“Have a good breakfast, a full lunch and a light dinner.” But just how important is the timing of meals? A recent study shows that when it comes to weight control, “when to eat” may be as crucial as “what to eat”, especially for those who are naturally more prone to gaining weight.
The study was recently published in the journal Obesity. The authors are a research team from institutions such as the University of Murcia in Spain and Harvard Medical School in the United States. Researchers analyzed over 1,100 overweight or obese adults, collecting data such as their meal times and weight changes, and calculated the obesity-related “polygenic Risk Score” (PRS-BMI) for them. The study has for the first time discovered a significant interaction between meal times and an individual’s genetic background.
Modern genetics has discovered that hundreds or even thousands of genes influence a person’s risk of obesity in a variety of complex ways, such as affecting appetite and satiety, metabolism, and fat storage. It’s like setting a “factory default value” for weight gain, but the final outcome is also greatly affected by lifestyle and environment. Meal times, as a signal regulating the biological clock, have long been regarded as related to metabolism and weight regulation. Previously, scientists have known that meal times and genetic factors each affect the risk of obesity, but how they interact with each other remains unclear.
The subjects of this study were 1,195 adults who participated in the Spanish study “Obesity, Nutritional Genetics, Time and the Mediterranean Diet” (ONTIME). The researchers first calculated the weighted average time of the first and last meals of each day for these participants throughout the week, and then took the midpoint between these two meals as the “midpoint of meals”, which was used as an indicator of the timing of meals. For instance, if a person has breakfast at 8 a.m. and dinner at 9 p.m. on average every day, then the “mealtime” would be 2:30 p.m.
Researchers used a “polygenic risk score” to assess the individual genetic susceptibility of participants. The results show that in people with a high genetic risk, for every hour the midpoint of a meal is delayed, their body mass index (BMI) increases by more than 2 kg/m². In other words, for this group of people, “eating late” is a significant risk factor for weight gain.
However, in people with a lower genetic risk, no such significant association was found between meal times and BMI. This indicates that eating earlier may be an effective personalized weight management strategy for people with an obesity “gene”. In addition, the research also found that later meal times are associated with poorer long-term weight maintenance after weight loss. For every hour that meal times are delayed, weight will increase by 2.2% in the long term.
This study is the first to prove that meal times can regulate the genetic risk of obesity. For those with a higher genetic risk of obesity, merely changing the time of meals and developing the habit of eating early may be a simple yet effective way to combat the tendency towards obesity.
The authors of the study also stated that it was an observational study and could not determine a causal relationship. Meanwhile, the study relies on the self-reported meal times of the participants, which may lead to recall bias. Future research will require a more diverse population and more objective measurement methods to verify these findings.