Do you steer clear of snacking late at night as you are scared of gaining weight? A recent review of five randomised controlled trials by examine.com sheds a bit more light on this issue, suggesting that munching in the morning or at night may not matter as much as some people think (at least with regard to weight gain).

In 2007 a study carried out on women in a metabolic ward found that late-night eating did not affect weight loss. The women went through three 18-day periods in which a similar range of calories (~900-1,000) were consumed at different times during the three periods. The study concluded that eating a similar number of calories, although at different times throughout the day, does not seem to have a major effect on weight gain. However this was a short term study on a small number or people in a highly controlled setting, so we need more evidence.

A 2012 study put 78 obese police officers on a 6-month trial where one group was assigned to eat most of their daily carbs at dinner (dinner-carb eaters), and the other group before dinner (day-carb eaters). The dinner- carb eaters actually lost more weight, inches off their waist and body fat than the day-carb eaters. Even better, these dinner carb eaters showed better improvements in blood lipids, insulin sensitivity, and inflammation. However, it is important to point out that these greater improvements could be due to the fact these dinner-carb eaters did start out with a higher average BMI, weight, and body fat percentage than day-carb eaters.

So I can eat at night and actually lose weight? Well…..two trials published in 2013 somewhat conflict the findings above. Both suggest that eating earlier in the day may distinctly benefit weight loss.

The first was carried out over 12 weeks and involved 74 overweight and obese women with metabolic syndrome. They were randomised into two groups, the name of the groups indicated the time they consumed most of their calories (1,400 kcal): the breakfast group and the dinner group, that both ate an identical amount of calories (1,400 kcal) “

“The breakfast group lost more weight and inches off their waist, and experienced a significantly greater decrease in fasting glucose, insulin, and HOMA-IR than the dinner group (although fasting glucose, insulin, and ghrelin were reduced in both groups). Furthermore, mean triglyceride levels decreased by 33.6% in the breakfast group, while they increased by 14.6% in the dinner group.”

The second trial was a 2-week crossover in healthy young adults of normal body weight. This study found that completely restricting food intake between 7 p.m. and 6 a.m. led to a moderate decrease (-239 kcal/day) in total daily caloric consumption, a reduction that could lead to considerable weight loss if sustained long-term.

A final study yielded some rather inconclusive results suggesting that both styles were effective for losing weight. In a crossover trial involving 10 overweight and obese adult women in a metabolic ward. The authors found that during the first crossover phase, participants who ate most of their daily food at night lost more fat and less lean mass than the morning eaters. However, when participants switched groups, morning eaters lost more fat than evening eaters. But this could be somewhat explained by the higher body fat percentage at the start of the study among participants who lost the most fat (those who were first in the p.m. group and then switched to the a.m. group), which typically makes fat loss easier.

What do these studies tell us? Out of this group of studies, one found greater weight loss in night eaters, two found greater weight loss in morning eaters, and two others either found no difference or had mixed results.

The scales may be tipped slightly in favour of daytime eating, however its pretty hard to reach any definite conclusions about which style of eating is better for maintaining or losing weight. The studies above on meal timing (and others which extend beyond what’s covered here) are extremely varied in who they studied, what diets were used, and a ton of other factors.

So, does eating at night lead to weight gain? What I can say is this: While late-night eating isn’t essentially bad, the impact of meal timing is probably quite different in different people: Some people have a tendency to binge on high calorie/tasty foods (chocolate, cookies, ice cream etc ) when they’re tired (so yes will put on weight), while others don’t get hungry at all in the hours before bed. If you are one of those that has a tendency to binge it might be worth trying a restricted eating period, such 8 a.m. to 8 p.m. Its important to note circadian rhythm factors are another reason why some might want to stay away from eating too much late at night, more on that another time.