WHO’s cancer research agency and the International Agency for Research on Cancer (IARC) determined aspartame to be a possible carcinogen after reviewing and assessing the potential carcinogenic effect of the sweetener but says it’s safe to consume in limited amounts.

The amount you would have to consume per day has to be 9 cans of Diet Coke or more to have any possible cancer-causing effects.

So, what does this all mean?

Just to put it into context alcohol is a much stronger carcinogen than aspartame in Diet Coke.

Also being obese is a much greater risk factor in causing cancer.

Being obese causes an increased risk of cancer of 17% which is massive. 

Excuse the pun.

If consuming a few diet fizzy drinks help you to stay lean, then this is a no brainer. 

As being obese is much more likely to increase your risk of cancer than drinking a couple of diet cokes.

In conclusion would I steer on the side of caution with diet fizzy drinks, yes!

I would but I don’t think having a few every so often is an issue.

Being overweight and drinking alcohol is a much bigger problem. 

If drinking some Diet coke helps you keep on track with your nutrition and stops you drinking alcohol on nights out. 

You should definitely go for it.

The Broader Point: Why Processed Food Choices Matter for Body Composition

The WHO’s determination on aspartame matters less for individual cancer risk — which remains very low even for heavy consumers — than for what it signals about our relationship with ultra-processed food and drink. The explosion in diet soft drink consumption over the past four decades reflects a broader cultural failure: the belief that engineered, synthetic alternatives to whole foods are a safe or adequate long-term strategy for managing weight and metabolic health.

At BTX, we counsel all of our North London clients away from habitual diet soft drink consumption — not primarily because of the aspartame controversy, but because the data on ultra-processed food consumption and metabolic health is consistently damaging. Regular diet drink consumers tend to have higher rates of insulin resistance, more disrupted appetite regulation, and poorer gut microbiome diversity than those who replace these drinks with water, black coffee, or herbal tea.

Simple Swaps That Improve Metabolic Health

Our nutrition coaching at BTX focuses on practical, sustainable habit change rather than rigid restriction. For most clients, replacing diet drinks with sparkling water or black coffee, prioritising whole food sources of sweetness (fruit, dark chocolate), and reducing overall ultra-processed food intake produces measurable improvements in body composition within weeks — not months. If you want evidence-based nutrition coaching in North London, get in touch with BTX at 529a Finchley Road, NW3.

For clients at BTX, the dietary focus is always on building a sustainable framework of food choices around whole, minimally processed foods — not on eliminating any single product. The aspartame story is a useful reminder that engineered alternatives to natural foods carry uncertainty, and that long-term health is best served by a diet built primarily around foods that existed before the industrial food system created them.