There are many reasons why nutrition science is really quite problematic, and you’ll hear more from me on that from time-to-time. But I think it might help at least to explain here why, when I’m looking for reliable scientific evidence to backup the health claims made for food, drinks or specific nutrients, I tend to favour systematic reviews or meta-analyses.
What these involve, in very basic terms, is a group of qualified reviewers looking for all the latest smaller scientific studies that have been conducted on a particular topic, and then pooling all their results into one big review to see what they tell us overall.
The conclusions from systematic reviews tend to be more powerful and more reliable than individual studies as they:
- help iron out any biases in the original research (e.g. was it sponsored by a company who had an interest in its results being positive?);
- it means that the results are based on the effects of a food, drink or nutrient seen across a much larger number of people combined, than in the original individual research studies themselves;
- this also means that ‘confounding’ factors e.g. socioeconomic and lifestyle factors which may be skewing the study results, have more chance of being flattened out across a greater number of people;
- in making an overall assessment, the reviewers can also take into account how many of the previous individual studies were of good quality, or used poor research methods and therefore have less reliable findings.
It may or may not come as a surprise to you that there are very few scientific findings that you can rely on 100%. And there may also be inconsistencies in the way that systematic reviews are conducted, so they are not infallible. They are also seldom likely to be the last word on a topic, as new scienctific discoveries are made all the time. But they should reflect the most up-to-date science available at the time of the review, and they remain generally regarded internationally as the most reliable source of evidence of the impact on human health of food, drinks, nutrients and medicines.