WHEN to eat may be just as important as WHAT you eat, according to a new Spanish study about the best time to eat for healthy weight loss.

You know how they say timing is everything? Timing is critical for a good joke to be successful and the same holds true for a healthy diet.

When to eat: the study

During the first few weeks of the 20-week study, run by researchers from Brigham and Women's Hospital in collaboration with Tufts University and the University of Murcia, all 420 subjects lost weight at about the same rate. But starting around week five, weight loss for dieters who ate their main meal after 3 p.m. began to stall and remained sluggish for the duration of the study. In the end, they lost 22 percent less weight than dieters who ate the bulk of their calories earlier during the day.

All of the subjects ate and burned off about the same number of calories and all followed a Mediterranean-style diet consisting of lean proteins, fruits and vegetables and healthy fats such as olive oil. The subjects consumed about 40% of their daily calories at lunch and all slept approximately the same number of hours each night. When tested, their appetite and hunger hormones were all normal. Even their genetics were similar.

So what gives?

The late-in-the-day eaters did tend to be breakfast-skippers and also showed a higher level of insulin resistance, however, researchers say this did not contribute to the subject’s stalled weight loss.

The researchers' best guess is that eating later in the day messes with the body's internal clock system, known as circadian rhythms, and this might somehow have an adverse effect on the metabolism.

One of the study’s coauthors, Frank Sheer, explained it this way:

“The circadian system is made up of a master clock in the brain and peripheral clocks in most cells throughout the body. Normally, the master clock synchronizes all peripheral clocks, similar to the conductor of an orchestra. When we don’t know when to eat, meal timing is abnormal this leads to de-synchronization between these different clocks, resulting in a cacophony.”

Should we be eating our biggest meal for lunch?

Sheer also pointed out that Spaniards tend to eat their largest meal midday whereas we eat our largest meal for dinner. Different cultures also have a different sense of when to eat. However, starting in the eighteenth century, as more people began getting factory jobs that did not allow them to run home for lunch, Americans began shifting their main meal toward the end of the day—which is still the norm today. This is why many Americans think dinner time is the best time to eat their biggest meal. Asking an American when to eat dinner will probably give you a few blank stares because eating breakfast, lunch and dinner around a certain time are so ingrained into our culture that it isn’t even a question of when to eat certain meals.

Sheer believes, however, that it’s too soon to relate his study’s outcomes to the American lifestyle, but he does think the timing of eating could be an important part of weight loss.

“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 of the study said.

What should I do to maintain a healthy weight?

To maintain healthy weight, it’s important to avoid eating late at night because that 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 simply just burned away. So, keep that in mind as you make your healthy meal choices.

Something to keep in mind

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