If you’re familiar with circadian rhythms, you know they represent 24-hour cycles of sleeping and wakefulness, body temperature fluctuations, hormonal secretions, and energy ups and downs. Your mood, your metabolic health, your sleeping patterns, and your ability to focus and pay attention while you work are all determined, at least in part, by how well your circadian rhythm system works in line with your day-to-day schedule.
Now, researchers at the Pennington Biomedical Research Center in Baton Rouge, Lousiana, say your circadian rhythm system also plays a role in your ability to lose weight and they’ve figured out how it happens. The secret, they say, is syncing your three meals a day to your circadian rhythm by eating those meals earlier in the day. Their study, published July 2019 in the journal Obesity, found that doing so won’t necessarily increase the rate at which you burn calories, but it can help reduce your appetite, burn fat more efficiently, and improve your overall metabolic health. To reap these benefits, the researchers suggest timing your last meal of the day as early as 2 p.m.
You’ve probably heard the old adage, “breakfast is the most important meal of the day,” and this could be an important reason why. Previous studies have found that people who eat a large breakfast manage their weight better than those who skimp on food first thing in the morning. Other studies have found that starting the day with a big meal and following it up with two lighter meals, especially a lighter dinner, also reduces overall appetite and encourages weight loss. Researchers also know that more energy is used (more calories are burned) during the earlier part of the day than later.
In the Pennington study, seven overweight men and four overweight women ate prescribed meals at 8 a.m., 2 p.m. and 8 p.m. for four days, then switched to eating their meals at 8 a.m., 11 a.m., and 2 p.m. for another four days. The meals provided enough calories for weight maintenance and were equally balanced with respect to major nutrients at 50% carbs, 35% fat and 15% protein. No other food or caloric beverages were provided or allowed to be consumed. Six times a day, the participants filled out surveys regarding their hunger levels, desire to eat, sense of fullness, and energy levels.
Lab results showed that restricting eating to earlier times of the day decreased levels of ghrelin, the “hunger hormone” that stimulates appetite, steadies hunger, decreases the desire to eat and increases the sense of fullness. While this study did not find that aligning meals to circadian rhythms increases the rate at which we burn calories, it did show that timing meals earlier in the day can help normalize appetite in those who are overweight. More research in this area could help determine just how shifting meals to earlier in the day affects overall energy and fat metabolism.
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Ravussin E, Beyl R, Poggiogalle E, Hsia DS, Peterson CM. Early time-restricted feeding reduces appetite and increases fat oxidation but does not affect energy expenditure in humans. Obesity. August 2019 (First published online July 24, 2019); 27(8):1244-1254.