So Why Does this Happen?Sometimes this water retention can just happen spontaneously, can be due to the menstrual cycle in females, sodium and potassium intake.  It can also be due to a hormone called cortisol, which your body produces in response to stress and dieting. Research has shown that increased levels of cortisol have increased water retention when dieting. [1&2]
An experiment conducted during WWII, Minnesota Starvation, where Ancel Keys and colleagues put 36 men through a period of semi-starvation of approximately 1,500 calories per day showed cortisol to do this. The men lost >25% of their weight, experienced anemia, fatigue, apathy, extreme weakness, irritability, neurological deficits, and lower extremity edema. The aim of the experiment was to understand human starvation and also understand the best strategies for the Allie relief mission. However, what they also found was that that body weight remained stable at several stages of dieting, but this was then followed by a big weight drop overnight. This was later found out to be due to water retention. This wasn't to say they were not losing weight over these stable periods, as they were in a calorie deficit losing fat and muscle, but the water retention masked the weight loss on the scales.
Why the Sudden Drop in Water Retention?About halfway through the experiment, a relief dinner was given of 2,300 calories. This meal resulted in a sudden drop in ‘stress’ and cortisol leading to a lot of water being lost at once from the body. The dramatic loss in weight overnight is what is now referred to as the ‘whoosh.’ This ‘whoosh’ in weight can be due to a random day of accidentally/purposely overeating or a scheduled re-feed.*
*A re-feed consists of raising your calories just above your total daily expenditure for a day, which can aid in lowering cortisol levels and stress within the body. While many feel this will also raise ‘metabolic boosting’ hormones (i.e leptin, insulin, thyroid) over a 24 hr period, this is becoming more and more unlikely, as a re-feed of 24hrs is too short to do this. A re-feed/diet break that lasts a few days/weeks is needed to rep the full benefits of resetting your hormonal profile, improving performance in the gym and psychological benefits.Now we are at the bit that we all want to know the answer to...
How To Prevent Water RetentionSometimes it is unpreventable and this is no big issue, physically, unless it becomes painful with bloating. Saying this, it can have strong psychological implications. Therefore; - Diet intelligently and do not crash diet whilst looking for a quick fix.
- Don’t conduct endless amounts of cardio daily
- Participate in weight training 2-3x per week
- Eat as much as you can while losing weight