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Do Diet Drinks Help With Weight Loss? It's Unclear

When forced to choose a soft drink, I go with the diet option, because too much sugar is bad for you. But water would be better.

This article was first published in The Montreal Gazette.

One of the ironies of life is that whenever you go to a medical conference, the food service invariably includes soft drinks. These are an especially egregious example of junk food. Soft drinks are loaded with sugar and increase your risk of gaining weight and developing diabetes.

The obvious solution is to cut out sugar. Water is the oldest sugar-free beverage, but since people want fizz and flavour, many choose diet sodas that contain artificial sweeteners or, as they are formally known, non-sugar sweeteners.

The question, though, is whether swapping out a regular soda, that contains sugar, for a diet soda, that contains a non-sugar sweetener, will actually lead to weight loss and prevent disease. As with most things in nutrition research, the data is equivocal and contradictory. While some analyses have found a benefit to using non-sugar sweeteners, others have not.

Why this should be the case is subject to some debate. Part of it may be flaws in the research methodology. If people who drink a fair amount of regular soft drinks also drink a fair amount of diet soft drinks, it will, of course, be hard to tease out what is actually to blame. Another theory is that drinking diet soft drinks makes you think that you are being healthy and subconsciously tricks you into overindulging at other times. It’s also possible that artificial sweeteners provide you with the taste of sweetness without delivering the expected bolus of sugar in your bloodstream, thus triggering your brain to go get its sugar fix elsewhere.

While there may be some merit to all of these theories, the only question that really matters is whether using non-sugar sweeteners can help people lose weight and prevent diabetes. A recent meta-analysis in the British Medical Journal did its best to summarize the evidence. The authors reviewed 56 studies and overall came to the conclusion that the quality of the evidence was not great. The studies were on average small and had short follow-ups, which limited their ability to draw any firm conclusions.

The main takeaway of the paper was that there was no benefit to non-sugar sweeteners in terms of weight loss. However, drilling down into the data revealed some interesting results. Overall, the weight loss with non-sugar sweeteners was small and possibly just statistical noise. But when you separated out the data into people with obesity and people with normal weights, you saw a rather large benefit in people with obesity (2 kg, or 4.4 pound, weight loss) compared with virtually no weight change in people with normal weight.

Why this discrepancy should exist is hard to explain. It’s very possible that if you were already at a normal weight, it would be very difficult to lose more weight no matter what you did. Also, these artificial sweeteners may help with weight loss only if you have the excess weight to lose in the first place.

In other analyses, non-sugar sweeteners resulted in people consuming 90 g less sugar and 1,000 fewer kilojoules (240 calories) per day on average. Concerns about artificial sweeteners and cancer have been bouncing around for years. But this paper found no link between non-sugar sweeteners and bladder cancer, lymphoma, leukemia, or brain tumours in children.

I’m often asked whether I drink regular or diet soft drinks. Truthfully, after looking over this data, it’s not clear that it makes much of a difference. I often say that when forced to choose, I go with the diet option because I’m certain too much sugar is bad for me, and I’m fairly certain non-sugar sweeteners are not objectively harmful. But when I’m really given a free choice, I choose water. It has zero calories every time.


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