It's commonly assumed that eat-ing late at night is more likely to promote weight gain than eating earlier on in the day. Indeed, many popular diets, such as the Atkins and South Beach diets, recommend limiting food intake in the evening. But is this assumption true, or is it just another weight-loss myth?
According to one team of researchers, the eat-late, gain-weight theory makes sense. "Because metabolic rate decreases during periods of sleep in humans and animals," they say, "it seems logical to assume that eating during a time when metabolic rate
is slowing may lead to less use of consumed energy and, therefore, more storage of energy and ultimately to weight gain" (Obes Res, 2005; 13: 2072-80).
Ironically, however, their research proved otherwise. In a one-year study of female rhesus monkeys, they put the monkeys on a weight-gaining regimen to examine whether those that ate a high percentage of calories at night were more likely to put on weight than those that ate most of their calories during the day.
As expected, the monkeys gained significant weight in six weeks, but this was not influenced by their night-time calories. Those with the highest night-time intakes gained no more weight than those with the lowest late-night intakes. This means that calories cause weight gain no matter when you eat them-at least in monkeys (Obes Res, 2005; 13: 2072-80).
However, studies in humans also support this conclusion. In a 10-year study of more than 7000 people, there was no correlation between night-time food intake and weight gain (Int J Obes Relat Metab Disord, 1997; 21: 407-12). Similarly, a study of 1800 women reported no link between obesity and night-time consumption of calories(J Am Coll Nutr, 1995; 14: 358-63).
In spite of these findings, however, there is evidence to support the eat-late, gain-weight hypothesis. In one study of 15 women, greater weight gain over a two-week period was observed in those who consumed a greater proportion of their daily total energy intake in the evening (Appetite, 1996; 26: 55-70). Also, several studies have reported that obese children consume a higher percentage of their calories at night compared with their leaner siblings and peers (J Pediatr, 1980; 96: 187-93; Appetite, 1988; 11: 111-8).
Furthermore, it appears that when we eat can also influence how much we eat. US scientists at the University of Texas have hypothesized that the satiating effect of food decreases over the course of the day, so eating more early on-when food is most likely to be satisfying-should result in a lower overall daily intake.
Sure enough, those who ate a large proportion of their total energy intake in the morning ate significantly less over the course of the day. In contrast, when the same people ate a high pro-portion of their total intake during the evening, they ate significantly more over the entire day.
The researchers speculate that a diet that encourages large amounts of food in the morning while restricting evening intake may reduce overall intake, and serve as a treatment or preventative for obesity (J Nutr, 2004; 134: 104-11).
Indeed, a few studies show that eating the largest meal in the morning and the smallest meal at night can influence body weight. A UK study involving more than 6700 middle-aged adults found that those who ate the highest percentage of their daily calories at breakfast had the lowest body mass index (BMI), despite the fact that their total caloric intake was higher. The researchers also found that those eating the most in the morning gained less weight than those eating more of their food later in the day (Am J Epidemiol, 2008; 167: 188-92).
Another study, involving 10 women put on a controlled weight-reducing regimen, showed greater weight loss with large morning meals compared with large evening meals. However, eating large meals at night resulted in better maintenance of fat-free tissue (J Nutr, 1997; 127: 75-82).
What's the verdict?
Although some studies have found no evidence that eating late will make you put on more weight, other research suggests that the way that food calories are distributed may affect hunger-and that, in turn, may affect weight gain. Yet other studies indicate that a regular eating pattern is a key factor in maintaining or achieving a healthy weight (Am J Clin Nutr, 2005; 81: 16-24).
However, as research findings are conflicting, it may be sensible to focus on what you eat, rather than when you eat it, if you're looking to lose weight.
More information about what works for weight loss-including the best diet and exercise programmes-can be found in WDDTY's The Secrets of Longevity, available from