You exercise mainly to lose fat, right? If you have a regular diet after a week of systematic exercise in the gym, it is normal to gain a little weight, so don't worry, because digestion and absorption will be better, and you should also do some weight-bearing training, which will promote protein synthesis, increase muscle content, improve flexibility and strength, and reduce fat content. Then the early weight gain is only the increase of your muscle content, not more fat, which is a good sign of your physical fitness. Then according to reasonable exercise habits and methods, such as continuing to combine aerobic exercise with anaerobic exercise, the effect will be better. Running can be extended for a period of time, and it is more efficient to burn fat with aerobic equipment such as treadmill or elliptical machine for more than 40 minutes. Because what you consume in the early stage is material energy and sugar in your body, plus proper weight-bearing and resistance training, step by step, adopting diversified exercise methods, and constantly giving new stimulation and changes to your body, the weight loss effect will avoid stagnation in a certain period and enter a platform period, which is more scientific than simply running, and make your body change towards your expected weight loss goal, so as to achieve a reasonable proportion of fat and protein content. There is also the diet structure and schedule to be arranged. After a period of adaptation, the exercise in the gym will yield a lot, which is not so complicated. You can consult some responsible coaches or experienced people for the usual action methods. As long as you stick to it, it will have an effect soon. I wish you can achieve your goal as you wish and make exercise a habit.