Is cola zero worse than regular cola? People ask me this in coaching all the time. They are afraid of cravings and of what it will do to the gut. The short version from the data is the opposite of the scare.
Short answer: for weight loss, diet cola is a better choice than regular cola. When diet sodas replaced sugary drinks, adults with overweight lost about 1 kg more on average, with small improvements in body fat and liver fat (PMID 35285920). The fear that cola zero wrecks the gut or makes you eat more later is not supported by most human trials so far, though the gut research is still young.
What the human data show
A small randomized, double-blind crossover trial (17 healthy adults, two weeks each on aspartame and sucralose) found minimal effect on gut bacteria (PMID 33171964). A 2023 review found mixed results in people: some trials saw changes in gut bacteria, many randomized trials saw none, and there is no scientific consensus yet (PMID 37111090).
On intake, in short-term trials, people who had a diet drink instead of a sugary one ate about 94 kcal less in total at the next meal, and about the same as after water (PMID 26365102). Compared with water, the weight picture is less clear. One meta-analysis found slightly more weight loss with diet drinks, but from only three comparisons (PMID 26365102). Another found no clear difference (PMID 35285920). Yes: diet cola beats regular cola for this job.
When we use the diet version on purpose, usually instead of a sugary soda, it makes the calorie target easier to hit for many of my clients. I do not see a risk in it when the rest of the diet has enough protein and vegetables. Liquid sugar itself is the leak. More on that in Is sugar bad for weight loss?
What to take from it
- For fat loss: swap sugary drinks for diet drinks. In trials, a diet drink instead of a sugary one meant fewer total calories, and it did not push people to eat more later (PMID 26365102). Sugary drinks are an easy place to cut added sugar.
- For the gut: nothing confirms that aspartame wrecks the human microbiome. If your gut is the worry, more fibre from vegetables, legumes and whole grains is a better place to start than cutting a diet soda.
- For the long run: diet soda is not a devil. Pair it with movement and sleep. If you have a diagnosis, talk to your doctor. If you have phenylketonuria (PKU), avoid aspartame. That is why drinks with aspartame carry a phenylalanine warning. This article is not medical treatment.
Drinks at dinners and events, including the alcoholic ones, are in drinks, dinners and social events. Hunger and sweet cravings on a diet are in cravings and hunger.
Frequently asked questions
Does the aspartame in diet cola wreck the gut microbiome?
Most human data do not show that, though the research is still young. A small randomized, double-blind crossover trial (17 healthy adults) found minimal effect of aspartame on gut bacteria. A 2023 review found mixed results in people: some trials saw changes, many randomized trials saw none, and there is no scientific consensus yet.
Do diet sodas increase a craving for sweet food?
The studies I cite did not measure cravings directly. What they do show: people who had a diet drink instead of a sugary one ate about 94 kcal less in total at the next meal, about the same as after water (PMID 26365102).
Is it better to swap a sugary soda for a diet soda, or for water?
Both are fine. The evidence that diet drinks beat water is thin and mixed (PMID 26365102, 35285920). Pick the one you will actually stick with.
Will diet cola instead of regular cola help me lose fat?
It can, if it replaces sugary drinks you would otherwise have. The sweetener does not burn fat. You just drink fewer calories. In trials, that came to about 1 kg more weight loss on average (PMID 35285920). Used on purpose, in place of a sugary soda, it helps fat loss, as long as the rest of the diet has enough protein and vegetables.
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1) PMID 35285920: network meta-analysis, diet drinks instead of sugary drinks, about 1 kg less body weight in adults with overweight
2) PMID 33171964: small randomized, double-blind crossover trial, aspartame and sucralose, minimal effect on gut bacteria
3) PMID 37111090: review, mixed human results on sweeteners and gut bacteria, no consensus yet
4) PMID 26365102: systematic review, sweeteners instead of sugar lowered calorie intake and body weight; versus water, limited data
Martin Barna
Online nutrition and fitness coach. Since 2013 I have helped 600+ people lose fat and keep the result. I coach with evidence and plans you can keep up.
Apply for coachingThis article is for information only. It is not medical advice. If you have a health condition, talk to your doctor.