A new study conducted by researchers in Spain and at Brigham and Women’s Hospital, Harvard Medical School, and Tufts University found that out of 420 middle-aged dieters in Spain, those who ate a late lunch (lunch being the largest meal of the day in Spain) lost significantly less weight and lost weight slower than those who ate lunch earlier.
The study was published on January 29, 2013 in the International Journal of Obesity.
“This is the first large-scale prospective study to demonstrate that the timing of meals predicts weight-loss effectiveness,” said Frank Scheer, PhD, MSc, Director of the Medical Chronobiology Program and Associate Neuroscientist at Brigham and Women’s Hospital in Boston, Assistant Professor of Medicine at Harvard Medical School, and a senior author of this study, according to a press release issued by Brigham and Women’s Hospital (BWH).
“Our results indicate that late eaters displayed a slower weight-loss rate and lost significantly less weight than early eaters, suggesting that the timing of large meals could be an important factor in a weight loss program,” Dr. Scheer said.
“There is emerging literature demonstrating a relationship between the timing of feeding and weight regulation in animals. However, whether the timing of food intake influences the success of a weight-loss diet in humans is unknown,” the authors wrote in background to the study.
The Study; Methodology
In order to “evaluate the role of food timing in weight-loss effectiveness,” the researchers studied a group of 420 overweight and obese individuals in Spain, who followed a 20-week weight-loss program.
Half of the participants were women, half men. Their mean age was 42, with an age range of plus or minus 11 years. All of the participants were overweight or obese (average BMI of 31.4) at the beginning of the study.
The participants were grouped in two groups: early lunch eaters and late lunch eaters, according to their self-selected timing of lunch, their main meal of the day. In Spain, by custom, the main meal of the day is lunch, with 40% of the day’s calories typically consumed at lunch. Of the study participants, 51% were early lunch eaters who ate lunch before 3:00 p.m., and 49% were late eaters, who ate lunch after 3:00 p.m. each day.
The researchers also studied, and controlled for other factors, including energy (calories) intake and expenditure, appetite hormones, CLOCK genotype, sleep duration and chronotype.
The researchers found that “energy intake, dietary composition, estimated energy expenditure, appetite hormones and sleep duration [all were] similar between both groups.”
However, surprisingly, “the late lunch eaters lost less weight and displayed a slower weight-loss rate during the 20 weeks of treatment than early eaters.”
The early-lunch participants (who ate lunch before 3:00 p.m.) lost an average of 22 pounds over the 20-week diet treatment program. The late lunch eaters (who ate lunch after 3:00 p.m.), lost an average of 17 pounds over the 20-week period — an average of 25% less weight loss than the early eaters.
The researchers found that “timing of the other (smaller) meals did not play a role in the success of weight loss. However, the late eaters—who lost less weight—also consumed fewer calories during breakfast and were more likely to skip breakfast altogether. Late-eaters also had a lower estimated insulin sensitivity, a risk factor for diabetes,” according to the BWH news release.
Controlling for other factors, the authors reported that “Neither sleep duration, nor CLOCK SNPs or morning/evening chronotype was independently associated with weight loss.”
“The researchers also examined other traditional factors that play a role in weight loss such as total calorie intake and expenditure, appetite hormones leptin and ghrelin, and sleep duration,” BWH stated in its release about the study. “Among these factors, researchers found no differences between both groups, suggesting that the timing of the meal was an important and independent factor in weight loss success,” the BWH release reported.
“The timing of the main meal by itself seems to be the most determinant factor in weight loss effectiveness, and therefore eating at the right time may be a relevant factor to consider in weight loss therapies,” the authors wrote.
“Eating late may influence the success of weight-loss therapy. Novel therapeutic strategies should incorporate not only the caloric intake and macronutrient distribution—as is classically done—but also the timing of food,” the authors wrote in conclusion.
While the study does show a significant correlation between eating the main meal of the day late and slower and less weight loss, nevertheless it does not definitively establish a cause-and-effect relationship, nor was the study designed to explain the mechanisms that underlie the correlation between meal time and rate of weight loss, Dr. Sheer, the senior author pointed out.
It remains unclear exactly why eating a late lunch may be related to slower weight loss. One theory, suggested by other professionals, is that the late lunchers (who also tended to eat less for breakfast or skip breakfast) may have been waiting too long between meals. This could have effects on metabolism, according to Connie Diekman, Director of University Nutrition at Washington University in St. Louis, who was not involved in the study.
Ms. Diekman told HealthDay that other studies have suggested that eating evenly spaced meals (every three to four hours) is helpful in weight control.
“As a registered dietitian, this study helps me feel comfortable with recommendations about the importance of meal spacing,” she said. “But it does not give an answer to why or what impacts that might have on weight.”
Dr. Scheer, a senior author of the study, noted that the current findings are consistent with animal research showing that meal timing seems to affect weight, as referenced in the background to the study.
Dr. Scheer suggested to HealthDay that the relationship between meal timing and weight loss “may have to do with effects on the body’s circadian rhythms, which influence a range of functions, including the sleep-wake cycle and metabolism.” “There is a ‘master clock’ in the brain that coordinates those rhythms, but there are also ‘peripheral clocks’ in tissue and cells throughout the body,” Dr. Scheer explained.
“In animals, unusual feeding times seem to disrupt some of those peripheral clocks and throw them out of sync with the master clock. In theory, that clock ‘decoupling’ could affect weight control,” according to Dr. Scheer’s hypothesis.
Sensitivity of weight loss to the timing and quantity of meals is consistent with the common belief that it is best to eat your largest meal earlier in the day, in order to increase your chances of burning off the calories you take in. In an interview with HealthDay, Dr. Scheer pointed to the popular advice to eat breakfast like a king, lunch like a prince, and dinner like a pauper.
Dr. Tim Church, director of the Laboratory of Preventive Medicine at the Pennington Biomedical Research Center in Baton Rouge, Louisiana, who was not involved in the study, suggested to CBS News, that “eating late at night can raise body temperature as well as blood glucose and insulin levels, which disrupts the fat-burning that generally occurs during sleep. Timing meals, especially the heaviest meals, can make a difference in whether calories are processed into extra pounds or burned away.”
“To maintain healthy weight, it’s also important to eat when you are hungry, and not just in response to food cravings,” Dr. Church said. “Hunger peaks when you expect it to peak at breakfast, lunch and dinner. Cravings peak after dinner,” he said.
However, Dr. Sheer, the senior author of the study, cautioned that more research is needed “to see whether the timing of a person’s main meal directly influences weight — and how important that influence really is.” This includes a need for further research to determine whether timing of the dinner meal — when dinner is the main meal of the day, as in the United States — may affect a person’s rate of weight loss, he indicated.
The new study is one of the first to address this issue in humans. “This study emphasizes that the timing of food intake itself may play a significant role in weight regulation” Marta Garaulet, PhD, professor of Physiology at the University of Murcia Spain, and lead author of the study, explained in the BWH release about the study.
She recommended that weight loss treatments should incorporate not only calorie and nutrient intake and distribution, but should also include attention to timing of meals.
The full report of the new study, “Timing of food intake predicts weight loss effectiveness,” was published on January 29, 2013 in the International Journal of Obesity.
See related HelpingYouCare® reports on:
- Weight Loss/ Maintaining a Healthy Weight: Physical Wellness;
- Diet & Nutrition: Physical Wellness;
- Exercise: Physical Wellness; and
- Other Areas of Wellness.
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