Does Skipping Breakfast Really Shorten Your Life? A Broader Look At The Research

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?

How Might Skipping Breakfast Lead To Increased Mortality?

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:

  • People who skip breakfast overeat later in the day: Perhaps skipping breakfast affects appetite in a way that makes people overcompensate later on in the day, meaning that people who skip breakfast actually end up eating more than people who don’t. However, the evidence doesn’t really support this: according to those randomised controlled trials that do exist, breakfast skippers consume fewer calories and lose more weight on average compared with breakfast eaters (with the caveat that the longest trial lasted 16 weeks).
  • Skipping breakfast disrupts the circadian rhythm: The body’s metabolism is influenced by the circadian rhythm, a genetically controlled internal clock that is ‘set’ by environmental stimuli, primarily the day/night cycle. When our activities do not align with our circadian rhythm (such as in the case of night-shift workers), we encounter metabolic problems – we are making our bodies digest food and be active during a time in which our metabolism is geared towards sleep. Perhaps skipping breakfast ‘confuses’ the circadian rhythm in a similar way to jet lag, leading to metabolic problems. Again, however, this isn’t really supported by the evidence – trials on time restricted feeding with an eating window that excludes breakfast show overwhelmingly beneficial effects on metabolism, such as improved responsiveness to the hormone insulin and reduced oxidative stress.
  • People who skip breakfast eat supper too late: Maybe people who skip breakfast eat larger suppers to compensate and do so later at night, which is associated with increased mortality. However, this is really just another confounding factor – this theory proposes that it is eating too much too late, and not the skipping of breakfast itself, that has a negative health impact.
  • People who skip breakfast have less energy for physical activity: This theory is plausible and has some supporting evidence, but again, the problem here is exercise levels and not breakfast-skipping itself.

What Do Other Studies Say? And Where Are The Randomised Trials?

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.

Design summary of studies included in the meta-analysis of randomised breakfast trials. All studies looked at either weight loss, daily energy intake or both.

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.

Unless otherwise specified, diamonds show changes in weight and daily energy intake for breakfast-eaters over the course of each study compared with breakfast skippers. Each row shows the findings for one of the included randomised studies.

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.

So… Are We Eating Breakfast Or Not Then?

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!

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