Posted on 2 November 2021
Last week, we covered a recent study suggesting that people who skipped breakfast were more likely to die from cancer and all causes, and discussed why this and similar studies can’t always be taken at face value. We ended on the note that while we can’t conclude from such observational studies that skipping breakfast causes cancer, this research isn’t useless either, and the relationship between breakfast consumption and health is worth looking into further. So, let’s explore the research on this topic a little further: is there any evidence for a causal link between breakfast skipping and mortality? Do we know of any biological mechanisms through which this effect might work?
As discussed last week, the data show that people who skip breakfast, which is widely perceived as unhealthy, tend to be people who engage in other unhealthy activities such as smoking. The difficulty of controlling for such confounding factors could explain the observed relationship between breakfast and mortality, but let’s just pretend for a moment that it doesn’t – that skipping breakfast does, directly or indirectly, have a negative impact on your health. What mechanisms in the body could explain this? A few theories have been proposed – for example:
In the previous article, we discussed why randomised trials are much more valuable than observational studies when it comes to working out whether A causes B. There are randomised trials of breakfast consumption, but because these kinds of trials generally have much smaller sample sizes and shorter durations, they measure changes that are observable at this sample size and timescale – things like body weight or blood sugar, for example.
To illustrate the problem, suppose you were to conduct a very unethical randomised controlled trial on cigarette smoke. You recruit 200 people for a trial that will last 16 weeks ( nearly the same conditions as the largest and longest-running randomised breakfast trial in the meta-analysis above), and split them into two random groups. One group smokes 5 fake cigarettes a day, and the other smokes 5 real ones. After the 16 weeks are up, would you expect to see any statistically significant differences in mortality between the two groups? Probably not, because even when it comes to something as deadly as smoking, chronic diseases take a long time to develop. So all we really know is that in randomised trials of breakfast consumption, skipping breakfast is associated with minor reductions in body weight and caloric intake (with significant variation between studies), and skipping breakfast as part of dietary restriction doesn’t appear to have any adverse metabolic effects.
As for the rest of the observational studies, it’s a mixed bag. The study covered last week certainly isn’t the first to find an association between breakfast skipping and mortality, nor will it be the last. However, we must stress again that these kinds of studies are not designed to show any kind of causal relationship. It’s also worth noting that there are also observational studies that fail to show associations, but these studies are less likely to be reported on by the media. One study in 2019 even looked at data from the exact same survey as the last article’s study, and while they found an association with cardiovascular mortality, they found no statistically significant relationship with all-cause mortality. This highlights how simply the way in which researchers choose to analyse the data and control for confounders can yield different results.
Personally, since conclusive evidence isn’t here yet, I would base my decision on personal circumstances. Are you able to skip breakfast without it negatively impacting your ability to function mentally and physically? Are you trying to lose weight? Is your habitual breakfast a tower of bacon and fried eggs? Then skip away free of guilt!