World Health Organization (WHO) studies show that worldwide obesity has nearly tripled since 1975. Data made available by the Organization show that nearly 2 billion adults over the age of 18 were overweight in 2016; of these adults more than 650 million were obese. The figures also reveal that over 340 million children and adolescents in the 5 to 19 age group were either overweight or obese. Meanwhile, the latest data on children under the age of 5 show that more than 39 million of them were overweight or obese in 2020. The World Obesity Federation now predicts that one billion people globally, including 1 in 5 women and 1 in 7 men, will be living with obesity by 2030.
The Federation’s projections are a startling reminder that obesity, a condition that is largely preventable, has not received the attention it deserves. Obesity is one of the main risk factors behind several chronic diseases, including diabetes, cancer and other adverse health conditions.
Among the reasons that lead to an increase in risk of the onset of obesity is an unhealthy diet and lifestyle that results in excess body weight. Although regulation of calorie intake from diet, the number of calories burned through physical activity, and molecular changes in fat tissue, have been identified as the three main pillars in body weight regulation, very few studies have comprehensively investigated the impact of diet timing on regulating diet.
A new study by investigators from Brigham and Women’s Hospital in the United States on the impact of late eating on body weight regulation has come up with the revelation that when we eat significantly impacts our energy expenditure, appetite, and molecular pathways in adipose tissue.
Previous studies by the same researchers had shown that late eating is associated with increased obesity risk, increased body fat, and impaired weight loss success. The new study attempted to understand why this was so. To test the mechanisms that may explain why late eating increases obesity risk, the study team explored different eating schedules while keeping everything else consistent. They found that eating four hours later makes a significant difference to hunger levels, the way calories are burned, and how the body stores fat.
The study involved 16 participants whose body mass index (BMI) was in the overweight or obese range. Each participant completed two laboratory protocols: one with a strictly scheduled early meal schedule, and the other with the exact same meals, each scheduled about four hours later in the day.
In the last two to three weeks before starting each of the in-laboratory protocols, participants maintained fixed sleep and wake schedules, and in the final three days before entering the laboratory, they strictly followed identical diets and meal schedules at home. In the lab, participants regularly documented their hunger and appetite, provided frequent small blood samples throughout the day, and had their body temperature and energy expenditure measured.
To measure how eating time affected molecular pathways involved in adipogenesis — the way that the body stores fat — investigators collected biopsies of adipose tissue from a subset of participants during laboratory testing in both the early and late eating protocols, to enable comparison of gene expression patterns and or levels between these two eating conditions.
Results revealed that eating later had profound effects on the hunger and appetite-regulating hormones leptin and ghrelin, which influence our inclination to eat. Specifically, levels of the hormone leptin, which signals satiety, were decreased across the 24 hours in the late eating condition compared to the early eating conditions. When participants ate later, they also burned calories at a slower rate and exhibited adipose tissue gene expression towards increased adipogenesis and decreased lipolysis, which promote fat growth.
These findings suggest that there could be converging physiological and molecular mechanisms underlying the correlation between late eating and increased obesity risk. Besides being consistent with a large body of research suggesting that eating later may increase one’s likelihood of developing obesity, the findings also shed new light on how this might occur. By using a randomized crossover study, and tightly controlling for behavioral and environmental factors such as physical activity, posture, sleep, and light exposure, investigators were able to detect changes in the different control systems involved in energy balance, a marker of how our bodies use the food we consume.
In future studies, the investigators aim to recruit more participants and widen the gender and age base to increase the generalizability of their findings to a broader section of the population. While this study cohort included only five female participants, the study was set up to control for the menstrual phase, reducing confounding but making recruiting women more difficult. Going forward, the researchers said they would also attempt to better understand the impact that mealtime and bedtime had on energy balance. They added that in future studies they would also consider how other behavioral and environmental variables alter the biological pathways underlying obesity risk.
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