Picture this scene if you will. You just started an exercise program. You made it every day the first week, you are working really hard, and you decide to see how much weight you have lost.
You step on the scale and you have to rub your eyes a few times to make sure. You gained weight! How is that even possible???
There are typically two main reasons I see for this initial weight gain. The first is nothing to worry about, while the second needs to be addressed.
The first culprit in this initial weight gain is water retention. This what happens to a lot of people when they start a strength training program. What you are doing when you are lifting weights is actually tearing the muscles down while you exercise.
The process of your body building the muscles while you are at rest is when the magic actually happens. That is why you don't want to lift weights using the same muscles on back to back days. You have to give the body time to repair itself.
This tearing down process makes the muscles inflamed. With this inflammation comes increased water retention. With this water retention comes "This stupid (insert your workout here) is terrible, it is causing me to gain weight rather than losing it!" freak out. I’ve seen it with my own eyes, it can be very frightening for a fitness coach.
The second reason the scale can go up when people first start working out is increased caloric intake. This especially occurs with resistance training because it really gets your metabolism revving, which increases your appetite. Think about how hard it is to burn 800 calories in an hour. Now think about how quick you can put that back in. 10 minutes maybe? You cannot out exercise a bad diet.
That is why I recommend keeping a food journal, so you can see in black and white what you have been eating. The rule with the food journal is, "If you bite it, you write it. You hog it, you log it." Feel free to come up with your own rhymes.
Everything that has calories that you ingest has to be recorded. Liquid calories can add up very quick if you are not wary of them. It is a very eye opening experience to a lot of people who have never kept track before.
You can use apps, write it down, or whatever method you will do consistently. If nothing else, try it for a week and see if you can identify patterns that need to be corrected. Use your food journal as a road map to figure out if it is the nutrition that needs to be assessed or something else.
The main lesson as always is: The scale is a fickle mistress, don't trust it. It is just part of a big picture of your progress, not the one thing that determines your happiness. The scale can go up or down 5-10 pounds in one day!
A much more accurate way to see how you are progressing is to see how many inches you have lost, how your clothes are fitting, your increased energy levels, or body fat percentage lost.