This week, we examine the short term changes in body composition following a three day ‘refeed’ diet.

Many athletes include either planned or ‘social’ refeeds into their diet –this is sometimes aimed to rescue performance and psychological strain of low calorie dieting, or sometimes because they’ve ‘gone large’ on the weekend and over-consumed calories.

Either way, high calorie intakes over consecutive days often happen.

Body fat accrual and weight gain occurs over a long(er) period of time where calorie intake exceeds calorie expenditure. However, what happens to body composition over a short three day period?

To find out, Sagayama et al (2014) recruited 10 healthy male subjects and placed them on a 1500kcal refeed for three days. In this study, they consumed their normal (maintenance) intake for 10 days, then ate an extra 4,500kcal over 72 hours.

It’s worth noting these subjects didn’t increase their activity level compared to normal – so controllable energy expenditure was maintained.

As you’d expect, bodyweight did increase, but not through gains in fat mass, but through gains in total body water. Of which, a trivial 0.7kg gain was seen on average.

1kg of adipose tissue (body fat) contains ~7,000kcal, therefore you’d expect to see over 0.5kg gain in fat during this overfeeding period, but they didn’t.

Although not measured, it was speculated that the subjects increased weight via: glycogen stores (+ associated water weight), fluid retention through increased sodium intake.

Additionally, some energy may have been used to breakdown the extra food consumed (diet induced thermogenesis).

Also, the net weight of food consumed increased by 800g, which could be a contributing factor to weight gain (and associated gastrointestinal water content).

Unsurprisingly, when they returned to their normal, lower calorie diets, bodyweight, composition and total body water normalised within days – meaning that it couldn’t have been fat mass gain.

If these subjects continued to overeat in this fashion and maintain a sedentary lifestyle for days and weeks on end, then they’d rapidly gain body fat. But this does show that short term overfeeding in healthy, non-obese individuals doesn’t really touch the sides.

By all means, this doesn’t give you the green-light to eat like an ass-hole every weekend, but it does provide insight that the expected increase in bodymass most likely isn’t related to fat mass, but instead through water retention.