You're not eating enough protein each day.
Protein is needed for muscle growth and maintenance. Are you eating enough of it weekly? Reyes says, "Aim at 80% of your body weight in pounds in protein grams each day. Start there and be consistent."
You're eating too much protein.
Protein, like everything else, is bad in excess. Protein overconsumption "displaces" other macronutrients. Reyes advises "Stick to the guideline in point one above." Using extremely high-volume weight training, you can get up to 100% to 120% of your body weight.
You're maintaining a calorie deficit for an extended period of time.
Losing weight requires a calorie deficit. However, long-term deficits may cause muscle atrophy. "Have a structured and planned out nutritional program where you set a goal for how long to be in a deficit," Reyes says.
You're not drinking enough water.
You may not realize it, but muscles are mostly water and need water to keep healthy. According to Reyes, "Thirst is delayed. Dehydration occurs before thirst. Thus, thirst is an imprecise indicator of hydration."
You're drinking too much alcohol.
Dehydration from drinking may destroy down muscles. "We aren't talking about the occasional social gathering and having a cocktail," Reyes adds. "We mean having a habit of alcohol making up a portion of the daily nutritional intake."
You don't have a structured nutritional plan in place.
Water, protein, and calories must be balanced. If not, you may lose muscle. "The best way to ensure that these are in sufficient quantities is to plan ahead and structure each day of the week," Reyes says.
You're a diet hopper.
All diets are "structured and planned program." Your body will be confused if you alter diets every few weeks. "Diet hopping." is inconsistent and ineffective.
You're not routinely keeping track of your body composition.
Not knowing can't damage you sometimes. You must know your body composition and weight reduction. "The best way to know if you are gaining, losing, or maintaining is to have body composition assessed," Reyes.