While one pound of fat weighs the same as one pound of muscle, muscle occupies about 18 percent less space. In addition, muscle burns calories while fat stores them. So, if your weight isn't decreasing but your clothes are starting to fit more loosely, you may be building muscle.
You've gained muscle.
And here's an often overlooked fact: Muscle tissue is more dense than fat tissue. So as you gain more muscle and lose fat, you change your overall body composition, which can result in a higher weight, but a smaller figure and better health.
This is called a weight loss plateau. The initial weight loss is usually just water weight and not fat loss. The plateau is caused by loss of muscle that occurs during weight loss (if you are not working out). To counter this, you can either cut more calories or increase your physical activity.
The diet doesn't have enough calories
Eating too little — say, 1,000 calories a day — can prevent you from losing weight, too. "When you don't eat enough, your body is starving and it's not going to lose any extra weight" because it needs those energy stores to keep you alive, Fakhoury said.
Your Metabolism Will Slow Down to Store Fat
The more you work out or manage your calorie intake to lose weight, the more your metabolism wants to compensate by slowing down to maintain your current weight, this is called metabolic compensation. It kicks in to preserve and store fat for future energy.
You're eating too much during your eating window.
“If you end up consuming the same number of calories (or more) during your eating windows as before you started intermittent fasting, then you won't lose weight.”
Eating too few calories can be the start of a vicious cycle that causes diet distress. When you cut your calories so low that your metabolism slows and you stop losing weight, you probably will become frustrated that your efforts are not paying off. This can lead you to overeat and ultimately gain weight.
At the most basic level, not reaching your weight loss goal can occur when calorie intake is equal to or higher than calorie use. Try strategies such as mindful eating, keeping a food diary, eating more protein, and doing strength exercises.
Your body needs protein to build and repair tissues, so if you aren't eating enough, your muscles won't have the material they need to grow. You could feel “punch drunk” after working out, your arms and other muscles might ache more than usual, and your body may even feel generally weaker.
If you eat too much junk food, then you probably won't lose any weight, and you may even gain weight. You should eat the same amount of food as if you hadn't been fasting at all. The 5:2 diet involves eating normally for five days per week, then restricting your calorie intake to 500–600 calories on the other two days.
The 16/8 intermittent fasting plan is one of the most popular styles of fasting for weight loss. The plan restricts food consumption and calorie-containing beverages to a set window of 8 hours per day. It requires abstaining from food for the remaining 16 hours of the day.
However, if you're finding it difficult to lose weight, a medical condition could be the cause. Polycystic ovary syndrome, hypothyroidism, insulin resistance, hormonal changes and mental health conditions can all cause weight gain or make it more difficult to lose excess weight.
Chronic dieting has been linked to mood dysregulation. This could be due to an increased focus on size and weight, affecting body image and self esteem. This is often characterised by negative self talk, body or mirror checking for flaws, causing drops in mood.
You've Gained Muscle Mass
If you're exercising regularly and doing a mix of cardio and strength training, it's very likely your body composition (ratio of muscle to fat) is changing for the better. If you're gaining muscle while losing fat, the scale may not show any weight change.
Fat burning typically begins after approximately 12 hours of fasting and escalates between 16 and 24 hours of fasting.
So, can you have a cheat day while intermittent fasting? Yes, absolutely. An occasional cheat day will not hinder your weight-loss progress if you do it right. In fact, it's scientifically proven that intentional cheat days can even enhance your metabolism [1].
Lifting and doing strength training without adequate nutrition, especially without enough protein, can actually lead to loss of muscle tissue. Furthermore, if you aren't eating right you won't have the energy to do the workouts that lead to muscle gain.
Most people require around 20 calories per pound (or 44 kcal / kg) of bodyweight to gain muscle mass. Using a 180-pound (82kg) male as an example, the required daily calorie intake is 3600 calories (20 kcal x 180 lb = 3600 kcal).
It is commonly said that if you eat too few calories, your metabolism will slow down to a point where you no longer lose weight. Part of this is true: as you lose weight your energy expenditure does drop. However, consuming too few calories cannot and will not cause you to gain weight. This is simply impossible.