer to a group that will drink only diet drinks or to a group than drinks only sugared drinks. We could then observe the effect on their weight.

The paper quotes one such study that examined 641 boys and girls. For 18 months, the children were asked to drink either a single artificially-sweetened drink or a single sugar-sweetened drink every day.

After 18 months, children who had drunk the artificially-sweetened drink gained less weight and had smaller increases in fat mass when compared to the children who had drunk the sugar-sweetened drink.

This suggests that the previously noted association of obesity with drinking diet drinks is the result of spontaneously obese individuals trying to take evasive action. In other words, it is a case of reverse causality.

So, what is the evidence that artificial sweeteners could make you fatter?

What the rodents did

In a different paper by the same author published in the journal Behavioural Neuroscience earlier in the year, she reported the results of a rat study she undertook with her colleagues.

They measured the weight gain in rats after feeding them yoghurt supplements sweetened with saccharin (an artificial sweetener) or yoghurt sweetened with glucose.

The authors found that when the rats were consuming a low-fat “healthy” diet, there was no difference in weight gain between the two groups of rats. But when the rats had a “Western” high-fat, high-sugar diet, the ones being supplemented with artificially sweetened yoghurt put on more weight than the others.

These effects were more pronounced in female rats from strains known to be susceptible to diet-induced obesity.

So this effect, if present in humans, will be more dramatic in genetically obese-prone women on a high-energy western diet. The study may also explain why the prospective study on children did not support the hypothesis; the children were not on a high-energy diet and the group contained both males and females.

Becoming desensitised

But how could artificial sweeteners encourage over-eating in some circumstances? According to Swithers, artificial sweeteners weaken the normal response of the body to the arrival of glucose in the system.

It receives confusing signals: there’s a sweet taste but it’s not accompanied by the usual effects of glucose such as the suppression of hunger mediated by glucose metabolism in the brain or the stimulation of appetite-suppressing hormones from the small bowel.

After a period of ingesting sweet-tasting but calorie-free drinks, the body may no longer respond to glucose containing foods with these appropriate appetite-suppressing mechanisms.

This may explain the finding that body weight increases only when sweet-tasting, calorie-containing foods are consumed. We normally rely on the appetite suppressing effects of glucose to limit our intake of these foods and will overeat if the response has been blunted.

Imaging studies of the human brain have shown that sucrose (table sugar) but not the artificial sweetener sucralose, activates brain areas related to reward of pleasantness and in other taste-related areas of the brain.

So what does all this mean for you?

Swithers ends her piece with a list of remaining questions to be answered and calls for more research. We clearly do need to learn more about this phenomenon.

But in the meantime, we should all (but especially obesity-prone females) review our consumption of artificially-sweetened drinks as they probably aren’t helping our fight to stay lean.

As always, plain water is the best drink.

Joseph Proietto is Professor of Medicine at University of Melbourne. He is Co-Chief Investigator on an NH&MRC grant investigating a phenomenon that is related to feeding fructose + fat to mice.

The ConversationThis article was originally published at The Conversation. Read the original article.


  • See, this is just muddying the waters, Oh and there should be the word “artificial” in that title too.
    Whether or not artificial sweeteners cause problems is just a side issue, the fact is that the loading of sugar is a major problem in processed foods in the modern diet. If artificial sweeteners are an issue they’re a minor issue. Reduce your intake of real sugar…

    • The artificial sweeteners does deserve research and discussion.

      I buy diet Coke / diet Pepsi / Max / Zero or whatever thinking that it has 0 calories, mainly because it says 0 calories, or something to that effect, on the bottle.

      If this has been a cause of me gaining weight then I want to know about it.

      I suspect it has been as I think I have gained weight in periods where I allow myself to have diet drinks, and have lost weight when I haven’t.

      Guess I’ll stick with water.

      • Yeah I’m not trying to diminish your issues, obviously if this has an effect on you, it’s important. I’m just pointing out that, sugar as a whole is the catalyst for these issues. In other words, if the amount of sugar in the diet of the population as a whole is too high then this issue with diet drinks is related to that…. 🙂

        • Yeah, i’m not disagreeing with you either.

          I’m just making the point that alot of us think that diet products do not, should not contribute to weight gain. I’ve always viewed diet Coke etc as being perfectly healthy. And if it’s not, we need to know about it.

          • I wouldn’t consider diet soft drink as perfectly healthy, as the amount of chemicals and shit they must put in it to make it sweet cant be that good for you. In saying that i still usually drink at least one diet drink a day whether it be pepsi max or sugarfree red bull, and i find i need that sweetness and caffine everyday(which i know isnt great). I used to be 40kg heavier, and i find that diet drinks are a guilt free treat that i can enjoy and helps me eat healthily throughout the week.

          • Yeah, diet drinks are great unless they’re not great.

            If they are indeed contributing to weight gain then they aren’t great.

            I think this article was the validation I need to quit allowing myself to indulge in a 2 litre bottle of Pepsi Max over the weekend. It’s just not worth it.

            It was a guilt free pleasure, but not any more.

            Back to orange juice. Oh no, wait.

            Still, i’m cool with water and might start treating myself to fizzy water again.

          • i think it comes down to the individual on whether sugar free beverages affect their dietary habits, even though it makes sense that they would it is certainly not always the case. either way its a great discussion piece. i certainly agree that sticking to water would make the world a better place. =p

      • Its long been believed that even ‘diet’ drinks will cause weight gain simply because the ‘fake’ sugar they have, while not REAL sugar, still makes your body THINK its sugar. Which is a huge problem. They also apparently cause other, different problems.

        The only real safe option is, as you said, to just drink water.

        • I think you’re getting confused. This article deals with artificial sweeteners which contain no sugar just chemicals and flavours to make them taste sweet. Are you using “fake” sugar to mean refined/processed? Because then that’s a different story.

          Artificial sweeteners will NOT have the same physiological effect on the body as sugar because your body isn’t about to start processing stuff that doesn’t exist. This deals more with the cause and effect of obesity and artificially sweetened drinks and how those two correlate.

  • That’s the whole point though. What’s the cutoff for “too high” of sugar in someone’s diet? For someone who’s obese that cutoff would be fairly low. For someone who exercises 2 hours a day everyday of the week then that cutoff would be much higher.

    Obviously for the majority of the population their intake of sugar is too high but it’s also extremely unhealthy for people to be advocating for people to have 0 sugar in their diet.

  • Great article (far better than the usual tripe put out by journalists and possibly a good model going forward for health media).

    Salacious headline by Lifehacker. Compare this headline with the original Conversation headline ‘Do diet drinks make you fatter?’.

    It works though. I ate that headline up like it was rice pudding, and washed it down with a Diet Coke.

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