Are ‘diet’ soft drinks better for you than ‘full-sugar’ soft drinks?

According to a 2022 meta-analysis of randomised controlled trials, the answer is yes.

Switching sugar-sweetened (‘full-sugar’) beverages for low- or no-calorie sweetened (‘diet’) beverages (for 12 weeks on average), was associated with small reductions in body weight, BMI, body fat, and liver fat.

This should come as no surprise. Full-sugar drinks deliver a lot of calories without filling you up (and in some cases may actually increase appetite). This is the perfect formula for non-conscious overeating, sustained calorie excess, fat gain, and metabolic illness. To make matters worse, the sugar in full-sugar drinks is at least 50% fructose (more in the case of fruit juice and drinks sweetened with high-fructose corn syrup), a sugar which is now thought to have additional (and serious) metabolic consequences beyond the calories it contains.

Diet drinks, on the other hand, deliver far fewer (if any) calories and little to no fructose. So, while they may still alter appetite regulation in various ways, the lack of calories and fructose means they don’t carry the same risks for weight gain and metabolic disease as full-sugar drinks.

So, if you’re a committed consumer of sweetened drinks, your body composition and cardiometabolic health would likely be improved by switching from full-sugar to diet drinks.

Of course, it would be better for your health to just drink plain old water. But here’s the wrinkle: For somebody accustomed to regularly consuming full-sugar drinks, water may be very unrewarding, and therefore far less motivating, and therefore difficult to stick to. Diet drinks – with their carbonation and sweetness (and comparable levels of caffeine) – may be almost as rewarding as their full-sugar counterparts (and certainly more rewarding than water). So, it would likely be an easier and more sustainable switch to make.

Interestingly, the meta-analysis also looked at the effect of switching full-sugar drinks for water. In this case, they found no significant effect on body weight and other cardiometabolic risk factors (although the direction of association favoured water in all cases). So, it makes diet drinks appear like a slightly better switch than water. But I don’t buy that, for two reasons:

  1. I suspect more people adhered to the diet drink switch than the water switch (for the reasons outlined above)
  2. Many of the authors have conflicts of interest with the food and drinks industry. If water looked like a clear winner, it wouldn’t be great for sales

Water is no doubt the best drink for your overall health. But we’re not chasing perfection here – we’re pursuing incremental improvement. And switching from full-sugar drinks to diet drinks is likely to be an effective and sustainable first step.

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