Are diet sodas and sweeteners bad for you, and if so, why?
For the occasional glass of diet soda, the risks have not yet been clearly demonstrated. If you drink large amounts every day, several large studies, especially those concerning aspartame and acesulfame-K, give reason for caution.
Diet soda is marketed as a healthy alternative, but the research picture is nuanced. There are both possible benefits and genuine concerns, and for most risks conclusive causal evidence in humans is still lacking.
When it comes to weight and blood sugar, the picture does not look bad. Long-term use of sweeteners appears to be beneficial for body weight and blood sugar regulation in people with type 2 diabetes, and is better for your teeth than regular sugar1. Some review studies also find no measurable negative effect on weight or blood sugar2.
For cancer, the signals are more worrying. A large French study with nearly 103,000 participants linked above-average intake of artificial sweeteners to a 13% higher risk of cancer. Aspartame was associated with a 15% higher overall cancer risk and a 22% higher breast cancer risk; acesulfame-K with a 13% higher cancer risk3. The researchers themselves cannot fully rule out confounding factors, but the scale of the study makes the findings worth taking seriously.
One possible explanation runs through your gut bacteria. Research from the Weizmann Institute showed that saccharin, sucralose and aspartame can disrupt the composition of your gut bacteria and thereby cause blood sugar problems. That effect was transferable via a gut transplant to mice without their own gut bacteria, which makes a causal link plausible4. A smaller study in 17 healthy adults found no effect at realistic doses after 14 days5. One author of that study received a honorarium from PepsiCo, which limits its independence.
Large observational studies also link sweetener consumption to cardiovascular disease, higher mortality, depression and childhood obesity6,2,7. A prospective study over 8 years among more than 12,000 Brazilians linked high intake of sweeteners, including sugar alcohols such as erythritol and xylitol, to faster cognitive decline, particularly in people under 60 years of age8. Here too, these are associations and confounding factors have not been fully ruled out. The fundamental problem remains: people who drink a lot of diet products also live differently in other ways. Genuine causal evidence in humans is almost entirely absent.
Ten studies used: large cohort studies (up to 102,865 participants), a prospective study over 8 years, a small randomised study (17 participants), studies in humans and mice from the Weizmann Institute, review articles and meta-analyses. Almost all of the evidence is associative. One study has a potential conflict of interest (PepsiCo honorarium). Total estimated number of participants across the clinical studies: over 130,000.
How harmful is too little daylight or sunlight?
Too little sunlight is demonstrably harmful, especially for your bones. For broader disease risks the associations are plausible but not yet proven causes, and a daily dose of 5 to 30 minutes of sunlight is already sufficient for most people.
Are smoothies and fresh juice just as healthy as whole fruit?
Whole fruit beats fruit juice: more fibre, greater satiety and fewer free sugars. Smoothies fall somewhere in between, but are not equivalent to whole fruit either.
Are ultra-processed products bad for your longevity?
Eating a lot of ultra-processed products is associated with a shorter lifespan and more chronic disease, but the effect varies considerably by product type and largely disappears when your overall diet quality is good. Eating less processed meat and improving your overall eating pattern offers the greatest benefit.
Is the taurine in energy drinks harmful?
Taurine in common energy drinks does not appear to be harmful, but keep an eye on the caffeine: that is the substance from which the documented risks of energy drinks originate.
How bad is ultra-processed food, and what does it do to you?
Eating a lot of ultra-processed food is consistently associated with higher risks of cardiovascular disease, diabetes, depression and premature death. The evidence is observational and not always of high quality, but the associations are broad enough to make limiting intake a sensible choice.
Am I consuming too much protein, and is that bad for my kidneys?
For people with healthy kidneys there is little reason to worry about a generous protein intake, but anyone who has kidney disease or was born with one kidney would be wise to limit their intake and consult a dietitian.