Can observational studies with self-reported diet data prove that food causes changes in mortality?

We analyzed the available evidence and found that observational studies relying on self-reported diet data can identify patterns between what people eat and their death rates, but they cannot prove that food choices cause changes in mortality [1]. These studies ask people to remember and report what they ate over time, which can lead to inaccuracies due to memory bias or misreporting. Even when strong links appear—like higher intake of processed foods being tied to higher death rates—we cannot say those foods directly caused the outcomes. Other factors, such as physical activity, sleep, stress, or genetics, may also be involved and are hard to fully account for in this type of research. The evidence we’ve reviewed so far leans toward the idea that while these studies are useful for spotting possible trends, they are not designed to establish cause-and-effect relationships. We have not found any studies that contradict this view. This means that if you see headlines claiming “Eating X increases your risk of dying,” the underlying research likely comes from this kind of observational data—and while it may point to something worth exploring further, it doesn’t confirm a direct link. For now, the best use of this data is to guide future experiments, not to make definitive personal health decisions. If you’re trying to improve your health, focus on consistent, balanced habits rather than single foods or strict rules based on observational findings.