Weight loss experts and dietitians have been dispelling the myth that “eating after 8:00 PM will make me fat” for years. And it’s still mostly true: the calories you eat at night won’t turn into flab simply because they’re north of 8:00 PM. But new research from the Salk Institute for Biological Studies has found that when we eat does affect our weight (as well as a variety of other functions) – but for other reasons than previously thought.
This is what (very complex) science tells us:
In the study, published in the journal Cell Metabolism, one group of mice ate a calorie-restricted, healthy diet; the other ate a high-fat, high-calorie diet. The second group was split into two groups; the first was allowed to snack 24/7, while the second was restricted to eating just 8 hours of the day. At the end of the study, the researchers found that the mice on the restricted but high-calorie diet stayed just as lean as the mice on the health-fare diet. Compared to the mice who noshed 24/7, the time-restricted feeding mice were protected not only from obesity, but also from hyperinsulinemia (elevated insulin levels, which is a symptom of Metabolic Syndrome), glucose intolerance, leptin resistance, and increased inflammation; they also showed improved motor coordination.
A previous study, published in PNAS, verified that our metabolic pathways are under control of circadian rhythms (the “human clock” that influences a number of human functions, including core body temperature, hormone production, and sleep). The new study essentially concludes that time-restricted feeding influences the expression of metabolism-related genes, turning them on and off in an efficient manner, and thereby improving the working metabolism and energy expenditure. When the time-restricted feeding group were in the “eating” phase, their metabolic genes were on; while they were fasting, their metabolic genes were off.
What does this mean for humans, obesity, and our eating habits?
As humans, we probably eat regularly from around 6 AM to at least 10 PM. This means that our bodies are working for 16 hours a day – and sometimes more – to digest and metabolize food and only “resting” for 8 hours – so we’re taking in calories even when our metabolism is functioning less effectively. Ultimately, this could lead to obesity as well as glucose intolerance as our livers are inundated with excess calories.
In terms of your diet, the conclusion from this study – that restricting meal times between certain hours, and certainly a smaller range than we’re used to, may prevent obesity and encourage a healthy metabolism – has a few take-away messages.
1. Try not to snack late at night. Because the genes that regulate metabolism and, possibly, obesity, are “turned on” at certain times and “off” at other times (like when we’re sleeping), it may be a good idea to restrict calories for a larger portion of the day than you’re used to. You don’t have to necessarily limit your eating to 8 hours per day, like the mice; but instead of heading to the kitchen for a midnight snack, opt for a cup of tea (or just head to bed). Most of the eating we do late at night is mindless munching anyway – we do it because we’re bored.
Also, most of the food we choose late at night is typically salty, sugary, fatty, and hypercaloric (foods that can add unwanted pounds no matter what time they’re ingested). The key word here is try; if you have real hunger, it’s advisable to pick a healthier snack, like 150 calories worth of fruit and nuts, toast, yogurt, or oatmeal. These high-fiber, high-protein foods put less of a strain on the liver. You don’t want to go to bed starving, nor do you ever want your hunger to get out of control.
2. It’s okay to go to bed hungry. In Bob Harper’s (of The Biggest Loser) new book, The Skinny Rules, Rule #18 is to “go to bed slightly hungry.” According to Harper, when your body is denied fuel for more than five hours, your body begins to burn fat and sugar. So the sooner you eat dinner, the sooner you stop eating, and the sooner your body can start effectively burning fat.
An indirect bonus: if you go to bed hungry, you’ll wake up hungry for breakfast, which jump starts your metabolism immediately. Many Americans skip breakfast because they’re not hungry and end up consuming the bulk of their calories in the afternoon and at night, at times when we don’t need those calories for energy. Cut out some of those end-of-the-day calories and shift them to breakfast.
3. This study is not an excuse to eat high-fat, high-calorie foods, even for a restricted period of time! Even though the time-restricted feeding mice ate a high-fat, high-calorie diet and stayed as lean as the mice eating a healthy diet, it’s still important to eat a whole foods-based diet high in fiber, lean protein, healthy fats, and plenty of fruits and vegetables. Besides controlling weight, these foods fight disease (cancer, cardiovascular disease, diabetes, stroke, high blood pressure, neurodegenerative diseases…) and boost health from improved immunity and better endurance to healthier skin and hair and improved cognitive functioning.