Why does body weight fluctuate?

Author: Mikhail Ziborov - author of the site makefitness.pro.
2026-04-16

A client comes to me and asks me to teach her how to do push-ups. She is 44, and she needs it for the GTO standards. In 2.5 months, we were able to reach the result of 30 push-ups per set while meeting the GTO rules. But during this period, in addition to the result, the client’s body weight also increased by 3 kg. This still bothers her. And she thinks she has gained fat. I explained to her that body weight can fluctuate in one direction or the other. And there are tons of factors that influence this. They are described below and in our Telegram community, where there is a lot of similar information that is not so easy to find.

Carbohydrates

1 g of carbohydrates retains 3-4 g of water in the body. In the muscles and liver of a non-training person there are approximately 300-500 g of carbohydrates. In a training person, there is more. Carbohydrates are stored in the form of glycogen. And together with glycogen, add 1.5-2 kg of water (during training, this figure will be even higher).

Training

Team sports that require acceleration, strength training — all this leads to the development of muscle tissue. And the more muscle mass there is, the more it can and even should contain nutrients. For example, glycogen. And as your fitness level improves, body weight may increase. All because your muscles can now store more carbohydrates. And water is required to store them.

So do not be surprised by an increase in body weight if you notice that your strength performance has improved recently. Strength has increased, which means you have gained muscle mass.

Extracellular fluid and salt

There is not just a lot of extracellular fluid in the body, there is a lot of it. Remember what a person is made of by 75-80%? Water. This is that very extracellular fluid. And there is also salt — sodium chloride (NaCl). And there is such a concept as the body’s water-salt balance. From the name itself it is clear that there must be a balance between water and salt in the body.

Increased the amount of fluid you drink? The body will try to retain sodium (salt) to balance their ratio.

Overate salt (added a lot to some dish) or the day before ate a large amount of salty foods — expect an increase in extracellular fluid of about 500-1000 g of water. This weight gain lasts for 1-2 days if you return to your usual diet and normal intake of salt and fluids.

Female cycles

Here everything is tied to hormones. And the female cycle is the rises and falls of these hormones. And such swings lead to fluid retention in the body. Around 500 g. Keep this in mind too. For those who need details:

an increase in estrogens leads to an increase in the level of another hormone — aldosterone, and it in turn affects the water-salt balance, retaining fluid in the body;

a decrease in progesterone levels leads to salt retention in the body and, as a result, fluid retention (under normal conditions, progesterone helps eliminate salt from the body);

vasopressin and prolactin also affect the retention and elimination of water from the body.

Food bolus

These are the very same fecal masses. And the composition of fecal masses can affect fluid retention. If you ate more fiber than usual, then expect water accumulation in the body (in the range of 300-400 g). That’s just how our body works. There is a lot of fiber in cabbage, beans, lentils, carrots, and other products such as fruits (apples, bananas).

Climate change

When you arrive from a cold region to a warm one, the blood plasma will increase its water share in order to make the blood thinner and make it easier for the heart to pump it under the changed environmental conditions. And you catch an extra 200-300 g.

Diet

For example, you decided to remove fast food and sweets from your life. Of course, I am against completely removing something. It is better to reduce it, but not eliminate it. But let’s say you gave up or significantly cut back on these products. And what were these products made of? Carbohydrates and salt (included in various sauces, for example). That is, the very nutrients that retain fluid in the body.

Now there is less of them, and the need for an increased volume of water has disappeared. Therefore, body weight may decrease. If your weight starts to fluctuate, think back to whether your diet has changed recently.

In conclusion. If you notice that your weight fluctuates every couple of days, or increases for some period and then decreases over the same period, do not panic — it is not fat. Fat does not grow that quickly. Most likely, it is just your body playing with water: it either stores it or gets rid of it. Because there are many factors that affect water retention. It is not easy to keep track of all of them.

Unlike a proper diet. Here we can definitely say whether excess weight will go away if you follow the meal plan. Because there are not so many variables — calories and the ratio of nutrients.

Therefore, if you notice weight fluctuations, do not panic. It is not subcutaneous fat. There is no need to immediately try to lose weight, starve yourself, give up sweets and baked goods, or work off the increased kilograms in training.