Overfeeding And Substrate Utilization
If you’ve ever had a larger scale binge (think Thanksgiving dinner or a big pasta supper buffet), you might have grown quickly concerned that this was going to lead to a massive weight gain. But often times it doesn’t. So, what’s really going on here?
What determines whether you will gain weight after a period of overeating or not?
This is something that researchers recently looked into to see what all was at play. Here’s what they found out.
The study was designed so a group of 34 male volunteers were fed a weight maintaining diet for four days prior to the study.
After this period, they were then allowed to select their food from a computerized vending machine that offered a wide variety of foods, after which their 24 hour energy and substrate oxidation rates would be measured.
During the freely chosen meals, the subjects overate by 54 +/- 32% above their maintenance requirements, which resulted in a 1-2 kg body weight gain.
The interesting thing to note though is that when compared to the baseline diets, the fifth day of the overeating period showed an increase in overall energy expenditure as well as an increase in total carbohydrate oxidation and decrease in fat oxidation.
So, these subjects were ramping up their burning of carbohydrates to mirror the increased incoming intake, while fat oxidation went down.
Protein oxidation remained unchanged during the overfeeding period.
This then suggests that when faced with a very high sudden food increase, the body will adjust its metabolism so that carbohydrate balance in the stores remained under control, while fat was the primary nutrient to go directly into storage during this time period.
The take home message from this then is that if you are going to be overeating, it is better to overeat in strictly carbohydrates, while keeping dietary fat intake as low as possible. This will cause the body to increase carbohydrate oxidation, but since there will not be incoming fat calories, this will not be converted directly to body fat (as they otherwise likely would be).
While this may not always be 100% practical (try having a very low fat Thanksgiving meal – it would be challenging), when you’re out and are worried that you’re overeating, at the very least try and do your best to keep your selections as low in fat as possible.
Reference:
Larson, DE., et al. (1995) Spontaneous overfeeding with a ‘cafeteria diet’ in men: effects on 24-hour energy expenditure and substrate oxidation. Int. J. Obes Relat. Metab. Disord. May;19(5):331-7.
