By Natalie Obermeyer
We constantly receive information on what and how much to eat. But, have you ever thought about when we should eat? A recent study by researchers of the Jean Mayer USDA Human Nutrition Research Center on Aging (HNRCA) at Tufts University suggests that eating your main meal earlier in the day may facilitate more weight loss than eating the meal later in the day.
Jose Ordovas of the HNRCA’s Nutritional Genomics Laboratory collaborated with researchers from Brigham and Women’s Hospital and the University of Murcia in Spain to track the weight of 420 men and women in Spain who were enrolled in a weight loss program. They found that people who ate their main meal earlier in the day lost 2.3% more body weight (21.8 lbs as compared to 16.9 lbs). Even though both early-eaters and late-eaters had equivalent calorie intakes, energy expenditures, and ate similar foods, the early-eaters lost more weight.
Interestingly, the researchers found no significant associations between timing of smaller meals and weight loss. The predictor of weight loss differences was the timing of the main meal, which in Spain is lunch and provides approximately 40% of daily energy intake. However, late-lunch eaters generally ate less for breakfast or were more likely to skip it altogether. Thus, eating a nutritious breakfast may also play a role.
This study was the first prospective, longitudinal study to show that timing of meals predicts weight loss effectiveness in humans. However, multiple animal studies have shown that timing of food intake predicts weight gain. For example, feeding nocturnal mice a high-fat diet during the day (when they usually sleep) causes them to gain more weight than feeding the mice a high-fat diet during the night, even though the mice’s calorie consumption and activity levels are the same.
Additionally, there is evidence emerging that adipose (fat) tissue contains a circadian clock inside it. For example, certain genes in fat tissue are expressed at certain times of the day. The temporal expression of these genes may cause the cells to be more susceptible to storing or mobilizing fat at certain times. Thus, eating a large meal when adipose tissue is in a more fat-storing mode may increase weight gain.
Finally, it is important to realize this was an observational study. While the study found a significant association between timing of food intake and weight loss, this does not necessarily mean that eating meals earlier in the day directly causes more weight loss. The association is novel and important, but more studies need to be done to determine if meal timing does indeed play a causal role in weight loss. Nevertheless, the study certainly suggests that it is important to factor in meal timing, in addition to food content, when planning weight-loss strategies.
Natalie Obermeyer is a first year student in the Nutrition Communication and Masters of Public Health programs. When she is not studying, reading, or writing, she loves to run, hike, ski, play outdoors in the sunshine, and experiment in the kitchen