A general rule of thumb, though, is that consuming about 500 less calories than what is needed to maintain one's weight is part of healthy weight loss. Otherwise, metabolism will go down too much to compensate. Resistance exercise in particular is part of keeping metabolism up(1). Increasing fiber and decreasing overall calorie consumption both need to be done gradually. Energy levels may go down temporarily for a time with calorie restriction, and then go up afterward. Cutting down on excess sugars may result in headaches, and may the need for a few extra healthy snacks at the commencement of a weight-loss protocol(2).
Sources:
1. Gunnars, Kris. "How Many Calories Should You Eat per Day to Lose Weight?" Healthline. Healthline Media. 16 Oct. 2020. Web. 26 Oct. 2020. https://www.healthline.com/nutrition/how-many-calories-per-day#calorie-counters.
2. "Switching to a Healthy Lifestyle: What to Expect." Isagenix Health. Isagenix Worldwide, Inc. 3 Nov. 2017. Web. 26 Oct. 2020. https://www.isagenixhealth.net/switching-healthy-lifestyle-expect/.