What happens when you overeat?
From Thanksgiving to New Years Eve, most of us try hard to maintain weight. But sometimes we just overeat. What is the fate of those excess calories? Do they all turn into body fat?
Dr. James Levine PhD of the Mayo Clinic designed a study to look at the biological mechanisms associated with overeating. Dr. Levine studied 16 non-obese subjects (12 males and 4 females), ranging in age from 25 to 36 years. They volunteered to eat 1,000 excess calories a day (above what they needed to maintain weight) for 8 weeks. The subjects were healthy, did not do purposeful exercise more than twice a week, and maintained a stable weight. Prior to being overfed, the researchers monitored the subjects for two weeks to learn how much food they regularly consumed to maintain their weight.
During the study, the subjects lived at their homes but ate supervised meals at the research center. The food had been carefully prepared and measured in a metabolic kitchen. The weight-gain diet was high in protein (20% of total calories) and fat (40% of calories), and low in carbohydrate (40%). The researchers accounted for almost all of the excess 1,000-calories a day. On average, ~430 of the 1,000 calories were stored as fat and ~530 were dissipated via increased energy expenditure. The researches even measured 3 days of poop before and at the end of the study to be sure the subjects did not excrete calories during overfeeding. Only 38 calories a day got flushed down the toilet during overfeeding — 13 calories more than during normal eating.
Here is the fate of the 1,000 excess calories the subjects ate:
Energy stored as fat ranged from 60-685 calories per day
Energy stored as muscle ranged from 15-80 calories per day
Additional calories burned by organs: about 80, on average
Additional calories used to digest the extra food: about 135, on average
Additional calories burned via NEAT ranged from none to 690.
The researchers used highly accurate methods to measure changes in body fat (DXA). Some of the subjects gained 10 times more fat than others, ranging from 0.8 to 9 lbs (0.36 – 4.23 kg). The overall weight gain ranged from 3 to 12 lbs (1.4 -5.5 kg), some of which was additional muscle. Non-exercise Activity Thermogenesis (NEAT; your daily activity apart from your purposeful exercise) explained the big variation in weight gain that occurred with the subjects in this overfeeding study. The subjects who gained the least weight were fidgety and puttered more than the other “mellower” subjects.
The average increase in NEAT was 336 calories a day, but this actually ranged from burning 98 calories less than baseline to burning 690 calories more than baseline. The subject who burned the most calories strolled around the research facility (or did equivalent movement) about 15 minutes more per hour than the other subjects.
The moral of the story: If you are going to overeat and want to suffer the least weight gain, stay active. You don’t have to start fidgeting, but you do need to get off the couch, turn off the TV, take some walks and be more active.
For more information on how to manage weight, enjoy the chapters about weight and body fat in Nancy Clark’s Sports Nutrition Guidebook.