The later you stay up at night, the higher your risk of tacking on unwanted body fat. That’s the somewhat strange story which has emerged from recent research carried out in France.
Putting these two observations together, French researchers wondered if diet-induced thermogenesis (DIT) might be different at night, compared to the daytime. DIT represents the extra calories your body bums – above and beyond routine metabolism – simply because you have eaten a meal. One part of DIT is simply the ‘cost’ of handling a meal – the energy required to mix food in your stomach, move it through the intestines, and so on. Another portion of the DIT energy pie may result from hormonal changes which occur after eating – changes which encourage various cells to become more active. If for some reason DIT is high in the morning and afternoon but bottoms out at night, then night-time eating would allow more ingested calories to be socked away as fat.
To see if DIT actually varied over the course of a day, the French researchers asked nine healthy, young, non-obese males to eat a 544-calorie meal at 0900, 1700, or 0100 on three separate occasions. There were at least five hours between meals, and the proportion of energy supplied by protein, fat, and carbohydrate was 15,35, and 50 per cent, respectively. After each meal, subjects sat quietly for several hours while reading or watching television as scientists measured their rates of calorie burning.
DIT burned up 16 per cent of the calories in the morning meal, 13.5 per cent of calories in the afternoon repast, and just 11 per cent of the calories in the night-time one. This suggests that an extra 27 calories from the nocturnal meal were available to be tucked away as fat, compared to morning eating. Over the course of a year, that might deposit nearly three extra pounds of blubber on the back and abdomen of an athlete who shuns breakfast and instead raids the refrigerator in the wee hours.
The bottom line? It makes sense for athletes to bias their food intake schedules toward the morning and afternoon hours. Such eating patterns help ensure that muscle glycogen levels are adequate for strenuous workouts carried out in the morning, afternoon, or evening, and morning & afternoon dining offers an additional bonus: surplus calories in a meal tend to be burned more readily in the morning and afternoon, helping the weight-conscious athlete to stay slim. The reasons for the rock-bottom DIT at night aren’t clear, but one thing is certain: if you don’t want to get burly, eat early.
‘Circadian Variation of Diet-lnduced Thermogenesis, ‘ American Journal of Clinical Nutrition, vol 57, pp. 476-480,1993