A while ago we discussed a study
suggesting that morning exercise before breakfast may help with weight-loss.
Although the mechanisms behind this are still a matter for debate , there has
been a research trend to consider how the timing of eating could affect weight
loss or lack thereof. One study in particular that has gained attention is a
longitudinal study from Spain.
The study, which was published in
International Journal of Obesity,
included a total of 420 overweight participants that took part in a weight-loss
programme for 20 weeks. The researchers measured physical variables such as
body fat, appetite, hormone levels, blood pressure and energy expenditure. In
addition to that, participants had to recall their diet from the past 24 hours
every day and keep a 7-day food diary. Participants were also asked about their
sleeping habits and sleep duration. Based on this information the researchers
split the participants into two groups: early and late eaters. When considering
the differences between early and late eaters the researchers noted that lunch
appeared the only mealtime related to weight loss. The key findings indicated
that individuals who were early eaters of lunch lost more weight from five
weeks into the programme up to the end of the study. In contrast to that,
individuals who were classified as late eaters appeared to lose less weight and
to lose it at a slower pace than early eaters. Based on the observation that
there were few other measured differences between the groups, the researchers
argued that there is a relationship between the timing of food intake and
weight-loss in humans and that this relates specifically to lunch-time.
This study is interesting,
because both groups were in similar environments that controlled factors that
have been suggested to affect obesity research in the past. These include
participants not sticking to a diet or exercise regime (but stating otherwise),
participants being in situations outside of the research project where it may
be challenging to say no to high calorie foods (i.e. parties, weddings etc.)
and research including participants whose sleeping patterns were disrupted due
to children or work (which indirectly could affect weight loss or lack
thereof). On the other hand, excluding these factors comes at a cost of
ecological validity. If many common problematic areas were controlled in the
study, then how would those individuals fare once the study is over? Similarly,
what behavioural factors can be considered to affect when an individual is keen
to eat?
Although this is an interesting
train of thought, it is worth mentioning that this consideration is not
relevant for the findings of the study. The purpose of the study appears to be
concerned with pin-pointing what observations are worthy of further research.
Given the nature of the study, it is not possible to establish the direction of
the relationships found or whether it is a case of a single linear association
or several mediated or moderated links. There are also further areas that need
to be explored in depth in future studies. These include the potential
relationship between timing of eating and timing of energy expenditure and the
development of tools for measuring these processes in a reliable way.
Overall, this study is valuable in terms of the research we hope to see grow out of it.
Although we are not surprised to read about the findings from this study, we
would still like to caution that they need a nuanced interpretation. This study
does not imply that eating an early lunch is a magic step to lose weight, as
the participants ate highly nutritious meals and were active throughout their period
of observation. Similarly, eating an early lunch may contribute to a higher
weight loss, but the difference between groups needs to be put into perspective
as the difference between early and late eaters was 2.2 kg on average, with the
late eaters losing 9.9 kg after 20 weeks. This can be due to a multitude of
reasons and we can only speculate what would have happened if the study had
continued for a longer time period. Unfortunately, at this stage, we do not
have access to any studies with such information. Nevertheless, this is an area
that we are following keenly and aim to update our readers of in the future.