Have you ever dieted Monday-Friday successfully losing some unwanted fat only to regain it and more after a slightly overindulgent weekend? This article is for you.
Michelle was a personal trainer I once managed. She was lean and toned as you would expect a trainer to be. She was a hard worker, constantly seeking perfection, always trying to improve the shape of her body. During the week, Michelle dieted her little heart out. She reduced the amount of food she was eating and particularly focused on consuming less carbohydrate. She was so strict that during the weekdays the majority of her meals consisted of salads and proteins.
Just like clients, all trainers should have goals. As Michelle’s manager, I was also coaching her. By the time it got to Friday, Michelle would hop on the scales to find her hard work had been rewarded. On this particular week, she had lost 1 kg and was now 59kg. We exchanged a 5 and for the remainder of the day, Michelle was high spirited. I even noticed her dancing around the studio when she thought no one was watching.
Monday morning came, as Mondays do. Michelle wasn’t supposed to weigh in until the next Friday, but of course she did. Michelle said she knew that it wasn’t going to be good, because she had overindulged a little. She was right. It was terrible. Michelle was now 61kg. Michelle’s emotions quickly switched to that of frustration and disappointment, the opposite of how she felt on Friday. All her hard work had seemingly been undone.
The real problem with this scenario was that it was a frequent occurrence. Michelle was slowly improving her physique over time; she was also riding a rollercoaster of emotions as her weight dramatically changed during the week.
I don’t like to use numbers, but each 1 kg of weight loss is equivalent to about 7000 calories. Unless you were eating approximately 14,000 calories extra over the weekend, it’s very unlikely you could gain 2kg over a weekend. Let’s put that in context. For those who party it’s about 200 vodka soda limes or for those who love fast food, it’s about 50 cheeseburgers. Knowing Michelle, as I did, that simply did not happen.
Michelle had consumed minimal carbohydrates during the week both because she was eating less food and because she had chosen to reduce them. Over the weekend she went out to dinner with friends and ate a little more liberally. She enjoyed some pasta, a little dessert, and a few glasses of wine. Michelle consumed more carbohydrates in her diet but this could hardly explain an extra 2kg on the scales.
How could this be you may ask?
Various studies attribute the rapid weight loss experienced by individuals on a low-carb diet is mostly due to water loss. In one of these studies subjects lost as an average of 1.7kg of water, with one subject losing 4.3kg. 
Even a small change to one’s diet such as dropping calories or changing the types of foods eaten will alter levels of water retention. It’s worth noting that individuals had very different weight loss responses.
In a separate study it was found that re-feeding of carbohydrates after a low carb diet can result in weight gain up to twice normal levels. Theoretically, if the average person lost 1.7kg after reducing carbohydrates they could potentially gain an additional 1.7kg and weigh an extra 3.4kg!
Water retention is a dangerous, often misunderstood psychological trap. Many a person has given up on their weight loss goals after a Monday morning weigh in. It’s the emergence of this weekday dieter just like Michelle which explains why society is becoming more and more ‘carbophobic’.
You haven’t lost or gained 2kg of fat.
It’s just water.
Kreitzman, S.N., et al. Glycogen storage: illusions of easy weight loss, excessive weight regain, and distortions in estimates of body composition. Am J Clin Nutr. 56:292S-293S, 1992.
Bergström, J., et al. Diet, muscle glycogen and physical performance. Acta Physiol Scand. 71(2):140-150, 1967.